Constitutive law for the shear strength of rock joints based on three-dimensional surface parameters

A new constitutive criterion, relating stress and displacements, is proposed to model the shear resistance of joints under constant normal load conditions. It is based on an empirical description of the surface, and on the results from more than 50 constant-normal-load direct-shear tests performed on replicas of tensile joints and on induced tensile fractures for seven rock types. This constitutive model is able to describe experimental shear tests conducted in the laboratory. Moreover, the parameters required in the model can be easily measured through standard laboratory tests. The proposed criterion was also used to estimate the joint roughness coefficient (JRC) value. The predicting values were successfully correlated with JRC values obtained by back analysis of shear tests.