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2022-11-11T07:19:10Z

Mburpee: added link

== This site is currently under construction ==

* [[Project Information Management Systems in the Deep Foundations Industry]]
* [[Terminology and Evaluation Criteria of Crosshole Sonic Logging (CSL) as applied to Deep Foundations]]
* [[Section 5.22 Frost Heave]]

Main Page

2022-11-11T07:16:49Z

Mburpee: added article link

==This Site is Under Construction==

* [[Project Information Management Systems in the Deep Foundations Industry]]
* [[Terminology and Evaluation Criteria of Crosshole Sonic Logging (CSL) as applied to Deep Foundations]]
* [[Section 5.22 Frost Heave]]

Section 5.22 Frost Heave

2022-11-11T07:15:32Z

Mburpee: Created page with "The design foundation lengths required to resist uplift against ground heave and structural uplift can be calculated from the soil side resistance below the frost zone. The depth of frost penetration and adfreeze bond strength is used to determine the ground heave portion of the load to be resisted. Published adfreeze values generally range from 10 psi to 20 psi, with some silts ranging as high as 45 psi. Many foundations have been installed according to the Tsytovic..."

The design foundation lengths required to resist uplift against ground heave and structural uplift can be calculated from the soil side resistance below the frost zone. The depth of frost penetration and adfreeze bond strength is used to determine the ground heave portion of the load to be resisted. Published adfreeze values generally range from 10 psi to 20 psi, with some silts ranging as high as 45 psi.

Many foundations have been installed according to the Tsytovich Rule, which is to embed the pile two to three times deeper than the frost depth. In some soil conditions and colder climates this rule can lead to excessive incorrect embedment depths.

Frost heave is a service limit state, consideration should be given to the appropriate use of load factors, phi factors, or safety factors to account for its transient nature.

== Prevention of Frost Heave ==

=== Surcharge ===
Heaving will be prevented if the structure has ample dead load in the micropile to resist the heaving forces. Dead load could be added to offset heaving forces in micropiles that are otherwise lightly loaded. Adding dead load can be achieved by increasing the pile cap dimensions and / or reducing the number of micropiles to increase the load per micropile.

=== Isolation ===
Micropiles have been isolated from frost heave by installing a casing through the frost zone and installing the micropile inside the casing. The annular space between the micropile and casing can be left open, if protected from water infiltration. It is preferable to fill the annular space with a frost-stable, low shear strength, material such as an oil-wax mixture or grease. The annular void space will reduce the lateral capacity and increase lateral deflections of the micropile.

=== Insulation ===
Another option to help mitigate frost heave is to incorporate an insulated layer below and extending past the pile cap. The thickness of the insulation and the extension of the insulation past the edge of the pile cap is dependent on air freezing index. The insulation is sized to keep the soil temperatures around and beneath the pile cap above freezing temperatures.

=== Non-Frost Susceptible Soils ===
Removing and replacing any frost-susceptible soils present below grade around the micropiles to the frost depth will help limit the potential for heaving, but not eliminate it. The backfill should be non-frost susceptible such as SP, SP-SM. This will require a site that is large enough that active water management can be installed. The bottom of the excavation should be sloped toward one or more collection points so that any water entering the backfill can be collected and removed. A series of perforated drainpipes should be installed to collect and dispose of infiltrating water and/or groundwater that could accumulate within the backfill. The piping should be connected to a sump to remove any accumulated water, or “day lighted” if grades permit. If the water is not removed this option will not be effective in controlling heave.

== References ==

# Canadian Geotechnical Society (2006), Canadian Foundation Engineering Manual, 4th Edition, 488p.
# NAHB Research Center (1994), Design Guide for Frost-Protected Shallow Foundations, U.S. Department of Housing and Urban Development Office of Policy Development and Research, 56p.
# Goldberg, L. F., (1999) Frost Protected Shallow Foundation Design Specifications, Minnesota Housing Finance Agency, 11p.
# Andersland, O. B., Ladanyi, B (2003) Frozen Ground Engineering, 2nd Edition, Wiley, 384p.

Guide to Working Platforms

2022-09-28T15:15:29Z

Mburpee: added page content

The importance of the stability of large and tall equipment when working on construction projects is undeniable. As the gruesome image below shows, the consequences of unstable platforms can be devastating.

In addition to the physical consequences, a rig toppling will certainly have a financial impact, it may lead to a delay to the project, have reputational ramifications and lead to civil claims or even criminal prosecution. A major cause of rig instability is a poor site surface or working platform. This may be due to a lack of design, poor quality installation, or a lack of maintenance or inspection. Given the consequences of a rig falling over, most would agree that each of these aspects should be carried out thoroughly and by competent people, yet on many sites, in many countries, this is still not done.

Nevertheless, there are examples of good practice that if shared and followed would do much to improve the quality of working platforms, not just for geotechnical equipment, but for all users of the site surface. However, because of the fragmented nature of the construction industry and its regional approach, it is not easy to effect a change for the better.

Therefore, this guide is not intended to prescribe or dictate the way in which working platforms should be managed, but rather pools the experiences from across the membership of the European Federation of Foundation Contractors (EFFC) and Deep Foundations Institute (DFI) to increase awareness of what has been achieved.

Whilst foundations contractors naturally focus on piling rigs and other geotechnical equipment, a working platform is used by everyone that accesses site. So the considerations highlighted in this document apply equally to cranes, concrete pumps, mobile access platforms, concrete trucks, delivery vehicles and even personnel. A properly designed and installed working platform benefits all and will enhance the efficient working of a site as well as ensuring a safe environment.

It is hoped that the document will provide a stimulus for how this important aspect of how we work is tackled by our industry and outline some possible tools for implementation. Fundamentally, we all wish to make photographs like ''Figure 1'' a thing of the past.

== Purpose and Scope ==
On a typical construction site, the provision of a safe surface to work on involves and affects a number of the contracting parties, and as a consequence, the organisation of its design, installation and maintenance can be complex. As it concerns money and liability it is often a contentious issue, but nonetheless one that needs to be addressed.

=== The parties that may get involved in the provision of a working platform are: ===

==== The client. ====
Some clients such as a national railway authority may have specifications that need to be met. Some may include an item in their bill of quantities for the provision of a working platform, whilst other clients will simply expect the general contractor1 to have included for it in the price.

==== The principal designer. ====
In some jurisdictions the designer of the scheme may have an over-arching safety co-ordination role. Regardless of whether there is this legal responsibility, the choice of foundation type and size will be a determining factor in deciding what equipment is necessary to install the works, and hence the requirements of the working platform.

==== The general contractor. ====
In accordance with the European ‘Construction Sites’ Directive [''Appendix 1''] the general contractor is likely to be the coordinator for safety and health matters in the project execution stage. This extends to the temporary works on the site and hence the working platform.

==== The specialist geotechnical contractor. ====
Again, under EU law, the geotechnical contractor will be responsible for the health and safety of their employees and this will extend to the provision of a safe place of work.

==== The working platform designer. ====
If it is not the principal designer, then a separate organisation or person may carry out the design for the platform (which is a part of the temporary works).

==== The working platform installer (earthworks contractor). ====
This is usually a subcontractor to the general contractor.

==== The platform tester. ====
In some cases, the platform might be tested to demonstrate its suitability. This might be done by an independent testing company.

==== The platform maintainer. ====
Once the platform is in use it is likely that it will need some maintenance. This would be either because it is heavily trafficked or perhaps it might have deteriorated because of weather conditions.

So, in summary, the provision of something that would seem to be basic and straightforward - namely a platform for the site to use and work from, actually becomes a difficult thing to arrange and look after. Several steps are necessary to make sure that the whole process can be properly executed.

This document takes each step in turn and describes what good practice is, with reference to documents and resources that have been made available through the EFFC and DFI.

In compiling this information responses have been collated from foundation contractors from; France, United Kingdom, the Czech Republic, Germany, Netherlands, Poland, Portugal, Romania, Sweden, Austria, Belgium, Denmark, Hungary, Italy and Sweden, USA and Canada.

The guide is set out in a chronological manner; that is it starts with the calculation of rig loads and platform design and then moves through installation and testing to maintenance. Contractual responsibility is covered, as is enforcement, albeit this can be a contentious subject. Finally some suggestions for training and improving general awareness are made.

Unsurprisingly different countries are at different levels of maturity, but the sequential process or the journey in ''Figure 2'' that needs to followed is broadly the same wherever you are. It is worth noting that each and every step should be properly considered and implemented prior to the next. Rushing the process or missing steps out is unlikely to be successful.
[[File:Fig2.2.png|alt=Steps in Implementing Effective Working Platforms|none|thumb|463x463px|FIGURE 2. Steps in Implementing Effective Working Platforms]]

More and more countries are adopting this approach and it is not just in Europe. Recently (November 2018) the main geotechnical federations in the U.S. (comprising the ADSC-IAFD (International Association of Foundation Drilling), the DFI (Deep Foundations Institute) and the PDCA (Pile Driving Contracts Association)) endorsed such a process [''Appendix 2''].

Similarly, Canadian regulations are addressing the issue head-on [''Appendix 15'']

== Tracked Plant Loading ==
It is necessary to provide the designer with loadings (amongst other things) so that the thickness of the platform may be determined. For tracked equipment this is not just the “dead-weight” of the machine spread over the contact or surface area of the tracks.

Since 2014 and the introduction of EN16228: Drilling and Foundation Equipment - Safety, the rig and equipment manufacturers should provide rig bearing pressures with all new equipment. However, older rigs may not have this information or modifications may mean that the working bearing pressures are changed.

Calculating the rig bearing pressure can be complex, as the way in which the rig is operated will have an impact upon the loading pattern. It is likely that different load cases will apply as the ancillary equipment carried by the machines (such as an auger or a hammer) will vary from time to time, even possibly on the same project. Consequently, there are a number of variables which need to be modelled if a precise assessment of rig bearing pressure is to be made.

The Federation of Piling Specialists (FPS) in the UK has developed a method of calculating track bearing pressures which is freely available [Appendix 3]. This is an excel spreadsheet into which the user can input the particular rig characteristics to derive the bearing pressure. From time to time the FPS also offers training in the use of the tool.
[[File:Fig3.png|alt=Other Users of the Platform|none|thumb|FIGURE 3. Other Users of the Platform]]

Another simple estimate especially useful for older equipment is:
[[File:Tracking.png|alt=tracking|none|thumb|1. Tracking]]

In the equation the entire load is on one track, to estimate the effect of eccentricity. The Track Length is the full flat length in contact with the ground surface. The result is double the average pressure.
[[File:Drilling.png|alt=drilling|none|thumb|2. Drilling]]

Again, all the load is on one track to estimate the effect of eccentricity. The Track Length is the full flat length in contact with ground surface.

However, there are ways of defining more generic rig bearing pressures. For example, the Association Belge des Entrepreneurs de Fondation (ABEF) simply requests a 25MPa pressure resistance [''Appendix 4''] whilst the Austrian Research Association for Roads, Railways and Transport (FSV) has compiled a list of loading details for typical generic geotechnical equipment ranging from piling rigs, to diaphragm walls and from micro-piling to ground anchoring [''Appendix 5'']. The Ontario regulations require an engineering analysis when any piece of equipment exerts a pressure of 200 kPa under its ties, tracks or outriggers.

One thing to be wary of is changes in rig types or rig configurations after the piling or working platform has been installed. This could arise in the event that a rig has to be replaced, perhaps in the case of a plant breakdown, or if the diameter or depth of the foundation changes for some reason. In these cases the new bearing pressure must be checked to ensure that the working platform is still adequate for the new loading. When thinking about rig loading it is also useful to consider the other users of the platform. For example, a fully loaded ready mix concrete truck or tipper truck carrying spoil may well exert a higher bearing pressure than the rigs.

== Working Platform Design ==
In the EU, the design of the platform is a temporary works consideration and hence its co-ordination falls under the requirements of the EU Directive 92/57/EEC 1992; the ‘Construction Sites Directive’. In this context, co-ordination means arranging the design and ensuring that the requirements of that design are met on the site. Ordinarily, these obligations fall to the general contractor.

In the US, whilst the design of the platform is not yet covered by a legal framework or standard, the OSHA Construction Standard Subpart R, CFR 1926.752 assigns the responsibility for, “A firm, properly graded, drained area, readily accessible to the work with adequate space for the safe storage of materials and the safe operation of the erector’s equipment” to the “controlling entity”.

The design of the platform should be carried out by a competent geotechnical engineer and they may use any form of analysis they deem appropriate and there are some established methods ranging from a simple spread footing calculation based on Terzaghi’s principles to finite element analyses.

The design brief should be developed as required for any other temporary works design, but in particular the following information should be supplied:

* Plant data sheets (dimensions, configurations, weights etc.);
* Track ground bearing pressures, outrigger or mast foot loads;
* Ground investigation report;
* Plan of the working platform and haul roads;
* Topographical survey;
* Existing services survey (above and below ground);
* Existing structures survey (below ground chambers, retaining walls, etc.);
* Constraints on reduced levels (formation, top of platform);
* Proposed compaction plant / method;
* Period of use (duration);
* Any information on existing shallow mining activities or other potential voids (i.e. chalk or salt dissolution, etc.);
* General construction traffic and their payloads including type of lorries, wagons, etc.
* Any works that may involve excavating through the platform and the planned method of reinstatement.

The most commonly used form of analysis is the Building Research Establishment’s (BRE) good practice guide BR 470. [''Appendix 7'']. This guide was published in June 2004 with the principal objective of improving safety by promoting the implementation of minimum design, installation and maintenance standards. In the guide the following limits are suggested:

* for unreinforced platforms the minimum platform thickness should be the lesser of 300mm [1ft] or half the track width; the maximum thickness is 1.5x track width;
* for reinforced platforms the minimum platform thickness should be 300mm [1ft]; the maximum thickness is the track width, and;
* the minimum cover over a geosynthetic reinforcement should be 300mm [1ft].

However, some criticise the guide as being overly conservative and there are concerns about the way in which the effect of geosynthetic reinforcement is evaluated. In these situations the manufacturers of geosynthetic products may be able to offer a cost-effective design, but it is important to identify where responsibility lies for the design, placement and operation of the platform. Indeed, Tensar have developed their own method of calculating the thickness of a platform, the “T Method”. Details of this are included in ''Appendix 20'', and a link to their app is in the references.

The French federation (SOFFONS) has published a method [''Appendix 6''] and this includes an easy-to-use excel spreadsheet. This document broadly follows the BRE document but with further details regarding the bearing capacity assessment based on pressuremeter tests and cone penetration tests which are more common in France.

More recently, the UK’s Institution of Civil Engineers (Temporary Works Forum) has been working on an improvement to the methods mentioned above and has issued a Guide to Good Practice TWf2019: 02 [''Appendix 8'']. This would appear to give more economical results than BR470, and suggests some other methods of analysis, which is to be welcomed; a competent designer could adopt its recommendations should they so decide.

Regardless of the method used, someone has to carry out the design of the working platform. In some jurisdictions this is a challenge as the principal geotechnical engineer may be employed by the client, and will be conflicted in some way. Other consultants may be unwilling to take on the design as frankly the task is too small to be commercially worthwhile. Where this is the case, it may fall to the geotechnical specialists to develop this service in-house. This can then be offered to the project, with an appropriate fee.

In some markets where the practice has been common place for a longer time, a market for smaller specialist geotechnical designers has developed and these organisations regularly design platforms, usually for the general contractors. The cost of the working platform is not insignificant and so a competitive design is a distinct advantage.

== Installation and Testing ==
Often the platform is installed by another contractor who is not the geotechnical specialist nor the general contractor. Indeed, the platform is likely to have been laid well before the geotechnical specialist even comes to site. Therefore, knowing whether the platform has been installed in accordance with the design becomes more difficult. Consideration needs to be given to how this assurance can be realised.

The UK federation (FPS) has the Working Platform Certificate [''Appendix 9''] which is widely used in the industry. This has a section (Part 2) which is to be signed by the general contractor as a verification that the platform has been installed in accordance with the design. The Dutch federation (NVAF) has a similar document [''Appendix 10'']. Also see the Ontario certificate [''Appendix 15'']. In reality the signing of a piece of paper can only go so far in validating the quality of the entire platform, but this procedure focusses people’s minds and makes everyone understand their obligations.

In order to obtain a higher level of assurance, testing could be specified. Presently the most common test is the Plate Load Test shown in ''Figure 4''. Whilst this is easy to conduct some caution is necessary as the plate loading test equipment is normally not representative of the loaded area, particularly in the case of rig tracks. It is possible that a test using the normal plate size (300 to 450mm [1 - 1.5ft] diameter), applied to the surface of a working platform, will have little influence on the sub-grade. However, research is currently being carried out on this particular subject which may provide some comfort on this point. The Dutch federation reports using a “penetrologger”, which may provide an alternative.
[[File:Fig4.png|alt=Plate Load Test Equipment|none|thumb|FIGURE 4. Plate Load Test Equipment]]

Proofrolling in combination with other appropriate verification techniques (such as the previously mentioned plate load test) could be considered to provide a higher level of assurance. A major cause of rig toppling is a lack of demarcation and the rig is inadvertently tracked to close to, or even off the edge of the platform. It is good practice that the working platform extends at least 2m [6.5ft] beyond the built footprint of the site to ensure sufficient safe working area.

== Inspection and Maintenance ==
Once the platform has been installed, it has to be maintained. Often the piling operation itself will result in the platform deteriorating and the excavation of obstructions and services can lead to soft spots. Several of the rig overturns that have been reported by the members of the EFFC and DFI were caused by a lack of maintenance rather than a poorly designed or constructed platform.

Systems should be in place to ensure that monitoring of the platform takes place regularly and this should involve a visual assessment of the performance of the platform and operating plant. It is a moot point as to who should carry out this inspection, although whoever does carry it out needs to be competent to do so. There are a number of proforma available for this purpose [''Appendix 9''] for example.

Drainage is key. Water and slurry that is allowed to build up on the surface can hide hazards such as recently constructed piles or uneven ground, and a poorly drained platform will deteriorate quickly.

A common cause for instability is where the platform has had to be excavated for some reason and then not reinstated properly. Perhaps an obstruction has had to be removed, or a service relocated. In these situations it is essential that reinstatement is done to the original design standard, including any geosynthetic reinforcement. It is good practice to include a sign off for this work, ideally on the inspection log.

On some sites platforms are now constructed using stabilised materials. These comprise hydraulically bound materials (HBM), including cement bound materials (CBM). It should be noted that HBM materials are likely to have very low permeability and hence drainage design is critical, to ensure that the platform remains suitable for use and does not become waterlogged, potentially creating plant instability and hazards to operatives. A slope or a fall can be constructed into the platform by means of grading during final compaction and large areas may require falls to several intermediate drains to keep the surface free from standing water.

In colder climates winter working needs consideration and in terms of stability particularly during thawing conditions. During prolonged periods below zero degrees the platform is likely to be solid and stable, but may become very soft as temperatures rise. This thawing of the platform is also likely to be uneven, so one track of a machine may be on solid frozen ground, whilst the other is on soft thawed soil. In terms of rig stability this is the arguably the worst case scenario and needs to be designed for.

Whilst this document focusses rightly on rig stability, the platform must also be used by pedestrians. Due consideration should be given to providing a surface that can be easily walked upon without trip hazards (such as protruding reinforcement or wire often associated with demolition waste). Drainage should be adequate to keep the surface free from surface water that would make traversing it by foot dangerous. Holes in the platform should be backfilled and not allowed to fill up with water.

== Responsibility ==
Any working platform scheme is unlikely to be successful if it creates a responsibility that otherwise did not exist. We must use the contractual relationships and the legal frameworks that are already in place to increase the understanding of where the existing obligations of the various parties to a project already lie. This is about seeking clarity on the relationships between the parties and fundamentally making sure individuals know what their obligations are, rather than changing them.

Some observers make the argument that their insurers would be reluctant to support a working platform scheme. General contractors suspect that their liability is increased in some way and designers are concerned about professional indemnity cover. In fact the insurance community is fully supportive of improving working platforms as they collectively see it as a way of preventing loss. As the insurers often re-insure or layer insurance between them, at some point in time they all suffer, so the primary objective is to avoid the loss from occurring in the first place, regardless of who is initially liable. This is discussed in a document by HSB Engineering [''Appendix 11''].

Contractual arrangements should ensure that the platform is properly designed, installed, maintained and, as necessary, repaired throughout its working life. The respective roles of the various parties should be clearly understood and the responsibilities

and liabilities of all parties should be defined in the relevant contract. This should start with the tender documents and several federations have useful standard terms and conditions that incorporate working platform requirements. The NVAF’s version is appended [''Appendix 12''] as is OSHA clarification [''Appendix 14''].

But, in terms of influencing the debate around which party is responsible for what, it is interesting to consider their relative positions:

=== The client ===
Under general health and safety law and in particular the European ‘Construction Sites’ Directive [Appendix 1] the client has certain obligations with regards to safety co-ordination for his project. Moreover, most clients would be very keen to avoid any bad publicity that an over-turned rig could result in, quite apart from any safety concerns. In this regard, larger corporate and governmental clients are the most readily persuaded that they need to make provisions in their contracts for proper working platforms. Some however, will consider that health and safety, particularly for the temporary works is a matter solely for the contractors.

=== The general contractor ===
The general contractor is likely to be the “controlling entity” in terms of health and safety and under EU as well as US law this is ordinarily the coordinator for safety and health matters during the project. The European ‘Construction Sites’ directive requires them to, at the execution stage, “coordinate implementation of the general principles of prevention and safety…when technical aspects are being decided, in order to plan the various items or stages of work which are to take place simultaneously or in succession”. Also the coordinator shall, “coordinate implementation of the relevant provisions in order to ensure that employers apply the principles referred to [selected text below] in a consistent manner:

# ''keeping the construction site in good order and in a satisfactory state of cleanliness;''
# ''choosing the location of workstations bearing in mind how access to these workplaces is obtained, and determining routes or areas for the passage and movement and equipment..;''
# ''technical maintenance, pre-commissioning checks and regular checks on installations and equipment with a view to correcting any faults which might affect the safety and health of workers;''
# ''the demarcation and laying-out of areas for the storage of various materials, in particular where dangerous materials or substances are concerned;''
# ''the storage and disposal or removal of waste and debris...”''

