Inversion of soil-water characteristic curve in unsaturated soil embankment using the underlying physics of S-wave and integrated geophysics

Abstract

The soil-water characteristic curve (SWCC) plays an important role in determining the hydraulic and mechanical properties of the unsaturated soils. SWCC is vital to evaluating the stability of a slope or a river embankment. The sensitivity of seismic shear-wave velocity to SWCC has recently been quantified. However, the inversion of SWCC from field-observed VS is challenging. In this research, we have explored the possibility of integrating shear-wave velocity, water saturation and bulk density obtained from independent geophysical measurements and utilizing the underlying physics of shear-wave in terms of suction, saturation and stress, to invert SWCC. We derive a formulation for the shear modulus by combining van Genuchten model with stress-, suction- and saturationdependence of shear modulus. The stress is estimated using FEM, thereby taking into account the effect of geometry of the embankment. Tests on realistic synthetic data indicates that the inversion is very stable. This new scheme allows, for the first time, to estimate in-situ SWCC from integrated geophysical measurements. This can potentially have a large impact in diverse applications related to stability of earth-retaining structures, natural slopes, as well as in problems involving dynamic transportation of fluids in the vadose zone.