Simulating the cyclic behaviour of unsaturated soil at various temperatures using a bounding surface model

Soils in many earth structures are often unsaturated and subjected to cyclic loads (e.g. subgrade soil in pavement under cyclic traffic loads) under various climatic conditions. Although many constitutive models have been reported for modelling unsaturated soil behaviour, none of them is developed purposely to capture the cyclic behaviour of unsaturated soil at various temperatures. In this note, a new cyclic thermo-mechanical model for unsaturated soil is developed using the bounding surface plasticity theory. Differently from conventional elastoplastic models, plastic strain is allowed inside the bounding surface to capture cyclic stress-strain relations. The new 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 unsaturated soil are fully coupled. Computed results from this model are compared with measured data from suction-and temperature-controlled cyclic triaxial tests on an unsaturated silt. It is shown that computed and measured plastic strains are generally consistent at various numbers of cycles, suctions and temperatures.