突出煤层钻进过程中的喷孔瓦斯超限是威胁矿井高效生产的安全隐患，分层切削钻进方法有助于在孔内削弱喷孔瓦斯压力，但分层切削形成的梯形钻孔周围瓦斯释放特征不明，限制了分层切削钻具结构设计和应用效果。

以不同层间距、层厚差的分层切削钻孔为研究对象，建立数学模型分析钻孔周围瓦斯流动规律，并定量描述了分层切削钻孔瓦斯流量与层间距、层厚差之间的关系，在此基础上，通过数值模拟分析了分层切削钻具瓦斯释放调控机制，优化了分层切削钻具结构，并开展了现场钻进工业性试验。

结果表明：(1)多次切削成孔方式使钻孔的揭露面积逐渐增大，有效控制了瓦斯释放面积，进而调控了瓦斯释放流量，通过合理设计钻孔层厚差H_j与层间距L_i，能够将瓦斯释放流量降低18.3%以上。(2)在一定层间距范围内，双层切削钻具调控效果将优于三层切削钻具，直径为63.5 mm刻槽阻尼钻杆在推力140 kN和扭矩4 600 N·m作用下，最小安全系数为3.009，满足强度设计要求。(3)优选双层切削钻具，其揭露直径73 mm，终孔直径113 mm，层间距0.8 m，通过工业性试验，钻遇高压瓦斯富集区时，孔口瓦斯体积分数降低了37.7%，孔口瓦斯体积分数均未超过0.5%。表明分层切削钻具调控钻孔周围煤体瓦斯释放量、削弱瓦斯释放强度的作用显著，为预防钻孔喷孔瓦斯超限问题提供了新的解决思路。

The overlimit gas bursting in the drilling process of outburst coal seam is a safety hazard that threatens the efficient production of the mine. The layered cutting drilling method helps to weaken the burst gas pressure in the borehole, but the characteristics of gas release around the trapezoidal borehole formed by layered cutting are unknown, which limits the structural design and application effect of the layered cutting drilling tool.

Herein, study was conducted based on the layered cutting boreholes with different layer spacing and layer thickness difference. Specifically, a mathematical model was established to analyze the gas flow law around the borehole, and the relationship between the gas flow rate of the layered cutting borehole and the layer spacing and the layer thickness difference was quantitatively described. On this basis, the gas release control mechanism of the layered cutting drilling tool was analyzed by numerical simulation, the structure of the layered cutting drilling tool was optimized, and the industrial test of field drilling was carried out.

The results show that: (1) Using the multi-cutting hole-forming method, the exposed area of the borehole gradually increases, which effectively controls the gas release area, and then regulates the gas release flow. By reasonably designing the layer thickness difference H_j and the layer spacing L_i of the borehole, the gas release flow could be reduced by more than 18.3%. (2) In a certain range of layer spacing, the control effect of the double-layer cutting drilling tool will be better than that of the three-layer cutting drilling tool. Under the condition with the thrust of 140 kN and the torque of 4 600 N·m, the grooved damping drill pipe with diameter of 63.5 mm has the minimum safety factor of 3.009, which meets the strength design requirements. (3) The optimized double-layer cutting drilling tool has an exposing diameter of 73 mm, a final hole diameter of 113 mm, and a layer spacing of 0.8 m. As shown in the industrial tests, the gas volume fraction in the borehole is reduced by 37.7% during the drilling into high-pressure gas-rich areas, and the gas volume fraction in the borehole does not exceed 0.5%. This indicates that the layered cutting drilling tool has a significant effect on regulating the gas release amount of the coal body around the borehole and weakening the gas release intensity, which provides a new solution for preventing the overlimit gas bursting in the borehole.