A Direct-Push Crosshole (DPCH) Test Method for the In Situ Evaluation of High-Resolution P- and S-Wave Velocities

Abstract

The direct-push crosshole (DPCH) test is a new, invasive, near-surface seismic testing method. DPCH combines the desirable characteristics of borehole-based crosshole seismic testing with the relative inexpensiveness and speed of direct-push testing methods like cone penetration testing (CPT). At each measurement depth (typically every 20–50 cm), compression (P) and shear (S) waves are generated simultaneously using hammer taps on one of the CPT push rods (a pushable, in-ground seismic source can also be used). These P- and S-waves are propagated between two instrumented seismic cones (i.e., a source and receiver cone). The instrumented cones contain a sensor package with three orthogonally oriented geophones to measure the seismic waveforms and a MEMS accelerometer to track the deviation/position of each cone as it is advanced into the ground. DPCH testing enables high-resolution profiles of P- and S-wave velocity to be measured over the top 20–30 meters of the subsurface for use in geotechnical engineering analyses. It also allows for testing across/through ground improvement elements like stone columns. The DPCH instrumentation, testing methodology, and data reduction techniques are explained in detail in this article, and results from several sites are discussed.