Influence of Shear Rate on the Shear Strength of Discontinuities with Different Joint Roughness Coefficients

Abstract Loading rate dependency is one of the significant time-dependent behaviors of rock and rock discontinuities. To investigate the shear rate– dependent behavior of the shear strength of discontinuities with different joint roughness coefficients (JRCs), direct shear tests with various shear rates were conducted on samples with artificial joint surfaces based on Barton’s standard profile lines. A new test method, called shear test with alternate shear rates, was introduced to verify the direct shear results, and a JRC weakening model was established to explain the mechanism of shear rate dependency of discontinuities and the influence of the JRC on shear rate dependency. Results revealed that the shear strength increased with an increase in shear rate and the shear rate dependency of discontinuities was significantly influenced by surface morphology. Hence, the greater the JRC is, the stronger the shear rate dependency will be. Results also demonstrated that the direct shear test is the process of the JRC resistance weakening and frictional resistance strengthening, and the shear rate dependency was caused by the time-dependent behavior of the crack growth.