Shear behavior of rectangular-shaped asperities in rock joints

Abstract

This study addresses the shear behavior of rectangular asperities on rock joints to highlight the role of asperity characteristics related to joint shear behavior. The shear strength and failure mode of a rectangular asperity are theoretically derived from force equilibrium analysis, and the relationship between shear strength and shear displacement of a unit asperity is obtained considering shear mechanisms and asperity characteristics. Two failure modes of a rectangular asperity are determined depending on its shape and critical aspect ratio: a dilative failure mode with an inclination of 45-ϕ f /2 and a non-dilative failure mode with shearing of asperity. The range of critical aspect ratio is 0.15 to 0.32 for general rocks. The shear strength of a rectangular asperity is also determined with peak friction angle, cohesion, basic friction angle, aspect ratio, and normal stress. Direct shear tests on artificial joints are performed to verify the theoretical analysis on a rectangular asperity and to explore the effect of asperity size distribution and progressive failure. Based on the analysis on a unit asperity, various effects, such as asperity geometric distribution, normal stress, and specimen size, are discussed in relation to the shear behavior of rock joints.