Constitutive modelling of shear stiffness degradation at various suctions and temperatures

Some thermo-mechanical models have been reported for unsaturated soils. None of them is developed purposely to capture the nonlinearity of stress-strain curves and stiffness degradation at small strains (less than 1%). These existing models cannot therefore accurately predict ground movements and the performance of many civil structures under working conditions. In this paper, a new thermo-mechanical model is developed by using the bounding surface plasticity theory. Different from conventional elastoplastic models, plastic strain is allowed inside the bounding surface for capturing the degradation of soil stiffness with strain. This model is developed in terms of mean Bishop's stress, deviator stress, suction, temperature, specific volume and degree of saturation. Thermal, hydraulic and mechanical behaviour of soil are fully coupled. To evaluate capability of the model, it is applied to simulate suction and temperature controlled triaxial shear tests on a compacted silt. It is evident that computed stress-strain relations and stiffness degradation curves are generally consistent with measured responses at various suctions and temperatures.