Shear mechanical model for soil-rock interface considering roughness effects

The shear mechanical properties of the soil-rock interface directly affect the stability of the binary structure slope. Among these factors, the joint roughness coefficient (JRC) of rock structural planes is a key parameter governing mechanical properties of the soil-rock interface. We combined laboratory direct shear tests with numerical simulations to investigate how varying JRC levels influence the shear properties of the soil-rock interface. An empirical formula for the shear strength of soil-rock interface considering different JRCs of the rock surface is proposed. The results indicate that: (1) The shear strength of the soil-rock interface increases with the increase of structural plane JRC, however, higher applied normal stress diminishes the JRC effect on enhancing the shear strength of the contact surface. (2) As structural roughness increases, the shear strength exhibits two stages: a rapid growth stage (JRC<13.42), during which the shear-sliding zone at the soil-rock interface fails; and a plateau stage (JRC≥13.42), during which internal shear failure of the soil occurs. Verification shows that the proposed empirical formula for soil-rock interface shear strength, which accounts for the influence of structural surface roughness, yields results that agree well with experimental data. These methods and findings provide a valuable reference for assessing the mechanical properties of soil–rock interfaces.