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
Methods
" for Cone Penetration Testing. Normal run-of-the-mill CPT testing (done by everyone) is covered by Category IGS-2S or IGS-2C. 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 Methods IGS-3S and IGS-3C (or even IGS-4C). We will seek your direction on the Test Method to adopt before each test - or overall for the project. But, if given no direction, our “default” will be Method 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.
Pore Pressure Dissipation Tests in fine-grained materials can run very quickly - eg a few minutes, or ve
ry slowly, over a few hours. The time taken depends on the material permeability and on the degree of dissipation being sought. Typically, clients request 50% - ie t50, but some clients pursue higher dissipation percentages; 90% is common enough.
Note that in the event that dissipations run slowly or you are keen to achieve high % dissipations, we can run tests overnight - usually achieving around 90% or better over (say) a 12-14 hour test period. A unit rate can be quoted for this; it is a cost-effective process.
The adjacent test plots show PPDT results from two very different materials - the top one reached 100% dissipation in 5 minutes, the lower one took 14 hours (overnight) to achieve something like 90%.
The best-possible Pore Pressure Dissipation Test results are normally achieved if IGS-3C or IGS-3S (or IGS-4C) Category testing is adopted for the CPTu
Note that IGS always adopts very rigorous lab-based piezometer filter saturation procedures, and on the rig subjects each piezo-cone to a final vacuum under de-aired fluid before starting each CPTu push, to achieve the best-achievable overall pore pressure response throughout the test and during dissipations, for any CPTu category.
| Name | Brief Description (and client role) | Typical Application | Methods Typically Employed by IGS Operator |
|---|---|---|---|
| IGS-1S or IGS-1C | STANDARD NON-PIEZO CONE TESTING
Client must (pre-testing) brief IGS on their choice of type. Little or no client involvement is required during testing progress. With data provided at the end of the shift. Objective is for the collection of data for profiling purposes. 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. No pore pressure measurements are collected and as such the data is not typically used for ‘detailed material characterisation’ May be the base test type chosen for a variable or unknown soil type for overall site profiling. If budget control is critical and site profiling and mapping is the objective. |
Recently calibrated 100MPa cone is used; either an S-Type cone or
a C-Type cone. A temperature stabilisation is conducted between 0.5m 1.5m to stabilise the cone to the ground temperature. A penetration rate of 20mm±5mm per second is adopted. Should difficult soil layers be encountered (eg gravely bands or hard fissured layers causing tilt), tests can sometimes be carefully continued – at discretion of IGS operator. Penetration readings are collected at 10mm intervals |
| IGS-2S or IGS-2C | PRODUCTION-ORIENTED PIEZO-CONE TESTING
Client must (pre-testing) brief IGS on their choice of category. Little or no client involvement is required during testing progress. With data provided at the end of the shift. Objective is data collection, including pore pressure (like any run of the mill CPT testing contractor would). Notably, if pore pressure response problems evolve in any “difficult” test zone, time is not invested trying to solve them. Typically, a client is hoping for reasonably high productivity using this method. |
The base test method chosen for a known soft clayey soil project
for overall “site characterisation and mapping”.
With IGS-2, good quality pore pressure response is usually achieved and “normal” dissipation tests can be made. |
Recently calibrated 100MPa cone is used; either an S-Type or a C-Type
cone. A temperature stabilisation is conducted between 0.5m and 1.5m to stabilise the cone to the ground temperatures. A penetration rate of 20mm±5mm per second is adopted. Cone is carefully prepared to ensure best reasonably achievable piezo saturation. Pore pressure measurements are made as test progresses. Should difficult soil layers be encountered (eg gravely bands or hard fissured layers causing tilt), the test can sometimes be carefully continued – at discretion of the IGS Operator. Penetration readings are collected at 10mm intervals |
| IGS-3S or IGS-3C | DATA-ORIENTED PIEZO CONE TESTING.
This is the default IGS Cone Penetration Test Method, unless instructed by the Client to do otherwise. Client must advise IGS of their expectations, as test productivity may sometimes be reduced using this method. Objective is best possible test data including pore pressure response in all ground, but still maintaining modestly high productivity. Client might intervene during progress to shift test method to either IGS-4 or IGS-2, accepting the test productivity or data quality consequences that result. |
Sometimes used at
targeted locations after site characterisation by IGS-1 or 2 testing. If the Client wishes to obtain inputs into determination of soil parameters to an “especially” high level the Client will more likely choose IGS-4. Typical objectives are for the assessment of soil properties for confident design. Dissipation tests should be achieved to a high standard. |
Recently calibrated 100, 25 or 10MPa cone is used; capacity is
selected to suit the ground being targeted; either an S-Type or a C-Type cone.
A temperature stabilisation is conducted between 0.5 and 1.5m to stabilise the cone to the ground temperatures. Additional temperature stabilisations may occur during the transition between dense and soft layers. A penetration rate of 20mm±5mm per second is adopted with readings at 10mm intervals. Cone is carefully prepared to ensure best achievable piezo saturation. 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). Should difficult soil layers be encountered (i.e., gravely bands or hard fissured layers causing tilt), the test can sometimes be carefully continued at slower speed – at the discretion of the IGS Operator. |
| IGS-4C or 4S | SPECIAL CLASS PIEZO CONE TESTING – ALL MATERIALS.
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 cone 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. |
Sometimes 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 are for the assessment of soil properties for confident design. Dissipation tests should be achieved to best possible standard. IGS-4 will not be adopted on the first test on any particular site. |
Recently calibrated 100, 25, 10MPa or 3MPa cone selected to suit
the ground being targeted. Either an S Type or C-Type cone is used. This is the only Method that the Special Purpose 3 or 10MPa cones will be deployed. A temperature stabilisation is conducted at 0.5m then again between 1.0 and 1.5m depth to stabilise the cone to the ground temperatures. Additional temperature stabilisations may occur when transitioning between dense and soft layers or where the IGS Operator identifies significant changes in temperature. A penetration rate of 20mm±2mm per second is adopted with readings at 10mm intervals. Cone is carefully prepared to ensure best achievable piezo saturation. 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. Should difficult soil layers be encountered (i.e., gravely bands or hard fissured layers causing tilt), the test can sometimes be carefully continued at slower speed – at discretion of the IGS Operator. The cone shall be cleaned and re-prepared prior final zero load checks at the end of each test. |
| "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. |
Both C-Type and S-Type can be piezo or non-piezo. If piezos the piezometer elements are the same in each - there is no difference in the accuracy of pore pressure readings made by either cone type.
Each cone type has a load cell 100% focused on measurement of tip resistance - there is no difference in the accuracy of tip readings made by either C-Type or S-Type cones.
In a C-Type cone the sleeve load cell is sized to suit the sleeve load capacity of the cone. This must arguably make it at least potentially more sensitive than determination of sleeve resistance by an S-Type cone; a small load cell is used to measure a small load. However it also limits the sleeve capacity available and in hard and dense soils this can “refuse” a test long before tip capacity is reached.
In an S-Type cone the sleeve friction is determined by subtracting the reading of one large load cell from that of another large load cell. This must arguably make it at least potentially less sensitive than determination of sleeve resistance by a C-Type cone. However in an S-Type cone there is effectively no limit to the sleeve capacity and thus in hard and dense soils deeper tests are typically possible.
There is no doubt that an S-Type cone is more stable during a test and during a job, showing less “drift” and less need for adjustment or repair during the calibration process. It is also much stronger and more durable physically and hence less damage/drift prone.
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