Geotechnical Testing

Geotechnical Testing

Gregg Drilling offers a number of specialized tests for geotechnical investigations. All are combined with standard rotary drilling techniques to implement the equipment. These tests include:

  • SPT Energy Calibration/Hammer Calibration
  • Vane Shear Testing (VST)
  • Pressuremeter Testing (PMT)

Gregg also offers Dilatometer testing (DMT) and Seismic DMT which can be advanced with the CPT equipment or direct push methods.


SPT Energy Calibration

Gregg operates the PDI SPT Analyzer system. This system calculates the energy transferred by SPT hammers using force and velocity measurements. Hammer energy can vary widely between different drill rigs and even for the same rig at different sites which makes energy measurement very important. Measured energies are used to adjust the measured SPT Nvalues to the normalized N60 (for a normalized 60% energy rate).


SPT Energy results are often low in the top 5-10ft when rod lengths are short

Energy results vary depending on the depth of the sample and soils encountered

For accurate results, equipment should be tested on your specific site

Auto-hammers often average much higher energy around 80-95%


Pressuremeter Testing

Gregg operates the TEXAM Pressuremeter manufactured by RocTest. The TEXAM PMT is deployed in a pre-drilled borehole. The PMT probe is filled with water in uniform increments and an insitu stress-strain curve is obtained by plotting the injected volume against pressure.

Vane Shear Testing

Gregg operates the Geonor H-10 vane system. The Geonor H-10 uses an up-hole motor to turn the downhole vane for the test. Vane shear testing provides an in-situ measurement of undrained shear strength. The system uses different vane sizes for downhole testing. Vane Selection is based upon the expected strength of the soils being tested.

Dilatometer & Seismic DMT Testing

Gregg deploys a seismic dilatometer (SDMT) made by Studio Marchetti in Italy. The probe is capable of conducting dilatometer and seismic testing down to 50m, or approx. 150ft in depth.

For additional information on the Dilatometer, please see our equipment page.

We’re ready for you

With over 35 years experience drilling in California and surrounding states, Gregg Drilling can handle any size project. We hope to demonstrate our value through quality equipment, knowledgeable and experienced personnel and our exceptional safety standards.