Experimental Study on Shear Behavior and a Revised Shear Strength Model for Infilled Rock Joints

To better understand the shear behavior of infilled rock joints with standard joint roughness coefficient (JRC) profiles, direct shear experiments are performed on sand and clay infilled joints prepared by reproducing the standard JRC profiles on a rock-like material and placing the infill material inside the joint. The results show that the shear behavior and strength of infilled joints are affected by the JRC, the infill material type, the infill thickness to joint asperity amplitude (t/a) ratio, and the applied normal stress. For most of the infilled joints, the shear stress versus shear displacement curve shows a residual shear stress value close to the peak value and no softening phase. The normal displacement of infilled joints shows pure compression or first compression and then dilatation. Under the same normal stress, the clean joints show the largest shear strength, followed by the sand infilled joints, and then the clay infilled joints. The peak shear strength of infilled joints decreases with larger t/a, following a nearly negative exponential relation, and reaches the shear strength value of the infill material when t/a is above a certain value. A revised shear strength model for infilled joints was proposed by incorporating the negative exponential relationship between friction angle and t/a in the Barton and Choubey shear strength criterion under constant normal load (CNL) condition. The good agreement between the prediction results from the revised shear strength model and experimental data indicates its capability in estimating the peak shear strength of infilled rock joints.