Small-strain behaviour of unsaturated silty clay: experiments and model interpretation

The experimental data dealing with the so-called small strain stiffness of soils are indispensable in developing and calibrating advanced numerical models. A literature review revealed a lack of such data for unsaturated soils. In this study, the laboratory measurements of very small and small strain stiffness are carried out in a double-walled triaxial cell using bender elements and LVDT transducers. The tested soil is a reconstituted silty clay, representing a typical soil encountered in engineering practice. A so-called effective stress for unsaturated soil is used in interpreting and numerically simulating the effects of suction magnitude, net stress magnitude and suction history on the initial elastic shear modulus, and on its decrease with increasing strain. The increase of both net stress and suction leads to increase in stiffness. This is observed by both elastic shear modulus and shear modulus reduction curve measurements. The “overconsolidation” by suction leads to the increase of stiffness, too. The experimental data are used for calibrating constitutive parameters and for assessing the capabilities of an advanced hypoplastic model for unsaturated soils. The model predictions are consistent with the laboratory measurements and the model can capture the increase of stiffness with respect to the increase of suction and net stress reasonably well. Moreover, the model is able to predict the increase of stiffness due to suction “overconsolidation”.