Thus it is clear that the general contractors already have a legal obligation both in the application of the European ‘Construction Sites’ Directive and also more generally in other health and safety legislation. In the US, there are several ANSI Standards that also set out similar responsibilities. The main concern is that not all general contractors understand this. Hence any platform scheme has to be designed not to impose additional obligations on the parties, but rather to ensure that everyone is clear on what the legal duties already are.

The FPS Working Platform Certificate sets out to do just this [''Appendix 9'']. The first section, Part 1, requests the name of the individual that has carried out a design of the platform. It does not ask for the design, nor even the installation criteria. This is done, so that liability for checking is not inadvertently passed down to other parties to the contract (such as the specialist geotechnical contractor). The act of asking for a name, is poignant as this is not a “tick-box” exercise; few people would write a name on the form unless they were satisfied that they had carried out the design and were competent to do so. This is not imposing any additional liability on the general contractor, no signature is required, it merely confirms that a temporary works design has been done and who completed it.

Part 2 also simply confirms that the general contractor has carried out their coordination role properly. It does not demand that the general contractor has to directly himself design, install, maintain, inspect or repair the platform, all of these duties may and often are subcontracted. But, it is the responsibility of the general contractor, the coordinator, to make sure that someone is fulfilling these roles.

=== The geotechnical specialist ===
The geotechnical specialist has a duty to supply the correct loading and to ensure that the loading patterns remain as originally intended. If rig changes are made then it is important that the platform design is reassessed. It is imperative that the right information is passed to the platform designer.

There is also a duty of care of the geotechnical contractor to flag-up any unsafe conditions that are identified either before or during the works. If there is a defect in the platform that is manifest, then the geotechnical specialist cannot simply rely on the platform certificate and assume that everything is fine with the working surface. Typical obligations of the specialist site management might include:

* Daily visual inspection of the working platform;
* Daily maintenance of the platform (housekeeping, ground levelling, keeping the platform as dry as possible;
* Briefing site personnel on the risks related with unsafe working platforms;
* Ensuring exclusion zones are maintained around rigs and cranes and reducing the number of people required to work around these machines;
* Carrying out risk assessments in the case of new rigs arriving on site or the presence of additional machines, and ultimately;
* Stopping the work if the working conditions are unsafe. Everyone on the site should have the authority to stop the work. From analyses of several years’ of rig overturns, we have learned that in several cases someone on the site knew that something was wrong, but they continued and took the risk nevertheless.

All of these relationships need to be understood in order to properly embed a working platform scheme in the industry. Getting the responsibilities clear and agreeing which party takes on which role is critical to success. Ignoring the problem and hoping for the best is not the answer.

Nevertheless, some may still be tempted to take shortcuts. It is hoped that by making sure the parties truly understand the risks, then this temptation can be avoided. Regardless, working platforms can represent a significant cost and hence, like any other part of the construction process, need to be engineered with value in mind. Economic designs that are not too conservative will help and so proficient platform designers are in demand. Geotechnical specialists also have their part to play. Compromises between the weight, size and stability of the rig and the installation process are now part of the value judgement, as well as the economy of the foundation solution itself.

== Enforcement ==
To give any scheme “teeth”, consideration should be given to enforcement measures. Where platform initiatives have been most successful there are ramifications for not following best practice.

The first level is to decide at a company level what stance is to be taken. In some jurisdictions it may be possible to be insistent that every site has to have a platform certificate before the rig is even erected or rigged up. In other regions this may be more difficult to enforce. For interest, Keller’s Group policy is attached in [''Appendix 23 and 24'']''.''

It may be possible to persuade some client bodies to implement a scheme that applies to their sites or across a country. The Austrian Transport Guide [''Appendix 5''] is a good example of this.

Could the national federations do more to enforce a standard working platform approach? In the UK (back in 2004) the members of the FPS resolved that, ''“work shall not commence until the Working Platform Certificate, properly completed, is passed to an authorised person representing the Member Company”''. In order to check compliance, the members are visited by an independent auditor that checks that certificates are in place on current sites and may ask to see historical paperwork for completed sites (as part of a wider three year membership audit programme).

Once this more systematic approach to providing working platforms is accepted by the industry, it becomes best practice and arguably this allows it to pass into law. Clearly, this is a powerful level of enforcement and becomes a good argument for the adherence to a scheme. Indeed in the UK there have been several prosecutions of general contractors (and indeed geotechnical specialists) relating to poor standards of working platform provision, where the requirements of the FPS Working Platform Certificate scheme were cited.

== Training and Awareness ==
Finally, to assist all the members of the EFFC, and DFI there is already a plethora of training material that may be used, adapted or copied, such as:

* Site posters to deliver the message to the workforce, as in Figure 5/6/7.
* Material for site briefings and tool box talks.
* Driver and Banksman (Operator and Oiler) training.
* Project Manager training
* Webinars on how to use the BRE calculator

As mentioned in the design section there may be some Federations that are willing to support others with designer training.

The Polish federation (PZWFS) produced an excellent video showing the effects of an over turned rig and the importance of a proper working platform. This has been widely shared and a link to the video is included in Appendix 13. The German federation has also produced a comprehensive guide “Stopp Maschinen Umstürze”, a link to which is found at Appendix 21.
[[File:Fig5.png|alt=FIGURE 5. Keller Poster Campaign|none|thumb|FIGURE 5. Keller Poster Campaign]]
[[File:Fig6.png|alt=FIGURE 6. ADSC Poster Campaign|none|thumb|FIGURE 6. ADSC Poster Campaign]]
[[File:Fig7.png|alt=FIGURE 7. PFSF Poster Campaign|none|thumb|FIGURE 7. PFSF Poster Campaign]]

== Summary ==
The provision of a proper working platform is essential to the safe (and often efficient) execution of geotechnical works. However, as this impacts upon a number of stakeholders in a project it is not always easy to ensure and there are sometimes conflicts of interest, not least led by the cost implications.

However, experience from around the world shows it is possible to influence the main players and bring the construction industry up to standard. In order to move forwards, a number of steps need to be taken, sequentially. Skipping a step will cause inertia and result in conflict later on. These are:

=== Raise Awareness ===

* Working with the national federation, identify the magnitude of the problem. If possible obtain statistics as to the number of rig over-turns per year in the market and also case studies. Photographs are always useful.
* Present to audiences comprising general contractors, large clients and governmental bodies.
* Involve unions and enforcement authorities.
* Impress upon those involved that the risk of rigs overturning due to poor working platforms can be mitigated almost entirely with the right scheme and everyone’s commitment.

=== Establish the Rig Loading Parameters ===

* Evaluate the sources of rig loading. What will be done where the manufacturers’ loading details are not available?
* The FPS (UK federation) Spreadsheet method could be adopted, or;
* Consider specifying a range of generic rig loading as promoted in the Austrian FSV guidance, or;
* Alternatively, a blanket loading requirement may be a good starting point, see the ABEF (Belgian federation) requirements.

=== Design the Working Platform ===

* Identify the current methods of design and promote a discussion amongst designers as to how to produce economic designs.
* If needed, create a market for a platform design service, supplied by the established consultants or perhaps independent geotechnical professionals;
* Otherwise, it may be necessary to develop internal competence, but this could be income generating.
* Devise a system whereby the “safety co-ordinator” (usually the general contractor) confirms that the design has been done.
* Implement Checks on the Platform Installation
* Develop a sign-off sheet to validate that the platform has been installed in accordance with the design.
* Produce guidance that covers the other requirements of the platform, such as it should be free draining, suitable for
* pedestrians, have maximum slope angles and have demarcation.
* Decide on testing requirements, whether this is necessary and if so what tests should be employed.

=== Inspect the Working Platform ===

* Identify who shall inspect the platform and how frequently.
* Establish a means of recording the inspection and how repairs to the platform are managed.

=== Enforce the Process ===

* Decide upon your own company’s policy.
* Persuade the federation to take a stance and come up with sanctions.
* Persuade general contractors or general contractor organisations to adopt the procedures.
* Encourage enforcement agencies to follow best practice and prosecute those who do not comply.
* Write working platform requirements into local specifications and codes.

=== Train and Promote ===

* Train your workforce and set out your expectations.
* Work with the federation to produce industry wide training material.
* Identify specific training needs outside your immediate influence, such as training on platform design methods.
* Copy the existing training material that exists!

== Route Forward ==
This guide is a compilation of current thinking in the our industry, but further work is required. For example, we need to develop other options for testing other than the plate load test, which may lead to academic research. Similarly, we could investigate the actual bearing pressures under the rigs during operation and, on a connected matter, we will need to gauge our response to those modern rigs that give the driver real-time feedback on the rig bearing pressures. It is therefore envisaged that this document will be updated to include these developments.

It is acknowledged that improving the situation is difficult and it takes time and persistence. But the ultimate objective in reducing the number of rigs that topple over is a worthwhile and important one. The steps that are detailed provide a road map but to make them effective still needs will and determination to drive the necessary changes.

However, change is possible and some jurisdictions have managed to implement comprehensive schemes and systems that have had a huge impact in improving the standard of working platforms. To support this statement and to provide some final encouragement, if it were needed, some photographs of good practice are included in [Appendix 25].

File:Fig7.png

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Mburpee:

FIGURE 7. PFSF Poster Campaign

File:Fig6.png

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Mburpee:

FIGURE 6. ADSC Poster Campaign

File:Fig5.png

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Mburpee:

FIGURE 5. Keller Poster Campaign

File:Fig4.png

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Mburpee:

FIGURE 4. Plate Load Test Equipment

File:Drilling.png

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Mburpee:

drilling

File:Tracking.png

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Mburpee:

tracking

File:Fig3.png

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Mburpee:

FIGURE 3. Other Users of the Platform

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Mburpee:

FIGURE 2. Steps in Implementing Effective Working Platforms

File:Fig2.png

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Mburpee:

FIGURE 2. Steps in Implementing Effective Working Platforms

Guide to Working Platforms

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Mburpee: The importance of the stability of large and tall equipment when working on construction projects is undeniable. As the gruesome image below shows, the consequences of unstable platforms can be devastating.

Terminology and Evaluation Criteria of Crosshole Sonic Logging (CSL) as applied to Deep Foundations

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Mburpee:

Nondestructive testing of drilled shaft foundations via Crosshole Sonic Logging (CSL) is often performed as part of the quality assurance process to assess the soundness of concrete. The intent of CSL testing is to identify irregularities such as soil intrusion, necking, soft bottom, segregation, voids and other defects that could result in poor structural performance of the foundation. Over time, CSL rating criteria based on first arrival time and relative energy have incorrectly evolved to often be the sole means of determining the acceptability of a shaft. Some of these criteria have found their way into regulatory agency specifications, with acceptance values often differing from agency to agency.

The purpose of this document is to review the state of the practice (including experience gained over the past 20 years), propose improved CSL rating criteria and make recommendations for additional assessment, as well as educate the industry on the proper interpretation of CSL test. CSL test results alone should not be the sole means of rejecting or accepting a shaft.

A task force of industry exerts was formed to review the existing CSL rating criteria and propose improvements where appropriate. The recommendations presented herein are the consensus of the task force, which believes that they should be incorporated into future criteria, codes and specifications.

This paper was produced as a joint effort between the Codes and Standards Committee, the Drilled Shafts Committee and Testing and Evaluation Committee. A task force was authorized under Testing and Evaluation Committee. The task force contributed their expertise in web-based discussions often every two weeks over a period of three years. Interested participants were invited to participate at any time. The document had two rounds of broad industry review, two rounds of DFI Technical Advisory Committee reviews, and a Public Comments process. All comments were considered in producing the final document.

== Literature Review ==
The construction of cast-in-situ deep foundation elements can introduce unintended structural flaws that, depending on size and location, can compromise the foundation performance. The causes of such flaws have been discussed by several researchers including Baker and Khan (1971), Reese and Wright (1977) and O’Neill (1991). Authors of the various references cited here often use the terms “flaw” and “defect” indiscriminately or interchangeably. The terminology used throughout this section is the terminology used in the original references; recommended terminology is provided subsequently in this document.

O’Neill (1991) categorized the causes of structural defects into five (5) categories, namely defects arising from

* general construction problems,
* drilling problems,
* casing management problems,
* slurry management problems, and
* design deficiencies.

O’Neill does not separately categorize defects arising from concrete placement, as they are included in all of the above categories.

The most commonly used testing methods for evaluation of the structural integrity of drilled deep foundations are:

* Low Strain Integrity Testing (ASTM D5882),
* Crosshole Sonic Logging (ASTM D6760),
* Gamma-Gamma Density Logging, and
* Thermal Integrity Profiling (ASTM D7949).

State-of-practice Non-Destructive Test (NDT) methods can detect some of these larger flaws, whereas smaller flaws can remain undetected. O’Neill and Sarhan (2004) state that large voids and soil inclusions, occupying more than 15% of the cross-sectional area of the shaft, can usually be detected with state-of-practice nondestructive evaluation methods. In their paper, the authors consider all flaws that can be identifiable by NDT methods as “not minor”, by definition. Sarhan and O’Neill (2002a) mention that “flaws large enough to be detected by non-destructive evaluation methods (NDE) are almost always repaired or the drilled shaft is replaced”, whereas the effect of minor undetectable flaws should be accounted for in the design.

Several researchers and industry practitioners have investigated the ability of NDT methods to detect flaws introduced during the construction process. Sarhan et al. (2002b) summarize some of these studies in their paper “Flexural Behavior of Drilled Shafts with Minor Flaws”. As presented in their summary:

* Baker et al. (1993) conclude “down-tube” techniques could detect flaws that occupied only 15% of the cross-sectional area of drilled shafts;
* Amir (personal communication) indicates cross-tube ultrasonic tests could reliably detect soft defects that comprise about 9% of the cross-sectional area of a 0.76m (30-in) diameter drilled shaft;
* Chernauskas and Paikowsky (1999 and 2000), through several case histories and using various NDT methods, conclude that these methods are useful in detecting flaws comprising 20% or more of the cross sections of drilled shafts;
* Iskander et al. (2001) conclude down-tube methods are generally able to identify flaws exceeding 10% of the cross-sectional area; and
* Sarhan et al. (2000) conclude that, after a field study on six full-scale drilled shafts installed in stiff clay and employing pre-installed void flaws of areas ranging from 10.7% to 16.7% of the cross-sectional area, void-type flaws occupying areas up to 15% of the cross-sectional area could remain undetected. The study employed NDT tests ranging from surface techniques to down-tube methods.

Amir and Amir (2009) found, in both controlled site testing and finite element modeling, that modern CSL equipment can detect flaws occupying 10% of the pile's cross-section, provided the flaw is within the reinforcing cage.

The previously referenced cross-sectional area percentages refer to defects located inside the reinforcing cage and confirm O’Neill’s findings that flaws occupying as little as 15% of the cross-sectional area can be detected. CSL methods can only detect defects when such defects are in the path between access tubes; and since the tubes are generally attached to the inside of the cage, defects outside the cage in the cover zone cannot be detected. If the entire cover is missing, the cross-section percentage can be significantly greater than 10% and be undetected.

Baker and Khan (1971) suggest the use of multiple NDT methods wherever feasible, as this approach will produce more definitive answers than the use of a single NDT method.

Several studies investigate the percentage of drilled shafts with detectable defects. O’Neill and Sarhan (2004) report rejection of 20% of drilled shafts in the Caltrans database constructed during the period of 1996-2000 under drilling slurry due to flaws identified by NDT methods. By their definition, flaws identifiable by NDT are “not minor”. Their paper reports other case study findings with similar percentages of shafts with identifiable flaws (18%, 20%, etc.). Faiella and Superbo (1998) present a study where CSL testing detected flaws in 25% of drilled shafts from 37 sites in Italy. The database included 6800 shafts.

Jones and Wu (2005) report in their paper that 56% of 299 drilled shafts tested with CSL in Mid-Western US presented some type of anomaly (defined as at least a 25% wave speed reduction). Most of the shaft anomalies (81%) were located within the top or bottom one meter of the shafts. Jones and Wu (2005) also comment that coring is problematic, is difficult to perform correctly, and may not necessarily confirm a CSL anomaly.

Camp et al. (2007) compiled a database of 400 CSL-tested shafts installed by ten different contractors in South Carolina. The authors found 33% of the tested shafts contained an anomaly (defined as at least a 20% wave speed reduction) and that 90% of anomalies were within the top or bottom two shaft diameters. Camp et al. (2007) also make a distinction between anomalies and actual defects that compromise the performance.

The real question to be answered is whether these flaws or defects affect the intended performance of the shafts. Proper defect characterization and assessment of their effect in the load-bearing capacity of the shaft should include analyzing the defects' shape, size and location, and other factors like the geotechnical capacity of the shaft, whether the defect is on the compression side in the flexural zone, etc. Defects occurring in zones of high load transfer and high internal stresses are critical. Therefore, defects occurring at the top of the shaft will likely affect foundation performance and are of greater concern. When combined with the O’Neill and Sarhan (2004) survey conclusion (the most probable location of a flaw to be within the upper five diameters of the shaft), the critical aspect of the proper evaluation of defects becomes obvious. Defects at the bottom of the shaft are important when end bearing is part of the design.

Sarhan et al. (2002b) investigated the effect of the shape of structural defects on the flexural capacity of the shaft in an experimental study including small scale and large-scale laboratory tests. The authors analyzed two types of flaws commonly observed in drilled shafts resulting from soil cuttings floating on the rising column of fluid concrete in a slurry pour:

* Type A flaw has most of its area lying outside of the reinforcement cage (only a small area is penetrating inside the cage), whereas
* Type B flaw penetrates inside the cage into the core of the shaft.

Both flaw types occupy 15% of the gross cross-sectional area (the limit of identifiable versus unidentifiable flaw size through NDT methods according to O’Neill). It was shown that the Type B void flaw associates with the greatest reduction in flexural resistance under flexural loading conditions. More specifically, the Type B flaw results in a reduction in flexural resistance of 32%, whereas the Type A flaw has a reduction of only 17%. The results of the full-scale laboratory tests show reduction in flexural resistance for the Type B flaw of 27%. The research demonstrates that the shaft acceptance process must consider both flaw location and mode of foundation resistance, not just flaw size.

O’Neill (1991) in the context of his paper defines defects “as structural flaws that may or may not affect the serviceability of the foundation. Only a careful evaluation of the location and extent of defects relative to zones of high load transfer and high internal stresses can determine whether the defect requires repair”. Many parameters (i.e. shape, size, and location of the defect, maximum stresses expected on the shaft, redundancy of the shaft, design parameters such as friction shaft or end-bearing shaft, seismic and uplift concerns) must be evaluated upon detection of flaws/defects via NDT testing in order to understand their effect on the performance of the shaft and whether the shaft should be accepted as is, repaired or rejected.

Webster et al. (2011) indicate that structural problems detected by NDT methods are significant and their effect on structural capacity has to be evaluated and, if deemed necessary, mitigated. They suggest a classification system for both CSL testing and low strain integrity testing. Many state departments of transportation currently use their CSL classification system and includes the separate terms of “flaw” and “defect”. The authors also discuss NDT result evaluation techniques and mitigation solutions - e.g. flaws have to be addressed if they are indicated in more than 50% of the profiles, whereas defects must be addressed if they are indicated to affect more than one profile and involve at least three tubes.

Rohrbach et al. (2012) list various factors unrelated to concrete quality that can cause anomalies in CSL test results and adversely affect their interpretation. The authors propose that improvements are needed in the terminology that CSL testing providers use in order to avoid terms that may be ambiguous or controversial. They also call for increased communication between CSL testing providers and Engineers of Record to provide the information necessary for the proper use of engineering judgment in drilled shaft acceptance.

The question of which CSL results may indicate an anomaly is addressed by the Chinese and French CSL standards (Amir & Amir, 2008), where both refer to First Arrival Time (FAT) and Relative Energy (a measure of the signal intensity at the receiver probe). Alternately (and as a matter of policy), ASTM D6760 avoids interpretation of test results and leaves shaft acceptance to engineering judgment. Likins et al. (2004) state that, although CSL testing is straightforward, “there is no general common consensus (in most parts of the world) concerning what reduction in amplitude or delay in first arrival time defines a defect”. The authors state that a 20% FAT delay is a commonly suggested limit for a defect (e.g. French code AFNOR NF P94-160-1) and suggest that either the signal amplitude or relative energy should be included in CSL rating criteria. They also recommend shafts with “local partial defects” (shafts not designated as “good” or clearly “defective”) be analyzed by 3D tomography in order to gain a clearer visual-spatial illustration of defects, allowing more effective remediation or evaluation by the structural engineer.

The current CSL rating criteria guideline developed for the Federal Highway Administration called the Concrete Condition Rating Criteria (CCRC) is based on the percentage of velocity (or wave speed) reduction from the nominal, rather than FAT delays. The CCRC has been modified by several state departments of transportation (DOTs) with respect to the range for “Questionable” concrete. Some state DOTs use velocity reductions of 10% to 20%, while others use 10% to 25% to indicate questionable concrete. Some authorities define “Poor” concrete as velocity reductions or FAT delays greater than 30%. Note that a 30% reduction in velocity is not equivalent to a 30% increase in FAT (see Table 1). Still, others utilize a combination of FAT delays (or velocity decreases) with energy reductions.

[[File:FAT-Table.png|alt=Relation between FAT increase and Velocity Decrease|thumb|1000x1000px|Table 1: Relation between FAT increase and Velocity Decrease|none]]

== Discussions and Recommendations ==
Over time, CSL rating criteria based on first arrival time (or wave speed) and relative energy have often incorrectly evolved to be the sole means of determining the acceptability of a shaft. Some of these measures have found their way into regulatory agency specifications, with acceptance values often differing from agency to agency. The literature review notes a lack of quantitative assessment for these measurements, suggesting that “hard” boundary values presently used by many for shaft acceptance overstep our industry’s current state of knowledge. Recommendations contained herein are based on the collective experience of the authors over the past 20 years. They are intended to replace current CSL rating criteria and place CSL testing in proper perspective, as part of the evaluation for shaft acceptance.

== Terminology ==
This document updates shaft evaluation using CSL rating criteria to incorporate industry experience collected since their inception, with the purpose of improving the current state-of-practice. The following sections present new recommended CSL rating criteria and exclude the use of words such as “flaw” and “defect”. There are opinions in the industry that the term “defect” should not be used until an irregularity has been proven likely to significantly reduce the shaft’s capacity or durability.

