Anchorage weakening effect of coal roadway sidewall with different destressing borehole diameters

Abstract The pressure relief with large‐diameter boreholes is one of the effective methods to prevent coal bumps in deep coal roadway. An unreasonable pressure relief design can cause the rockbolt support failure and aggravate the deformation of the surrounding rocks. In this paper, a coupling model of roadway sidewall considering borehole pressure relief and rockbolt support was established. The influence of the destressing borehole diameter on the rockbolt located in the plastic zone and the roadway deformation was studied by theoretical calculation and numerical simulation. The results show that there is a critical zone of the borehole diameter for the influence on the rockbolt normal stress and roadway convergence. When the destressing borehole diameter exceeds the critical zone, the rockbolt normal stress decreases sharply. Considering the existence of the broken zone in the surrounding rock, the bolehole diameters in the critical zone increase with the increase of the distance between the borehole and the rockbolt, the residual strength, and decrease with the increase of initial stress. In the engineering analysis, with the increase of the destressing borehole diameter, the ultimate pullout force of rockbolt decrease, and the plastic zone of surrounding rock, the roadway deformation, the maximum axial force, and slippage of the rockbolt all increase. Therefore, to better keep the stability of the surrounding rock in coal roadway, the borehole pressure relief needs to be coordinated with the rockbolt support. The destressing borehole diameter in the pressure relief design should not be greater than the critical zone.