Study On Stress Evolution Law And Outburst Prevention Technology In High Stress And Strong Outburst Area Of Pingdingshan No.8 Coal Mine

With the increase of coal mining depth,in-situ stress becomes the main control factor of coal and gas outbursts,and the value and distribution of the stress affect the outburst risk of the coal seam to a large extent.At present,the research on stress distribution mainly focuses on the mining of short distance small pillar or short distance coal seam,while the research on the combined effect of large pillar superimposed coal seam mining is less studied.Under the influence of significant coal pillar stubble pressing and adjacent working face mining,the lower coal stress redistributes and forms the stress concentration area.Therefore,the study of stress evolution and coal characteristics in high stress and strong outburst area helps predict coal seam outburst risk and the formulation of corresponding efficient gas control measures.In this paper,laboratory experiments,numerical simulation,and engineering practice are combined to measure the coal body’s basic characteristics in Ji 15-22080 working face of Pingdingshan No.8 coal mine.This paper studies the stress evolution law of working face under the influence of Ding group coal pillar stubble pressing and Wu group coal seam mining.This paper analyzes the difference between coal permeability and outburst risk in different stress areas,and finally puts forward partition and classification treatment measures for different risk areas,and carries out an effective test.The main conclusions are as follows.1)The geological structure of the Pingdingshan No.8 coal mine is complex,and the mine’s coal body is seriously damaged under the action of tectonic movement.Through the low-temperature N₂and CO₂adsorption experiments,it is found that the pore fissure structure of the coal body is significantly developed,which has obvious structural coal characteristics,the internal pore connectivity of the coal body is good,and the micropore structure accounts for the largest proportion of the total pores.The measured gas content is 9.91m³/t,which indicates that the existence of a large number of micropores provides a place for gas adsorption,making the coal seam gas content higher.The initial velocity of gas emission is 19mm Hg,and the firmness coefficient is0.252,which indicates that the coal sample belongs to soft and easily broken outburst coal.The gas pressure of the working face is relatively high,reaching 1.4MPa.During the drilling of the low drainage roadway in the machine roadway,a serious spray hole occurred.The amount of coal ejected from a single hole is 6.0t,and the amount of gas ejected is 650m³.Comprehensive data show that Ji 15-22080 working face has the risk of coal and gas outburst.2)According to the spatial position relationship of Ji 15-22080 working face,Wu coal seam working face,and Ding group protective coal pillar,the corresponding model is established by FLAC^3Dsoftware to simulate the stress evolution law of working face,and the stress distribution state of working face is analyzed.The simulation results show that:under the influence of Ding group coal pillar stubble pressing and Wu group coal seam mining,there is a significant gap in the stress distribution of the working face,and the stress concentration phenomenon is distributed in the whole machine roadway,especially in the range of 400m from the outside of the machine roadway,in which the maximum horizontal stress is 37.7MPa,and the maximum vertical stress is 27.5MPa,which increases by 4.7MPa and 7MPa respectively compared with the initial stress;Besides,there is an original stress area between the stress concentration area and the pressure relief area.From the simulation results,it can be seen that the stress distribution state of the working face is complex,so there will be some differences in the occurrence state of coal seam gas.3)According to the simulated stress distribution of the working face,the permeability evolution model is selected to calculate coal’s permeability in different stress areas.The results show that the fracture rate of coal in the high-stress area is about 47%lower than that in the original stress area,and the permeability is about79%.The decrease of fracture rate leads to the increase of gas pressure gradient,and the coal seam is more prone to blowout and outburst when disturbed by drilling,so the outburst risk of the high-stress area is greater than that of the normal area;on the contrary,the permeability of coal seam in pressure relief area increases,the difficulty of gas drainage and control is lower,and the outburst risk is more negligible.4)According to the different outburst risks in different working faces,the working face is divided into general outburst risk area,medium outburst risk area,severe outburst risk area,and corresponding control measures are formulated for different risk areas.For the high-stress area,the treatment idea of unloading gas energy first and then stress-energy is put forward,which is mainly carried out by pre drainage of the common through layer drilling,and then unloading and strengthening drainage by hydraulic punching technology.5)Advanced high-pressure hydraulic punching integrated equipment was used to carry out field tests in the working face,and the gas control effect of machine roadway in high stress and severe outburst danger area was investigated.The results show that:the total coal production is 1543t,the powder discharge rate is 1.89%,and the gas drainage rate is 40.6%.The measured residual gas content and maximum pressure are 5.37m³/t and 0.48MPa,respectively;up to 380m of machine roadway,the maximum initial gas emission velocity q is 2.68L/min,the maximum drilling cuttings quantity index S is 4.6kg/m,the gas emission of working face is always less than3m³/min during driving.All the gas emission indexes meet the control requirements.It shows that the zoning and classification control measures are effective,and the pre drainage of coal seam gas by hydraulic punching technology obviously reduces the outburst risk of coal in a high-stress area.There are 63 figures,32 tables and 84 references in this paper.