Researchers and engineers often use the terms “flaw” and “defect” indiscriminately or interchangeably. Moreover, some practitioners assume an “anomaly” to be a “defect”. The following definitions are proposed in an effort to eliminate misuse or confusion in the industry among these terms (Figure 1):

=== Anomaly ===
Abnormal data that deviates from expectations, and may indicate a flaw or defect.

=== Flaw ===
Any imperfection in the planned shape or material of the foundation that may not necessarily affect its performance.

=== Defect ===
Any flaw that, because of size, location and inferred concrete properties, will have a significant adverse effect on the performance of the foundation.
[[File:Figure1-optimized.png|alt=Anomalies, flaws and defects|none|thumb|468x468px|Figure 1: Anomalies, flaws and defects]]

''This paper defines other important terms discussed as follows:''

=== Profile ===
The graphical representation versus depth of the CSL data between two tubes.

=== First Arrival Time (FAT) ===
The time required for the leading edge of the ultrasonic pulse to travel from the transmitter to the receiver.

=== Relative Energy (RE) ===
The relative signal strength of the pulse arriving at the receiver compared with a reference signal strength.

=== Tomography or tomographic analysis ===
A mathematical procedure applied to CSL data in order to provide a 2D or 3D map of the wave speed data (and therefore a visual identification of potential flaws or defects within a shaft).

=== Engineer of Record ===
A professional who is responsible for acceptance of the foundation. Foundation acceptance requires the evaluation of a wide array of information and should not be based on the CSL data alone.

== Assessing CSL Data Anomalies ==
From the reviewed published literature, the authors of this document suggest that the use of the word “anomaly” be restricted to describing only the test data, i.e. the CSL test data are either acceptable or abnormal. Where abnormal test data are observed, the first steps taken by the tester and/or the analyst must be to verify proper function and operation of the test equipment, according to the appropriate standards (such as ASTM D6760) and manufacturer’s recommendations.

Possible causes of abnormal CSL results (not necessarily related to flaws and defects in the shaft) include but are not limited to

* insufficient wait time between concrete placement and testing;
* tube disturbance while the concrete is setting;
* non-parallel tube alignments or over-sized tube diameters;
* the differential rate of hydration curing (e.g. concrete mix variability, shaft stick-up in water or air, moving water etc.);
* bleed water channels along the interface between the tubes and the concrete, especially in cased shafts;
* structural attachments within the shaft and other interferences within the rebar cage (e.g. multiple concentric cages, cage stiffeners, embedded bi-directional load cells, etc.);
* tubes placed outside the reinforcing cage;
* tube connectors, tapes and foreign substances on the tubes;
* concrete mix quality (e.g. shrinkage cracks);
* debonding; and
* lack of water or insufficient water in one or more access tubes at the time of testing.

If any of the aforementioned reasons are applicable, they should be discussed in the report. This information is vital so that the Engineer of Record can assess the validity of the CSL data results relative to other installation records and testing performed on the shaft.

== Proposed CSL Rating Criteria ==
CSL data should be used as a part of the shaft acceptance process, and thus needs some form of classification to delineate acceptable versus abnormal results. Once the possibility of equipment malfunction or improper testing procedures has been eliminated, CSL test results for each profile should be classified into one of the following categories:

'''Class A: Acceptable CSL test results.'''

'''Class B: Conditionally acceptable CSL test results.'''

'''Class C: Highly abnormal CSL test results.'''

The definition of each Class is as follows (see Figure 2):
[[File:Figure2.png|alt=Proposed CSL rating criteria |none|thumb|Figure 2: Graphical representation of the proposed CSL rating criteria |379x379px]]

=== Class A: Acceptable CSL test results ===

==== For any section of the profile ====

* First Arrival Time (FAT) increases are less than 15% of the local average FAT value, AND reductions in relative energy are less than 9 dB of the local average value of relative energy.

==== Recommendations ====

* Data within normal ranges. No additional assessment needed.

=== Class B: Conditionally acceptable CSL test results ===

==== For any section of the profile ====

* First Arrival Time (FAT) increases are between 15 and 30% of the local average FAT value, AND reductions in relative energy are less than 12 dB of the local average value of relative energy.

OR

* First Arrival Time (FAT) increases are less than 15% of the local average FAT value, AND reductions in relative energy are greater than 9 dB of the local average value of relative energy.

Once abnormal CSL data are observed within the shaft, an assessment is needed to determine the significance of the results relative to shaft performance.

The number of affected CSL profiles at any given depth should be considered when evaluating Class B results. The tester should report the number of Class B occurrences and their respective locations. ''These observations are not to be interpreted as a single overall evaluation of the shaft as being Class B.''

==== Recommendations (the following are recommended in no particular order and as appropriate): ====

* If the abnormal CSL data are observed near the top of the shaft (possible tube debonding), consider flooding the top of the shaft with water to restore the bond. Retesting after at least 30 minutes allows the water to seep down the interface between the tubes and the concrete and may improve the CSL results.
* For shafts with six or more access tubes and where not all tube combinations were tested during the original investigation, additional testing including the remaining tube combinations can improve delineation of any potential flaws.
* Class B results suggest that a detailed desktop evaluation may find the shaft as acceptable for the intended function. The desktop evaluation should consider:
** the number of affected profiles, depth and vertical extent of affected zones, and severity (proximity to the upper or lower limits of Class B);
** low or high concrete strength (a low overall estimated wave speed, even if consistent with depth, may indicate low strength concrete. Similarly, a high overall estimated wave speed may indicate higher strength concrete and should be considered when evaluating local FAT delays in relation to the application of the CSL results. Wave speed should be evaluated preferably from the major diagonal profiles. Perimeter profiles with shorter tube spacings are more sensitive to errors related to tube alignment and the path length through water within the tubes.); and
** construction records.
* Tomography should be considered where it may help to define the extent of the affected zone as accurately as possible.
* If the concrete is too young or retarders were used in the mix, retesting after a sufficient waiting period could improve test results. If the data improve significantly, then the Class B result can perhaps be accepted, particularly if the result is now near the lower Class B limit.
* The Engineer of Record may recommend retesting using another independent tester.
* Consider performing other tests having complementary capabilities. Depending on the horizontal extent and vertical location of the affected zone, use of alternative testing methods or investigations such as low strain impact integrity testing (ASTM D5882) may provide additional information for the foundation assessment.
* Near-surface excavation could be done to facilitate visual inspection for necking. Additionally, sampling through the side of the shaft (i.e. by chipping) for contaminated concrete may help to further define the extent and nature of the flaw.
* If after retesting, the Class B CSL result is still near the upper rating criteria limit given in Figure 2 and occurs in many profiles, consideration for additional recommended measures as presented in the following discussion of Class C would be prudent.

=== Class C: Highly abnormal CSL test results ===

==== For any section of the profile ====

* First Arrival Time (FAT) increases are greater than 30% of the local average FAT value.

OR

* First Arrival Time (FAT) increases are greater than 15% of the local average FAT value, AND reductions in relative energy are greater than 12 dB of the local average value of relative energy.

Once anomalous data are observed within the shaft, an assessment is needed to determine the significance of the results relative to shaft performance.

The number of affected CSL profiles at any given depth should be considered when evaluating Class C results. The tester should report the number of Class C occurrences and their respective locations. ''These observations are not to be interpreted as a single overall evaluation of the shaft as being Class C.''

Class C results typically need more evaluation, often requiring an assessment by the Engineer of Record and have a greater likelihood of requiring more invasive field testing and potentially shaft remediation.

==== Recommendations ====

* Follow all relevant Class B recommendations listed previously, plus consider performing a direct assessment of concrete quality and strength:
** Core sampling may help to further define the extent and nature of the affected zone. If coring is performed, the selection of the core diameter should consider aggregate size, testing purpose and potential remediation options.
** Perform compressive strength testing of core sample(s) from the affected zone. Compare test results with the specified minimum design strength, as well as with the strength of samples from a “normal” zone.

== Shaft Acceptance ==
The CSL testing specialist has been contracted to perform a specific test using well-established CSL procedures (ASTM D6760) and report findings in the form of arrival times, relative energy and a “waterfall diagram” for each tube combination profile. The client or specifying agency should understand that the CSL testing specialist is rarely provided with installation records or foundation design parameters. Therefore, the CSL testing specialist is usually not in a position to decide shaft acceptability. The Engineer of Record and the Design Team, with possible feedback from the CSL testing specialist, should review all the CSL data and construction records to determine the likely effect on foundation performance and decide shaft acceptability.

== Suggestions for Future Research ==
The literature review highlights the lack of quantitative assessment relating CSL test results (FAT increase and relative energy) to deficiencies in reinforced concrete drilled shaft foundations. The problem is compounded by the proliferation and variety of standards for evaluation of CSL results. Moreover, FAT increase and energy reduction limits noted herein are the collective experience of the authors and reflect the general bounds of current guidelines and long-time industry experience. The goal of this document is to propose improved CSL rating criteria and help in adopting more uniform standards. However, this is intended to be a living document and the following suggestions are provided to focus future research studies to further improve the proposed CSL rating criteria:

* Perform analyses (statistical or other quantitative approaches) to evaluate FAT increase and/or energy decrease limits in relation to foundation deficiencies (flaws/defects). A quantitative assessment of existing empirical guidelines is recommended, encompassing both existing and new data via field case studies.
* Quantitatively assess the relative importance of FAT increase versus energy decrease to determine if one or both should be used as CSL rating criteria.
* Perform analysis to determine a quantitative relation between energy reductions and concrete strength and condition.
* Perform assessment in large diameter shafts to quantify the advantage of testing all profiles.

== Conclusions ==
There are no universal or standard criteria to evaluate CSL test results. The current CSL rating criteria developed for the Federal Highway Administration called the Concrete Condition Rating Criteria (CCRC) is based on the percentage of velocity (or wave speed) reduction from the nominal, rather than the proposed FAT delays. The CCRC is outdated and does not reflect the collective industry experience and research over the last 20 years since CCRC was originally developed. FAT delays are recommended instead of velocity reductions because the tubes are often not parallel, and therefore the velocities calculated from top spacings may not be accurate.

Based on this task force’s collective experience the CSL rating criteria proposed herein present an improvement over commonly used criteria. More specifically:

* Terminology is improved to avoid ambiguous or misused terms like “anomaly”, “defect”, “questionable” etc. that often lead to improper interpretation or application of CSL test results.
* CSL rating criteria are simplified to three categories and thresholds are updated to reflect accumulated industry experience since the inception of the original rating criteria.
* Differentiation is made between abnormal CSL test results and shaft acceptability. The tester should report the number of Class B and C occurrences and their respective locations. These observations are not to be interpreted as a single overall evaluation of the shaft as being Class B or C. The Engineer of Record and the Design Team, with possible feedback from the CSL testing specialist, should review all the CSL data and construction records to determine the likely effect on foundation performance and decide shaft acceptability.
* CSL test results alone should not be the sole means of rejecting or accepting a shaft.
* Recommendations are given in a step-by-step fashion to assist the engineer in resolving any potential issues arising from the CSL test results.

The recommendations presented herein are the consensus of the task force, which believes that they should be incorporated into future criteria, codes and specifications. These guidelines are intended as a living document. As more research and experience are accumulated, the criteria recommended herein can be further improved.

== Acknowledgments ==
The assistance, comments, encouragement and interest in this project from DFI and their technical committees (Augered-Cast-In-Place Piles, Codes and Standards, Drilled Shafts, and Testing & Evaluation) are gratefully appreciated. The editorial expertise of Mary Kandaris improved the final document.

== References ==

# Amir, J.M and Amir, E.I. (2008). “Critical Comparison of Ultrasonic Pile Testing Standards,” Proc. 8th Intl. Conf. on Application of Stress Wave Theory to Piling, Lisbon, pp. 453-457.
# Amir, J.M. and Amir, E.I. (2009). ”Capabilities and Limitations of Cross Hole Ultrasonic Testing of Piles,” Proc. IFCEE, Orlando, FL.
# ASTM D5882-16, “Standard Test Method for Low Strain Impact Integrity Testing of Deep Foundations”, ASTM International, West Conshohocken, PA, 2016, www.astm.org
# ASTM D6760-16, “Standard Test Method for Integrity Testing of Concrete Deep Foundations by Ultrasonic Crosshole Testing”, ASTM International, West Conshohocken, PA, 2016, www.astm.org
# ASTM D7949-14, “Standard Test Methods for Thermal Integrity Profiling of Concrete Deep Foundations”, ASTM International, West Conshohocken, PA, 2014, www.astm.org
# Baker, C. N., and Khan, F. (1971). “Caisson Construction Problems and Correction in Chicago,” Journal of the Soil Mechanics and Foundation Division, ASCE, Vol. 97, No. 2, pp. 417-440.
# Baker, C. N., Drumright, E. E., Briaud, J-L., Mensah, F. D., and Parikh, G. (1993). “Drilled Shafts for Bridge Foundations,” Publications No. FHWA-RD-92-004, Federal Highway Administration, Washington DC, 336 pages.
# Camp III, W. M., Holley, D. W., and Canivan, G. J. (2007). “Crosshole Sonic Logging of South Carolina Drilled Shafts: A Five Year Summary,” ASCE Geo Denver, Denver CO.
# Chernauskas, L. R., and Paikowsky, S. G. (1999). “Deep Foundation Integrity Testing: Techniques and Case Histories,” Civil Engineering Practice, Vol. 14, No.1, Boston Soc. of Civil Eng Sec/ASCE, pp. 39-56.
# Chernauskas, L. R., and Paikowsky, S. G. (2000). “Defect Detection and Examination of Large Drilled Shafts using a New Cross-Hole Sonic Logging System,” ASCE Specialty Conference, Performance Verification of Constructed Geotechnical Facilities, University of Massachusetts, Amherst, April 9-12.
# Faiella, D., and Superbo, S. (1998). “Integrity Non-Destructive Tests of Deep Foundations by Means of Sonic Methods - Analysis of the Results Collected on 137 Sites in Italy,” Proceedings of 3rd International Geotechnical Seminar on Deep Foundations on Bored and Auger Piles, Ghent, Belgium, 19-21 Oct., Balkema, Rotterdam, pp. 209-213.
# Iskander, M., Roy, D., Ealy, C., and Kelly, S. (2001). “Class-A Prediction of Construction Defects in Drilled Shafts,” Transportation Research Record 1772, Paper No. 01-0308, Washington DC.
# Jones, W. C., and Wu, Y. (2005). “Experiences with Cross-Hole Sonic Logging and Concrete Coring for Verification of Drilled Shaft Integrity,” Proc. GEO Construction Quality Assurance/Quality Control Tech. Conf., Dallas-Ft. Worth TX, pp. 376-387.
# Likins, G., Webster, S., and Saavedra M. (2004). ”Evaluation of Defects and Tomography for CSL,” Proceedings of the Seventh International Conference on the Application of Stresswave Theory to Piles, Petaling Jaya, Selangor, Malaysia, pp. 381-386.
# O'Neill, M.W. (1991). “Construction Practices and Defects in Drilled Shafts,” Transportation Research Record 1331, Washington DC, pp. 6-14.
# O'Neill, M. W., and Sarhan H. A. (2004). ”Structural Resistance Factors for Drilled Shafts Considering Construction Flaws,” Current Practices and Future Trends in Deep Foundations, GSP 125 ASCE, pp. 166-185.
# Reese, L.C., and Wright, S.J. (1977). “Drilled shaft Manual: Vol 1: Construction Procedures and Design for Axial Loading,” Report IP77-21, FHWA, US Department of Transportation.
# Rohrbach, M. A., Kovacs, T. R., and Saidin, F. (2012). “Uncertainties in CSL Test Interpretations and Recommendations towards a More Efficient Process,” Proceedings of the DFI 37th Annual Conference, Houston TX.
# Sarhan, H. A., O’Neill, M. W., and Tabsh, S. W. (2000). “Structural Resistance Factors for Drilled Shafts with Minor Anomalies-Deterministic Study,” Department of Civil and Environmental Engineering, University of Houston, Houston, Texas.
# Sarhan, H. A., and O'Neill, M. W. (2002a). “Aspects of Structural Design of Drilled shafts for Flexure,” ASCE Intl. Deep Foundation Cong., GSP 116, Orlando FL, pp. 1151-1165.
# Sarhan, H. A., Tabsh, S. W., O'Neill, M. W., Ata, A., and Ealy, C. (2002b). “Flexural Behavior of Drilled Shafts with Minor Flaws,” Proc. Intl. Deep Foundation Congress, GSP No.116, Reston, VA, pp. 1136-1150.
# Webster, K., Rausche, F., and Webster, S. (2011). “Pile and Shaft Integrity Test Results, Classification, Acceptance and/or Rejection,” Compendium of Papers of the Transportation Research Board (TRB) 90th Annual Meeting, Washington, DC.

Terminology and Evaluation Criteria of Crosshole Sonic Logging (CSL) as applied to Deep Foundations

2022-09-26T20:50:12Z

Mburpee:

Nondestructive testing of drilled shaft foundations via Crosshole Sonic Logging (CSL) is often performed as part of the quality assurance process to assess the soundness of concrete. The intent of CSL testing is to identify irregularities such as soil intrusion, necking, soft bottom, segregation, voids and other defects that could result in poor structural performance of the foundation. Over time, CSL rating criteria based on first arrival time and relative energy have incorrectly evolved to often be the sole means of determining the acceptability of a shaft. Some of these criteria have found their way into regulatory agency specifications, with acceptance values often differing from agency to agency.

The purpose of this document is to review the state of the practice (including experience gained over the past 20 years), propose improved CSL rating criteria and make recommendations for additional assessment, as well as educate the industry on the proper interpretation of CSL test. CSL test results alone should not be the sole means of rejecting or accepting a shaft.

A task force of industry exerts was formed to review the existing CSL rating criteria and propose improvements where appropriate. The recommendations presented herein are the consensus of the task force, which believes that they should be incorporated into future criteria, codes and specifications.

This paper was produced as a joint effort between the Codes and Standards Committee, the Drilled Shafts Committee and Testing and Evaluation Committee. A task force was authorized under Testing and Evaluation Committee. The task force contributed their expertise in web-based discussions often every two weeks over a period of three years. Interested participants were invited to participate at any time. The document had two rounds of broad industry review, two rounds of DFI Technical Advisory Committee reviews, and a Public Comments process. All comments were considered in producing the final document.

== Literature Review ==
The construction of cast-in-situ deep foundation elements can introduce unintended structural flaws that, depending on size and location, can compromise the foundation performance. The causes of such flaws have been discussed by several researchers including Baker and Khan (1971), Reese and Wright (1977) and O’Neill (1991). Authors of the various references cited here often use the terms “flaw” and “defect” indiscriminately or interchangeably. The terminology used throughout this section is the terminology used in the original references; recommended terminology is provided subsequently in this document.

O’Neill (1991) categorized the causes of structural defects into five (5) categories, namely defects arising from

* general construction problems,
* drilling problems,
* casing management problems,
* slurry management problems, and
* design deficiencies.

O’Neill does not separately categorize defects arising from concrete placement, as they are included in all of the above categories.

The most commonly used testing methods for evaluation of the structural integrity of drilled deep foundations are:

* Low Strain Integrity Testing (ASTM D5882),
* Crosshole Sonic Logging (ASTM D6760),
* Gamma-Gamma Density Logging, and
* Thermal Integrity Profiling (ASTM D7949).

State-of-practice Non-Destructive Test (NDT) methods can detect some of these larger flaws, whereas smaller flaws can remain undetected. O’Neill and Sarhan (2004) state that large voids and soil inclusions, occupying more than 15% of the cross-sectional area of the shaft, can usually be detected with state-of-practice nondestructive evaluation methods. In their paper, the authors consider all flaws that can be identifiable by NDT methods as “not minor”, by definition. Sarhan and O’Neill (2002a) mention that “flaws large enough to be detected by non-destructive evaluation methods (NDE) are almost always repaired or the drilled shaft is replaced”, whereas the effect of minor undetectable flaws should be accounted for in the design.

Several researchers and industry practitioners have investigated the ability of NDT methods to detect flaws introduced during the construction process. Sarhan et al. (2002b) summarize some of these studies in their paper “Flexural Behavior of Drilled Shafts with Minor Flaws”. As presented in their summary:

* Baker et al. (1993) conclude “down-tube” techniques could detect flaws that occupied only 15% of the cross-sectional area of drilled shafts;
* Amir (personal communication) indicates cross-tube ultrasonic tests could reliably detect soft defects that comprise about 9% of the cross-sectional area of a 0.76m (30-in) diameter drilled shaft;
* Chernauskas and Paikowsky (1999 and 2000), through several case histories and using various NDT methods, conclude that these methods are useful in detecting flaws comprising 20% or more of the cross sections of drilled shafts;
* Iskander et al. (2001) conclude down-tube methods are generally able to identify flaws exceeding 10% of the cross-sectional area; and
* Sarhan et al. (2000) conclude that, after a field study on six full-scale drilled shafts installed in stiff clay and employing pre-installed void flaws of areas ranging from 10.7% to 16.7% of the cross-sectional area, void-type flaws occupying areas up to 15% of the cross-sectional area could remain undetected. The study employed NDT tests ranging from surface techniques to down-tube methods.

Amir and Amir (2009) found, in both controlled site testing and finite element modeling, that modern CSL equipment can detect flaws occupying 10% of the pile's cross-section, provided the flaw is within the reinforcing cage.

The previously referenced cross-sectional area percentages refer to defects located inside the reinforcing cage and confirm O’Neill’s findings that flaws occupying as little as 15% of the cross-sectional area can be detected. CSL methods can only detect defects when such defects are in the path between access tubes; and since the tubes are generally attached to the inside of the cage, defects outside the cage in the cover zone cannot be detected. If the entire cover is missing, the cross-section percentage can be significantly greater than 10% and be undetected.

Baker and Khan (1971) suggest the use of multiple NDT methods wherever feasible, as this approach will produce more definitive answers than the use of a single NDT method.

Several studies investigate the percentage of drilled shafts with detectable defects. O’Neill and Sarhan (2004) report rejection of 20% of drilled shafts in the Caltrans database constructed during the period of 1996-2000 under drilling slurry due to flaws identified by NDT methods. By their definition, flaws identifiable by NDT are “not minor”. Their paper reports other case study findings with similar percentages of shafts with identifiable flaws (18%, 20%, etc.). Faiella and Superbo (1998) present a study where CSL testing detected flaws in 25% of drilled shafts from 37 sites in Italy. The database included 6800 shafts.

