| Coal is an industrial food,it is also the driving force of economic development.How to ensure the safety and efficient production of mines is a problem that can not be ignored.In recent years,with the advancement of mining technology and equipments,especially the use of fully mechanized mining and high efficient mining technologies such as top coal caving and large height mining,coal mining strength increases,the occurrence of relatively good conditions of coal resources are nearing completion.In order to improve the coal production and increase the service life of the mines,for the mining of more difficult coal seam groups,especially the close distance coal seams are gaining more and more attention by the mining industry.The space distance between 9~# and 10~# coal seam in Shangyu Quan colliery is 3m~20m,the average is 8.0m,it belongs to close distance coal seams,because of the close distance,the influence between them is large.Mining of 9~# coal seam has finished,the changeable structure of roof rock layers and mining technology factors will directly influence the strata behaviors of 10~# coal seam mining.This paper focuses on the first I031001 mining face in south area of coal field,there exists a left forward coal pillar on the position of 82#~94# hydraulic support which has a 20 m width in 9~# coal seam,it will influence the whole process of mining,combine theoretical analysis,numerical simulation and field measurement methods to research the stress distribution under the coal pillar,the rock burst factors during roof pressurization and develop measures of preventing and eliminating the rock burst and the mining roadways layout and support of under coal seam mining face below the coal pillar.The main conclusions are:(1)Because of the close space between 9~# and 10~# coal seam,the changeable structure of roof rock layers after mining 9~# coal seam will influence the strata behaviors of 10~# coal seam.According to mechanics criterion which determines the stability of interlayer roof the same as safety mining thickness for closer distance coal seams,in the condition of sandstone roof: under the goaf of 9~# coal seam,without considering the premise of hydraulic support,the safety thickness is not less than 3.24 m,on the opposite,it can decrease to 2.59m;under the coal pillar of 9~# coal seam,without considering the premise of hydraulic support,the safety thickness is not less than 40.9m,on the opposite,it can decrease to 40.7m.Thus,under the goaf of 9~# coal seam,it can guarantee the safety mining of 10~# coal seam without taking special measures,under the coal pillar,because the space is less than the minimum safe thickness,it must take some special measures to guarantee the safety.(2)The range plastic area of left coal pillar of 9~# coal seam is 4m by calculating based on SMP principle,the stress distribution on the top of pillar is saddle shape,there is an elastic core in the middle of pillar and it's a stability coal pillar which can satisfy the strength requirements to protect the roadway.In the horizontal direction of floor rock below the pillar,the stress is bigger when it is closer to the peak of supporting pressure in the same depth,on the opposite,it's smaller;in the vertical direction,the stress decreases when it is further to the pillar.Within the range of 26 m from the bottom of the numerical model,the stress under the coal pillar exceeds the stress of the original rock,the range under the influence of concentrated stress is far more than the 8m layer spacing,so the mining of 10~# coal seam is seriously influenced by the coal pillar.(3)Treat the interlayer roof between 9~# and 10~# coal seam as fixed beam and cantilever beam,to predict the first weighting distance and periodical weighting distance of I031001 mining face by calculating,the theoretical prediction of first weighting distance is about 28 m and the periodical weighting distance is about 12 m.By analysis,the factors of rock burst in I031001 mining face are strain energy caused by the changable structure during the roof movement and concentration stress of forward coal pillar.According to numerical simulation results,in the process of mining,the range of supporting pressure under the influence of coal pillar is more than the influence under the goaf,the value of supporting pressure increases.By defining a variable ze in the software to represent the strain energy,during the mining process,especially in the time of roof pressurization,the strain energy of mining area under the coal pillar is larger,it's about 3×104J/m3.Because of the large accumulated strain energy of mining area under the coal pillar,it's easy to cause the rock burst and needs to develop measures of preventing and eliminating the rock burst.(4)The mining roadways of 10~# coal seam are suitable for adopting sparklet-inboard-type,the stagger distance can not be less than 8m.The roadways layout of I031001 had been set,the positions are suitable,the surrounding rock is stability and it's easy for the roadway maintenances.By adopting the ultrasonic method in the field,the average distance of the loosening circle of the mining roadway is 1.34 m.Based on the suspension theory to design the mining roadway support parameters,length of roof bolt can not be less than 1.65 m,length of anchor cable can not be less than 7.7m,length of roadway wall bolt can not be less than 1.4m.In the process of production,length of roof bolt is 1.8m,length of anchor cable is 8.0m,length of roadway wall bolt is 1.6m.The selection of mining roadway supporting parameters and layout position are in line with the technical requirements,supporting strength is sufficient,the roadway surrounding rock is stability and can meet the requirements of safe maintenance for the roadway.This paper systematically studied the stress distribution,rock burst,roadway layout and support under the influence of forward coal pillar in the mining face,which can provide reference for the production of other similar conditions in the future. |
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