Modelling Time-lapse S-wave Velocity Changes in an Unsaturated River Dyke Due to Water Infiltration

Abstract

Understanding the effect of saturation is important in assessing the failure mechanism on the land-side of a river-dyke due to rising water level in a river after heavy rainfall. S-wave velocity is controlled by soil suction and degree of saturation. Therefore, there is a possibility to estimate the unsaturated soil properties from the temporal changes in S-wave velocity. For this purpose, we model the temporal changes in S-wave velocity due to seepage of water in a dyke under rainfall. We propose a new approach for interpolating/extrapolating experimental data, in order to obtain shear modulus as a function of suction and confining stress. The seepage analysis of a river dyke under heavy rainfall shows that the temporal change in the S-wave velocity is determined more by the shear modulus than by the density. Furthermore, the S-wave velocity at shallow depths is more sensitive to seepage than the S-wave velocity at greater depths. These, together with the fact that a simple relationship exists between the shear modulus, suction and saturation, lead us to the new possibility of predicting shear modulus as a function of suction from the time-lapse S-wave velocity monitoring.