Jones and Wu (2005) report in their paper that 56% of 299 drilled shafts tested with CSL in Mid-Western US presented some type of anomaly (defined as at least a 25% wave speed reduction). Most of the shaft anomalies (81%) were located within the top or bottom one meter of the shafts. Jones and Wu (2005) also comment that coring is problematic, is difficult to perform correctly, and may not necessarily confirm a CSL anomaly.

Camp et al. (2007) compiled a database of 400 CSL-tested shafts installed by ten different contractors in South Carolina. The authors found 33% of the tested shafts contained an anomaly (defined as at least a 20% wave speed reduction) and that 90% of anomalies were within the top or bottom two shaft diameters. Camp et al. (2007) also make a distinction between anomalies and actual defects that compromise the performance.

The real question to be answered is whether these flaws or defects affect the intended performance of the shafts. Proper defect characterization and assessment of their effect in the load-bearing capacity of the shaft should include analyzing the defects' shape, size and location, and other factors like the geotechnical capacity of the shaft, whether the defect is on the compression side in the flexural zone, etc. Defects occurring in zones of high load transfer and high internal stresses are critical. Therefore, defects occurring at the top of the shaft will likely affect foundation performance and are of greater concern. When combined with the O’Neill and Sarhan (2004) survey conclusion (the most probable location of a flaw to be within the upper five diameters of the shaft), the critical aspect of the proper evaluation of defects becomes obvious. Defects at the bottom of the shaft are important when end bearing is part of the design.

Sarhan et al. (2002b) investigated the effect of the shape of structural defects on the flexural capacity of the shaft in an experimental study including small scale and large-scale laboratory tests. The authors analyzed two types of flaws commonly observed in drilled shafts resulting from soil cuttings floating on the rising column of fluid concrete in a slurry pour:

* Type A flaw has most of its area lying outside of the reinforcement cage (only a small area is penetrating inside the cage), whereas
* Type B flaw penetrates inside the cage into the core of the shaft.

Both flaw types occupy 15% of the gross cross-sectional area (the limit of identifiable versus unidentifiable flaw size through NDT methods according to O’Neill). It was shown that the Type B void flaw associates with the greatest reduction in flexural resistance under flexural loading conditions. More specifically, the Type B flaw results in a reduction in flexural resistance of 32%, whereas the Type A flaw has a reduction of only 17%. The results of the full-scale laboratory tests show reduction in flexural resistance for the Type B flaw of 27%. The research demonstrates that the shaft acceptance process must consider both flaw location and mode of foundation resistance, not just flaw size.

O’Neill (1991) in the context of his paper defines defects “as structural flaws that may or may not affect the serviceability of the foundation. Only a careful evaluation of the location and extent of defects relative to zones of high load transfer and high internal stresses can determine whether the defect requires repair”. Many parameters (i.e. shape, size, and location of the defect, maximum stresses expected on the shaft, redundancy of the shaft, design parameters such as friction shaft or end-bearing shaft, seismic and uplift concerns) must be evaluated upon detection of flaws/defects via NDT testing in order to understand their effect on the performance of the shaft and whether the shaft should be accepted as is, repaired or rejected.

Webster et al. (2011) indicate that structural problems detected by NDT methods are significant and their effect on structural capacity has to be evaluated and, if deemed necessary, mitigated. They suggest a classification system for both CSL testing and low strain integrity testing. Many state departments of transportation currently use their CSL classification system and includes the separate terms of “flaw” and “defect”. The authors also discuss NDT result evaluation techniques and mitigation solutions - e.g. flaws have to be addressed if they are indicated in more than 50% of the profiles, whereas defects must be addressed if they are indicated to affect more than one profile and involve at least three tubes.

Rohrbach et al. (2012) list various factors unrelated to concrete quality that can cause anomalies in CSL test results and adversely affect their interpretation. The authors propose that improvements are needed in the terminology that CSL testing providers use in order to avoid terms that may be ambiguous or controversial. They also call for increased communication between CSL testing providers and Engineers of Record to provide the information necessary for the proper use of engineering judgment in drilled shaft acceptance.

The question of which CSL results may indicate an anomaly is addressed by the Chinese and French CSL standards (Amir & Amir, 2008), where both refer to First Arrival Time (FAT) and Relative Energy (a measure of the signal intensity at the receiver probe). Alternately (and as a matter of policy), ASTM D6760 avoids interpretation of test results and leaves shaft acceptance to engineering judgment. Likins et al. (2004) state that, although CSL testing is straightforward, “there is no general common consensus (in most parts of the world) concerning what reduction in amplitude or delay in first arrival time defines a defect”. The authors state that a 20% FAT delay is a commonly suggested limit for a defect (e.g. French code AFNOR NF P94-160-1) and suggest that either the signal amplitude or relative energy should be included in CSL rating criteria. They also recommend shafts with “local partial defects” (shafts not designated as “good” or clearly “defective”) be analyzed by 3D tomography in order to gain a clearer visual-spatial illustration of defects, allowing more effective remediation or evaluation by the structural engineer.

The current CSL rating criteria guideline developed for the Federal Highway Administration called the Concrete Condition Rating Criteria (CCRC) is based on the percentage of velocity (or wave speed) reduction from the nominal, rather than FAT delays. The CCRC has been modified by several state departments of transportation (DOTs) with respect to the range for “Questionable” concrete. Some state DOTs use velocity reductions of 10% to 20%, while others use 10% to 25% to indicate questionable concrete. Some authorities define “Poor” concrete as velocity reductions or FAT delays greater than 30%. Note that a 30% reduction in velocity is not equivalent to a 30% increase in FAT (see Table 1). Still, others utilize a combination of FAT delays (or velocity decreases) with energy reductions.

[[File:FAT-Table.png|alt=Relation between FAT increase and Velocity Decrease|thumb|1000x1000px|Table 1: Relation between FAT increase and Velocity Decrease|none]]

== Discussions and Recommendations ==
Over time, CSL rating criteria based on first arrival time (or wave speed) and relative energy have often incorrectly evolved to be the sole means of determining the acceptability of a shaft. Some of these measures have found their way into regulatory agency specifications, with acceptance values often differing from agency to agency. The literature review notes a lack of quantitative assessment for these measurements, suggesting that “hard” boundary values presently used by many for shaft acceptance overstep our industry’s current state of knowledge. Recommendations contained herein are based on the collective experience of the authors over the past 20 years. They are intended to replace current CSL rating criteria and place CSL testing in proper perspective, as part of the evaluation for shaft acceptance.

== Terminology ==
This document updates shaft evaluation using CSL rating criteria to incorporate industry experience collected since their inception, with the purpose of improving the current state-of-practice. The following sections present new recommended CSL rating criteria and exclude the use of words such as “flaw” and “defect”. There are opinions in the industry that the term “defect” should not be used until an irregularity has been proven likely to significantly reduce the shaft’s capacity or durability.

Researchers and engineers often use the terms “flaw” and “defect” indiscriminately or interchangeably. Moreover, some practitioners assume an “anomaly” to be a “defect”. The following definitions are proposed in an effort to eliminate misuse or confusion in the industry among these terms (Figure 1):

=== Anomaly ===
Abnormal data that deviates from expectations, and may indicate a flaw or defect.

=== Flaw ===
Any imperfection in the planned shape or material of the foundation that may not necessarily affect its performance.

=== Defect ===
Any flaw that, because of size, location and inferred concrete properties, will have a significant adverse effect on the performance of the foundation.
[[File:Figure1.png|alt=Anomalies, flaws and defects |none|thumb|390x390px|Figure 1: Anomalies, flaws and defects ]]

''This paper defines other important terms discussed as follows:''

=== Profile ===
The graphical representation versus depth of the CSL data between two tubes.

=== First Arrival Time (FAT) ===
The time required for the leading edge of the ultrasonic pulse to travel from the transmitter to the receiver.

=== Relative Energy (RE) ===
The relative signal strength of the pulse arriving at the receiver compared with a reference signal strength.

=== Tomography or tomographic analysis ===
A mathematical procedure applied to CSL data in order to provide a 2D or 3D map of the wave speed data (and therefore a visual identification of potential flaws or defects within a shaft).

=== Engineer of Record ===
A professional who is responsible for acceptance of the foundation. Foundation acceptance requires the evaluation of a wide array of information and should not be based on the CSL data alone.

== Assessing CSL Data Anomalies ==
From the reviewed published literature, the authors of this document suggest that the use of the word “anomaly” be restricted to describing only the test data, i.e. the CSL test data are either acceptable or abnormal. Where abnormal test data are observed, the first steps taken by the tester and/or the analyst must be to verify proper function and operation of the test equipment, according to the appropriate standards (such as ASTM D6760) and manufacturer’s recommendations.

Possible causes of abnormal CSL results (not necessarily related to flaws and defects in the shaft) include but are not limited to

* insufficient wait time between concrete placement and testing;
* tube disturbance while the concrete is setting;
* non-parallel tube alignments or over-sized tube diameters;
* the differential rate of hydration curing (e.g. concrete mix variability, shaft stick-up in water or air, moving water etc.);
* bleed water channels along the interface between the tubes and the concrete, especially in cased shafts;
* structural attachments within the shaft and other interferences within the rebar cage (e.g. multiple concentric cages, cage stiffeners, embedded bi-directional load cells, etc.);
* tubes placed outside the reinforcing cage;
* tube connectors, tapes and foreign substances on the tubes;
* concrete mix quality (e.g. shrinkage cracks);
* debonding; and
* lack of water or insufficient water in one or more access tubes at the time of testing.

If any of the aforementioned reasons are applicable, they should be discussed in the report. This information is vital so that the Engineer of Record can assess the validity of the CSL data results relative to other installation records and testing performed on the shaft.

== Proposed CSL Rating Criteria ==
CSL data should be used as a part of the shaft acceptance process, and thus needs some form of classification to delineate acceptable versus abnormal results. Once the possibility of equipment malfunction or improper testing procedures has been eliminated, CSL test results for each profile should be classified into one of the following categories:

'''Class A: Acceptable CSL test results.'''

'''Class B: Conditionally acceptable CSL test results.'''

'''Class C: Highly abnormal CSL test results.'''

The definition of each Class is as follows (see Figure 2):
[[File:Figure2.png|alt=Proposed CSL rating criteria |none|thumb|Figure 2: Graphical representation of the proposed CSL rating criteria |379x379px]]

=== Class A: Acceptable CSL test results ===

==== For any section of the profile ====

* First Arrival Time (FAT) increases are less than 15% of the local average FAT value, AND reductions in relative energy are less than 9 dB of the local average value of relative energy.

==== Recommendations ====

* Data within normal ranges. No additional assessment needed.

=== Class B: Conditionally acceptable CSL test results ===

==== For any section of the profile ====

* First Arrival Time (FAT) increases are between 15 and 30% of the local average FAT value, AND reductions in relative energy are less than 12 dB of the local average value of relative energy.

OR

* First Arrival Time (FAT) increases are less than 15% of the local average FAT value, AND reductions in relative energy are greater than 9 dB of the local average value of relative energy.

Once abnormal CSL data are observed within the shaft, an assessment is needed to determine the significance of the results relative to shaft performance.

The number of affected CSL profiles at any given depth should be considered when evaluating Class B results. The tester should report the number of Class B occurrences and their respective locations. ''These observations are not to be interpreted as a single overall evaluation of the shaft as being Class B.''

==== Recommendations (the following are recommended in no particular order and as appropriate): ====

* If the abnormal CSL data are observed near the top of the shaft (possible tube debonding), consider flooding the top of the shaft with water to restore the bond. Retesting after at least 30 minutes allows the water to seep down the interface between the tubes and the concrete and may improve the CSL results.
* For shafts with six or more access tubes and where not all tube combinations were tested during the original investigation, additional testing including the remaining tube combinations can improve delineation of any potential flaws.
* Class B results suggest that a detailed desktop evaluation may find the shaft as acceptable for the intended function. The desktop evaluation should consider:
** the number of affected profiles, depth and vertical extent of affected zones, and severity (proximity to the upper or lower limits of Class B);
** low or high concrete strength (a low overall estimated wave speed, even if consistent with depth, may indicate low strength concrete. Similarly, a high overall estimated wave speed may indicate higher strength concrete and should be considered when evaluating local FAT delays in relation to the application of the CSL results. Wave speed should be evaluated preferably from the major diagonal profiles. Perimeter profiles with shorter tube spacings are more sensitive to errors related to tube alignment and the path length through water within the tubes.); and
** construction records.
* Tomography should be considered where it may help to define the extent of the affected zone as accurately as possible.
* If the concrete is too young or retarders were used in the mix, retesting after a sufficient waiting period could improve test results. If the data improve significantly, then the Class B result can perhaps be accepted, particularly if the result is now near the lower Class B limit.
* The Engineer of Record may recommend retesting using another independent tester.
* Consider performing other tests having complementary capabilities. Depending on the horizontal extent and vertical location of the affected zone, use of alternative testing methods or investigations such as low strain impact integrity testing (ASTM D5882) may provide additional information for the foundation assessment.
* Near-surface excavation could be done to facilitate visual inspection for necking. Additionally, sampling through the side of the shaft (i.e. by chipping) for contaminated concrete may help to further define the extent and nature of the flaw.
* If after retesting, the Class B CSL result is still near the upper rating criteria limit given in Figure 2 and occurs in many profiles, consideration for additional recommended measures as presented in the following discussion of Class C would be prudent.

=== Class C: Highly abnormal CSL test results ===

==== For any section of the profile ====

* First Arrival Time (FAT) increases are greater than 30% of the local average FAT value.

OR

* First Arrival Time (FAT) increases are greater than 15% of the local average FAT value, AND reductions in relative energy are greater than 12 dB of the local average value of relative energy.

Once anomalous data are observed within the shaft, an assessment is needed to determine the significance of the results relative to shaft performance.

The number of affected CSL profiles at any given depth should be considered when evaluating Class C results. The tester should report the number of Class C occurrences and their respective locations. ''These observations are not to be interpreted as a single overall evaluation of the shaft as being Class C.''

Class C results typically need more evaluation, often requiring an assessment by the Engineer of Record and have a greater likelihood of requiring more invasive field testing and potentially shaft remediation.

==== Recommendations ====

* Follow all relevant Class B recommendations listed previously, plus consider performing a direct assessment of concrete quality and strength:
** Core sampling may help to further define the extent and nature of the affected zone. If coring is performed, the selection of the core diameter should consider aggregate size, testing purpose and potential remediation options.
** Perform compressive strength testing of core sample(s) from the affected zone. Compare test results with the specified minimum design strength, as well as with the strength of samples from a “normal” zone.

== Shaft Acceptance ==
The CSL testing specialist has been contracted to perform a specific test using well-established CSL procedures (ASTM D6760) and report findings in the form of arrival times, relative energy and a “waterfall diagram” for each tube combination profile. The client or specifying agency should understand that the CSL testing specialist is rarely provided with installation records or foundation design parameters. Therefore, the CSL testing specialist is usually not in a position to decide shaft acceptability. The Engineer of Record and the Design Team, with possible feedback from the CSL testing specialist, should review all the CSL data and construction records to determine the likely effect on foundation performance and decide shaft acceptability.

== Suggestions for Future Research ==
The literature review highlights the lack of quantitative assessment relating CSL test results (FAT increase and relative energy) to deficiencies in reinforced concrete drilled shaft foundations. The problem is compounded by the proliferation and variety of standards for evaluation of CSL results. Moreover, FAT increase and energy reduction limits noted herein are the collective experience of the authors and reflect the general bounds of current guidelines and long-time industry experience. The goal of this document is to propose improved CSL rating criteria and help in adopting more uniform standards. However, this is intended to be a living document and the following suggestions are provided to focus future research studies to further improve the proposed CSL rating criteria:

* Perform analyses (statistical or other quantitative approaches) to evaluate FAT increase and/or energy decrease limits in relation to foundation deficiencies (flaws/defects). A quantitative assessment of existing empirical guidelines is recommended, encompassing both existing and new data via field case studies.
* Quantitatively assess the relative importance of FAT increase versus energy decrease to determine if one or both should be used as CSL rating criteria.
* Perform analysis to determine a quantitative relation between energy reductions and concrete strength and condition.
* Perform assessment in large diameter shafts to quantify the advantage of testing all profiles.

== Conclusions ==
There are no universal or standard criteria to evaluate CSL test results. The current CSL rating criteria developed for the Federal Highway Administration called the Concrete Condition Rating Criteria (CCRC) is based on the percentage of velocity (or wave speed) reduction from the nominal, rather than the proposed FAT delays. The CCRC is outdated and does not reflect the collective industry experience and research over the last 20 years since CCRC was originally developed. FAT delays are recommended instead of velocity reductions because the tubes are often not parallel, and therefore the velocities calculated from top spacings may not be accurate.

Based on this task force’s collective experience the CSL rating criteria proposed herein present an improvement over commonly used criteria. More specifically:

* Terminology is improved to avoid ambiguous or misused terms like “anomaly”, “defect”, “questionable” etc. that often lead to improper interpretation or application of CSL test results.
* CSL rating criteria are simplified to three categories and thresholds are updated to reflect accumulated industry experience since the inception of the original rating criteria.
* Differentiation is made between abnormal CSL test results and shaft acceptability. The tester should report the number of Class B and C occurrences and their respective locations. These observations are not to be interpreted as a single overall evaluation of the shaft as being Class B or C. The Engineer of Record and the Design Team, with possible feedback from the CSL testing specialist, should review all the CSL data and construction records to determine the likely effect on foundation performance and decide shaft acceptability.
* CSL test results alone should not be the sole means of rejecting or accepting a shaft.
* Recommendations are given in a step-by-step fashion to assist the engineer in resolving any potential issues arising from the CSL test results.

The recommendations presented herein are the consensus of the task force, which believes that they should be incorporated into future criteria, codes and specifications. These guidelines are intended as a living document. As more research and experience are accumulated, the criteria recommended herein can be further improved.

== Acknowledgments ==
The assistance, comments, encouragement and interest in this project from DFI and their technical committees (Augered-Cast-In-Place Piles, Codes and Standards, Drilled Shafts, and Testing & Evaluation) are gratefully appreciated. The editorial expertise of Mary Kandaris improved the final document.

== References ==

# Amir, J.M and Amir, E.I. (2008). “Critical Comparison of Ultrasonic Pile Testing Standards,” Proc. 8th Intl. Conf. on Application of Stress Wave Theory to Piling, Lisbon, pp. 453-457.
# Amir, J.M. and Amir, E.I. (2009). ”Capabilities and Limitations of Cross Hole Ultrasonic Testing of Piles,” Proc. IFCEE, Orlando, FL.
# ASTM D5882-16, “Standard Test Method for Low Strain Impact Integrity Testing of Deep Foundations”, ASTM International, West Conshohocken, PA, 2016, www.astm.org
# ASTM D6760-16, “Standard Test Method for Integrity Testing of Concrete Deep Foundations by Ultrasonic Crosshole Testing”, ASTM International, West Conshohocken, PA, 2016, www.astm.org
# ASTM D7949-14, “Standard Test Methods for Thermal Integrity Profiling of Concrete Deep Foundations”, ASTM International, West Conshohocken, PA, 2014, www.astm.org
# Baker, C. N., and Khan, F. (1971). “Caisson Construction Problems and Correction in Chicago,” Journal of the Soil Mechanics and Foundation Division, ASCE, Vol. 97, No. 2, pp. 417-440.
# Baker, C. N., Drumright, E. E., Briaud, J-L., Mensah, F. D., and Parikh, G. (1993). “Drilled Shafts for Bridge Foundations,” Publications No. FHWA-RD-92-004, Federal Highway Administration, Washington DC, 336 pages.
# Camp III, W. M., Holley, D. W., and Canivan, G. J. (2007). “Crosshole Sonic Logging of South Carolina Drilled Shafts: A Five Year Summary,” ASCE Geo Denver, Denver CO.
# Chernauskas, L. R., and Paikowsky, S. G. (1999). “Deep Foundation Integrity Testing: Techniques and Case Histories,” Civil Engineering Practice, Vol. 14, No.1, Boston Soc. of Civil Eng Sec/ASCE, pp. 39-56.
# Chernauskas, L. R., and Paikowsky, S. G. (2000). “Defect Detection and Examination of Large Drilled Shafts using a New Cross-Hole Sonic Logging System,” ASCE Specialty Conference, Performance Verification of Constructed Geotechnical Facilities, University of Massachusetts, Amherst, April 9-12.
# Faiella, D., and Superbo, S. (1998). “Integrity Non-Destructive Tests of Deep Foundations by Means of Sonic Methods - Analysis of the Results Collected on 137 Sites in Italy,” Proceedings of 3rd International Geotechnical Seminar on Deep Foundations on Bored and Auger Piles, Ghent, Belgium, 19-21 Oct., Balkema, Rotterdam, pp. 209-213.
# Iskander, M., Roy, D., Ealy, C., and Kelly, S. (2001). “Class-A Prediction of Construction Defects in Drilled Shafts,” Transportation Research Record 1772, Paper No. 01-0308, Washington DC.
# Jones, W. C., and Wu, Y. (2005). “Experiences with Cross-Hole Sonic Logging and Concrete Coring for Verification of Drilled Shaft Integrity,” Proc. GEO Construction Quality Assurance/Quality Control Tech. Conf., Dallas-Ft. Worth TX, pp. 376-387.
# Likins, G., Webster, S., and Saavedra M. (2004). ”Evaluation of Defects and Tomography for CSL,” Proceedings of the Seventh International Conference on the Application of Stresswave Theory to Piles, Petaling Jaya, Selangor, Malaysia, pp. 381-386.
# O'Neill, M.W. (1991). “Construction Practices and Defects in Drilled Shafts,” Transportation Research Record 1331, Washington DC, pp. 6-14.
# O'Neill, M. W., and Sarhan H. A. (2004). ”Structural Resistance Factors for Drilled Shafts Considering Construction Flaws,” Current Practices and Future Trends in Deep Foundations, GSP 125 ASCE, pp. 166-185.
# Reese, L.C., and Wright, S.J. (1977). “Drilled shaft Manual: Vol 1: Construction Procedures and Design for Axial Loading,” Report IP77-21, FHWA, US Department of Transportation.
# Rohrbach, M. A., Kovacs, T. R., and Saidin, F. (2012). “Uncertainties in CSL Test Interpretations and Recommendations towards a More Efficient Process,” Proceedings of the DFI 37th Annual Conference, Houston TX.
# Sarhan, H. A., O’Neill, M. W., and Tabsh, S. W. (2000). “Structural Resistance Factors for Drilled Shafts with Minor Anomalies-Deterministic Study,” Department of Civil and Environmental Engineering, University of Houston, Houston, Texas.
# Sarhan, H. A., and O'Neill, M. W. (2002a). “Aspects of Structural Design of Drilled shafts for Flexure,” ASCE Intl. Deep Foundation Cong., GSP 116, Orlando FL, pp. 1151-1165.
# Sarhan, H. A., Tabsh, S. W., O'Neill, M. W., Ata, A., and Ealy, C. (2002b). “Flexural Behavior of Drilled Shafts with Minor Flaws,” Proc. Intl. Deep Foundation Congress, GSP No.116, Reston, VA, pp. 1136-1150.
# Webster, K., Rausche, F., and Webster, S. (2011). “Pile and Shaft Integrity Test Results, Classification, Acceptance and/or Rejection,” Compendium of Papers of the Transportation Research Board (TRB) 90th Annual Meeting, Washington, DC.

