Destruction Mechanism And Control Method Of Mining Roadway In Lower Layer In Close-Range Residual Coal Pillar Area

In the process of close coal seam mining,the control of surrounding rock in the lower layer of the mining roadway in the residual coal pillar area has always been a difficult problem in the field of roadway support.Accidents such as roof fall and broken bolts（cables）have seriously affected the safe and efficient production of coal mines.In recent years,short-distance coal seam mining has gradually become normalized in the mining process of coal mines in my country.Due to the influence of the spatial structure of coal seams and the law of force transfer,the interaction and manifestation of mining pressure between excavation roadways and working faces between adjacent coal seams is more obvious.When the short-distance coal seam group is mined in a downward manner,the stress state of the roof surrounding rock of the lower coal seam changes due to the coal pillars and goafs formed and left over in the upper coal seam,which affects the tunneling and support of the lower coal seam and the mining of the working face has a great influence,and the surrounding rock of this kind of roadway is very prone to serious deformation and damage.China Coal Group Tashan Coal Mine 30503 ventilation roadway is located on the west side of30501 work face,the 2#coal pillar is located above it at a vertical distance of 18m and a horizontal distance of 15m.The width of the coal pillar is 20m.The 30503ventilation roadway has a large deformation and closure phenomenon,and the roadway is very seriously damaged.The 30503 return air roadway was renovated.During the process of 860m,the roof and floor of the roadway and the displacement of the two sides of the roadway continued to increase.The damage mechanism and control of the mining roadway became a difficult problem.Therefore,a detailed analysis and research is needed to address this issue.The plastic failure of the surrounding rock of the roadway leads to the deformation and failure of the surrounding rock of the roadway,and the size,shape and distribution of the plastic zone determine the damage characteristics and distribution range of the surrounding rock.The failure mechanism of the surrounding rock needs to analyze the formation and development law of the surrounding rock plastic zone of the roadway.Based on the background of the lower mining roadway in the residual coal pillar area in the short-distance coal seam mining process of China Coal Group’s Tashan Coal Mine,this thesis uses theoretical analysis,field testing,numerical simulation and other comprehensive engineering research methods to study the formation and development of the surrounding rock plastic zone in the roadway.,analyzed the deformation and failure characteristics of the surrounding rock of the roadway and the temporal and spatial evolution of the mining stress.Based on the butterfly plastic zone theory,the butterfly deformation and failure mechanism of the lower mining roadway in the short-distance residual coal pillar area was deduced,and the short-distance residual coal pillar area was proposed.The selection method of the reasonable position of the lower mining roadway,the support technology of the lower mining roadway in the short-distance residual coal pillar area is studied,and the following main conclusions and innovative achievements are obtained:（1）The deformation and failure characteristics of the China Coal Tashan Coal Mine’s 30503 ventilation roadway were detected in detail by three methods:surface displacement,deep base point displacement,and roof drilling peep,the damage law of the surrounding rock of the lower mining roadway in the residual coal pillar area in the process of short-distance coal seam mining was obtained.Affected by the residual coal pillars in the upper coal seam,the roof of the roadway has experienced different degrees of roof fall and roof subsidence,and with the passage of time,the displacement of the roadway roof and the two sides has an increasing trend.The displacement range of the roof is 1-35mm,and the displacement range of the two gangs is 0-66mm.There is a large deformation and closing phenomenon,and there is no sign of stopping.The main displacement range and maximum displacement at 868m in the repaired section is 22mm,the excavation section still has a tendency to continue to separate from the bed,and the roof shows asymmetrical subsidence.From the perspective of the overall displacement,the displacement of the roof gradually increases with the advancement of the roadway head,and the delamination of the roof decreases after the roadway is supported,but there is still a certain displacement.The damage to the roof near the coal pillar is more serious,and the damage range of the roof at the center of the roadway is larger.After the roof is peeped,and there are interlayer areas in the coal seam,most damage occurs.According to the results of roof drilling at different distances in the axial direction of the roadway,it is concluded that the roof damage mainly occurs in the range of 0～1m,2m～4m,6.5m～8m.Affected by the remaining coal pillars in the upper coal seam and the near mining of the coal seam,the deformation and failure form of the surrounding rock show an"asymmetric"deformation distribution.The subsidence of the roof is larger than that of the two sides,and the subsidence of the symmetrical position of the roof is obviously different,showing a butterfly-shaped failure trend.