Macro-mesoscopic study of the deformation and failure mechanism of through-boundary type locked rock masses

Abstract

The instability of the locked segment in rock structures is a common geological hazard and has been widely studied. However, the instability of through-boundary type locked segment structures with rock bridges of the same length but different angles has not been fully reported. In this paper, three failure modes and the tensile-shear failure characteristics of the fracture surface were identified by physical experiments. Using PFC2D, the local displacement field, force field distribution, and crack evolution characteristics were studied. The results show that under different rock bridge inclinations, the rock mass penetration modes can be categorized into three types: penetration at the joint tip and upper end, penetration of the rock bridge between adjacent joint tips, and oblique straight-line penetration at the upper and lower ends. The local scratch surface exhibits three distinct distribution characteristics: the locked rock mass above the rock bridge, within the rock bridge region, and around the joint region. As the rock bridge inclination increases, the peak stress tend to decrease, with crack development becoming more concentrated (excluding 90°). The minimum local displacement field in the central part transitions from a shell shape to a core shape. In the direction of the force source, stress concentration at the ends of the rock bridge (LM1 and RM1, LM3 and RM3) becomes more pronounced, but the degree of concentration is constrained by the rock bridge inclination. The distribution range of normal contact forces increases, and the maximum tangential contact force deviates toward the axial direction.