File:Figure1-optimized.png

2022-09-26T20:48:28Z

Mburpee:

Anomalies, flaws and defects

Terminology and Evaluation Criteria of Crosshole Sonic Logging (CSL) as applied to Deep Foundations

2022-09-26T20:36:43Z

Mburpee:

Nondestructive testing of drilled shaft foundations via Crosshole Sonic Logging (CSL) is often performed as part of the quality assurance process to assess the soundness of concrete. The intent of CSL testing is to identify irregularities such as soil intrusion, necking, soft bottom, segregation, voids and other defects that could result in poor structural performance of the foundation. Over time, CSL rating criteria based on first arrival time and relative energy have incorrectly evolved to often be the sole means of determining the acceptability of a shaft. Some of these criteria have found their way into regulatory agency specifications, with acceptance values often differing from agency to agency.

The purpose of this document is to review the state of the practice (including experience gained over the past 20 years), propose improved CSL rating criteria and make recommendations for additional assessment, as well as educate the industry on the proper interpretation of CSL test. CSL test results alone should not be the sole means of rejecting or accepting a shaft.

A task force of industry exerts was formed to review the existing CSL rating criteria and propose improvements where appropriate. The recommendations presented herein are the consensus of the task force, which believes that they should be incorporated into future criteria, codes and specifications.

This paper was produced as a joint effort between the Codes and Standards Committee, the Drilled Shafts Committee and Testing and Evaluation Committee. A task force was authorized under Testing and Evaluation Committee. The task force contributed their expertise in web-based discussions often every two weeks over a period of three years. Interested participants were invited to participate at any time. The document had two rounds of broad industry review, two rounds of DFI Technical Advisory Committee reviews, and a Public Comments process. All comments were considered in producing the final document.

== Literature Review ==
The construction of cast-in-situ deep foundation elements can introduce unintended structural flaws that, depending on size and location, can compromise the foundation performance. The causes of such flaws have been discussed by several researchers including Baker and Khan (1971), Reese and Wright (1977) and O’Neill (1991). Authors of the various references cited here often use the terms “flaw” and “defect” indiscriminately or interchangeably. The terminology used throughout this section is the terminology used in the original references; recommended terminology is provided subsequently in this document.

O’Neill (1991) categorized the causes of structural defects into five (5) categories, namely defects arising from

* general construction problems,
* drilling problems,
* casing management problems,
* slurry management problems, and
* design deficiencies.

O’Neill does not separately categorize defects arising from concrete placement, as they are included in all of the above categories.

The most commonly used testing methods for evaluation of the structural integrity of drilled deep foundations are:

* Low Strain Integrity Testing (ASTM D5882),
* Crosshole Sonic Logging (ASTM D6760),
* Gamma-Gamma Density Logging, and
* Thermal Integrity Profiling (ASTM D7949).

State-of-practice Non-Destructive Test (NDT) methods can detect some of these larger flaws, whereas smaller flaws can remain undetected. O’Neill and Sarhan (2004) state that large voids and soil inclusions, occupying more than 15% of the cross-sectional area of the shaft, can usually be detected with state-of-practice nondestructive evaluation methods. In their paper, the authors consider all flaws that can be identifiable by NDT methods as “not minor”, by definition. Sarhan and O’Neill (2002a) mention that “flaws large enough to be detected by non-destructive evaluation methods (NDE) are almost always repaired or the drilled shaft is replaced”, whereas the effect of minor undetectable flaws should be accounted for in the design.

Several researchers and industry practitioners have investigated the ability of NDT methods to detect flaws introduced during the construction process. Sarhan et al. (2002b) summarize some of these studies in their paper “Flexural Behavior of Drilled Shafts with Minor Flaws”. As presented in their summary:

* Baker et al. (1993) conclude “down-tube” techniques could detect flaws that occupied only 15% of the cross-sectional area of drilled shafts;
* Amir (personal communication) indicates cross-tube ultrasonic tests could reliably detect soft defects that comprise about 9% of the cross-sectional area of a 0.76m (30-in) diameter drilled shaft;
* Chernauskas and Paikowsky (1999 and 2000), through several case histories and using various NDT methods, conclude that these methods are useful in detecting flaws comprising 20% or more of the cross sections of drilled shafts;
* Iskander et al. (2001) conclude down-tube methods are generally able to identify flaws exceeding 10% of the cross-sectional area; and
* Sarhan et al. (2000) conclude that, after a field study on six full-scale drilled shafts installed in stiff clay and employing pre-installed void flaws of areas ranging from 10.7% to 16.7% of the cross-sectional area, void-type flaws occupying areas up to 15% of the cross-sectional area could remain undetected. The study employed NDT tests ranging from surface techniques to down-tube methods.

Amir and Amir (2009) found, in both controlled site testing and finite element modeling, that modern CSL equipment can detect flaws occupying 10% of the pile's cross-section, provided the flaw is within the reinforcing cage.

The previously referenced cross-sectional area percentages refer to defects located inside the reinforcing cage and confirm O’Neill’s findings that flaws occupying as little as 15% of the cross-sectional area can be detected. CSL methods can only detect defects when such defects are in the path between access tubes; and since the tubes are generally attached to the inside of the cage, defects outside the cage in the cover zone cannot be detected. If the entire cover is missing, the cross-section percentage can be significantly greater than 10% and be undetected.

Baker and Khan (1971) suggest the use of multiple NDT methods wherever feasible, as this approach will produce more definitive answers than the use of a single NDT method.

Several studies investigate the percentage of drilled shafts with detectable defects. O’Neill and Sarhan (2004) report rejection of 20% of drilled shafts in the Caltrans database constructed during the period of 1996-2000 under drilling slurry due to flaws identified by NDT methods. By their definition, flaws identifiable by NDT are “not minor”. Their paper reports other case study findings with similar percentages of shafts with identifiable flaws (18%, 20%, etc.). Faiella and Superbo (1998) present a study where CSL testing detected flaws in 25% of drilled shafts from 37 sites in Italy. The database included 6800 shafts.

Jones and Wu (2005) report in their paper that 56% of 299 drilled shafts tested with CSL in Mid-Western US presented some type of anomaly (defined as at least a 25% wave speed reduction). Most of the shaft anomalies (81%) were located within the top or bottom one meter of the shafts. Jones and Wu (2005) also comment that coring is problematic, is difficult to perform correctly, and may not necessarily confirm a CSL anomaly.

Camp et al. (2007) compiled a database of 400 CSL-tested shafts installed by ten different contractors in South Carolina. The authors found 33% of the tested shafts contained an anomaly (defined as at least a 20% wave speed reduction) and that 90% of anomalies were within the top or bottom two shaft diameters. Camp et al. (2007) also make a distinction between anomalies and actual defects that compromise the performance.

The real question to be answered is whether these flaws or defects affect the intended performance of the shafts. Proper defect characterization and assessment of their effect in the load-bearing capacity of the shaft should include analyzing the defects' shape, size and location, and other factors like the geotechnical capacity of the shaft, whether the defect is on the compression side in the flexural zone, etc. Defects occurring in zones of high load transfer and high internal stresses are critical. Therefore, defects occurring at the top of the shaft will likely affect foundation performance and are of greater concern. When combined with the O’Neill and Sarhan (2004) survey conclusion (the most probable location of a flaw to be within the upper five diameters of the shaft), the critical aspect of the proper evaluation of defects becomes obvious. Defects at the bottom of the shaft are important when end bearing is part of the design.

Sarhan et al. (2002b) investigated the effect of the shape of structural defects on the flexural capacity of the shaft in an experimental study including small scale and large-scale laboratory tests. The authors analyzed two types of flaws commonly observed in drilled shafts resulting from soil cuttings floating on the rising column of fluid concrete in a slurry pour:

* Type A flaw has most of its area lying outside of the reinforcement cage (only a small area is penetrating inside the cage), whereas
* Type B flaw penetrates inside the cage into the core of the shaft.

Both flaw types occupy 15% of the gross cross-sectional area (the limit of identifiable versus unidentifiable flaw size through NDT methods according to O’Neill). It was shown that the Type B void flaw associates with the greatest reduction in flexural resistance under flexural loading conditions. More specifically, the Type B flaw results in a reduction in flexural resistance of 32%, whereas the Type A flaw has a reduction of only 17%. The results of the full-scale laboratory tests show reduction in flexural resistance for the Type B flaw of 27%. The research demonstrates that the shaft acceptance process must consider both flaw location and mode of foundation resistance, not just flaw size.

O’Neill (1991) in the context of his paper defines defects “as structural flaws that may or may not affect the serviceability of the foundation. Only a careful evaluation of the location and extent of defects relative to zones of high load transfer and high internal stresses can determine whether the defect requires repair”. Many parameters (i.e. shape, size, and location of the defect, maximum stresses expected on the shaft, redundancy of the shaft, design parameters such as friction shaft or end-bearing shaft, seismic and uplift concerns) must be evaluated upon detection of flaws/defects via NDT testing in order to understand their effect on the performance of the shaft and whether the shaft should be accepted as is, repaired or rejected.

Webster et al. (2011) indicate that structural problems detected by NDT methods are significant and their effect on structural capacity has to be evaluated and, if deemed necessary, mitigated. They suggest a classification system for both CSL testing and low strain integrity testing. Many state departments of transportation currently use their CSL classification system and includes the separate terms of “flaw” and “defect”. The authors also discuss NDT result evaluation techniques and mitigation solutions - e.g. flaws have to be addressed if they are indicated in more than 50% of the profiles, whereas defects must be addressed if they are indicated to affect more than one profile and involve at least three tubes.

Rohrbach et al. (2012) list various factors unrelated to concrete quality that can cause anomalies in CSL test results and adversely affect their interpretation. The authors propose that improvements are needed in the terminology that CSL testing providers use in order to avoid terms that may be ambiguous or controversial. They also call for increased communication between CSL testing providers and Engineers of Record to provide the information necessary for the proper use of engineering judgment in drilled shaft acceptance.

The question of which CSL results may indicate an anomaly is addressed by the Chinese and French CSL standards (Amir & Amir, 2008), where both refer to First Arrival Time (FAT) and Relative Energy (a measure of the signal intensity at the receiver probe). Alternately (and as a matter of policy), ASTM D6760 avoids interpretation of test results and leaves shaft acceptance to engineering judgment. Likins et al. (2004) state that, although CSL testing is straightforward, “there is no general common consensus (in most parts of the world) concerning what reduction in amplitude or delay in first arrival time defines a defect”. The authors state that a 20% FAT delay is a commonly suggested limit for a defect (e.g. French code AFNOR NF P94-160-1) and suggest that either the signal amplitude or relative energy should be included in CSL rating criteria. They also recommend shafts with “local partial defects” (shafts not designated as “good” or clearly “defective”) be analyzed by 3D tomography in order to gain a clearer visual-spatial illustration of defects, allowing more effective remediation or evaluation by the structural engineer.

The current CSL rating criteria guideline developed for the Federal Highway Administration called the Concrete Condition Rating Criteria (CCRC) is based on the percentage of velocity (or wave speed) reduction from the nominal, rather than FAT delays. The CCRC has been modified by several state departments of transportation (DOTs) with respect to the range for “Questionable” concrete. Some state DOTs use velocity reductions of 10% to 20%, while others use 10% to 25% to indicate questionable concrete. Some authorities define “Poor” concrete as velocity reductions or FAT delays greater than 30%. Note that a 30% reduction in velocity is not equivalent to a 30% increase in FAT (see Table 1). Still, others utilize a combination of FAT delays (or velocity decreases) with energy reductions.

[[File:FAT-Table.png|alt=Relation between FAT increase and Velocity Decrease|thumb|1000x1000px|Table 1: Relation between FAT increase and Velocity Decrease|none]]

== Discussions and Recommendations ==
Over time, CSL rating criteria based on first arrival time (or wave speed) and relative energy have often incorrectly evolved to be the sole means of determining the acceptability of a shaft. Some of these measures have found their way into regulatory agency specifications, with acceptance values often differing from agency to agency. The literature review notes a lack of quantitative assessment for these measurements, suggesting that “hard” boundary values presently used by many for shaft acceptance overstep our industry’s current state of knowledge. Recommendations contained herein are based on the collective experience of the authors over the past 20 years. They are intended to replace current CSL rating criteria and place CSL testing in proper perspective, as part of the evaluation for shaft acceptance.

== Terminology ==
This document updates shaft evaluation using CSL rating criteria to incorporate industry experience collected since their inception, with the purpose of improving the current state-of-practice. The following sections present new recommended CSL rating criteria and exclude the use of words such as “flaw” and “defect”. There are opinions in the industry that the term “defect” should not be used until an irregularity has been proven likely to significantly reduce the shaft’s capacity or durability.

Researchers and engineers often use the terms “flaw” and “defect” indiscriminately or interchangeably. Moreover, some practitioners assume an “anomaly” to be a “defect”. The following definitions are proposed in an effort to eliminate misuse or confusion in the industry among these terms (Figure 1):

=== Anomaly ===
Abnormal data that deviates from expectations, and may indicate a flaw or defect.

=== Flaw ===
Any imperfection in the planned shape or material of the foundation that may not necessarily affect its performance.

=== Defect ===
Any flaw that, because of size, location and inferred concrete properties, will have a significant adverse effect on the performance of the foundation.
[[File:Figure1.png|alt=Anomalies, flaws and defects |none|thumb|468x468px|Figure 1: Anomalies, flaws and defects ]]

''This paper defines other important terms discussed as follows:''

=== Profile ===
The graphical representation versus depth of the CSL data between two tubes.

=== First Arrival Time (FAT) ===
The time required for the leading edge of the ultrasonic pulse to travel from the transmitter to the receiver.

=== Relative Energy (RE) ===
The relative signal strength of the pulse arriving at the receiver compared with a reference signal strength.

=== Tomography or tomographic analysis ===
A mathematical procedure applied to CSL data in order to provide a 2D or 3D map of the wave speed data (and therefore a visual identification of potential flaws or defects within a shaft).

=== Engineer of Record ===
A professional who is responsible for acceptance of the foundation. Foundation acceptance requires the evaluation of a wide array of information and should not be based on the CSL data alone.

== Assessing CSL Data Anomalies ==
From the reviewed published literature, the authors of this document suggest that the use of the word “anomaly” be restricted to describing only the test data, i.e. the CSL test data are either acceptable or abnormal. Where abnormal test data are observed, the first steps taken by the tester and/or the analyst must be to verify proper function and operation of the test equipment, according to the appropriate standards (such as ASTM D6760) and manufacturer’s recommendations.

Possible causes of abnormal CSL results (not necessarily related to flaws and defects in the shaft) include but are not limited to

* insufficient wait time between concrete placement and testing;
* tube disturbance while the concrete is setting;
* non-parallel tube alignments or over-sized tube diameters;
* the differential rate of hydration curing (e.g. concrete mix variability, shaft stick-up in water or air, moving water etc.);
* bleed water channels along the interface between the tubes and the concrete, especially in cased shafts;
* structural attachments within the shaft and other interferences within the rebar cage (e.g. multiple concentric cages, cage stiffeners, embedded bi-directional load cells, etc.);
* tubes placed outside the reinforcing cage;
* tube connectors, tapes and foreign substances on the tubes;
* concrete mix quality (e.g. shrinkage cracks);
* debonding; and
* lack of water or insufficient water in one or more access tubes at the time of testing.

If any of the aforementioned reasons are applicable, they should be discussed in the report. This information is vital so that the Engineer of Record can assess the validity of the CSL data results relative to other installation records and testing performed on the shaft.

== Proposed CSL Rating Criteria ==
CSL data should be used as a part of the shaft acceptance process, and thus needs some form of classification to delineate acceptable versus abnormal results. Once the possibility of equipment malfunction or improper testing procedures has been eliminated, CSL test results for each profile should be classified into one of the following categories:

'''Class A: Acceptable CSL test results.'''

'''Class B: Conditionally acceptable CSL test results.'''

'''Class C: Highly abnormal CSL test results.'''

The definition of each Class is as follows (see Figure 2):
[[File:Figure2.png|alt=Proposed CSL rating criteria |none|thumb|Figure 2: Graphical representation of the proposed CSL rating criteria |379x379px]]

=== Class A: Acceptable CSL test results ===

==== For any section of the profile ====

* First Arrival Time (FAT) increases are less than 15% of the local average FAT value, AND reductions in relative energy are less than 9 dB of the local average value of relative energy.

==== Recommendations ====

* Data within normal ranges. No additional assessment needed.

=== Class B: Conditionally acceptable CSL test results ===

==== For any section of the profile ====

* First Arrival Time (FAT) increases are between 15 and 30% of the local average FAT value, AND reductions in relative energy are less than 12 dB of the local average value of relative energy.

OR

* First Arrival Time (FAT) increases are less than 15% of the local average FAT value, AND reductions in relative energy are greater than 9 dB of the local average value of relative energy.

Once abnormal CSL data are observed within the shaft, an assessment is needed to determine the significance of the results relative to shaft performance.

The number of affected CSL profiles at any given depth should be considered when evaluating Class B results. The tester should report the number of Class B occurrences and their respective locations. ''These observations are not to be interpreted as a single overall evaluation of the shaft as being Class B.''

==== Recommendations (the following are recommended in no particular order and as appropriate): ====

* If the abnormal CSL data are observed near the top of the shaft (possible tube debonding), consider flooding the top of the shaft with water to restore the bond. Retesting after at least 30 minutes allows the water to seep down the interface between the tubes and the concrete and may improve the CSL results.
* For shafts with six or more access tubes and where not all tube combinations were tested during the original investigation, additional testing including the remaining tube combinations can improve delineation of any potential flaws.
* Class B results suggest that a detailed desktop evaluation may find the shaft as acceptable for the intended function. The desktop evaluation should consider:
** the number of affected profiles, depth and vertical extent of affected zones, and severity (proximity to the upper or lower limits of Class B);
** low or high concrete strength (a low overall estimated wave speed, even if consistent with depth, may indicate low strength concrete. Similarly, a high overall estimated wave speed may indicate higher strength concrete and should be considered when evaluating local FAT delays in relation to the application of the CSL results. Wave speed should be evaluated preferably from the major diagonal profiles. Perimeter profiles with shorter tube spacings are more sensitive to errors related to tube alignment and the path length through water within the tubes.); and
** construction records.
* Tomography should be considered where it may help to define the extent of the affected zone as accurately as possible.
* If the concrete is too young or retarders were used in the mix, retesting after a sufficient waiting period could improve test results. If the data improve significantly, then the Class B result can perhaps be accepted, particularly if the result is now near the lower Class B limit.
* The Engineer of Record may recommend retesting using another independent tester.
* Consider performing other tests having complementary capabilities. Depending on the horizontal extent and vertical location of the affected zone, use of alternative testing methods or investigations such as low strain impact integrity testing (ASTM D5882) may provide additional information for the foundation assessment.
* Near-surface excavation could be done to facilitate visual inspection for necking. Additionally, sampling through the side of the shaft (i.e. by chipping) for contaminated concrete may help to further define the extent and nature of the flaw.
* If after retesting, the Class B CSL result is still near the upper rating criteria limit given in Figure 2 and occurs in many profiles, consideration for additional recommended measures as presented in the following discussion of Class C would be prudent.

=== Class C: Highly abnormal CSL test results ===

==== For any section of the profile ====

* First Arrival Time (FAT) increases are greater than 30% of the local average FAT value.

OR

* First Arrival Time (FAT) increases are greater than 15% of the local average FAT value, AND reductions in relative energy are greater than 12 dB of the local average value of relative energy.

Once anomalous data are observed within the shaft, an assessment is needed to determine the significance of the results relative to shaft performance.

The number of affected CSL profiles at any given depth should be considered when evaluating Class C results. The tester should report the number of Class C occurrences and their respective locations. ''These observations are not to be interpreted as a single overall evaluation of the shaft as being Class C.''

Class C results typically need more evaluation, often requiring an assessment by the Engineer of Record and have a greater likelihood of requiring more invasive field testing and potentially shaft remediation.

==== Recommendations ====

* Follow all relevant Class B recommendations listed previously, plus consider performing a direct assessment of concrete quality and strength:
** Core sampling may help to further define the extent and nature of the affected zone. If coring is performed, the selection of the core diameter should consider aggregate size, testing purpose and potential remediation options.
** Perform compressive strength testing of core sample(s) from the affected zone. Compare test results with the specified minimum design strength, as well as with the strength of samples from a “normal” zone.

== Shaft Acceptance ==
The CSL testing specialist has been contracted to perform a specific test using well-established CSL procedures (ASTM D6760) and report findings in the form of arrival times, relative energy and a “waterfall diagram” for each tube combination profile. The client or specifying agency should understand that the CSL testing specialist is rarely provided with installation records or foundation design parameters. Therefore, the CSL testing specialist is usually not in a position to decide shaft acceptability. The Engineer of Record and the Design Team, with possible feedback from the CSL testing specialist, should review all the CSL data and construction records to determine the likely effect on foundation performance and decide shaft acceptability.

