Laboratory measurement of wave velocities of unsaturated soils

Abstract

Ultrasonic testing has been used for non-destructive evaluation of materials and structures and there is an increasing interest in using Primary (P) and Secondary (S) waves due to its applicability in areas such as geo-prospecting, site investigation and the determination of geometrical properties like degree of saturation (Sr) and stiffness. This project attempts to measure wave velocities of unsaturated soil and investigate the relationship of P and S wave velocities with degree of saturation. The project attempts to understand the propagation of P and S waves using two forms of test, namely, using bender element and ultrasonic platen. For ultrasonic experiments, two different transducers were used. The effect of frequency on the P wave velocity (Vp) and S wave velocity (Vs) is important because while many laboratory experiments and in-situ seismic survey have been conducted to measure them, the data from different sources should strictly not be used interchangeably as different P waves may be measured at different frequencies. Experiments were conducted on kaolin and sand to determine the effects of frequency and degree of saturation on Vp and Vs. It was found that the bender element was more effective in capturing S waves signals and the ultrasonic platen is more effective in capturing P waves but was unable to capture S waves. The tests showed similar relationship and were able to determine reasonably wave velocities of unsaturated soils. In general, the Vp and Vs decreases with decreasing saturation.