The shear mechanical behaviour of hard undulating discontinuities under unloading normal stress

This study investigated the shear mechanical behaviour of hard undulating discontinuities with different undulation shapes. A series of direct shear tests with unloading normal stress were conducted at different initial shear stresses. The failure, deformation, and strength characteristics were analyzed. The shear strength criterion governed by the undulating angle, initial stress, and failure pattern under unloading normal stress was proposed. Analyzing the experimental results and establishing modified Patton and Barton strength criteria provided theoretical support for understanding the rock mass failure mechanism and stability evaluation in excavating slopes and underground caverns under normal unloading conditions.