真三轴应力条件下钻孔围岩塑性区及增透半径研究

深部岩体处于三维应力场中受开挖扰动影响钻孔、巷道围岩处于明显的真三轴应力状态。钻孔抽采技术是煤矿广泛用于瓦斯治理的重要措施，钻孔周围塑性区是瓦斯流动的优质通道，研究钻孔围岩塑性区特性对于抽采钻孔的优化布置至关重要。为研究钻孔围岩的塑性区特性，基于广义平面应变理论分析围岩应力分布，比较几种常用强度准则（MC、Mises、D-P、MLC、SMP）的适用性和精确性，对比试验结果表明，MLC准则能较好地表征岩石的真三轴强度特性。基于MLC准则推导了围岩塑性区半径公式，分析偏应力、中间主应力、岩石内摩擦角、岩石黏聚力和钻孔半径对增透半径的影响，结果表明，增透半径随着偏应力的增大而增大，随中间主应力的增加先减小后增大，随岩石内摩擦角、岩石黏聚力的增加而逐渐减小，随钻孔半径的增加而线性增大。研究结果可为实际工程中巷道支护、煤层瓦斯抽采等技术的参数设计等提供重要参考。

Study on plastic zone and permeability-increasing radius of borehole surrounding rock under true triaxial stress conditions

The deep rock mass is in a three-dimensional stress field, and the surrounding rock of the borehole or roadway is in an obvious true triaxial stress state due to the excavation-induced disturbance. Extraction technology is widely used as an important measure for gas control in coal mines. The plastic zone around a borehole is a good channel for gas flow. Therefore, it is important to study the characteristics of the plastic zone of the surrounding rock for the optimal layout of the extraction borehole. To study the plastic zone characteristics of drilling borehole surrounding rock, we analyze the stress distribution of surrounding rock based on the generalized plane strain theory, and compare the applicability and accuracy of several commonly used strength criteria (e.g. MC, Mises, DP, MLC, SMP). The results show that the MLC criterion can better characterize the true triaxial strength of rocks. Based on the MLC criterion, we derive a formula for the radius of the surrounding rock plastic zone, and analyze the effects of deviatoric stress, intermediate principal stress, internal friction angle, cohesion and radius of drilling hole on the permeability-increasing circular area. It is found that the permeability-increasing radius increases with the increase of deviatoric stress, decreases first and then increases with the increase of the intermediate principal stress, decreases with the increase of the internal friction angle or the cohesion of rock, and increases linearly as the radius of drilling hole increases. This research results can provide an important reference for the parameter design of engineering technology such as roadway support and coal seam gas drainage in practical projects.