A three-dimensional state-dependent model of soil–structure interface for monotonic and cyclic loadings

An elasto-plastic model based on critical state soil mechanics and generalised plasticity was modified to capture the three-dimensional (3D) behaviour of soil–structure interfaces. The modified model assumed isotropic behaviour in different directions of a soil–structure interface. Two circular surfaces were defined on the plane of normalised shear stresses, and the cyclic interface response was determined by the distances of the normalised shear stress on this plane. With a single set of parameters, the modified model simulated the monotonic and cyclic 3D behaviour of soil–structure interfaces over a wide range of soil densities, normal pressures and normal stiffnesses. A unified description of the particle breakage under monotonic and cyclic loading conditions was incorporated, and the considerable contractive behaviour under cyclic loading can be captured by employing a more obvious translating critical state line related to particle breakage. Most of the model parameters have definite physical meanings and can be calibrated through conventional direct shear or simple shear tests. The modified model was validated against published tests of sand–steel interfaces and gravel–steel interfaces under both monotonic and cyclic loadings in 2D and 3D stress paths.