Anisotropic shear behavior of rock joint replicas

In this study, an anisotropic shear behavior of joint replicas is investigated under constant normal load condition (CNL). A new anisotropic peak shear strength model is proposed incorporating actual peak dilation angle and shear component of asperities. In this model, peak dilation angle is modified with mean plane to find out actual dilation angle and shear component is back calculated from experimental results. The results show that as the ratio of normal stress to compressive strength increases, peak dilation angle decreases exponentially whereas shear component increases in power function form. Further, an empirical model for estimation of peak shear displacement is proposed based on maximum asperity angle and friction angle. Afterwords, shear stiffness is calculated as a ratio of predicted shear strength and peak shear displacement. To conduct this study, three different natural joint roughness is transferred to silicon rubber molds and these molds are used to make joint replicas of mated joint of 90 mm diameter and 50 mm height by mixture of cement, sand, and water in the ratio of 1:1.5:0.45 by weight. The surface cloud of joint surface are generated using 3D non-contact type profiler. In this study, total 144 direct shear tests are conducted on prepared joint replicas using four normal stresses (0.25, 0.5, 1, and 1.5 MPa).