== Suggestions for Future Research ==
The literature review highlights the lack of quantitative assessment relating CSL test results (FAT increase and relative energy) to deficiencies in reinforced concrete drilled shaft foundations. The problem is compounded by the proliferation and variety of standards for evaluation of CSL results. Moreover, FAT increase and energy reduction limits noted herein are the collective experience of the authors and reflect the general bounds of current guidelines and long-time industry experience. The goal of this document is to propose improved CSL rating criteria and help in adopting more uniform standards. However, this is intended to be a living document and the following suggestions are provided to focus future research studies to further improve the proposed CSL rating criteria:

* Perform analyses (statistical or other quantitative approaches) to evaluate FAT increase and/or energy decrease limits in relation to foundation deficiencies (flaws/defects). A quantitative assessment of existing empirical guidelines is recommended, encompassing both existing and new data via field case studies.
* Quantitatively assess the relative importance of FAT increase versus energy decrease to determine if one or both should be used as CSL rating criteria.
* Perform analysis to determine a quantitative relation between energy reductions and concrete strength and condition.
* Perform assessment in large diameter shafts to quantify the advantage of testing all profiles.

== Conclusions ==
There are no universal or standard criteria to evaluate CSL test results. The current CSL rating criteria developed for the Federal Highway Administration called the Concrete Condition Rating Criteria (CCRC) is based on the percentage of velocity (or wave speed) reduction from the nominal, rather than the proposed FAT delays. The CCRC is outdated and does not reflect the collective industry experience and research over the last 20 years since CCRC was originally developed. FAT delays are recommended instead of velocity reductions because the tubes are often not parallel, and therefore the velocities calculated from top spacings may not be accurate.

Based on this task force’s collective experience the CSL rating criteria proposed herein present an improvement over commonly used criteria. More specifically:

* Terminology is improved to avoid ambiguous or misused terms like “anomaly”, “defect”, “questionable” etc. that often lead to improper interpretation or application of CSL test results.
* CSL rating criteria are simplified to three categories and thresholds are updated to reflect accumulated industry experience since the inception of the original rating criteria.
* Differentiation is made between abnormal CSL test results and shaft acceptability. The tester should report the number of Class B and C occurrences and their respective locations. These observations are not to be interpreted as a single overall evaluation of the shaft as being Class B or C. The Engineer of Record and the Design Team, with possible feedback from the CSL testing specialist, should review all the CSL data and construction records to determine the likely effect on foundation performance and decide shaft acceptability.
* CSL test results alone should not be the sole means of rejecting or accepting a shaft.
* Recommendations are given in a step-by-step fashion to assist the engineer in resolving any potential issues arising from the CSL test results.

The recommendations presented herein are the consensus of the task force, which believes that they should be incorporated into future criteria, codes and specifications. These guidelines are intended as a living document. As more research and experience are accumulated, the criteria recommended herein can be further improved.

== Acknowledgments ==
The assistance, comments, encouragement and interest in this project from DFI and their technical committees (Augered-Cast-In-Place Piles, Codes and Standards, Drilled Shafts, and Testing & Evaluation) are gratefully appreciated. The editorial expertise of Mary Kandaris improved the final document.

== References ==

# Amir, J.M and Amir, E.I. (2008). “Critical Comparison of Ultrasonic Pile Testing Standards,” Proc. 8th Intl. Conf. on Application of Stress Wave Theory to Piling, Lisbon, pp. 453-457.
# Amir, J.M. and Amir, E.I. (2009). ”Capabilities and Limitations of Cross Hole Ultrasonic Testing of Piles,” Proc. IFCEE, Orlando, FL.
# ASTM D5882-16, “Standard Test Method for Low Strain Impact Integrity Testing of Deep Foundations”, ASTM International, West Conshohocken, PA, 2016, www.astm.org
# ASTM D6760-16, “Standard Test Method for Integrity Testing of Concrete Deep Foundations by Ultrasonic Crosshole Testing”, ASTM International, West Conshohocken, PA, 2016, www.astm.org
# ASTM D7949-14, “Standard Test Methods for Thermal Integrity Profiling of Concrete Deep Foundations”, ASTM International, West Conshohocken, PA, 2014, www.astm.org
# Baker, C. N., and Khan, F. (1971). “Caisson Construction Problems and Correction in Chicago,” Journal of the Soil Mechanics and Foundation Division, ASCE, Vol. 97, No. 2, pp. 417-440.
# Baker, C. N., Drumright, E. E., Briaud, J-L., Mensah, F. D., and Parikh, G. (1993). “Drilled Shafts for Bridge Foundations,” Publications No. FHWA-RD-92-004, Federal Highway Administration, Washington DC, 336 pages.
# Camp III, W. M., Holley, D. W., and Canivan, G. J. (2007). “Crosshole Sonic Logging of South Carolina Drilled Shafts: A Five Year Summary,” ASCE Geo Denver, Denver CO.
# Chernauskas, L. R., and Paikowsky, S. G. (1999). “Deep Foundation Integrity Testing: Techniques and Case Histories,” Civil Engineering Practice, Vol. 14, No.1, Boston Soc. of Civil Eng Sec/ASCE, pp. 39-56.
# Chernauskas, L. R., and Paikowsky, S. G. (2000). “Defect Detection and Examination of Large Drilled Shafts using a New Cross-Hole Sonic Logging System,” ASCE Specialty Conference, Performance Verification of Constructed Geotechnical Facilities, University of Massachusetts, Amherst, April 9-12.
# Faiella, D., and Superbo, S. (1998). “Integrity Non-Destructive Tests of Deep Foundations by Means of Sonic Methods - Analysis of the Results Collected on 137 Sites in Italy,” Proceedings of 3rd International Geotechnical Seminar on Deep Foundations on Bored and Auger Piles, Ghent, Belgium, 19-21 Oct., Balkema, Rotterdam, pp. 209-213.
# Iskander, M., Roy, D., Ealy, C., and Kelly, S. (2001). “Class-A Prediction of Construction Defects in Drilled Shafts,” Transportation Research Record 1772, Paper No. 01-0308, Washington DC.
# Jones, W. C., and Wu, Y. (2005). “Experiences with Cross-Hole Sonic Logging and Concrete Coring for Verification of Drilled Shaft Integrity,” Proc. GEO Construction Quality Assurance/Quality Control Tech. Conf., Dallas-Ft. Worth TX, pp. 376-387.
# Likins, G., Webster, S., and Saavedra M. (2004). ”Evaluation of Defects and Tomography for CSL,” Proceedings of the Seventh International Conference on the Application of Stresswave Theory to Piles, Petaling Jaya, Selangor, Malaysia, pp. 381-386.
# O'Neill, M.W. (1991). “Construction Practices and Defects in Drilled Shafts,” Transportation Research Record 1331, Washington DC, pp. 6-14.
# O'Neill, M. W., and Sarhan H. A. (2004). ”Structural Resistance Factors for Drilled Shafts Considering Construction Flaws,” Current Practices and Future Trends in Deep Foundations, GSP 125 ASCE, pp. 166-185.
# Reese, L.C., and Wright, S.J. (1977). “Drilled shaft Manual: Vol 1: Construction Procedures and Design for Axial Loading,” Report IP77-21, FHWA, US Department of Transportation.
# Rohrbach, M. A., Kovacs, T. R., and Saidin, F. (2012). “Uncertainties in CSL Test Interpretations and Recommendations towards a More Efficient Process,” Proceedings of the DFI 37th Annual Conference, Houston TX.
# Sarhan, H. A., O’Neill, M. W., and Tabsh, S. W. (2000). “Structural Resistance Factors for Drilled Shafts with Minor Anomalies-Deterministic Study,” Department of Civil and Environmental Engineering, University of Houston, Houston, Texas.
# Sarhan, H. A., and O'Neill, M. W. (2002a). “Aspects of Structural Design of Drilled shafts for Flexure,” ASCE Intl. Deep Foundation Cong., GSP 116, Orlando FL, pp. 1151-1165.
# Sarhan, H. A., Tabsh, S. W., O'Neill, M. W., Ata, A., and Ealy, C. (2002b). “Flexural Behavior of Drilled Shafts with Minor Flaws,” Proc. Intl. Deep Foundation Congress, GSP No.116, Reston, VA, pp. 1136-1150.
# Webster, K., Rausche, F., and Webster, S. (2011). “Pile and Shaft Integrity Test Results, Classification, Acceptance and/or Rejection,” Compendium of Papers of the Transportation Research Board (TRB) 90th Annual Meeting, Washington, DC.

Terminology and Evaluation Criteria of Crosshole Sonic Logging (CSL) as applied to Deep Foundations

2022-09-26T20:34:58Z

Mburpee: image edits

Nondestructive testing of drilled shaft foundations via Crosshole Sonic Logging (CSL) is often performed as part of the quality assurance process to assess the soundness of concrete. The intent of CSL testing is to identify irregularities such as soil intrusion, necking, soft bottom, segregation, voids and other defects that could result in poor structural performance of the foundation. Over time, CSL rating criteria based on first arrival time and relative energy have incorrectly evolved to often be the sole means of determining the acceptability of a shaft. Some of these criteria have found their way into regulatory agency specifications, with acceptance values often differing from agency to agency.

The purpose of this document is to review the state of the practice (including experience gained over the past 20 years), propose improved CSL rating criteria and make recommendations for additional assessment, as well as educate the industry on the proper interpretation of CSL test. CSL test results alone should not be the sole means of rejecting or accepting a shaft.

A task force of industry exerts was formed to review the existing CSL rating criteria and propose improvements where appropriate. The recommendations presented herein are the consensus of the task force, which believes that they should be incorporated into future criteria, codes and specifications.

This paper was produced as a joint effort between the Codes and Standards Committee, the Drilled Shafts Committee and Testing and Evaluation Committee. A task force was authorized under Testing and Evaluation Committee. The task force contributed their expertise in web-based discussions often every two weeks over a period of three years. Interested participants were invited to participate at any time. The document had two rounds of broad industry review, two rounds of DFI Technical Advisory Committee reviews, and a Public Comments process. All comments were considered in producing the final document.

== Literature Review ==
The construction of cast-in-situ deep foundation elements can introduce unintended structural flaws that, depending on size and location, can compromise the foundation performance. The causes of such flaws have been discussed by several researchers including Baker and Khan (1971), Reese and Wright (1977) and O’Neill (1991). Authors of the various references cited here often use the terms “flaw” and “defect” indiscriminately or interchangeably. The terminology used throughout this section is the terminology used in the original references; recommended terminology is provided subsequently in this document.

O’Neill (1991) categorized the causes of structural defects into five (5) categories, namely defects arising from

* general construction problems,
* drilling problems,
* casing management problems,
* slurry management problems, and
* design deficiencies.

O’Neill does not separately categorize defects arising from concrete placement, as they are included in all of the above categories.

The most commonly used testing methods for evaluation of the structural integrity of drilled deep foundations are:

* Low Strain Integrity Testing (ASTM D5882),
* Crosshole Sonic Logging (ASTM D6760),
* Gamma-Gamma Density Logging, and
* Thermal Integrity Profiling (ASTM D7949).

State-of-practice Non-Destructive Test (NDT) methods can detect some of these larger flaws, whereas smaller flaws can remain undetected. O’Neill and Sarhan (2004) state that large voids and soil inclusions, occupying more than 15% of the cross-sectional area of the shaft, can usually be detected with state-of-practice nondestructive evaluation methods. In their paper, the authors consider all flaws that can be identifiable by NDT methods as “not minor”, by definition. Sarhan and O’Neill (2002a) mention that “flaws large enough to be detected by non-destructive evaluation methods (NDE) are almost always repaired or the drilled shaft is replaced”, whereas the effect of minor undetectable flaws should be accounted for in the design.

Several researchers and industry practitioners have investigated the ability of NDT methods to detect flaws introduced during the construction process. Sarhan et al. (2002b) summarize some of these studies in their paper “Flexural Behavior of Drilled Shafts with Minor Flaws”. As presented in their summary:

* Baker et al. (1993) conclude “down-tube” techniques could detect flaws that occupied only 15% of the cross-sectional area of drilled shafts;
* Amir (personal communication) indicates cross-tube ultrasonic tests could reliably detect soft defects that comprise about 9% of the cross-sectional area of a 0.76m (30-in) diameter drilled shaft;
* Chernauskas and Paikowsky (1999 and 2000), through several case histories and using various NDT methods, conclude that these methods are useful in detecting flaws comprising 20% or more of the cross sections of drilled shafts;
* Iskander et al. (2001) conclude down-tube methods are generally able to identify flaws exceeding 10% of the cross-sectional area; and
* Sarhan et al. (2000) conclude that, after a field study on six full-scale drilled shafts installed in stiff clay and employing pre-installed void flaws of areas ranging from 10.7% to 16.7% of the cross-sectional area, void-type flaws occupying areas up to 15% of the cross-sectional area could remain undetected. The study employed NDT tests ranging from surface techniques to down-tube methods.

Amir and Amir (2009) found, in both controlled site testing and finite element modeling, that modern CSL equipment can detect flaws occupying 10% of the pile's cross-section, provided the flaw is within the reinforcing cage.

The previously referenced cross-sectional area percentages refer to defects located inside the reinforcing cage and confirm O’Neill’s findings that flaws occupying as little as 15% of the cross-sectional area can be detected. CSL methods can only detect defects when such defects are in the path between access tubes; and since the tubes are generally attached to the inside of the cage, defects outside the cage in the cover zone cannot be detected. If the entire cover is missing, the cross-section percentage can be significantly greater than 10% and be undetected.

Baker and Khan (1971) suggest the use of multiple NDT methods wherever feasible, as this approach will produce more definitive answers than the use of a single NDT method.

Several studies investigate the percentage of drilled shafts with detectable defects. O’Neill and Sarhan (2004) report rejection of 20% of drilled shafts in the Caltrans database constructed during the period of 1996-2000 under drilling slurry due to flaws identified by NDT methods. By their definition, flaws identifiable by NDT are “not minor”. Their paper reports other case study findings with similar percentages of shafts with identifiable flaws (18%, 20%, etc.). Faiella and Superbo (1998) present a study where CSL testing detected flaws in 25% of drilled shafts from 37 sites in Italy. The database included 6800 shafts.

Jones and Wu (2005) report in their paper that 56% of 299 drilled shafts tested with CSL in Mid-Western US presented some type of anomaly (defined as at least a 25% wave speed reduction). Most of the shaft anomalies (81%) were located within the top or bottom one meter of the shafts. Jones and Wu (2005) also comment that coring is problematic, is difficult to perform correctly, and may not necessarily confirm a CSL anomaly.

Camp et al. (2007) compiled a database of 400 CSL-tested shafts installed by ten different contractors in South Carolina. The authors found 33% of the tested shafts contained an anomaly (defined as at least a 20% wave speed reduction) and that 90% of anomalies were within the top or bottom two shaft diameters. Camp et al. (2007) also make a distinction between anomalies and actual defects that compromise the performance.

The real question to be answered is whether these flaws or defects affect the intended performance of the shafts. Proper defect characterization and assessment of their effect in the load-bearing capacity of the shaft should include analyzing the defects' shape, size and location, and other factors like the geotechnical capacity of the shaft, whether the defect is on the compression side in the flexural zone, etc. Defects occurring in zones of high load transfer and high internal stresses are critical. Therefore, defects occurring at the top of the shaft will likely affect foundation performance and are of greater concern. When combined with the O’Neill and Sarhan (2004) survey conclusion (the most probable location of a flaw to be within the upper five diameters of the shaft), the critical aspect of the proper evaluation of defects becomes obvious. Defects at the bottom of the shaft are important when end bearing is part of the design.

Sarhan et al. (2002b) investigated the effect of the shape of structural defects on the flexural capacity of the shaft in an experimental study including small scale and large-scale laboratory tests. The authors analyzed two types of flaws commonly observed in drilled shafts resulting from soil cuttings floating on the rising column of fluid concrete in a slurry pour:

* Type A flaw has most of its area lying outside of the reinforcement cage (only a small area is penetrating inside the cage), whereas
* Type B flaw penetrates inside the cage into the core of the shaft.

Both flaw types occupy 15% of the gross cross-sectional area (the limit of identifiable versus unidentifiable flaw size through NDT methods according to O’Neill). It was shown that the Type B void flaw associates with the greatest reduction in flexural resistance under flexural loading conditions. More specifically, the Type B flaw results in a reduction in flexural resistance of 32%, whereas the Type A flaw has a reduction of only 17%. The results of the full-scale laboratory tests show reduction in flexural resistance for the Type B flaw of 27%. The research demonstrates that the shaft acceptance process must consider both flaw location and mode of foundation resistance, not just flaw size.

O’Neill (1991) in the context of his paper defines defects “as structural flaws that may or may not affect the serviceability of the foundation. Only a careful evaluation of the location and extent of defects relative to zones of high load transfer and high internal stresses can determine whether the defect requires repair”. Many parameters (i.e. shape, size, and location of the defect, maximum stresses expected on the shaft, redundancy of the shaft, design parameters such as friction shaft or end-bearing shaft, seismic and uplift concerns) must be evaluated upon detection of flaws/defects via NDT testing in order to understand their effect on the performance of the shaft and whether the shaft should be accepted as is, repaired or rejected.

Webster et al. (2011) indicate that structural problems detected by NDT methods are significant and their effect on structural capacity has to be evaluated and, if deemed necessary, mitigated. They suggest a classification system for both CSL testing and low strain integrity testing. Many state departments of transportation currently use their CSL classification system and includes the separate terms of “flaw” and “defect”. The authors also discuss NDT result evaluation techniques and mitigation solutions - e.g. flaws have to be addressed if they are indicated in more than 50% of the profiles, whereas defects must be addressed if they are indicated to affect more than one profile and involve at least three tubes.

Rohrbach et al. (2012) list various factors unrelated to concrete quality that can cause anomalies in CSL test results and adversely affect their interpretation. The authors propose that improvements are needed in the terminology that CSL testing providers use in order to avoid terms that may be ambiguous or controversial. They also call for increased communication between CSL testing providers and Engineers of Record to provide the information necessary for the proper use of engineering judgment in drilled shaft acceptance.

The question of which CSL results may indicate an anomaly is addressed by the Chinese and French CSL standards (Amir & Amir, 2008), where both refer to First Arrival Time (FAT) and Relative Energy (a measure of the signal intensity at the receiver probe). Alternately (and as a matter of policy), ASTM D6760 avoids interpretation of test results and leaves shaft acceptance to engineering judgment. Likins et al. (2004) state that, although CSL testing is straightforward, “there is no general common consensus (in most parts of the world) concerning what reduction in amplitude or delay in first arrival time defines a defect”. The authors state that a 20% FAT delay is a commonly suggested limit for a defect (e.g. French code AFNOR NF P94-160-1) and suggest that either the signal amplitude or relative energy should be included in CSL rating criteria. They also recommend shafts with “local partial defects” (shafts not designated as “good” or clearly “defective”) be analyzed by 3D tomography in order to gain a clearer visual-spatial illustration of defects, allowing more effective remediation or evaluation by the structural engineer.

The current CSL rating criteria guideline developed for the Federal Highway Administration called the Concrete Condition Rating Criteria (CCRC) is based on the percentage of velocity (or wave speed) reduction from the nominal, rather than FAT delays. The CCRC has been modified by several state departments of transportation (DOTs) with respect to the range for “Questionable” concrete. Some state DOTs use velocity reductions of 10% to 20%, while others use 10% to 25% to indicate questionable concrete. Some authorities define “Poor” concrete as velocity reductions or FAT delays greater than 30%. Note that a 30% reduction in velocity is not equivalent to a 30% increase in FAT (see Table 1). Still, others utilize a combination of FAT delays (or velocity decreases) with energy reductions.

[[File:FAT-Table.png|alt=Relation between FAT increase and Velocity Decrease|thumb|1000x1000px|Table 1: Relation between FAT increase and Velocity Decrease|none]]

== Discussions and Recommendations ==
Over time, CSL rating criteria based on first arrival time (or wave speed) and relative energy have often incorrectly evolved to be the sole means of determining the acceptability of a shaft. Some of these measures have found their way into regulatory agency specifications, with acceptance values often differing from agency to agency. The literature review notes a lack of quantitative assessment for these measurements, suggesting that “hard” boundary values presently used by many for shaft acceptance overstep our industry’s current state of knowledge. Recommendations contained herein are based on the collective experience of the authors over the past 20 years. They are intended to replace current CSL rating criteria and place CSL testing in proper perspective, as part of the evaluation for shaft acceptance.

== Terminology ==
This document updates shaft evaluation using CSL rating criteria to incorporate industry experience collected since their inception, with the purpose of improving the current state-of-practice. The following sections present new recommended CSL rating criteria and exclude the use of words such as “flaw” and “defect”. There are opinions in the industry that the term “defect” should not be used until an irregularity has been proven likely to significantly reduce the shaft’s capacity or durability.

Researchers and engineers often use the terms “flaw” and “defect” indiscriminately or interchangeably. Moreover, some practitioners assume an “anomaly” to be a “defect”. The following definitions are proposed in an effort to eliminate misuse or confusion in the industry among these terms (Figure 1):

=== Anomaly ===
Abnormal data that deviates from expectations, and may indicate a flaw or defect.

=== Flaw ===
Any imperfection in the planned shape or material of the foundation that may not necessarily affect its performance.

=== Defect ===
Any flaw that, because of size, location and inferred concrete properties, will have a significant adverse effect on the performance of the foundation.
[[File:Figure1.png|alt=Anomalies, flaws and defects |none|thumb|468x468px|Figure 1: Anomalies, flaws and defects ]]

''This paper defines other important terms discussed as follows:''

=== Profile ===
The graphical representation versus depth of the CSL data between two tubes.

=== First Arrival Time (FAT) ===
The time required for the leading edge of the ultrasonic pulse to travel from the transmitter to the receiver.

=== Relative Energy (RE) ===
The relative signal strength of the pulse arriving at the receiver compared with a reference signal strength.

=== Tomography or tomographic analysis ===
A mathematical procedure applied to CSL data in order to provide a 2D or 3D map of the wave speed data (and therefore a visual identification of potential flaws or defects within a shaft).

=== Engineer of Record ===
A professional who is responsible for acceptance of the foundation. Foundation acceptance requires the evaluation of a wide array of information and should not be based on the CSL data alone.

