Shearing characteristics of rock joints strongly depend on the surface roughness. BARTON (1973) proposed an empirical equation to estimate the shear strength of rock joints, introducing the parameter of JRC (joint roughness coefficient). BARTON and CHOUBEY (1977) conducted shear tests of 10 different rock joints and decided the value of JRC for each joint from back calculation using the equation. The values of JRC and the joint profiles are adopted in the suggested methods for the quantitative description of discontinuities in rock masses (ISRM, 1978). However, to decide the value of JRC for a rock joint in question, the joint profile must be visually compared with the 10 typical profiles. In addition, Barton and Choubey's procedure itself includes a few problems to discuss.
In this study, 10 specimens having Barton and Choubey's typical profiles and no roughness in the direction perpendicular to the profiles were made with a numerically controlled cutting technique, and were used in push tests (corresponding to shear tests) and tilt tests. The test results show that some of the profiles do not present the value of JRC correctly, and that the friction angles at the left and right shear directions are different by 20 degrees in one profile. With increase in JRC, the friction angles obtained from the push tests become greater than those from the tilt tests. Shear forces acting along a joint can be estimated from only changes in the dilation associated with shearing, in the case of no damage on the joint surface. In such a case, the parameter of arctan Sm, where Sm is the maximum slope in a profile, is well related to the friction angle of the profile, and can be regarded as a useful one to quantify a profile.
