Shear behaviors of rock masses containing nonpersistent joints affected by normal stress rebound under excavations and river incisions

摘要

The catastrophic mechanism of rock masses with discontinuities under excavations and river incisions is very complex. Basedon this engineering background, a standard direct shear test under unloading normal stress is performed on sandstone specimenscontaining nonpersistent joints to investigate their shear behaviors. The results obtained are compared and discussedwith those of conventional direct shear tests. An overall instantaneous coalescence under unloading conditions is presentedon the rock bridge without a precursor, while the failure under loading conditions is a segmented progressive coalescence.This overall cracking behavior, driven by tensile damage, triggers a constant dilation rate. The cohesion is smaller and theinternal friction angle is larger at a larger continuity factor under unloading conditions, while the relationship under loadingconditions is the opposite. The evolution mechanism of the shear strength parameter affected by the continuity factor isrevealed by analyzing the damage degree of the rock bridge per unit length. Interestingly, there is a polished and scratchedarea on the failure plane under unloading conditions, while the failure plane is smooth with some polishing without striatedscratches under loading conditions. These failure plane characteristics reflect the basement sliding behavior of a rockslide.The striated scratch-like gullies are caused by tensile damage from the analysis of the microscopic three-dimensional topography.This investigation reveals the failure mechanism of rock masses under tensile-shear stress conditions.