Characterizing saturation state of loess using P-wave velocity

Abstract

A conventional approach to characterize the degree of saturation of soils uses the pore pressure parameter, also known as B-value in laboratory experiments. Given a recent advance that the P-wave velocity was derived as a function of the B-value with progressive saturation based on the poroelasticity theory, it sheds a light on applicability of the P-wave velocity to evaluate saturation of soils in an effective manner. Yet, previous studies in this regard often focus on granular materials, the feasibility of using the relationship for cohesive soils, such as loess, was less extensively studied and remained poorly understood. This paper presents an experimental study on the P-wave velocity of loess using a pair of piezoceramic extender elements at a sequence of saturation states. Moist tamping method was used to prepare loess samples of different water contents (5% and 14%), and the influence of initial water content on the relationship between the P-wave velocity and the B-value was examined. It was found that, in general, as the B-value increases, the P-wave arrives earlier for the loess specimen having a lower initial water content (5%). Though the P-wave velocity increases with the B-value, that is approximately in line with theoretical predictions, departures from predictions were observable at higher B-values. A relevant hypothesis was given that attributed the observed discrepancies to the local variation of pore connections and the associated distribution of air bubbles in the specimen. Correspondently, numerical evidences were also provided by using the program FLAC3D.