In simple shear test

under the constant stress increment ratio (CSIR) stress path

some soil-structure interfaces have the mechanical properties of strain softening and shear dilatation. Based on generalized potential theory

an elastoplastic model for soil-structure interface under the CSIR stress path is proposed. In the model

soil-structure interface problem is regard as a two-dimensional mathematical question in stress field; normal stress and tangential stress are taken as two potential functions respectively

and plastic state equations are used to replace the traditional yield surface. Relation curves of normal stress and normal strain in axial compression tests is described by an exponential function; and relation curves of stress ratio and tangential strain in simple shear test is simulated by a complex exponential function. Then

another complex exponential function is presented to express normal dilatancy and tangential strain relation curves. Furthermore

the model undetermined coefficient expressions are got by the differential of above fitting functions. Finally

the model prediction results have been compared with experimental data; and the results show that the model is reasonable and practical