Effect of joint sets on the anisotropic strength of rock masses

In this paper, a series of physical model tests of jointed rock masses with several skew joint set is performed to investigate the interaction between intact rock and joints. Through this study, it is found that: (1) The failure modes of rock masses can be simply divided into three types: (a) fracture mode; (b) sliding mode; (c) mixed fracture-sliding mode of (a) and (b). (2) Superposition of joint sets on rock mass strength is only correct for the fracture and the sliding failure modes which the interaction of joints can be ignored. For the mixed failure mode, the strength of rock masses with two skew joint sets might reduce to 50% of those with one single joint set, mainly due to the strong interaction of joints for different sets. The strength of the rock mass with two skew joint sets is dominated by the weakest set of joint sets.