the Direct-Push Crosshole (DPCH) Test for In-Situ Evaluation of Near-Surface P&S-Wave Velocities

The direct-push crosshole (DPCH) test is an invasive, near-surface seismic testing method, which combines the high-quality, high-resolution velocity measurements of borehole-based crosshole (CH) seismic testing with the relative cost effectiveness and speed of direct-push testing methods, such as cone penetration testing (CPT). At each measurement depth (typically, at 20 to 50 cm intervals), constrained compression (P) and shear (S) waves are generated simultaneously by tapping on one of the cone push rods (an in-ground source may also be used). These P- and S-waves are propagated between two instrumented seismic cones (i.e, a source and receiver cone) along a predominantly horizontal direct travel path. The instrumented cones contain a sensor package with two or three orthogonally oriented geophones to measure the seismic waveforms and a tri-axial MEMS accelerometer to track the deviation/position of each cone as it is advanced into the ground. DPCH testing enables the measurement of high-resolution profiles of P- and S-wave velocity over the top 20 – 30 m of the subsurface for use in geotechnical engineering analyses, such as the evaluation in-situ degree of soil saturation, liquefaction triggering potential, and seismic site response analyses. Another potential application of high-quality velocity measurements obtained via DPCH testing is the evaluation of in-situ soil porosity/void ratio. The DPCH method also allows for testing across/through ground improvement elements such as stone columns