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 "
". 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.
Pore Pressure Dissipation Tests in fine-grained materials can run very quickly - eg a few minutes, or very 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.
At IGS we define “quality service” as being satisfactory implementation of the class or type of test required by the client, to suit their particular needs. Note that:
Particularly, for instance, if that class or type of test takes longer (and thus costs more) than a test that would otherwise have fully suited the client’s needs.
As we offer a range of different CPT test types, all of “high quality” for their particular application, it is convenient to tabulate these and define a system of test designation (ie test-type-name) to assist in communicating with clients and helping them direct IGS as succinctly as possible in regard to their needs.
There is no international or Australian standard to guide us in preparing this classification system so we have prepared our own hierarchy of test types and unambiguously designated these Types IGS-1, IGS-1N, IGS-2, IGS-3 and IGS-4 and IGS-R as tabulated below. The classification system has evolved from our own experience with our own clients and is a reflection of our own current opinions. We would appreciate any feedback from any client and advise that the classification system might evolve with time and with hoped-for constructive client feedback.
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.
Keep up to date with our latest news and developments.