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.

节理粗糙度系数（JRC）是预测岩石节理峰值剪切强度的关键因素。在本文中，我们提出了一种定量计算二维岩石节理 JRC 的新方法。首先，定义了累积相对起伏幅度（CRRA）和加权平均梯度（WAG）两个无量纲指标来表示关节剖面的形态特征。其次，将 Barton 和 Choubey 建议的十个标准粗糙度轮廓数字化，并计算每个轮廓的 CRRA 和 WAG 值。基于标准接头剖面的JRC、CRRA和WAG结果，利用多重非线性拟合方法，提出了以CRRA和WAG为输入的JRC计算公式。最后，通过对具有不同 JRC 的 12 个接头剖面进行实验室和数值直剪试验，研究了所提出方法的有效性。结果表明，建立的方程可以准确地量化二维关节的JRC。然而，JRC 的精度很大程度上取决于沿关节剖面的采样间隔。采样间隔推荐长度不大于（1/120） 升。