Numerical Study on the Pressure Relief Characteristics of a Large-Diameter Borehole

Large-diameter drilling is an effective method for preventing rock burst disasters in coal mines. In this paper, the roadway stability of the W1123 fully mechanized caving work face of the Kuangou coal mine, located in northwest China, is investigated. A set of numerical modelling techniques were carried out to study the characteristics of stress, displacement, strain energy and the plastic zone of the roadway side rock with different parameters, including the large-diameter drilling hole diameter, depth and spacing. The results showed that: (1) after drilling, the peak values of the stress and strain energy are reduced and transferred to a deeper location, and the control effect presents a positive correlation with the diameter of the drilling hole; (2) when L-h < L-P, there are no pressure relief and energy release effects, which may induce impact, whereas when L-P < L-h <= 2.5L(P), with the increase of the hole depth, the effects of pressure relief and energy release are enhanced, and further extension is not conducive to the long-term stability of the roadway; and (3) when the hole spacing decreases, the plastic zone and the broken zone between the holes are gradually penetrated, and the stress pattern transforms from a double peak to a saddle shape and then to single peak. Reducing the hole diameter reduces the efficiency of the plastic zone, failure zone and the stress form transformation between the boreholes, and weakens the pressure relief effect. Therefore, the main factor affecting the pressure relief effect is the hole diameter, and the secondary factor is the hole spacing. The engineering practice employed here showcases how a larger-diameter hole is an effective way of enhancing the effect of pressure relief and controlling the occurrence of rock burst. These research results are of great significance for guiding engineering practice.