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CPTu, PPDT & Test Categories

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CPT Testing (Cone Penetration Testing)

IGS undertakes all CPT testing and CPTu testing using "industry best practice". Part of this is to follow the intent of the de facto "world benchmark standard" ISO 22476-1-2012.  

As our experience shows that CPTu sensors all drift slightly with use, we will commit to; 

(a) provide fresh calibrations for every cone used at the start of your job and 

(b) re-calibrate every deployed cone at the end of the job. 

Re-calibrations will be compared to pre-job calibrations to confirm CPT accuracy during the whole project. Note that this is IGS "business as usual"

We calibrate, qc, fs, u and NAR (Net Area Ratio).   

We refer you to the below information that explains IGS's system of " Test Categories " for Cone Penetration Testing. Normal run-of-the-mill CPT testing (done by everyone) is covered by Category IGS-1S or IGS-1C. Note that this can be a trade-off between pore pressure response and productivity, with a bias to productivity (to suit many clients' wishes).

A more rigorous approach to management of pore pressure response is covered under the IGS Categories IGS-3S and IGS-3C (or even IGS-4C). We will seek your direction on the Test Category to adopt before each test - or overall for the project. But, if given no direction, our “default” will be Category 3C or 3S.  

Note that as some materials are dilatant, rigorous management of pore pressure response under these categories can slow test rates (ie productivity) somewhat.  

Name Brief Description (and client role) Typical Application Methods Typically Employed by IGS Operator
IGS-1S or IGS-1C Standard Piezo / Non-Piezo Cone Testing

Client must (pre-testing) brief IGS on their choice of category. Little or no client involvement is required during testing progress.Objective is good quality data, including good pore pressure response. However, if pore pressure response problems evolve in any “difficult” test zone, time is not squandered trying to solve them.Typically a client is hoping for reasonably high productivity using this method.
For use when clients want a reliable soil profile and to establish design parameters to historically-normal levels of client expectation.May be the base test type chosen for a known soft clayey soil project for overall site profiling.With IGS-1, good quality pore pressure response is usually achieved and “normal” dissipation tests can be made. Usually a 100MPa cone is used; either an S-Type cone or a C- Type cone. 1S denotes an S-Type cone, 1C denotes a C-Type cone. Cone is carefully prepared to ensure best reasonably achievable piezo saturation and absence of trapped or dissolved air. Pore pressure measurements are made as test progresses. If soil behaviour spoils piezo response in some zones, test penetration is paused (but only briefly) to promote “catch up”. Should difficult soil layers be encountered (eg gravely bands or hard fissured layers causing tilt), test type IGS-1S can sometimes be carefully continued – at discretion of IGS operator.
IGS-2S or IGS-2C Non-Piezo-Cone Testing

Client must (pre-testing) brief IGS on their choice of category. Little or no client involvement is required during testing progress.

As cone does not have a piezo-element, cone preparation is much simpler and quicker – leads to higher project productivity.
For use when clients want a reliable soil profile and to establish design parameters at “site characterisation” level. But pore pressure response is not required.May be the base test type chosen for a variable or unknown soil type for overall site profiling.IGS recommends this if budget control is critical and site characterisation is the objective. Usually 100MPa cone is used; either an S-Type cone or a C-Type cone.  2S denotes an S-Type cone, 2C denotes a C-Type cone.

Should difficult soil layers be encountered (eg gravely bands or hard fissured layers causing tilt), test type IGS-2S can sometimes be carefully continued – at discretion of IGS operator.
IGS-3S or IGS-3C Special-Class Testing.

Client must (pre-testing) brief IGS on their choice of category. Client must advise IGS of their expectations, as test productivity may sometimes be reduced using this method.

Objective is best possible pore pressure response in “difficult” ground, but still maintaining modestly high productivity.

Client might intervene during progress to shift test type to IGS-4C, accepting lower test productivity that results in this shift.
Typically used at targeted locations after site characterisation by IGS-1 or IGS-2 testing.

If client wishes to obtain inputs into determination of soil parameters to a “specially” high level he will more likely choose IGS-3C.

Typical objectives may be assessment of soil properties for design of embankments or preloads over soft to firm and stiffer clay-type foundation soils.

Dissipation tests should be achieved to a high standard.
Either and S-Type cone or a C-Type Cone can be used. 3S denotes an S-Type cone, 3C a C-Type cone. Cone capacity is selected to suit the ground being targeted; eg 100MPa or 25MPa* or 10MPa* (*C-Type only) cone choice is made.

Pore pressure measurements are closely watched as test progresses. If soil behaviour spoils piezo response in any zones, test penetration is stopped while response monitoring continues.

If piezo “recovers” in (say) 10-15 minutes test penetration is restarted. If piezo does not “recover” in (say) 10-15 minutes, test penetration might also be started but client accepts consequences of possible zones of reduced pore pressure response. (Note that client can up-grade to IGS-4 if desired).
IGS-4C Quasi-Research Class Testing.

Client must be closely engaged in decision process as in extreme conditions test productivity may be quite low using this method.

Objective is best possible pore pressure response in “difficult” ground, more-or-less regardless of productivity, and a degree of management of the possible effects of temperature change within the cone.
Typically used at targeted locations after site characterisation by IGS-1 or IGS-2 testing.

Client wishes to obtain inputs into determination of soil parameters to the highest practically achievable level. Typical objectives may be assessment of preconsolidation pressure of very soft clays, or assessment of preload progress based on qc or qt parameters. Dissipation tests should be achieved to best possible standard.
Cone capacity is selected to suit the ground being targeted (eg 100MPa or 25MPa or 10MPa cone choice is made). C-Type compression cone is normally used.

Pore pressure measurements are closely watched as test progresses. If soil behaviour spoils piezo response in any zones, test penetration is stopped while response monitoring continues. If piezo “recovers”, test penetration is re-started. If piezo does not “recover”, cone may be pulled out, hole may be water-filled and test may be recommenced with a re-prepped cone.

If the cone is pushed through dense or hard soils over weaker soils, the cone will likely heat up. The push will be interrupted for 10 minutes as close as reasonably possible below the interface, to allow push-generated temperature increases to stabilise to ground temperature in the weaker layer.
"Seis" Seismic CPTu.

Client must (pre-Establishment) brief IGS on their choice of seismic CPTu. Little or no client involvement is required during testing progress. Seismic CPT at IGS is available at present in the form of a 15cm 2 C-Type cone.
Used when the client wants a seismic shear wave velocity profile as well as the usual CPTu (piezo-cone) test outputs.

Testing can follow any one of the procedures described above for Categories 1C, 3C or 4C.
In addition to the processes described above, the CPT push is halted at agreed intervals (typically 0.5m or 1.0m - but can be any) and subjected to a seismic shear wave generated at the ground surface by one of IGS’s shear wave hammers. The shear wave signal is received by the cone’s geophone and processed.

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