CPT Testing vs. SPT Testing
What is CPT Testing?
Cone Penetration Testing (CPT) is fast, safe, and offers digital in situ soil behavior type (SBT) instantly. The in situ data gathered can inform geotechnical design and field characterization decisions immediately. CPT’s versatility in obtaining shear wave velocity, sediment pore pressure dissipation, and discrete sampling offers users increased functionality and digital sounding files.
Not only is CPT highly accurate, it also manages to be relatively inexpensive compared to other testing methods. CPT in general is three times as fast as SPT site characterization; tripling your productivity and reducing your inderived waste generated (cuttings).
The data generated can be exported and utilized in multiple modeling software to accurately assess risk in design and inform geotechnical decisions. CPT data offers high resolution in situ results versus SPT, which often utilizes variable intervals and limited grab samples from various depths.
For example, Vertek’s S4 CPT Sounding System is a versatile, affordable push system that is compatible with construction equipment and can have a dedicated trailer system. The S4 is capable of providing superior soil testing almost anywhere SPT Testing can be performed.
Additionally, if your organization utilizes SPT for site characterization, a small capital investment into a CPT Drill Rig Conversion Kit allows you to quickly conduct CPT testing and offer both services to your customer.
The Federal Highway Administration even notes CPT is one technology that allows
“optimization of subsurface exploration programs for improved site characterization and maximum return-on-investment.”
What is SPT Testing?
Standard Penetration Test (SPT) is a low-cost and straightforward testing procedure widely used in the geotechnical examination to determine the relative density and angle of shearing resistance of cohesionless soils and also the strength of stiff cohesive soils.
Mud rotary drilling, for example, has come up in the past along with one of the best-known soil testing procedures out there: the Standard Penetration Test (SPT). Like Cone Penetration Testing, SPT Testing is widely used. But can it outperform CPT Testing?
SPT Testing uses a thick sample tube to determine the relative density of granular deposits, typically sand and gravel.
The sample tube is placed at the bottom of a borehole and struck with a heavy slide hammer repeatedly. The number of hammer strikes is important; the test operator must track how many strikes it takes to drive the sample tube 6 inches into the soil. The test is completed when the sample tube reaches 18 inches deep.
As you might imagine, a test that requires only a sample tube and a hammer offers a few notable benefits, namely that it is simple and inexpensive to perform.
SPT Testing does have its drawbacks, though. Most notably, it’s inaccurate compared to more advanced methods, especially when sampling coarse sands or clay. Additionally, with CPT, you can easily and quickly conduct seismic soundings.
As President and Principal Engineer of GEOLINES, Otto Holmquist stated, “Every time a geotechnical engineer sees how efficient it is, they are hooked.”
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