Sensitivity Analysis Of Influencing Factors Of Plastic Zone In Surrounding Rock Of Gas Coal Roadway

As the shallow and central coal resources are increasingly exhausted,the mining of coal resources extends to the deep one after another,the mining conditions continue to deteriorate,and the gas pressure keeps increasing.The original gas pressure of some coal seams in mining areas reaches 6～8MPa.The gas pressure weakens the strength of coal body,leading to the acceleration of surrounding rock deformation,instability and failure process.The roadway is excavated before and repaired after repeated repair,which cannot achieve long-term stability and keeps high maintenance cost.Therefore,this paper takes the sensitivity of influencing factors in the plastic zone of surrounding rock of coal roadway with gas pressure as the core research object.Relying on the National Natural Science Foundation of China(51804109),the sensitivity analysis of influencing factors in the plastic zone of surrounding rock of coal roadway with gas pressure is carried out by using the comprehensive research method combining theoretical analysis,numerical simulation and field test.The deformation,failure and instability mechanism of surrounding rock of coal roadway under gas pressure is revealed and verified by engineering test,and the supporting scheme is optimized.Based on the elastoplastic theory and more-Coulomb strength theory,the mechanical model of surrounding rock of circular roadway containing gas pressure was constructed,and the recessive boundary equation of surrounding rock plastic zone was derived considering the influence of gas pressure.The sensitivity of plastic zone to lateral pressure coefficient,cohesion,internal friction Angle,gas pressure,supporting strength and radius of roadway were analyzed by using "absolute grey correlation degree" analysis method.FLAC3 D simulation software was also used to build a numerical model of surrounding rock of coal roadway containing gas,and the variation of plastic zone of surrounding rock was observed by changing the lateral pressure coefficient,cohesion,internal friction Angle,gas pressure,supporting strength and radius of roadway.Finally,taking 130902 return air gas coal roadway of Gada Coal mine as the experimental research object,the failure mechanism of surrounding rock of gas coal roadway is analyzed,and a targeted support scheme is put forward for controlling large deformation of surrounding rock of gas coal roadway.The main research results are as follows:(1)There are three distribution forms of plastic zone in surrounding rock of gas coal roadway: round,oval and butterfly.The distribution form and scope of plastic zone in surrounding rock of gas coal roadway are affected by side pressure coefficient,gas pressure,roadway radius,cohesion of surrounding rock and internal friction Angle.(2)The sensitivity order of influencing factors of plastic zone in surrounding rock of gas coal roadway is as follows: lateral pressure coefficient > internal friction Angle > cohesion >roadway radius > gas pressure > support strength.(3)The original rock stress has the greatest influence on the plastic zone morphology and radius change rate of surrounding rock.When the horizontal stress is equal to the vertical stress,the surrounding rock stability of gas coal roadway is the best,and the plastic zone radius change rate is the lowest.(4)In this paper,a comprehensive support technology scheme of "hollow grouting anchor cable + borehole pressure relief + gas extraction" is put forward,supplemented by "grouting anchor rod + metal mesh + shotcrete",which has achieved good results in engineering practice.