A new 3D JRC calculation method of rock joint based on laboratory-scale morphology testing and its application in shear strength analysis

In order to study the 3D joint roughness coefficient (JRC), a series of direct shear tests were carried out and the surface morphologies of joints were tested using laser scanning technology. A digital method was put forward to convert the 3D surface morphology of a joint into an average height 2D profile. JRC values of 15 joints were calculated on the basis of the statistical parameter Z₂ (root mean square first derivative values). The maximum profile angles of the converted average height 2D joint profile lines were measured and inserted into the Barton’s empirical formula to calculate the peak shear strength of the rock joint. Comparison between laboratory specimen scale test results and calculation results shows that the improved shear strength calculation model based on Barton’s empirical formula can exactly calculate the peak shear strength of rock joints. The arithmetic of converting the 3D joint surface morphology into a 2D average height joint profile is reliable in the laboratory study of joint shear mechanical characteristics.