Numerical Study on Shear Strength and Failure Pattern of Jointed Rock under Shear Testing

The purpose of this paper is to investigate shear strength and failure pattern of rock containing two parallel open joints with different horizontal separations using RFPA2D (rock failure process analysis) code. Specimens are placed in a direct shear box. The upper is invariably loaded with normal stress 0.15MPa, the left is controlled by a constant increasing horizontal displacement 0.002mm/step. The whole shear failure process is visually represented and the failure pattern in reasonable accordance with previous experimental results is obtained. In general, only mixed mode (tensile and shear) is observed for the failure pattern in the numerical tests. Tensile cracks initiate from the tips of pre-existing joints respectively with an initiation angle of about 45°, then propagate towards another joint in a single stria; Shear cracks occur in the further process and the main direction of shear failure surface is roughly parallel to shear loading. The failure pattern of bridged rock is mainly controlled by the joint separation and the roughness of wavy shear failure surface is different, which is mostly influenced by the joint separation in the same way. The peak shear load, related to the failure patterns, decreases with the increase of joint separation, but the shear strength of intact rock is invariable.