Macro-meso shear mechanical behaviors of coalescent rock joints with different morphologies

To investigate the macro-meso shear mechanical behaviors of coalescent saw-tooth (wavy) rock joints considering the impact of the first-order (second-order) asperities, the laboratory direct shear tests and PFC^2D numerical simulations are conducted. The results indicate that: (1) The macro-damage mass increases, the peak shear stress (displacement) approximately linearly increases (decreases) and the stress drop increases first then decreases as the first-order undulant angle increases under the same normal stress. The macro-damage increases, the peak shear stress (displacement) approximately linearly increases, and the stress drop increases (saw-tooth) or increases first then decreases (wavy) as the normal stress increases under the same first-order undulant angle. (2) There are five stages in the macro-meso damage evolution process, i.e., initial nonlinear deformation (compacting effect), approximately linear-elastic deformation (climbing effect), nonlinear deformation due to compression-shear fracture (climbing-gnawing effect), plastic deformation due to a drop in the brittle stress (gnawing effect) and ideal plastic flow deformation (sliding effect). (3) The macro-meso shear failure modes include compacting-climbing failure, climbing-gnawing failure and gnawing-sliding failure. The curves of the meso-damage crack quantity (energy) include three stages, i.e., a slight, steep and slow increase in the initial, middle and later stages, respectively, and the meso-damage particles are distributed near the rock joints in an approximately "trapezoidal-shape". (4) According to the limit equilibrium and strength reduction methods, the rationality of shear strength estimation formulas for the rock joints is verified through the stability analysis of rock slope examples.