Effective evaluation of pressure relief drilling for reducing rock bursts and its application in underground coal mines

Rock bursts are an extreme behaviour in coal mine strata that can cause fatalities and severe economic losses. Pressure relief drilling is a widely used method in coal mines to release high stress concentrations and effectively reduce the rock mass volumetric elastic potential energy; thus, this method can effectively reduce the occurrence of rock bursts in underground coal mines. Based on actual geologic conditions in the area of a rock burst that occurred in the Yangcheng Mine, a series of experimental studies on mechanical properties are conducted using gypsum-type coal-like materials with different numbers and configurations of pressure relief boreholes. The change in parameters, such as the strength and energy dissipation index of bored coal-like materials under a uniaxial compression, is studied, and the fracture propagation characteristics in the rock surrounding the boreholes in the experiments are analysed. FRACOD, which is a numerical code that predicts the explicit fracturing process in rocks using fracture mechanical principles, is then used to simulate the laboratory tests, and the numerical results are compared with the experimental results. The code is also used to study the relief effect of three boreholes with different geometrical configurations; thus, local fracture initiation and propagation around the boreholes are investigated. Combined with the characteristics of the stress change in the rock surrounding the boreholes, the optimal configurations of the pressure relief boreholes for the Yangcheng coal mine are determined. The results have shown that the larger the drilling density is, the more the rock fracture development around the boreholes, the greater the energy release and, hence, the more effective the relief effect. Finally, this study presents a new methodology for choosing the optimal layout parameters for pressure relief drilling, which could aid future research in related fields.