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Abstract
Among the three overburden zones (the caving zone, the fracture zone, and the continuous deformation zone) in longwall coal mining, the continuous deformation zone is often considered to be continuous without cracks, so continuum mechanics can be used to calculate the subsidence of overburden strata. Longwall coal mining, however, will induce the generation of wide cracks in the surface and thus may cause the continuous deformation zone to fracture. In this paper, whether there are cracks in the continuous deformation zone as well as the height of overburden fracture in longwall face and the subsidence and deformation of strata of different fracture penetration ratios were studied by means of physical simulation, theoretical analysis and numerical simulation. The results show that: (1) Rock stratum starts to fracture as long as it has slightly subsided for only tens of millimeters, and the height of fracture development is the height of working face overburden. (2) With the increase of fracture penetration ratio, the subsidence of key strata remains basically unchanged; the surface deformation range and the maximum compression deformation decrease, while the maximum horizontal movement and maximum horizontal tensile deformation increase. Therefore, the subsidence of overburden strata which have fractured but have not broken can be calculated through the continuum mechanics method.
Highlights
Coal mining will lead to roof caving, overburden fracturing, surface subsidence and environmental damage, resulting in groundwater pollution, surface water flow cutoff, vegetation withering and farmland waterlogging [1,2,3,4,5,6,7,8,9,10]
Field observations and physical model simulations have shown that the key strata (KS) dynamically controls the surface subsidence [11,12], which means that the KS and the controlled soft rocks obtain synchronous subsidence and subsidence speed
After longwall mining, the surface subsidence coefficient gets greater than 0.6 which is relatively large for medium-thick coal seams [17], so there will usually be some wide fractures in the surface of these coal seams
Summary
Coal mining will lead to roof caving, overburden fracturing, surface subsidence and environmental damage, resulting in groundwater pollution, surface water flow cutoff, vegetation withering and farmland waterlogging [1,2,3,4,5,6,7,8,9,10]. After longwall mining, the surface subsidence coefficient gets greater than 0.6 which is relatively large for medium-thick coal seams [17], so there will usually be some wide fractures in the surface of these coal seams This indicates that fractures may exist in strata of continuous deformation zone, and it is doubtful whether KS subsidence can be calculated by using the continuum mechanics method. The development of fractures in the overburden of continuous deformation zone was qualitatively analyzed firstly by means of physical simulation, and the critical subsidence conditions of strata fracture were given by combining mechanics theory. Two-dimensional model is often used to simulate the fractures and subsidence of longwall overburden strata, and it has the following advantages compared with
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