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.