== Assessing CSL Data Anomalies ==
From the reviewed published literature, the authors of this document suggest that the use of the word “anomaly” be restricted to describing only the test data, i.e. the CSL test data are either acceptable or abnormal. Where abnormal test data are observed, the first steps taken by the tester and/or the analyst must be to verify proper function and operation of the test equipment, according to the appropriate standards (such as ASTM D6760) and manufacturer’s recommendations.

Possible causes of abnormal CSL results (not necessarily related to flaws and defects in the shaft) include but are not limited to

* insufficient wait time between concrete placement and testing;
* tube disturbance while the concrete is setting;
* non-parallel tube alignments or over-sized tube diameters;
* the differential rate of hydration curing (e.g. concrete mix variability, shaft stick-up in water or air, moving water etc.);
* bleed water channels along the interface between the tubes and the concrete, especially in cased shafts;
* structural attachments within the shaft and other interferences within the rebar cage (e.g. multiple concentric cages, cage stiffeners, embedded bi-directional load cells, etc.);
* tubes placed outside the reinforcing cage;
* tube connectors, tapes and foreign substances on the tubes;
* concrete mix quality (e.g. shrinkage cracks);
* debonding; and
* lack of water or insufficient water in one or more access tubes at the time of testing.

If any of the aforementioned reasons are applicable, they should be discussed in the report. This information is vital so that the Engineer of Record can assess the validity of the CSL data results relative to other installation records and testing performed on the shaft.

== Proposed CSL Rating Criteria ==
CSL data should be used as a part of the shaft acceptance process, and thus needs some form of classification to delineate acceptable versus abnormal results. Once the possibility of equipment malfunction or improper testing procedures has been eliminated, CSL test results for each profile should be classified into one of the following categories:

'''Class A: Acceptable CSL test results.'''

'''Class B: Conditionally acceptable CSL test results.'''

'''Class C: Highly abnormal CSL test results.'''

The definition of each Class is as follows (see Figure 2):
[[File:Figure2.png|alt=Proposed CSL rating criteria |none|thumb|Figure 2: Graphical representation of the proposed CSL rating criteria ]]

=== Class A: Acceptable CSL test results ===

==== For any section of the profile ====

* First Arrival Time (FAT) increases are less than 15% of the local average FAT value, AND reductions in relative energy are less than 9 dB of the local average value of relative energy.

==== Recommendations ====

* Data within normal ranges. No additional assessment needed.

=== Class B: Conditionally acceptable CSL test results ===

==== For any section of the profile ====

* First Arrival Time (FAT) increases are between 15 and 30% of the local average FAT value, AND reductions in relative energy are less than 12 dB of the local average value of relative energy.

OR

* First Arrival Time (FAT) increases are less than 15% of the local average FAT value, AND reductions in relative energy are greater than 9 dB of the local average value of relative energy.

Once abnormal CSL data are observed within the shaft, an assessment is needed to determine the significance of the results relative to shaft performance.

The number of affected CSL profiles at any given depth should be considered when evaluating Class B results. The tester should report the number of Class B occurrences and their respective locations. ''These observations are not to be interpreted as a single overall evaluation of the shaft as being Class B.''

==== Recommendations (the following are recommended in no particular order and as appropriate): ====

* If the abnormal CSL data are observed near the top of the shaft (possible tube debonding), consider flooding the top of the shaft with water to restore the bond. Retesting after at least 30 minutes allows the water to seep down the interface between the tubes and the concrete and may improve the CSL results.
* For shafts with six or more access tubes and where not all tube combinations were tested during the original investigation, additional testing including the remaining tube combinations can improve delineation of any potential flaws.
* Class B results suggest that a detailed desktop evaluation may find the shaft as acceptable for the intended function. The desktop evaluation should consider:
** the number of affected profiles, depth and vertical extent of affected zones, and severity (proximity to the upper or lower limits of Class B);
** low or high concrete strength (a low overall estimated wave speed, even if consistent with depth, may indicate low strength concrete. Similarly, a high overall estimated wave speed may indicate higher strength concrete and should be considered when evaluating local FAT delays in relation to the application of the CSL results. Wave speed should be evaluated preferably from the major diagonal profiles. Perimeter profiles with shorter tube spacings are more sensitive to errors related to tube alignment and the path length through water within the tubes.); and
** construction records.
* Tomography should be considered where it may help to define the extent of the affected zone as accurately as possible.
* If the concrete is too young or retarders were used in the mix, retesting after a sufficient waiting period could improve test results. If the data improve significantly, then the Class B result can perhaps be accepted, particularly if the result is now near the lower Class B limit.
* The Engineer of Record may recommend retesting using another independent tester.
* Consider performing other tests having complementary capabilities. Depending on the horizontal extent and vertical location of the affected zone, use of alternative testing methods or investigations such as low strain impact integrity testing (ASTM D5882) may provide additional information for the foundation assessment.
* Near-surface excavation could be done to facilitate visual inspection for necking. Additionally, sampling through the side of the shaft (i.e. by chipping) for contaminated concrete may help to further define the extent and nature of the flaw.
* If after retesting, the Class B CSL result is still near the upper rating criteria limit given in Figure 2 and occurs in many profiles, consideration for additional recommended measures as presented in the following discussion of Class C would be prudent.

=== Class C: Highly abnormal CSL test results ===

==== For any section of the profile ====

* First Arrival Time (FAT) increases are greater than 30% of the local average FAT value.

OR

* First Arrival Time (FAT) increases are greater than 15% of the local average FAT value, AND reductions in relative energy are greater than 12 dB of the local average value of relative energy.

Once anomalous data are observed within the shaft, an assessment is needed to determine the significance of the results relative to shaft performance.

The number of affected CSL profiles at any given depth should be considered when evaluating Class C results. The tester should report the number of Class C occurrences and their respective locations. ''These observations are not to be interpreted as a single overall evaluation of the shaft as being Class C.''

Class C results typically need more evaluation, often requiring an assessment by the Engineer of Record and have a greater likelihood of requiring more invasive field testing and potentially shaft remediation.

==== Recommendations ====

* Follow all relevant Class B recommendations listed previously, plus consider performing a direct assessment of concrete quality and strength:
** Core sampling may help to further define the extent and nature of the affected zone. If coring is performed, the selection of the core diameter should consider aggregate size, testing purpose and potential remediation options.
** Perform compressive strength testing of core sample(s) from the affected zone. Compare test results with the specified minimum design strength, as well as with the strength of samples from a “normal” zone.

== Shaft Acceptance ==
The CSL testing specialist has been contracted to perform a specific test using well-established CSL procedures (ASTM D6760) and report findings in the form of arrival times, relative energy and a “waterfall diagram” for each tube combination profile. The client or specifying agency should understand that the CSL testing specialist is rarely provided with installation records or foundation design parameters. Therefore, the CSL testing specialist is usually not in a position to decide shaft acceptability. The Engineer of Record and the Design Team, with possible feedback from the CSL testing specialist, should review all the CSL data and construction records to determine the likely effect on foundation performance and decide shaft acceptability.

== Suggestions for Future Research ==
The literature review highlights the lack of quantitative assessment relating CSL test results (FAT increase and relative energy) to deficiencies in reinforced concrete drilled shaft foundations. The problem is compounded by the proliferation and variety of standards for evaluation of CSL results. Moreover, FAT increase and energy reduction limits noted herein are the collective experience of the authors and reflect the general bounds of current guidelines and long-time industry experience. The goal of this document is to propose improved CSL rating criteria and help in adopting more uniform standards. However, this is intended to be a living document and the following suggestions are provided to focus future research studies to further improve the proposed CSL rating criteria:

* Perform analyses (statistical or other quantitative approaches) to evaluate FAT increase and/or energy decrease limits in relation to foundation deficiencies (flaws/defects). A quantitative assessment of existing empirical guidelines is recommended, encompassing both existing and new data via field case studies.
* Quantitatively assess the relative importance of FAT increase versus energy decrease to determine if one or both should be used as CSL rating criteria.
* Perform analysis to determine a quantitative relation between energy reductions and concrete strength and condition.
* Perform assessment in large diameter shafts to quantify the advantage of testing all profiles.

== Conclusions ==
There are no universal or standard criteria to evaluate CSL test results. The current CSL rating criteria developed for the Federal Highway Administration called the Concrete Condition Rating Criteria (CCRC) is based on the percentage of velocity (or wave speed) reduction from the nominal, rather than the proposed FAT delays. The CCRC is outdated and does not reflect the collective industry experience and research over the last 20 years since CCRC was originally developed. FAT delays are recommended instead of velocity reductions because the tubes are often not parallel, and therefore the velocities calculated from top spacings may not be accurate.

Based on this task force’s collective experience the CSL rating criteria proposed herein present an improvement over commonly used criteria. More specifically:

* Terminology is improved to avoid ambiguous or misused terms like “anomaly”, “defect”, “questionable” etc. that often lead to improper interpretation or application of CSL test results.
* CSL rating criteria are simplified to three categories and thresholds are updated to reflect accumulated industry experience since the inception of the original rating criteria.
* Differentiation is made between abnormal CSL test results and shaft acceptability. The tester should report the number of Class B and C occurrences and their respective locations. These observations are not to be interpreted as a single overall evaluation of the shaft as being Class B or C. The Engineer of Record and the Design Team, with possible feedback from the CSL testing specialist, should review all the CSL data and construction records to determine the likely effect on foundation performance and decide shaft acceptability.
* CSL test results alone should not be the sole means of rejecting or accepting a shaft.
* Recommendations are given in a step-by-step fashion to assist the engineer in resolving any potential issues arising from the CSL test results.

The recommendations presented herein are the consensus of the task force, which believes that they should be incorporated into future criteria, codes and specifications. These guidelines are intended as a living document. As more research and experience are accumulated, the criteria recommended herein can be further improved.

== Acknowledgments ==
The assistance, comments, encouragement and interest in this project from DFI and their technical committees (Augered-Cast-In-Place Piles, Codes and Standards, Drilled Shafts, and Testing & Evaluation) are gratefully appreciated. The editorial expertise of Mary Kandaris improved the final document.

== References ==

# Amir, J.M and Amir, E.I. (2008). “Critical Comparison of Ultrasonic Pile Testing Standards,” Proc. 8th Intl. Conf. on Application of Stress Wave Theory to Piling, Lisbon, pp. 453-457.
# Amir, J.M. and Amir, E.I. (2009). ”Capabilities and Limitations of Cross Hole Ultrasonic Testing of Piles,” Proc. IFCEE, Orlando, FL.
# ASTM D5882-16, “Standard Test Method for Low Strain Impact Integrity Testing of Deep Foundations”, ASTM International, West Conshohocken, PA, 2016, www.astm.org
# ASTM D6760-16, “Standard Test Method for Integrity Testing of Concrete Deep Foundations by Ultrasonic Crosshole Testing”, ASTM International, West Conshohocken, PA, 2016, www.astm.org
# ASTM D7949-14, “Standard Test Methods for Thermal Integrity Profiling of Concrete Deep Foundations”, ASTM International, West Conshohocken, PA, 2014, www.astm.org
# Baker, C. N., and Khan, F. (1971). “Caisson Construction Problems and Correction in Chicago,” Journal of the Soil Mechanics and Foundation Division, ASCE, Vol. 97, No. 2, pp. 417-440.
# Baker, C. N., Drumright, E. E., Briaud, J-L., Mensah, F. D., and Parikh, G. (1993). “Drilled Shafts for Bridge Foundations,” Publications No. FHWA-RD-92-004, Federal Highway Administration, Washington DC, 336 pages.
# Camp III, W. M., Holley, D. W., and Canivan, G. J. (2007). “Crosshole Sonic Logging of South Carolina Drilled Shafts: A Five Year Summary,” ASCE Geo Denver, Denver CO.
# Chernauskas, L. R., and Paikowsky, S. G. (1999). “Deep Foundation Integrity Testing: Techniques and Case Histories,” Civil Engineering Practice, Vol. 14, No.1, Boston Soc. of Civil Eng Sec/ASCE, pp. 39-56.
# Chernauskas, L. R., and Paikowsky, S. G. (2000). “Defect Detection and Examination of Large Drilled Shafts using a New Cross-Hole Sonic Logging System,” ASCE Specialty Conference, Performance Verification of Constructed Geotechnical Facilities, University of Massachusetts, Amherst, April 9-12.
# Faiella, D., and Superbo, S. (1998). “Integrity Non-Destructive Tests of Deep Foundations by Means of Sonic Methods - Analysis of the Results Collected on 137 Sites in Italy,” Proceedings of 3rd International Geotechnical Seminar on Deep Foundations on Bored and Auger Piles, Ghent, Belgium, 19-21 Oct., Balkema, Rotterdam, pp. 209-213.
# Iskander, M., Roy, D., Ealy, C., and Kelly, S. (2001). “Class-A Prediction of Construction Defects in Drilled Shafts,” Transportation Research Record 1772, Paper No. 01-0308, Washington DC.
# Jones, W. C., and Wu, Y. (2005). “Experiences with Cross-Hole Sonic Logging and Concrete Coring for Verification of Drilled Shaft Integrity,” Proc. GEO Construction Quality Assurance/Quality Control Tech. Conf., Dallas-Ft. Worth TX, pp. 376-387.
# Likins, G., Webster, S., and Saavedra M. (2004). ”Evaluation of Defects and Tomography for CSL,” Proceedings of the Seventh International Conference on the Application of Stresswave Theory to Piles, Petaling Jaya, Selangor, Malaysia, pp. 381-386.
# O'Neill, M.W. (1991). “Construction Practices and Defects in Drilled Shafts,” Transportation Research Record 1331, Washington DC, pp. 6-14.
# O'Neill, M. W., and Sarhan H. A. (2004). ”Structural Resistance Factors for Drilled Shafts Considering Construction Flaws,” Current Practices and Future Trends in Deep Foundations, GSP 125 ASCE, pp. 166-185.
# Reese, L.C., and Wright, S.J. (1977). “Drilled shaft Manual: Vol 1: Construction Procedures and Design for Axial Loading,” Report IP77-21, FHWA, US Department of Transportation.
# Rohrbach, M. A., Kovacs, T. R., and Saidin, F. (2012). “Uncertainties in CSL Test Interpretations and Recommendations towards a More Efficient Process,” Proceedings of the DFI 37th Annual Conference, Houston TX.
# Sarhan, H. A., O’Neill, M. W., and Tabsh, S. W. (2000). “Structural Resistance Factors for Drilled Shafts with Minor Anomalies-Deterministic Study,” Department of Civil and Environmental Engineering, University of Houston, Houston, Texas.
# Sarhan, H. A., and O'Neill, M. W. (2002a). “Aspects of Structural Design of Drilled shafts for Flexure,” ASCE Intl. Deep Foundation Cong., GSP 116, Orlando FL, pp. 1151-1165.
# Sarhan, H. A., Tabsh, S. W., O'Neill, M. W., Ata, A., and Ealy, C. (2002b). “Flexural Behavior of Drilled Shafts with Minor Flaws,” Proc. Intl. Deep Foundation Congress, GSP No.116, Reston, VA, pp. 1136-1150.
# Webster, K., Rausche, F., and Webster, S. (2011). “Pile and Shaft Integrity Test Results, Classification, Acceptance and/or Rejection,” Compendium of Papers of the Transportation Research Board (TRB) 90th Annual Meeting, Washington, DC.

Terminology and Evaluation Criteria of Crosshole Sonic Logging (CSL) as applied to Deep Foundations

2022-09-26T16:13:20Z

Mburpee: added page content

Nondestructive testing of drilled shaft foundations via Crosshole Sonic Logging (CSL) is often performed as part of the quality assurance process to assess the soundness of concrete. The intent of CSL testing is to identify irregularities such as soil intrusion, necking, soft bottom, segregation, voids and other defects that could result in poor structural performance of the foundation. Over time, CSL rating criteria based on first arrival time and relative energy have incorrectly evolved to often be the sole means of determining the acceptability of a shaft. Some of these criteria have found their way into regulatory agency specifications, with acceptance values often differing from agency to agency.

The purpose of this document is to review the state of the practice (including experience gained over the past 20 years), propose improved CSL rating criteria and make recommendations for additional assessment, as well as educate the industry on the proper interpretation of CSL test. CSL test results alone should not be the sole means of rejecting or accepting a shaft.

A task force of industry exerts was formed to review the existing CSL rating criteria and propose improvements where appropriate. The recommendations presented herein are the consensus of the task force, which believes that they should be incorporated into future criteria, codes and specifications.

This paper was produced as a joint effort between the Codes and Standards Committee, the Drilled Shafts Committee and Testing and Evaluation Committee. A task force was authorized under Testing and Evaluation Committee. The task force contributed their expertise in web-based discussions often every two weeks over a period of three years. Interested participants were invited to participate at any time. The document had two rounds of broad industry review, two rounds of DFI Technical Advisory Committee reviews, and a Public Comments process. All comments were considered in producing the final document.

== Literature Review ==
The construction of cast-in-situ deep foundation elements can introduce unintended structural flaws that, depending on size and location, can compromise the foundation performance. The causes of such flaws have been discussed by several researchers including Baker and Khan (1971), Reese and Wright (1977) and O’Neill (1991). Authors of the various references cited here often use the terms “flaw” and “defect” indiscriminately or interchangeably. The terminology used throughout this section is the terminology used in the original references; recommended terminology is provided subsequently in this document.

O’Neill (1991) categorized the causes of structural defects into five (5) categories, namely defects arising from

* general construction problems,
* drilling problems,
* casing management problems,
* slurry management problems, and
* design deficiencies.

O’Neill does not separately categorize defects arising from concrete placement, as they are included in all of the above categories.

The most commonly used testing methods for evaluation of the structural integrity of drilled deep foundations are:

* Low Strain Integrity Testing (ASTM D5882),
* Crosshole Sonic Logging (ASTM D6760),
* Gamma-Gamma Density Logging, and
* Thermal Integrity Profiling (ASTM D7949).

State-of-practice Non-Destructive Test (NDT) methods can detect some of these larger flaws, whereas smaller flaws can remain undetected. O’Neill and Sarhan (2004) state that large voids and soil inclusions, occupying more than 15% of the cross-sectional area of the shaft, can usually be detected with state-of-practice nondestructive evaluation methods. In their paper, the authors consider all flaws that can be identifiable by NDT methods as “not minor”, by definition. Sarhan and O’Neill (2002a) mention that “flaws large enough to be detected by non-destructive evaluation methods (NDE) are almost always repaired or the drilled shaft is replaced”, whereas the effect of minor undetectable flaws should be accounted for in the design.

Several researchers and industry practitioners have investigated the ability of NDT methods to detect flaws introduced during the construction process. Sarhan et al. (2002b) summarize some of these studies in their paper “Flexural Behavior of Drilled Shafts with Minor Flaws”. As presented in their summary:

* Baker et al. (1993) conclude “down-tube” techniques could detect flaws that occupied only 15% of the cross-sectional area of drilled shafts;
* Amir (personal communication) indicates cross-tube ultrasonic tests could reliably detect soft defects that comprise about 9% of the cross-sectional area of a 0.76m (30-in) diameter drilled shaft;
* Chernauskas and Paikowsky (1999 and 2000), through several case histories and using various NDT methods, conclude that these methods are useful in detecting flaws comprising 20% or more of the cross sections of drilled shafts;
* Iskander et al. (2001) conclude down-tube methods are generally able to identify flaws exceeding 10% of the cross-sectional area; and
* Sarhan et al. (2000) conclude that, after a field study on six full-scale drilled shafts installed in stiff clay and employing pre-installed void flaws of areas ranging from 10.7% to 16.7% of the cross-sectional area, void-type flaws occupying areas up to 15% of the cross-sectional area could remain undetected. The study employed NDT tests ranging from surface techniques to down-tube methods.

Amir and Amir (2009) found, in both controlled site testing and finite element modeling, that modern CSL equipment can detect flaws occupying 10% of the pile's cross-section, provided the flaw is within the reinforcing cage.

The previously referenced cross-sectional area percentages refer to defects located inside the reinforcing cage and confirm O’Neill’s findings that flaws occupying as little as 15% of the cross-sectional area can be detected. CSL methods can only detect defects when such defects are in the path between access tubes; and since the tubes are generally attached to the inside of the cage, defects outside the cage in the cover zone cannot be detected. If the entire cover is missing, the cross-section percentage can be significantly greater than 10% and be undetected.

Baker and Khan (1971) suggest the use of multiple NDT methods wherever feasible, as this approach will produce more definitive answers than the use of a single NDT method.

Several studies investigate the percentage of drilled shafts with detectable defects. O’Neill and Sarhan (2004) report rejection of 20% of drilled shafts in the Caltrans database constructed during the period of 1996-2000 under drilling slurry due to flaws identified by NDT methods. By their definition, flaws identifiable by NDT are “not minor”. Their paper reports other case study findings with similar percentages of shafts with identifiable flaws (18%, 20%, etc.). Faiella and Superbo (1998) present a study where CSL testing detected flaws in 25% of drilled shafts from 37 sites in Italy. The database included 6800 shafts.

Jones and Wu (2005) report in their paper that 56% of 299 drilled shafts tested with CSL in Mid-Western US presented some type of anomaly (defined as at least a 25% wave speed reduction). Most of the shaft anomalies (81%) were located within the top or bottom one meter of the shafts. Jones and Wu (2005) also comment that coring is problematic, is difficult to perform correctly, and may not necessarily confirm a CSL anomaly.

Camp et al. (2007) compiled a database of 400 CSL-tested shafts installed by ten different contractors in South Carolina. The authors found 33% of the tested shafts contained an anomaly (defined as at least a 20% wave speed reduction) and that 90% of anomalies were within the top or bottom two shaft diameters. Camp et al. (2007) also make a distinction between anomalies and actual defects that compromise the performance.

The real question to be answered is whether these flaws or defects affect the intended performance of the shafts. Proper defect characterization and assessment of their effect in the load-bearing capacity of the shaft should include analyzing the defects' shape, size and location, and other factors like the geotechnical capacity of the shaft, whether the defect is on the compression side in the flexural zone, etc. Defects occurring in zones of high load transfer and high internal stresses are critical. Therefore, defects occurring at the top of the shaft will likely affect foundation performance and are of greater concern. When combined with the O’Neill and Sarhan (2004) survey conclusion (the most probable location of a flaw to be within the upper five diameters of the shaft), the critical aspect of the proper evaluation of defects becomes obvious. Defects at the bottom of the shaft are important when end bearing is part of the design.

