Study on Macro–Meso Shear Characteristics of Geogrid–Silty Clay Interface

This study investigates the macro–meso shear characteristics of the geogrid–silty clay interface under cyclic loading through a combination of laboratory cyclic direct shear tests and numerical simulations. The effects of geogrid roughness, soil moisture content, shear displacement amplitude, and normal stress on the interface behavior are systematically analyzed. The results show that the interface shear strength and shear stiffness exhibit a three-stage evolution with increasing cycle numbers. This evolution is characterized by rapid attenuation in the early stage, gradual change in the middle stage, and stabilization in the later stage. The main degradation occurs within the first 1–10 cycles, while the interface response tends to stabilize after approximately 25 cycles. Increasing geogrid roughness and normal stress significantly enhances the interface shear strength and restrains cyclic degradation. In contrast, the shear strength reaches a maximum at the optimum moisture content level of 13%. The damping ratio shows an opposite trend to stiffness, increasing with cycle number and gradually approaching stability. Numerical simulation results are in good agreement with the experimental data, with relative errors within 5%. At the mesoscopic level, shear stress is mainly concentrated at the intersections of geogrid ribs, and the soil zone within 0–20 mm above the interface is identified as the primary region of shear deformation.