DEM investigation on the shear mechanical behavior of rock fractures with the same roughness level

Geometric morphological features significantly influence the shear mechanical properties of rock fractures, which are quantitatively assessed using roughness indicators. However, it remains uncertain whether fractures with identical roughness indicators exhibit similar shear mechanical behavior. This study employed three-dimensional scanning and the roughness index θ^*_max/(C + 1) to investigate the roughness of fracture profiles oriented differently on the fracture surface. The findings confirm that natural fracture profiles can have similar roughness levels but distinct morphologies. Consequently, a methodology was proposed to construct fractures with identical roughness but differing morphologies, based on 10 fracture profiles exhibiting varying roughness gradients. Numerical models of rough fracture samples were established, and direct shear tests were conducted using the discrete element method (DEM). The results reveal significant variability in shear strength, shear deformation, and macro-microscopic failure characteristics among fracture samples with identical roughness levels. As the θ^*_max/(C + 1) of fractures increases, more morphological asperities contribute to resisting external shear forces, although both the mean values and variability of shear mechanical indicators across fracture samples demonstrate an increasing trend. The distribution of fracture morphological features notably influences the characteristics of contact force distribution, as well as the scale and orientation of microcrack development within fracture samples. The contribution of different segments of fractures to resisting external shear forces correlates closely with their specific morphological feature distribution, particularly the location where θ^*_max/(C + 1)​ occurs.