Permeability Evolution And Control Mechanism Of Mining Floor Of Thick Coal Seam Above High Confined Aquifer In Longquan Coal Mine

Coal mining in North China is threatened by high water pressure and strong water rich Ordovician karst aquifer,especially when there is concentrated fracture area in the floor,it is easy to cause a large amount of water gushing in the working face.In this paper,Longquan coal mine 4301 working face with fractured zone floor as the research object,comprehensive use of theoretical analysis,similar material experiment and numerical simulation means to study the mining deformation and failure law of fractured zone floor,permeability evolution and water resisting layer control mechanism.The main achievements are as follows:(1)Based on the theoretical analysis of beam structure,the maximum failure position of the floor with fracture zone is located at the top of the fracture zone,and the maximum failure depth is 34m;Through the physical simulation experiment,it is found that under the condition of complete rock stratum,the floor mining fracture zone presents inverted saddle shape distribution,and the deepest position of fracture development is at the coal wall at the front end of the working face,with the maximum of 18m;Under the condition of containing fracture zone,the floor fractures are distributed in the form of shallow at both ends and deep in the middle.The deepest position of fracture development is at the top of fracture zone,and the maximum is 34m;Under the condition of complete strata,the maximum volume strain of floor strata occurs at the floor of goaf near the coal wall.Under the condition of fracture zone,the maximum volume strain of floor strata occurs at the top of fracture zone.(2)By constructing the coupling model of mining stress and seepage,the evolution law of mining permeability of intact floor and floor with fracture zone is studied.The results show that:during the mining process,the permeability of the intact floor experiences the process of"decrease increase restore";the vertical section of the coal seam floor after mining can be divided into permeability decrease area,permeability increase area and permeability restore area;in the vertical direction,the permeability of the floor decreases with depth in the form of power function;for the floor with fracture zone,the mining permeability increases The large area is connected with the fracture zone,and the permeability of this area increases first and then decreases.(3)The influence of mining parameters on the permeability of floor with fracture zone is analyzed quantitatively.The simulation results show that:when the mining height is more than 6m and the length of working face is more than 200m,the permeability of goaf floor increases,and the area will be connected with the fracture zone;the maximum development depth of plastic zone of floor increases with the increase of mining height and working face length,but the influence of mining height on it is greater than the length of working face;it is clear that the water channel of floor is located in the fracture zone under the working condition of 4301 working face.(4)This paper establishes the groundwater system migration model of Longquan coal mine,studies the groundwater flow field distribution of Fengfeng formation fracture zone and Benxi Formation Fracture Zone after modification,and determines that the grouting modification effect is better in Benxi Formation Fracture Zone.Simulation and field industrial test show that:under this scheme,the drawdown depth of the water level of the observation hole OW1 is the smallest,and the water level of the observation hole OW2 rises by 9.6m,and the water inflow of the working face decreases from 130m~3/h to 50m~3/h.at the same time,the water level of the Ordovician limestone aquifer basically tends to be stable,realizing the goal of in-situ protection of the Ordovician limestone aquifer in the floor.This paper has 66 pictures,13 tables and 88 references.