Particle flow simulation on shear mechanical behaviors, energy evolution, and fracture responses of rough layered rock mass

This study aims to investigate the mechanical properties and failure mechanisms of layered rock masses in direct shear tests. PFC2D (Particle Flow Code) model with dimensions of 100 × 100 mm was first established, and the fine-scale parameters were calibrated by the results of laboratory uniaxial tests on standard samples of rock-like materials of matrix and then conducted direct shear simulations in terms of various bedding inclinations (α = 15°–75°), joint roughness coefficients (JRC = 2–20), and initial normal stresses (σn = 1–4 MPa). The results show that the bedding inclination, the joint roughness coefficients (JRC), and the initial normal stress significantly impact the evolution mechanism of the cracks and instability-slip. With the increase in bedding inclination, JRC, and initial normal stress, the shear slipping shifts from interlayer-controlled to matrix-controlled. The inhibitory effect of the initial normal stress on shear slipping gradually shifts to a slow enhancement with increasing initial normal stress. Notably, the layered rock samples with high normal stress and JRC exhibit a significant pre-failure phase before shear slipping. The increasing bedding inclination inhibits the development and expansion of cracks along the layers, resulting in the morphology of shear failure surfaces to experience the evolution of “along layers shape – V-shape – arc-shape – linear shape.” As bedding inclination increases from 15° to 75°, the proportion of shear cracks initiating from joint surfaces decreases by 25%, 2%, 0%, and 1%, respectively; however, the proportion of tensile cracks initiating from matrix increases by 23%, 3%, 2%, and 3%. The interfacial transition zone can be observed in the displacement fields of the layered rock samples, and the direction of interfacial transition zone is consistent with the layers and deviates gradually with the increasing bedding inclination. With the increasing bedding inclination and JRC, numerous secondary cracks originate from the matrix, eventually connecting with the joint surfaces. Consequently, numerous discontinuous rock blocks are generated between the upper and lower plates, leading to a significantly increase in the area of the force chain missing zone. Furthermore, the stress-inducing effect of joint surfaces bulges is further enhanced. The findings will contribute to a better understanding of the mechanical responses and failure mechanisms of the rock mass with multiple parallel rough joint surfaces.