Study On Overburden Failure Law And The Characteristics Of Strata Behavior In Downhill Mining Of Close Distance Coal Seams

The downlink mining of the close distance coal seams is different from the single coal seam mining,and the mining of the lower coal seam in the goaf area causes secondary disturbances to the overburden,resulting in a large display of mineral pressure.The middle group coal（7₂ coal and 8₂ coal）in the Huaibei mining area belongs to the close-range coalbed group,and the coal re-mining in the middle group of the 83 lower mining area of Xutuan Coal Mine belongs to the downlink mining of the close-range coal seam.The working surface of 8₂312 is the first mining working surface of the close coal seam goaf in the 83 lower mining area,and the relevant experience of the non-overlying rock transportation and breaking law in the mining area can be used as a reference,and the research on the occurrence law of ore pressure is in the exploratory stage.In this paper,taking the 8₂312 comprehensive mining working surface of Xutuan Coal Mine as the engineering background,this paper uses theoretical analysis,physical similarity simulation,numerical simulation,on-site measurement and other methods to study the damage characteristics of the rock formation between the 7₂ and 8₂ coal seams and the stability characteristics of the rock formation between the 7₂ and 8₂ coal seams,analyzes the law of the return mining pressure of the first mining working surface under the goaf area,and reveals the movement and failure characteristics of the overburden and the deformation of the surrounding rock.The main research results are as follows:（1）Based on elastoplastic theory,the bottom plate failure depth of 7₂ coal seam is analyzed,and the bottom plate failure depth of 7₂coal seam is h_max=12.12m;The height development range of the 7₂ coal working surface after re-mining is16.81-26.23m,the development range of the water-conduction fracture zone is53.84-74.68,the height development range of the 8₂ coal working surface after re-mining is 23.07-32.49m,and the development range of the water-conduction fissure zone is 71.42-92.26m;（2）The average compressive step distance of 7₂ coal working surface after recovery is 19.3m,the development height of the water conduction fracture zone is62.5m,the average compressive step distance of the 8₂ coal working surface after the recovery process is 16.7m,and the development height of the water conduction fracture zone is 86m,which is consistent with the theoretical calculation results;（3）After the recovery of the working face of 7₂ coal in the close coal seam group through numerical simulation analysis,the subsidence and disturbance degree of overburden in the middle of the goaf are the most obvious,the supporting effect of the coal pillars on both sides is the strongest,and the stress concentration phenomenon is the most obvious,and the type of interlayer structure between 7₂ coal and 8₂ coal is the basic top of the interlayer partial damage,which is consistent with the theoretical calculation results;（4）The core taking and drilling peep methods were used at the site,and the analysis and judgment of the entire borehole was within the damage range of the 7₂312working surface base,the surrounding rock integrity was poor,and the fracture development was consistent,which was consistent with the theoretical calculation;The law of overburden rock migration during the 8₂312 working surface remining period was studied,and the average compressive step distance of the 8₂312 working surface was 15.81m,and the on-site cycle compressive step distance was basically consistent with the similar simulation test results（cycle compressive step distance 16.7m）,and when it entered the influence range of the advanced support pressure,the more obvious ore pressure display characteristics of the two lanes were generally manifested as broken anchors,steel belt tearing,and gang drum gang（mainly occurring in the coal seam part of the alley）.Figure 51 Table 7 References 84...