Sarhan et al. (2002b) investigated the effect of the shape of structural defects on the flexural capacity of the shaft in an experimental study including small scale and large-scale laboratory tests. The authors analyzed two types of flaws commonly observed in drilled shafts resulting from soil cuttings floating on the rising column of fluid concrete in a slurry pour:

* Type A flaw has most of its area lying outside of the reinforcement cage (only a small area is penetrating inside the cage), whereas
* Type B flaw penetrates inside the cage into the core of the shaft.

Both flaw types occupy 15% of the gross cross-sectional area (the limit of identifiable versus unidentifiable flaw size through NDT methods according to O’Neill). It was shown that the Type B void flaw associates with the greatest reduction in flexural resistance under flexural loading conditions. More specifically, the Type B flaw results in a reduction in flexural resistance of 32%, whereas the Type A flaw has a reduction of only 17%. The results of the full-scale laboratory tests show reduction in flexural resistance for the Type B flaw of 27%. The research demonstrates that the shaft acceptance process must consider both flaw location and mode of foundation resistance, not just flaw size.

O’Neill (1991) in the context of his paper defines defects “as structural flaws that may or may not affect the serviceability of the foundation. Only a careful evaluation of the location and extent of defects relative to zones of high load transfer and high internal stresses can determine whether the defect requires repair”. Many parameters (i.e. shape, size, and location of the defect, maximum stresses expected on the shaft, redundancy of the shaft, design parameters such as friction shaft or end-bearing shaft, seismic and uplift concerns) must be evaluated upon detection of flaws/defects via NDT testing in order to understand their effect on the performance of the shaft and whether the shaft should be accepted as is, repaired or rejected.

Webster et al. (2011) indicate that structural problems detected by NDT methods are significant and their effect on structural capacity has to be evaluated and, if deemed necessary, mitigated. They suggest a classification system for both CSL testing and low strain integrity testing. Many state departments of transportation currently use their CSL classification system and includes the separate terms of “flaw” and “defect”. The authors also discuss NDT result evaluation techniques and mitigation solutions - e.g. flaws have to be addressed if they are indicated in more than 50% of the profiles, whereas defects must be addressed if they are indicated to affect more than one profile and involve at least three tubes.

Rohrbach et al. (2012) list various factors unrelated to concrete quality that can cause anomalies in CSL test results and adversely affect their interpretation. The authors propose that improvements are needed in the terminology that CSL testing providers use in order to avoid terms that may be ambiguous or controversial. They also call for increased communication between CSL testing providers and Engineers of Record to provide the information necessary for the proper use of engineering judgment in drilled shaft acceptance.

The question of which CSL results may indicate an anomaly is addressed by the Chinese and French CSL standards (Amir & Amir, 2008), where both refer to First Arrival Time (FAT) and Relative Energy (a measure of the signal intensity at the receiver probe). Alternately (and as a matter of policy), ASTM D6760 avoids interpretation of test results and leaves shaft acceptance to engineering judgment. Likins et al. (2004) state that, although CSL testing is straightforward, “there is no general common consensus (in most parts of the world) concerning what reduction in amplitude or delay in first arrival time defines a defect”. The authors state that a 20% FAT delay is a commonly suggested limit for a defect (e.g. French code AFNOR NF P94-160-1) and suggest that either the signal amplitude or relative energy should be included in CSL rating criteria. They also recommend shafts with “local partial defects” (shafts not designated as “good” or clearly “defective”) be analyzed by 3D tomography in order to gain a clearer visual-spatial illustration of defects, allowing more effective remediation or evaluation by the structural engineer.

The current CSL rating criteria guideline developed for the Federal Highway Administration called the Concrete Condition Rating Criteria (CCRC) is based on the percentage of velocity (or wave speed) reduction from the nominal, rather than FAT delays. The CCRC has been modified by several state departments of transportation (DOTs) with respect to the range for “Questionable” concrete. Some state DOTs use velocity reductions of 10% to 20%, while others use 10% to 25% to indicate questionable concrete. Some authorities define “Poor” concrete as velocity reductions or FAT delays greater than 30%. Note that a 30% reduction in velocity is not equivalent to a 30% increase in FAT (see Table 1). Still, others utilize a combination of FAT delays (or velocity decreases) with energy reductions.

[[File:FAT-Table.png|alt=Relation between FAT increase and Velocity Decrease|center|thumb|605x605px|Table 1: Relation between FAT increase and Velocity Decrease]]

== Discussions and Recommendations ==
Over time, CSL rating criteria based on first arrival time (or wave speed) and relative energy have often incorrectly evolved to be the sole means of determining the acceptability of a shaft. Some of these measures have found their way into regulatory agency specifications, with acceptance values often differing from agency to agency. The literature review notes a lack of quantitative assessment for these measurements, suggesting that “hard” boundary values presently used by many for shaft acceptance overstep our industry’s current state of knowledge. Recommendations contained herein are based on the collective experience of the authors over the past 20 years. They are intended to replace current CSL rating criteria and place CSL testing in proper perspective, as part of the evaluation for shaft acceptance.

== Terminology ==
This document updates shaft evaluation using CSL rating criteria to incorporate industry experience collected since their inception, with the purpose of improving the current state-of-practice. The following sections present new recommended CSL rating criteria and exclude the use of words such as “flaw” and “defect”. There are opinions in the industry that the term “defect” should not be used until an irregularity has been proven likely to significantly reduce the shaft’s capacity or durability.

Researchers and engineers often use the terms “flaw” and “defect” indiscriminately or interchangeably. Moreover, some practitioners assume an “anomaly” to be a “defect”. The following definitions are proposed in an effort to eliminate misuse or confusion in the industry among these terms (Figure 1):

=== Anomaly ===
Abnormal data that deviates from expectations, and may indicate a flaw or defect.

=== Flaw ===
Any imperfection in the planned shape or material of the foundation that may not necessarily affect its performance.

=== Defect ===
Any flaw that, because of size, location and inferred concrete properties, will have a significant adverse effect on the performance of the foundation.
[[File:Figure1.png|alt=Anomalies, flaws and defects |none|thumb|468x468px|Figure 1: Anomalies, flaws and defects ]]

''This paper defines other important terms discussed as follows:''

=== Profile ===
The graphical representation versus depth of the CSL data between two tubes.

=== First Arrival Time (FAT) ===
The time required for the leading edge of the ultrasonic pulse to travel from the transmitter to the receiver.

=== Relative Energy (RE) ===
The relative signal strength of the pulse arriving at the receiver compared with a reference signal strength.

=== Tomography or tomographic analysis ===
A mathematical procedure applied to CSL data in order to provide a 2D or 3D map of the wave speed data (and therefore a visual identification of potential flaws or defects within a shaft).

=== Engineer of Record ===
A professional who is responsible for acceptance of the foundation. Foundation acceptance requires the evaluation of a wide array of information and should not be based on the CSL data alone.

== Assessing CSL Data Anomalies ==
From the reviewed published literature, the authors of this document suggest that the use of the word “anomaly” be restricted to describing only the test data, i.e. the CSL test data are either acceptable or abnormal. Where abnormal test data are observed, the first steps taken by the tester and/or the analyst must be to verify proper function and operation of the test equipment, according to the appropriate standards (such as ASTM D6760) and manufacturer’s recommendations.

Possible causes of abnormal CSL results (not necessarily related to flaws and defects in the shaft) include but are not limited to

* insufficient wait time between concrete placement and testing;
* tube disturbance while the concrete is setting;
* non-parallel tube alignments or over-sized tube diameters;
* the differential rate of hydration curing (e.g. concrete mix variability, shaft stick-up in water or air, moving water etc.);
* bleed water channels along the interface between the tubes and the concrete, especially in cased shafts;
* structural attachments within the shaft and other interferences within the rebar cage (e.g. multiple concentric cages, cage stiffeners, embedded bi-directional load cells, etc.);
* tubes placed outside the reinforcing cage;
* tube connectors, tapes and foreign substances on the tubes;
* concrete mix quality (e.g. shrinkage cracks);
* debonding; and
* lack of water or insufficient water in one or more access tubes at the time of testing.

If any of the aforementioned reasons are applicable, they should be discussed in the report. This information is vital so that the Engineer of Record can assess the validity of the CSL data results relative to other installation records and testing performed on the shaft.

== Proposed CSL Rating Criteria ==
CSL data should be used as a part of the shaft acceptance process, and thus needs some form of classification to delineate acceptable versus abnormal results. Once the possibility of equipment malfunction or improper testing procedures has been eliminated, CSL test results for each profile should be classified into one of the following categories:

'''Class A: Acceptable CSL test results.'''

'''Class B: Conditionally acceptable CSL test results.'''

'''Class C: Highly abnormal CSL test results.'''

The definition of each Class is as follows (see Figure 2):
[[File:Figure2.png|alt=Proposed CSL rating criteria |none|thumb|Figure 2: Graphical representation of the proposed CSL rating criteria ]]

=== Class A: Acceptable CSL test results ===

==== For any section of the profile ====

* First Arrival Time (FAT) increases are less than 15% of the local average FAT value, AND reductions in relative energy are less than 9 dB of the local average value of relative energy.

==== Recommendations ====

* Data within normal ranges. No additional assessment needed.

=== Class B: Conditionally acceptable CSL test results ===

==== For any section of the profile ====

* First Arrival Time (FAT) increases are between 15 and 30% of the local average FAT value, AND reductions in relative energy are less than 12 dB of the local average value of relative energy.

OR

* First Arrival Time (FAT) increases are less than 15% of the local average FAT value, AND reductions in relative energy are greater than 9 dB of the local average value of relative energy.

Once abnormal CSL data are observed within the shaft, an assessment is needed to determine the significance of the results relative to shaft performance.

The number of affected CSL profiles at any given depth should be considered when evaluating Class B results. The tester should report the number of Class B occurrences and their respective locations. ''These observations are not to be interpreted as a single overall evaluation of the shaft as being Class B.''

==== Recommendations (the following are recommended in no particular order and as appropriate): ====

* If the abnormal CSL data are observed near the top of the shaft (possible tube debonding), consider flooding the top of the shaft with water to restore the bond. Retesting after at least 30 minutes allows the water to seep down the interface between the tubes and the concrete and may improve the CSL results.
* For shafts with six or more access tubes and where not all tube combinations were tested during the original investigation, additional testing including the remaining tube combinations can improve delineation of any potential flaws.
* Class B results suggest that a detailed desktop evaluation may find the shaft as acceptable for the intended function. The desktop evaluation should consider:
** the number of affected profiles, depth and vertical extent of affected zones, and severity (proximity to the upper or lower limits of Class B);
** low or high concrete strength (a low overall estimated wave speed, even if consistent with depth, may indicate low strength concrete. Similarly, a high overall estimated wave speed may indicate higher strength concrete and should be considered when evaluating local FAT delays in relation to the application of the CSL results. Wave speed should be evaluated preferably from the major diagonal profiles. Perimeter profiles with shorter tube spacings are more sensitive to errors related to tube alignment and the path length through water within the tubes.); and
** construction records.
* Tomography should be considered where it may help to define the extent of the affected zone as accurately as possible.
* If the concrete is too young or retarders were used in the mix, retesting after a sufficient waiting period could improve test results. If the data improve significantly, then the Class B result can perhaps be accepted, particularly if the result is now near the lower Class B limit.
* The Engineer of Record may recommend retesting using another independent tester.
* Consider performing other tests having complementary capabilities. Depending on the horizontal extent and vertical location of the affected zone, use of alternative testing methods or investigations such as low strain impact integrity testing (ASTM D5882) may provide additional information for the foundation assessment.
* Near-surface excavation could be done to facilitate visual inspection for necking. Additionally, sampling through the side of the shaft (i.e. by chipping) for contaminated concrete may help to further define the extent and nature of the flaw.
* If after retesting, the Class B CSL result is still near the upper rating criteria limit given in Figure 2 and occurs in many profiles, consideration for additional recommended measures as presented in the following discussion of Class C would be prudent.

=== Class C: Highly abnormal CSL test results ===

==== For any section of the profile ====

* First Arrival Time (FAT) increases are greater than 30% of the local average FAT value.

OR

* First Arrival Time (FAT) increases are greater than 15% of the local average FAT value, AND reductions in relative energy are greater than 12 dB of the local average value of relative energy.

Once anomalous data are observed within the shaft, an assessment is needed to determine the significance of the results relative to shaft performance.

The number of affected CSL profiles at any given depth should be considered when evaluating Class C results. The tester should report the number of Class C occurrences and their respective locations. ''These observations are not to be interpreted as a single overall evaluation of the shaft as being Class C.''

Class C results typically need more evaluation, often requiring an assessment by the Engineer of Record and have a greater likelihood of requiring more invasive field testing and potentially shaft remediation.

==== Recommendations ====

* Follow all relevant Class B recommendations listed previously, plus consider performing a direct assessment of concrete quality and strength:
** Core sampling may help to further define the extent and nature of the affected zone. If coring is performed, the selection of the core diameter should consider aggregate size, testing purpose and potential remediation options.
** Perform compressive strength testing of core sample(s) from the affected zone. Compare test results with the specified minimum design strength, as well as with the strength of samples from a “normal” zone.

== Shaft Acceptance ==
The CSL testing specialist has been contracted to perform a specific test using well-established CSL procedures (ASTM D6760) and report findings in the form of arrival times, relative energy and a “waterfall diagram” for each tube combination profile. The client or specifying agency should understand that the CSL testing specialist is rarely provided with installation records or foundation design parameters. Therefore, the CSL testing specialist is usually not in a position to decide shaft acceptability. The Engineer of Record and the Design Team, with possible feedback from the CSL testing specialist, should review all the CSL data and construction records to determine the likely effect on foundation performance and decide shaft acceptability.

== Suggestions for Future Research ==
The literature review highlights the lack of quantitative assessment relating CSL test results (FAT increase and relative energy) to deficiencies in reinforced concrete drilled shaft foundations. The problem is compounded by the proliferation and variety of standards for evaluation of CSL results. Moreover, FAT increase and energy reduction limits noted herein are the collective experience of the authors and reflect the general bounds of current guidelines and long-time industry experience. The goal of this document is to propose improved CSL rating criteria and help in adopting more uniform standards. However, this is intended to be a living document and the following suggestions are provided to focus future research studies to further improve the proposed CSL rating criteria:

* Perform analyses (statistical or other quantitative approaches) to evaluate FAT increase and/or energy decrease limits in relation to foundation deficiencies (flaws/defects). A quantitative assessment of existing empirical guidelines is recommended, encompassing both existing and new data via field case studies.
* Quantitatively assess the relative importance of FAT increase versus energy decrease to determine if one or both should be used as CSL rating criteria.
* Perform analysis to determine a quantitative relation between energy reductions and concrete strength and condition.
* Perform assessment in large diameter shafts to quantify the advantage of testing all profiles.

== Conclusions ==
There are no universal or standard criteria to evaluate CSL test results. The current CSL rating criteria developed for the Federal Highway Administration called the Concrete Condition Rating Criteria (CCRC) is based on the percentage of velocity (or wave speed) reduction from the nominal, rather than the proposed FAT delays. The CCRC is outdated and does not reflect the collective industry experience and research over the last 20 years since CCRC was originally developed. FAT delays are recommended instead of velocity reductions because the tubes are often not parallel, and therefore the velocities calculated from top spacings may not be accurate.

Based on this task force’s collective experience the CSL rating criteria proposed herein present an improvement over commonly used criteria. More specifically:

* Terminology is improved to avoid ambiguous or misused terms like “anomaly”, “defect”, “questionable” etc. that often lead to improper interpretation or application of CSL test results.
* CSL rating criteria are simplified to three categories and thresholds are updated to reflect accumulated industry experience since the inception of the original rating criteria.
* Differentiation is made between abnormal CSL test results and shaft acceptability. The tester should report the number of Class B and C occurrences and their respective locations. These observations are not to be interpreted as a single overall evaluation of the shaft as being Class B or C. The Engineer of Record and the Design Team, with possible feedback from the CSL testing specialist, should review all the CSL data and construction records to determine the likely effect on foundation performance and decide shaft acceptability.
* CSL test results alone should not be the sole means of rejecting or accepting a shaft.
* Recommendations are given in a step-by-step fashion to assist the engineer in resolving any potential issues arising from the CSL test results.

The recommendations presented herein are the consensus of the task force, which believes that they should be incorporated into future criteria, codes and specifications. These guidelines are intended as a living document. As more research and experience are accumulated, the criteria recommended herein can be further improved.

== Acknowledgments ==
The assistance, comments, encouragement and interest in this project from DFI and their technical committees (Augered-Cast-In-Place Piles, Codes and Standards, Drilled Shafts, and Testing & Evaluation) are gratefully appreciated. The editorial expertise of Mary Kandaris improved the final document.

== References ==

# Amir, J.M and Amir, E.I. (2008). “Critical Comparison of Ultrasonic Pile Testing Standards,” Proc. 8th Intl. Conf. on Application of Stress Wave Theory to Piling, Lisbon, pp. 453-457.
# Amir, J.M. and Amir, E.I. (2009). ”Capabilities and Limitations of Cross Hole Ultrasonic Testing of Piles,” Proc. IFCEE, Orlando, FL.
# ASTM D5882-16, “Standard Test Method for Low Strain Impact Integrity Testing of Deep Foundations”, ASTM International, West Conshohocken, PA, 2016, www.astm.org
# ASTM D6760-16, “Standard Test Method for Integrity Testing of Concrete Deep Foundations by Ultrasonic Crosshole Testing”, ASTM International, West Conshohocken, PA, 2016, www.astm.org
# ASTM D7949-14, “Standard Test Methods for Thermal Integrity Profiling of Concrete Deep Foundations”, ASTM International, West Conshohocken, PA, 2014, www.astm.org
# Baker, C. N., and Khan, F. (1971). “Caisson Construction Problems and Correction in Chicago,” Journal of the Soil Mechanics and Foundation Division, ASCE, Vol. 97, No. 2, pp. 417-440.
# Baker, C. N., Drumright, E. E., Briaud, J-L., Mensah, F. D., and Parikh, G. (1993). “Drilled Shafts for Bridge Foundations,” Publications No. FHWA-RD-92-004, Federal Highway Administration, Washington DC, 336 pages.
# Camp III, W. M., Holley, D. W., and Canivan, G. J. (2007). “Crosshole Sonic Logging of South Carolina Drilled Shafts: A Five Year Summary,” ASCE Geo Denver, Denver CO.
# Chernauskas, L. R., and Paikowsky, S. G. (1999). “Deep Foundation Integrity Testing: Techniques and Case Histories,” Civil Engineering Practice, Vol. 14, No.1, Boston Soc. of Civil Eng Sec/ASCE, pp. 39-56.
# Chernauskas, L. R., and Paikowsky, S. G. (2000). “Defect Detection and Examination of Large Drilled Shafts using a New Cross-Hole Sonic Logging System,” ASCE Specialty Conference, Performance Verification of Constructed Geotechnical Facilities, University of Massachusetts, Amherst, April 9-12.
# Faiella, D., and Superbo, S. (1998). “Integrity Non-Destructive Tests of Deep Foundations by Means of Sonic Methods - Analysis of the Results Collected on 137 Sites in Italy,” Proceedings of 3rd International Geotechnical Seminar on Deep Foundations on Bored and Auger Piles, Ghent, Belgium, 19-21 Oct., Balkema, Rotterdam, pp. 209-213.
# Iskander, M., Roy, D., Ealy, C., and Kelly, S. (2001). “Class-A Prediction of Construction Defects in Drilled Shafts,” Transportation Research Record 1772, Paper No. 01-0308, Washington DC.
# Jones, W. C., and Wu, Y. (2005). “Experiences with Cross-Hole Sonic Logging and Concrete Coring for Verification of Drilled Shaft Integrity,” Proc. GEO Construction Quality Assurance/Quality Control Tech. Conf., Dallas-Ft. Worth TX, pp. 376-387.
# Likins, G., Webster, S., and Saavedra M. (2004). ”Evaluation of Defects and Tomography for CSL,” Proceedings of the Seventh International Conference on the Application of Stresswave Theory to Piles, Petaling Jaya, Selangor, Malaysia, pp. 381-386.
# O'Neill, M.W. (1991). “Construction Practices and Defects in Drilled Shafts,” Transportation Research Record 1331, Washington DC, pp. 6-14.
# O'Neill, M. W., and Sarhan H. A. (2004). ”Structural Resistance Factors for Drilled Shafts Considering Construction Flaws,” Current Practices and Future Trends in Deep Foundations, GSP 125 ASCE, pp. 166-185.
# Reese, L.C., and Wright, S.J. (1977). “Drilled shaft Manual: Vol 1: Construction Procedures and Design for Axial Loading,” Report IP77-21, FHWA, US Department of Transportation.
# Rohrbach, M. A., Kovacs, T. R., and Saidin, F. (2012). “Uncertainties in CSL Test Interpretations and Recommendations towards a More Efficient Process,” Proceedings of the DFI 37th Annual Conference, Houston TX.
# Sarhan, H. A., O’Neill, M. W., and Tabsh, S. W. (2000). “Structural Resistance Factors for Drilled Shafts with Minor Anomalies-Deterministic Study,” Department of Civil and Environmental Engineering, University of Houston, Houston, Texas.
# Sarhan, H. A., and O'Neill, M. W. (2002a). “Aspects of Structural Design of Drilled shafts for Flexure,” ASCE Intl. Deep Foundation Cong., GSP 116, Orlando FL, pp. 1151-1165.
# Sarhan, H. A., Tabsh, S. W., O'Neill, M. W., Ata, A., and Ealy, C. (2002b). “Flexural Behavior of Drilled Shafts with Minor Flaws,” Proc. Intl. Deep Foundation Congress, GSP No.116, Reston, VA, pp. 1136-1150.
# Webster, K., Rausche, F., and Webster, S. (2011). “Pile and Shaft Integrity Test Results, Classification, Acceptance and/or Rejection,” Compendium of Papers of the Transportation Research Board (TRB) 90th Annual Meeting, Washington, DC.

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Graphical representation of the proposed CSL rating criteria

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Relation between FAT increase and Velocity Decrease

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Anomalies and flaws diagram

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Relation between FAT increase and Velocity Decrease

Terminology and Evaluation Criteria of Crosshole Sonic Logging (CSL) as applied to Deep Foundations

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== INTRODUCTION ==