Comparison between Empirical Estimation by JRC-JCS Model and Direct Shear Test for Joint Shear Strength

In order to study the reliability of the empirical estimation of joint shear strength by the JRC (joint roughness coefficient)-JCS (joint compressive strength) model, natural rock joints of different lithologic characteristics and different sizes were selected as samples, and their shear strengths under dry and saturated conditions were measured by direct shear test and compared to those estimated by the JRC-JCS model. Comparison results show that for natural rock joints with joint surfaces closely matched, the average relative error of joint shear strength between empirical estimation and direct shear test is 9.9%; the reliability of the empirical estimation of joint shear strength by the JRC-JCS model is good under both dry and saturated conditions if the JRC is determined accounting for directional statistical measurements, scale effect and surface smoothing during shearing. However, for natural rock joints with joint surfaces mismatched, the average relative error of joint shear strength between empirical estimation and direct shear test is 39.9%; the reliability of empirical estimation of joint shear strength by the JRC-JCS model is questionable under both dry and saturated conditions.