Influence of water saturation on horizontal and vertical motion at a porous soil interface induced by incident P wave

Abstract

This paper describes a study on the influence of water saturation on horizontal and vertical motion at the interface between porous soil and rock formation due to an incident P wave. The soil is modeled as a partially water-saturated porous material with a small amount of air inclusions, while the underlying rock is approximately regarded as an ordinary one-phase solid. Theoretical formulation is developed for the computation of motion amplitudes in both horizontal and vertical components, which are considered as functions of the degree of saturation, the angle of incidence as well as the frequency. Numerical results are provided to illustrate the effect of saturation on displacement amplitudes in both components and their ratios. The results show that even a slight decrease of complete saturation may lead to a substantial change in the motion amplitudes in both horizontal and vertical components. In general, partial saturation may cause lower horizontal-to-vertical ratios over the entire range of incident angles except the normal incidence, implying the potential importance of saturation effects in the interpretation of field observations.