Shear contraction mechanism and mechanical behavior of shear-induced rock bridge fractures under constant normal stiffness conditions

Shear-induced rock bridge fractures greatly threaten the stability of rock slopes and deep rock masses, owing to their connection with pre-existing discontinuities. In this research, direct shear tests on sandstone rock bridges were performed under constant normal stiffness (CNS) conditions. The effects of rock bridge length, initial normal stress and normal stiffness on the shear behavior of rock bridges were carefully investigated, encompassing both the pre-failure (cracking phase) and post-failure (sliding phase) stages. Test results revealed that these three factors variably impact the shear strength, dilation characteristics, failure pattern and acoustic emission response of the rock bridges. In particular, normal stiffness was found to greatly affect the post-peak slip behavior. It was observed that shear-induced rock bridge fractures exhibit distinctive shear contraction characteristics, which contrast with tension-induced splitting fractures that are typically marked by shear dilation. The shear contraction mechanism of rock bridge fractures was elucidated using a conceptual cracking model, termed the TST model. This research contributes fresh insights to the comprehension of dynamic slip hazards prompted by the rupture of rock bridges in deep rock engineering.