# Numerical Study on the Pressure Relief Characteristics of a Large-Diameter Borehole
###### Abstract  
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 \(L_{\text{h}}<L_{\text{P}}\), there are no pressure relief and energy release effects, which may induce impact, whereas when \(L_{\text{P}}<L_{\text{h}}\)\(\leq 2.5L_{P}\), 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. rock burst; large-diameter borehole; pressure relief characteristics; numerical experiment 2020 July 2020 8 August 20220 8 August  
concentration, energy accumulation and impact risk by studying the reasonable advancing speed [13]. The key to the prevention and control of rock burst is to weaken the high stress and release the elastic energy accumulated in the coal and rock mass. The methods of pressure relief in the roadway include blasting, water injection, slotting, drilling, and so on. Among them, the borehole has the characteristics of minimal engineering quantity, simple and convenient operation, simple construction and little disturbance to the coal and rock mass, and it does not affect normal mining activities; thus, it has strong economic benefits as a measure for preventing rock burst in coal mines [14; 15; 16; 17; 18]. Many scholars have made advances in research on borehole pressure relief. [PERSON] et al. verified the pressure relief effect of nonequal-diameter holes through numerical simulations performed in FLAC3D [19]. [PERSON] et al. carried out a numerical study that indicated that a larger borehole diameter can result in a better stress relief effect [20]. [PERSON] et al. proposed an analytical model for the hard roof over the coal seam that suggests that the increase of the pressure relief distance is a better method than the increase of the pressure relief degree in reducing the abutment stress [21]. [PERSON] et al. suggested an evaluation method using six parameters to evaluate the stress relief effect of large-diameter drilling [22]. [PERSON] et al., based on the theory of elastoplastic mechanics, conducted an analysis of the stress distribution around the borehole and studied the mechanism of pressure relief in segmented enlarged-diameter boreholes [23]. [PERSON] et al. carried out a set of case studies with different borehole layout strategies that resulted in different AE characteristics, as well as strength reduction and rock failure patterns [24]. [PERSON] et al.