Laboratory and numerical experiments on pressure relief mechanism of large-diameter boreholes

The technology of borehole pressure relief is an effective way to reduce the elastic energy accumulation in the surrounding rock of roadways, which can reduce the risk of regional rock bursts. Therefore, the studies on the pressure relief mechanism of large-diameter boreholes and the corresponding reasonable parameters are of high engineering application value. A series of laboratory experiments are conducted to analyze the effects of different parameters such as borehole radius, spacing and depth on the uni-axial compression strength (UCS) and failure patterns of samples. The particle flow code (PFC) is used to quantify the micro-cracks and simulate their corresponding propagation process. The laboratory and numerical results show that the stress release resulting from propagation and coalescence of micro-cracks is the basic reason for the pressure relief around the surrounding rock of boreholes. The micro-cracks around the surrounding rock increase with the increase of radius and depth of boreholes, and the main crack becomes much more serious, resulting in larger pressure relief. In addition, as the borehole spacing decreases, UCS of samples decreases and the corresponding failure pattern changes from independent one to transfixing one, leading to a much more obvious pressure relief effect.