Shear deformation characteristics and shear strength considering the interaction between joints and rock bridges

Nonpersistent joints that commonly exist in nonpersistent discontinuities exhibit complex shearing behavior due to the intervals between rock bridges. The influence of rock bridges on the bearing capacity of joints is difficult to determine due to two main factors: uncertainty of the proportion of the rock bridge area (or joint area) in terms of geometry and the resulting variation in normal stress distribution in terms of dynamics. As an innovative study, this paper investigates the effects of normal stress and joint persistence on the sequence of mobilization and stress distribution of rock bridges and joints by recording the deformation pattern of the two parts during a direct shear test. The test results show that the normal stress is not a weighted average according to the length of the joints and the rock bridge. Since the vertical deformation of joints is affected by the rock bridge, the normal stress borne by the rock bridge is greater than the weighted average. This difference changes the distribution of shear stress across the rock bridge and joints. On the basis of the Lajtai model, a shear strength model for nonpersistent joints that considers the interaction between rock bridges and joints was proposed, which shows agreement with the shear strength values obtained through experiments.