（2）Taking the 30503 working face ventilation roadway of China Coal Group Tashan Coal Mine as the engineering background,the maximum and minimum principal stresses of the residual coal pillar were obtained through FLAC^3D numerical simulation study.The ratio is 1.49～5.49,and the angle between the maximum principal stress and the Z axis is deflected from 61°to 4.5°and then to 83.9°.The principal stress characteristics,principal stress ratio and the angle between the maximum principal stress and the Z axis of the three survey lines under the residual coal pillar are obtained.The maximum principal stress values on the top,midline,and bottom measuring lines at the left edge of the working face are:19.93MPa,19.43MPa,and20.39MPa,respectively.The maximum principal stress peaks are 1.42,1.38,and 1.45times the original rock stress,respectively.The minimum principal stress on the roadway range is:4.21MPa～4.59MPa,5.13MPa～5.74MPa,3.2MPa～3.88MPa.The angles between the maximum principal stress and the Z-axis of the top,midline and bottom lines were changed from 88°to 1.44°,from 83.4°to 0.16°,and from 78°to1.02°,respectively.The maximum principal stress ratios were 5,3.71,and 5.83,respectively.On the side view of the roadway,the maximum principal stress ranges from 9.11MPa to 24MPa,and the minimum principal stress ranges from 2.27MPa to19.12MPa.The angle between the maximum principal stress and the Z axis gradually increases from 21.8°to 67.89°.°decreased to 43.78°,then increased to 70.81°and finally turned to 21.02°,and the principal stress ratio ranged from 1.4 to 5.09.（3）Taking the 30503 working face ventilation roadway of China Coal Group Tashan Coal Mine as the engineering background,The stress distribution around the circular roadway in the non-uniform stress field under the deflection of the principal stress direction is analyzed by FLAC^3D numerical simulation.When the bidirectional stress ratio is large,the plastic zone of the surrounding rock of the roadway presents a butterfly shape.The mechanical mechanism of butterfly failure of circular roadway in non-uniform stress field under deflection of principal stress direction is obtained.The damage of the surrounding rock of the roadway is the result of the combined effect of the strength of the surrounding rock and the regional stress.The influence of the internal causes of the surrounding rock（Internal friction force,internal friction angle）,the stress field in the region where it is located（Principal stress ratio,principal stress magnitude and principal stress direction）,and the combination of different layered lithologies on the failure of the surrounding rock of the roadway are studied in detail,and the failure law of the surrounding rock of the roadway under the corresponding influencing factors is obtained.The failure characteristics of the remaining coal pillars in the upper layer of the short-distance coal seam and the deformation and failure characteristics of the roadway after the mining of the coal seam working face in the lower layer are analyzed.The relationship between the deformation and failure of surrounding rock in the mining roadway is explored,and the non-uniform butterfly failure mechanism of the roadway is obtained.（4）Taking the 30503 working face ventilation roadway of China Coal Group Tashan Coal Mine as the engineering background,Through the FLAC^3D numerical simulation study,it is concluded that in the tunnel excavation stage,from the perspective of the upper and lower layers,the plastic zone range along the bottom of the tunnel is smaller than that along the top and the bottom coal,the roadway deformation law is not obvious.From the perspective of the horizontal horizon,the smaller the coal pillar,the smaller the plastic zone of the surrounding rock of the roadway,and the smaller the roadway deformation,that is,the roadway should be arranged along the bottom,and the smaller the coal pillar size,the more stable the roadway.（5）Taking the 30503 working face ventilation roadway of China Coal Group Tashan Coal Mine as the engineering background,through theoretical analysis and FLAC^3D numerical simulation,a small coal pillar roadway flexible support technology based on the distribution of the butterfly-shaped plastic zone of the surrounding rock is proposed,that is to use flexible supporting materials with large elongation instead of conventional bolt cables to control the rock formation with large damage depth in the plastic zone of the roof.Give full play to the deformation ability of flexible materials,do not break and fail in the process of surrounding rock deformation,improve the stability of the rock formation with plastic damage to the roof,and prevent roof collapse accidents.The surrounding rock control technology provides a good reference value for the same type of roadway.