Shear Properties and Failure Mechanism of Matched Discontinuities Between Two Different Rock Types Under Direct Shear

The shear mechanical properties of rock discontinuities with different joint wall compressive strengths are a practical basis for the stability analysis of layered rock mass. Shear tests on discontinuities possessing different joint wall strengths were carried out. The shear strength and failure characteristics were analyzed, and the influences of discontinuity morphology on its shear properties were investigated. Meanwhile, numerical tests were performed to study the shear mechanical behavior and dilation evolution of discontinuities possessing different joint wall compressive strengths. Results show that the shear process of discontinuities possessing different joint wall strengths can be divided into four stages: meshing and compacting, climbing wear of soft rock and crack formation of hard rock, shear of part of soft rock and crack expansion of hard rock, complete shearing of the rock discontinuity. Shear failure of discontinuities was mainly concentrated on the morphological structure facing the shear direction. The dilatancy evolution process of discontinuities was mainly affected by the roughness and normal stress. The magnitude of dilation, peak shear strength and residual shear strength of discontinuities possessing different joint wall strengths were between the discontinuities possessing identical joint wall strengths composed of soft and hard rock, under the same loading condition.