Shear Mechanical Properties of the Interphase between Soil–Rock Mixtures and Benched Bedrock Slope Surfaces

A series of benched excavations are typically carried out on bedrock slope surfaces to improve the stability of soil–rock mixtures (SRMs) on the fill slopes. In this paper, the shear characteristics and micromechanisms of SRMs–bedrock interphases were studied by means of large direct shear tests and discrete-element numerical simulation. In the process, this study also investigated the influences of rock block content and interface roughness by combining the direct shear test and discrete-element method (DEM) numerical simulation results. This showed that the samples exhibit obvious bulk shrinkage during shearing. As the rock block content increases, fluctuations in the postpeak shear stress–displacement curves become more obvious. Cohesion is more sensitive to roughness, while internal friction angle is insensitive to roughness. Also, the internal friction angle is very sensitive to rock block content. Moreover, the shear strength and cohesion of the interphase increase along with the superficial roughness, demonstrating a quadratic correlation with rock block content. However, this increase in roughness also increases the fracturing of rock blocks in the interphase. Within a certain interval, the shear strength of SRMs–bedrock interphases can be estimated according to a fitted empirical formula.