Influence of humidity conditions on shear strength of clay rock discontinuities

The shear strength of rock discontinuities strongly depends on the water content especially when the rocks contain clay materials. To assess the decrease in the mechanical properties of clay-infilled discontinuities due to water saturation, a series of direct shear tests was performed using an advanced shear box that allows the injection of water into the discontinuity. Results show that both the friction coefficient and the cohesion decrease when the discontinuity is saturated. Overall, the shear strength of the discontinuity is considerably reduced to approximately 50% of its original value. This reduction has to be accounted for when conducting stability analyses of rock slopes, dam foundations or underground openings.

► Direct shear tests on marl discontinuities were carried out.
► The tested marl discontinuities were dry or saturated.
► Tests were performed in constant load or in Constant Volume conditions.
► Discontinuity contraction is more pronounced in saturated conditions.
► Saturation leads to a substantial decrease of discontinuity shear strength as well as stiffness moduli.