A state-dependent generalized plasticity constitutive model for coarse-grained soil-structure interfaces

Understanding and modeling the mechanical response of coarse-grained soil-structure interfaces is fundamental to geotechnical engineering, particularly for maintaining the safety and functionality of critical structures, including dams and retaining systems. To characterize the nonlinear mechanical response of these interfaces under monotonic and cyclic loading, this study proposes a state-dependent elastoplastic constitutive model formulated within a generalized plasticity framework incorporating critical state soil mechanics. The shear dilatancy formulation was refined using directional parameters to distinguish between loading and unloading paths, thereby capturing cyclic volumetric contraction and dilation. Furthermore, a new plastic modulus formulation was proposed to describe the stiffness degradation and recovery behavior under cyclic loading. These enhancements enable unified modeling of monotonic and cyclic interface behaviors, including strain hardening/softening, cumulative contraction, and dilation-contraction transitions. To validate the model’s robustness and applicability, three typical interface types—rockfill-concrete, gravel-steel, and cushion layer-extrusion wall—are simulated and compared with experimental data. Results show that the proposed model effectively captures the interface response under various initial densities, normal stresses, and loading histories, providing a reliable tool for constitutive modeling and numerical simulation of complex soil-structure interactions.