Laboratory study of the effects of grouted rebar bolts on shear failure of structural planes in deep hard rocks

Abstract

Rock hazards induced by shear slip along discontinuities are often encountered in deep hard rock excavations. At present, grouted rebar bolts are still the most widely used supporting tools in underground engineering. However, as the in-situ stress increases, the anchoring effect of bolts on rock discontinuities change significantly compared with that in a shallow environment. It is of great significance to study the influence of rebar bolts on the shear failure characteristics of structural planes under high stress to ensure the safety of engineering construction at deeper depths. In this study, shear tests were conducted on split granite structural planes secured with bolts under various normal stresses to investigate the supporting effect of the rebar bolts on the hard rock structural planes under high stress. The stress, deformation, acoustic emission, and rock failure characteristics in the tests were fully investigated and analyzed, and the effects of the rebar bolts on the dynamic failure of the hard rock structural plane and a simplified model were investigated through comparison with the shear failure characteristics of unreinforced granite joints. The experimental results show that when a bolt is inserted through a highly stressed granite structural plane, before the bolt fractures, it can change the slip mode of the structural plane from stick-slip to stable-slip, which effectively delays the occurrence of shear-induced dynamic failure. After the bolt fractures, the interaction between the bolt and structural plane causes the stress drop events to increase, but it greatly weakens the energy emitted by a single shear stress drop, thus effectively reducing the intensity and destructiveness of the dynamic failure during shearing. The findings of this study have significant implications for the management and control of structural-slip rock hazards in deep rock tunnels.