An elastoplastic model for unsaturated soil-structure interfaces considering different initial states, boundary conditions and suctions

Soil -structure interfaces in shallow foundations, embankments and other geo-systems are usually unsaturated, which has great influences to the performance of geo-structures. However, researches on unsaturated soilstructure interfaces are still kept in very limited numbers, particularly for the theoretical part. This paper proposes a state -dependent model for unsaturated soil -structure interfaces based on two independent stress state variables: net stress and suction. To consider the effects of initial state, stress level, and suction, a state -dependent dilatancy and suction -induced relocation of critical state line is introduced, and a rigorous, exhaustive and schematic calibration procedure of the proposed model is presented. Thereafter, simulations of direct shear tests on sand -steel, sand-geotextile, silt -steel and soil-cement interfaces with different initial states, boundary conditions and suctions are carried out. Results show that, shear strengths of interfaces increase with initial density, normal stiffness and suction, and the strain softening and dilatancy behavior are significantly enhanced by initial density and suction, while normal stiffness makes a contrary contribution. More importantly, calculations of the proposed model are fairly consistent with measurements, indicating such features of strain softening, stateand suction -dependent dilatancy, as well as the improved peak and critical shear strengths, are well captured by the model.