A new approach for quantifying the two-dimensional joint roughness coefficient (JRC) of rock joints

The joint roughness coefficient (JRC) is the key factor in predicting the peak shear strength of a rock joint. In this paper, we present a new approach for quantitatively calculating the JRC of two-dimensional rock joints. First, the two dimensionless indexes of cumulative relative relief amplitude (CRRA) and weighted average gradient (WAG) are defined to represent the morphology characteristics of a joint profile. Second, the ten standard roughness profiles suggested by Barton and Choubey are digitized, and the values of CRRA and WAG for each profile are calculated. Based on the JRC, CRRA and WAG results of the standard joint profiles, an equation for calculating the JRC, which takes the CRRA and WAG as inputs, is proposed by utilizing the multiple nonlinear fitting method. Finally, the validity of the proposed method is investigated by performing laboratory and numerical direct shear tests of 12 joint profiles with different JRCs. The results show that the established equation can accurately quantify the JRC of a two-dimensional joint. However, the accuracy of the JRC greatly depends on the sampling interval along the joint profile. The recommended length of the sampling interval is no greater than (1/120) L.