Direct shear strength test on rocks along discontinuities, under laboratory conditions

This paper presents a brief summary of the main existing shear strength test methods on both intact and fractured rocks, such as the triaxial, half-half notched specimen and direct shear strength tests. A detailed description of how to carry out a direct shear strength test on rocks along discontinuities are provided, supported by test results. The analyses include the interpretation of the tests and the calculation of the maximal and residual shear strength, as well as their angle of friction and apparent cohesion. These parameters depend on the properties of the rock and the discontinuity, such as the joint surface roughness, the rock texture orientation, the filling material, the thickness of the discontinuities, the scale effect and the magnitude of the applied normal force during the test. Their effect is discussed