Abstract: The soil-rock mixture-bedrock contact surface represents as the primary control interface for the stability of accumulated landslides, and the morphological characteristics of bedrock interface represent a pivotal element of the design. Large-scale direct shear tests were conducted on the contact surface under varying morphological parameters of the bedrock interface. The objective of these tests was to investigate the influence of the aforementioned parameters on the shear mechanical properties of the contact surface. A generalized model was developed to describe the movement of soil and rock particles at the contact surface. A simplified composite power exponential (CPE) model was established to describe the shear behavior of the contact surface. Results show that as the roughness of the contact surface increases, the shear strength of the contact surface progressively enhances. This is accompanied by a nonlinear upward convex growth trend in the apparent internal friction angle and a quasi-linear increase in the apparent cohesion. As the sawtooth height increases, the shear strength of the contact surface initially rises and subsequently declines. The impact on apparent cohesion is more pronounced when sawtooth height increases. The relationship curve between shear stress and shear relative displacement at the contact surface generally exhibits a weak hardening pattern. The compactness of the soil-rock particle skeleton is observed to decrease with increasing roughness, but to increase initially and then decrease with the elevation of sawtooth height. The movement of soil-rock particles at the contact surface is primarily characterized by interlocking, rolling and slipping, while particle fragmentation and shear failure at the bedrock tips occur under conditions of higher normal stress. The model parameters k, b, and n are found to exhibit a linear relationship with the dimensionless normal stress n/Pa. n is normal stress, and Pa is standard atmospheric pressure. The fitting coefficient ai (i = 1, 2) remains unaffected by the morphological parameters of the bedrock interface. Moreover, fitting coefficients bi and gi demonstrate a linear relationship with roughness R and sawtooth height D, respectively. The simplified CPE model effectively simulates the entire process of shear deformation at the soil-rock mixture-bedrock contact surface under varying morphological parameters of the bedrock interface. The model demonstrates good applicability, and the method for determining the parameters is both reasonable and feasible.

Key words: soil rock mixtures, bedrock interface, morphological parameters, shear characteristic, constitutive model