Laboratory investigation on the failure characteristics of rock-like materials with fully closed non-persistent joints

Due to dynamic geological conditions, a non-persistent joint network in a fully closed state is often developed in a rock mass, which will seriously affect the cracking process and strength characteristics of the rock mass after excavation and exposure. To reveal the weakening mechanism of closed non-persistent joints in terms of the rock mass strength and the resulting weakening degree, a “layered and embedded pouring” method for preparing rock-like specimens with closed non-persistent joints is proposed and verified, which overcomes the restriction of specimen preparation technology in research on laboratory testing of the mechanical properties of specimens with fully closed non-persistent joints. On this basis, uniaxial compression testing of specimens with closed non-persistent joint sets of different geometric characteristics is carried out. It is found that the joint orientation is the main factor controlling the failure mode of specimens. With increasing joint dip angle, the failure mode changes from splitting failure to stepped failure, planar failure and, finally, splitting failure. The strength anisotropy characteristics show a typical “U” shape; the strength of jointed specimens with a 0° dip angle is greater than that with a 90° dip angle, and the center of the distribution of dip angles corresponding to the minimum specimen strength is greater than 45°. This result is related to the friction characteristics of the joint surfaces, and the corresponding failure mode is stepped failure. Finally, by comparing the failure characteristics of specimens with a single open non-persistent joint and a set of such joints, the difference in the anisotropic weakening mechanisms and degrees of rock strength caused by fully closed and open joints are further revealed, which provides clearer differential cognition for establishing the strength theory of rock masses with non-persistent joints in different contact states.