卸压钻孔应力场分区及长度优化设计

利用极坐标和直角坐标系建立卸压钻孔力学模型，分析了巷道侧向支承压力与卸压钻孔周围煤体应力之间的联系，得到巷帮煤体的卸载应力及卸压系数；根据卸压前后巷帮煤体的应力状态，将卸压钻孔应力场划分为4个应力区，分别为塑—塑性区、弹—塑性区、塑—弹性区和弹—弹性区，卸压作用主要在塑—弹性区和弹—弹性区；结合卸压前巷帮煤体的应力场分区，分析了卸压钻孔的最优长度，指出钻孔长度应根据卸压前巷道侧向支承压力分布进行设计；施工卸压钻孔后，卸载应力呈中间高两边低的规律，而在未施工钻孔的区域，煤体应力保持不变。采用数值模拟的方法，对比研究了薛湖煤矿不同长度钻孔的卸压效果，得到最优钻孔长度为20 m左右。

Stress Field Zoning and Length Optimization Design of Pressure Relief Borehole

The pressure relief drilling mechanics model established by polar and rectangular coordinate system was used to analyze the relationship between the lateral abutment pressure of roadway and the stress distribution of coal body around pressure relief borehole,the unloading stress and the pressure relief coefficient of coal body were obtained.According to the stress state of the coal body before and after pressure relief,the stress field of pressure relief borehole was divided into four stress zones.They were plastic - elastic zone,elastic - plastic zone,plastic - elastic zone and elastic - elastic zone.The pressure relief was mainly in plastic - elastic zone and elastic - elastic zone.The optimal length of pressure relief borehole was analyzed combined with the stress field zoning of coal body before pressure relief.The results showed that borehole length should be designed according to the lateral abutment pressure distribution of roadway before pressure relief.The unloading stress was middle high and both sides low after pressure relief borehole,while the coal body stress remained unchanged in the area without pressure relief borehole.The numerical simulation method was used to study the pressure relief effect of different borehole length in Xuehu coal mine,then came to the conclusion that the optimal borehole length was about 20 m.