Seismic measurements in sand specimens with varying degrees of saturation using piezoelectric transducers

Abstract

Small-strain seismic measurements in sand specimens were undertaken in the laboratory using piezoelectric transducers. The measurements involved determining both constrained compression wave and shear wave velocities, Vpand Vs, respectively. The piezoelectric transducers were discs (PDs) for Vpmeasurements and bender elements (BEs) for Vsmeasurements. An instrumented triaxial chamber (ITC) was developed and associated support instrumentation was assembled to perform the seismic measurements. The same PDs and BEs were installed in a combined resonant column and torsional shear (RCTS) device. The soil tested in both devices was washed mortar sand. The sand was tested in dry, unsaturated, and saturated conditions in the ITC, while only dry sand was tested in the RCTS. Development, calibration, and operation of the PDs and BEs are discussed. Example waveforms are presented, which are associated with different stress levels, saturation conditions, and frequencies of excitation for P and S waves. A critical factor in performing successful measurements is the driving of each type of piezoelectric transducer at the optimum frequency, which depends on the effective confining pressure ([Formula: see text]), degree of saturation, and soil type. The excitation frequency used for PDs was found to be important when the sand specimens were at nearly or fully saturated conditions.