Effect of pretension on the mechanical behaviour of bolted rock

ABSTRACT: A stepwise pull-and-shear test (SPST) scheme that numerically analyses the mechanical behaviour of bolted rock joints subjected to simultaneous pull-shear loading. The SPST scheme allows us to identify the optimum pretension stress magnitude at which the bolting system exhibits its ultimate shear capacity. The micro-mechanical properties of grout and bolt-grout interface were calibrated against the laboratory data. The micro-mechanical parameters of rock were calibrated against the laboratory data of coal and shale, and the micro-mechanical properties of rock joint interface were identified by reproducing the laboratory behaviour of coal-shale interface under the direct shear test. Then, the SPST scheme was employed to study the effect of pretension stress magnitude on the macroscopic behaviour of bolted coal. The numerical results revealed that at yield pretension stress magnitude (pull-out test) the rock bolting system could exhibit its ultimate shear performance.