Study On Regulation Of Overburden Strata And Surface Movement Caused By Mining Nearly Flat And Extremely Thick Coal Seam With Shallow Depth

Mining subsidence is the trouble root of the geological disaster in mining area. A lot of research work about the mechanism of mining subsidence, monitoring and estimation of subsidence has been performed by domestic and foreign scholars, but there is only a few of studies have been done about the discontinuity and variability on the overburden rock.To solve this problem, we have conducted this research which supported by National Nature Science Foundation of China(Grant No. 41172289) and Fundamental Research Funds for the Central Universities(Project Approval No. 2652015125). Anjialing No. 1 underground coal mine is chosen by this research as an engineering example. By using similar material simulation and numerical simulation, study on the regulation of overburden strata and surface movement caused by initial and repeat mining nearly flat and extremely thick shallow coal seam with shallow depth is performed, and results of this research are as follows:1. The regulation of overburden strata and surface dynamic and static movement caused by initial and repeat mining nearly flat and extremely thick coal seam with shallow depth is analyzed by using similar material simulation. The results show that the subsidence coefficient of rock which overlie coal seam with shallow depth is raised with increasing of the depth, and it also increased under the influence of the repeat mining; Although repeat mining can aggravate the degree of surface movement and deformation, to a certain extent, it can shorten the time to reach a new steady state; After mining stop, the area which located on the center of the goaf reaches new steady state in first, and then the area near the stopping line, and finally the area near the open-off cut.2. The variation of separated layer ratio under the key stratum is analyzed by using similar material simulation. The results show that during the initial mining, overburden rock is influenced by self weight and the side extrusion pressure successively, which leads to repeated open and closed of bed separated fissures on the overburden strata near the open-off cut. This inference is proved by finding a small horizontal movement which towards the open-off cut.3. Based on fractal geometry theory, the variation of rock fracture fractal dimension and the influence of repeat mining on the rock fracture fractal dimension are analyzed. The result shows that under the same working face advanced distance, the rock fracture fractal dimension of caved zone is smaller than that of groundwater flow fracture zone, but bigger than that of bed zone. The rock fracture fractal dimensions are significantly increased under the influence of repeat mining because the compaction degree of mining-induced fracture is strengthened.4. The boundaries and characteristics of vertical zoning for overburden rock are predicted by using similar material simulation, theoretical calculation and numerical methods, the results of similar material simulation are proved to be reliable in comparison of the results calculated by the other two methods.