Shear Behaviors of the Binary Structural Plane

Binary-medium contact interfaces widely exist in rock engineering. They have significant impacts on the safety of rock engineering due to their poor shear behavior. A material of different strength is produced by pouring mortar of a different sand-to-cement ratio on the top of a rock-like mortar material (with the ratio of 1:1), thereby forming a binary-medium structural plane. Then, direct shear test is performed on the structural plane by applying different normal stresses. The shear strength parameters of the structural plane (cohesion \(c\) and friction angle \(\varphi\)) are obtained from the Mohr–Coulomb criterion. Moreover, the mechanical behaviors of the structural plane are compared with the unitary-medium specimen in the shearing process. A similar shear stress–shear displacement rule is observed in the shearing process. However, the peak and residual shear strengths of the binary structural plane are far lower than those of the unitary ones. The difference between the unitary and binary planes at cohesion \(c\) decreases with the increasing sand–cement ratio, whereas a up-down trend is observed in the friction angle \(\varphi\) with the increasing sand-to-cement ratio. When the upper and lower parts of the structural plane are different in sand-to-cement ratio, the cohesion \(c\) of the structural plane slightly increases with the increasing ratio of the upper specimen. However, when the two parts are identical in ratio, the cohesion of the structural plane reaches the peak, and its friction angle \(\varphi\) substantially increases with the increasing ratio of the upper part.