Scaling Shear Modulus from Small to Finite Strain for Unsaturated Soils

Abstract

The stress-dependent curve of shear modulus degradation with increasing shear strain amplitude is a fundamental mechanical property of soils. Although it is well known that the degree of saturation has an important impact on the small strain shear modulus of unsaturated soils, its role on the shear modulus evolution with strain has not been thoroughly investigated. A testing program has revealed strong correlations between two key parameters of the shear modulus degradation curve, the reference strain and the coefficient of curvature, and parameters of the soil water retention curve (SWRC). An SWRC model capable of distinguishing between soil water in the capillary and adsorption regimes was used to correlate the reference strain to the maximum adsorption water content and pore size distribution of a soil, and to correlate the curvature coefficient to the maximum adsorption water content. A hyperbolic equation for the shear modulus reduction curve using these correlations shows good performance in predicting the shear modulus under unsaturated small or finite strain conditions. The new model was validated using the shear modulus reduction curve of independent data sets measured at different shear strains.