Characterization of Rock Joint Roughness from the Classified and Weighted Uphill Projection Parameters

To reflect the contributions of different-ordered asperities to the peak shear strength, a directional uphill projection area parameter was proposed to estimate the joint roughness coefficient (JRC) for two-dimensional joint roughness profiles. Using Barton's 10 reference profiles, a series of 2D JRC estimation formulae were established by weighting the two-ordered uphill projection area parameters at different sampling intervals (SI) to consider the effects of both shear resistance and shear dilatancy. Next, the 2D uphill projection area parameter was extended to a 3D uphill projection volume parameter, which shows good agreement with the worn areas of rock joints. Based on the shear tests of 36 square sandstone joints, a new 3D JRC estimation formula was proposed, and this was successfully applied to the JRC estimation of 29 rock joints with irregular profiles. Comparison of three different calculation methods of joint length indicates that equivalent length is more suitable to estimate the JRC of irregular rock joints. This proposed method can also reflect the anisotropic characterization of a rock joint.