Study On The Movement Of Surrounding Rocks In Shallow Buried Close Distance Thick Coal Seams During Repeated Mining

Papers in god close in bulianta coal mine east mining area coal seam group mining as the main research object,the theoretical analysis, computer numerical simulation, indoor stereoscopic 3 d methods of similar material model test, t overburden structure of migration characteristics, fracture distribution along with the change of forward distance, repeating mining stope stress distribution and evolution laws and cause of fracture and the surface conditions are studied, mainly from the following conclusion:?1?Close distance coal seam group of strata structure model between coal seam and the condition of instability1) According to the close distance coal seam group in bulianta coal mine rock strata layers distribution characteristics, nearly distance coal seam group strata structure between the layers is divided into: without the key layer between coal seam and coal seam between the two types of key stratum. When the coal seam between the key stratum, the final key stratum stope overburden will exist "masonry beam" structure and "steps Yan Liang" structure of two kinds of structure forms.2) The key strata break after the key block mechanics model is set up, respectively obtained by rock deformation sliding instability and rotary instability condition of basic roof fracture after drawn to "masonry beam structure" or "steps Yan Liang" existence condition of the structure.?2?Close distance coal seam group mining of FLAC3 D numerical simulation experimental research1) The structure of close distance coal seam group mining strata movement characteristicsWith the increase of working face advancing distance, goaf overburden distribution of plastic zone is gradually expanding.(1^-2 of the upper coal seam), in the process of mining coal floor unloading damage happens, mined-out area and floor strata in advance after a certain distance to the bottom of the plastic zone no longer increases damage depth, just as the working face advancing, floor towards the boundary of plastic zone was pushed forward.In the plastic zone damage state of the overburden, mining fissure development, fissure zone until below the key strata, the key layer was not destroyed.Mining process, the overburden the plastic zone size was nearly unchanged.Bottom plastic zone along the working face advancing direction with the change of working face advancing small, within a certain depth in the bottom plastic zone almost no, this is due to the coal seam mining, the coal floor stress release, therefore, in the process of mining 2^-2 coal roof plastic zone development scope is small.When 2^-2 coal seam in advance to 300 m, the bottom of coal seam roof and floor, near the coal seam and terminal mining line starting cut plastic zone development.Overburden height of the plastic zone continue to increase, reach the top of the model, the plastic zone development height of 200 m.2) Close thick coal seam group mining stress distribution ruleBecause of the upper coal seam(1^-2 coal seam) have, the lower coal seam?2?- 2 coal working face in mining coal under, surrounding rock stress on the evolution law and different coal mining, mining from began to gradually by the open cut coal mining goaf stress after the formation of the stress reducing area- compaction area to stress lowers area.The next within the coal working face with the working face advancing and the overburden to compaction, gradually formed a new abutment pressure area, the working face and goaf ahead compaction area is less than the peak abutment pressure on coal seam mining, but because of the overburden fractured zone and bending subsidence zone increases, cut and stop picking at the abutment pressure increases accordingly.?3?Close distance coal seam group mining three-dimensional similar material model test research1) The lower coal seam mining, the direct roof initial caving step distance and basic roof breaking interval are less than the upper coal seam mining.When immediate roof in coal bed mining caving step distance of about 40 m, and the coal seam of about 30 m.2) The mining of coal seam, because the upper coal seam and have 1^-2 coal seam spacing and 33 m, and we have thicker interlayer between two layers of coal, the stability of the sandstone layer, can become the key strata.With the working face advancing, the coal seam and the key strata gradually achieve tensile limit periodic fracture, meanwhile, the structure of coal seam fracture and to achieve balance in lower basic roof rotary slide instability, exacerbating the face to pressure phenomenon.Therefore, when the coal seam between the key stratum structure, face to the pressure by the periodic fracture, the upper coal seam roof key stratum articulated equilibrium structure instability of double effect.3) In the coal seam working face advancing, in the process of coal wall front abutment pressure peak value on the rise as a whole.However, due to coal seam is located in the upper goaf under unloading effect on the coal bed mining, coal seam working face under the overall in the stress reducing area, the peak stress is less than the mining coal seam working face on the front of the same distance of the peak stress, but face in mining line up the bearing stress of coal wall but on coal seam mining are substantially rise, this is mainly due to the increase in mining area, which resulted in increased fracture zone, make both sides bear the load increase, the coal wall support area.