Theory And Application Of Seepage Stability Of Overlying Strata For Shallow Coal Seam Mining

With the development of energy and the promotion of ecological construction,the balanced development of "energy-ecology" has become the research focus.The green mining of combination of mining and ecological protection has become an inevitable trend.The basic theoretical research on water resources protection in coal mining focus on Northwest China is a major requirement for the healthy development of the industry,even the region and the country.It is necessary to consider resource mining,ecological resource protection as an organically integrated entirety.The theory of overlying strata and seepage stability of mining,with the flow of water resources,has great significance for the exploitation and sustainable development of coal resources in ecological fragile region in western China.In order to further study the relationship between overlying rock migration and ecological water dynamic response in the northwestern China.This paper focuses on the seepage stability of overlying strata of mining,and combines in situ investigation,experimental testing,theoretical analysis,numerical simulation,and program calculation for definition of the equivalent permeability stability criterion of overlying strata.Mainly testing hydraulic characteristics of overburden,establishing the stress distribution model and equivalent layer analysis method of shallow buried overlying strata of seepage,and designing numerical calculation program for overlying strata equivalent permeability.Finally,analyzing the ecological water permeability stability of overlying strata of mining in shallow coal seam in northwestern China.The main results are as follows,The macroscopic and microscopic structures of the natural rock samples in the Northwest were observed,and the material properties were tested.The results show that with the increase of confining pressure,the strength of various sandstones gradually increases,and the growth trend is roughly linear.The permeability coefficient of fractured rock samples gradually decreases with the increase of confining pressure.The maximum change rate is above 60%,and the minimum is less than 1%.A similarity model of overlying strata was established,a mining simulation was performed in a mining area in Northwest China,and the laws of overlying strata migration and stress evolution were analyzed.The "progressive" failure mode of rock strata was revealed,and a beam model based on the " progressive " failure mode was established to analyze and simulate the evolution law of the overburden stress field.By comparing with the numerical solution,the relative error of stress is less than 10%.After mining,the overlying strata structure presents an obvious "three-zone" structure.The surface subsidence is “funnel”.The height of the fracture zone is about 45% of the total thickness of the overlying strata.Based on the seepage characteristics of layered rock mass,an equivalent seepage flow model based on the combined rock layer system was established.A method for analyzing the overlying strata feature area is proposed.The influence of the proportion of the characteristic zone on the equivalent permeability coefficient is analyzed,and it is known that the height of the fracture zone is the main reason for the influence of the permeability coefficient.The change of the equivalent permeability coefficient of overburden formations is determined by the permeability of multiple formations.Based on MATLAB,a numerical calculation model of random fissure network seepage was set up.And because of the existence of randomness,the simulation of the cracked network is better than the finite element software.A method for calculating the equivalent permeability coefficient of rock layers based on the characteristic area and the permeability coefficient of each characteristic area was established.The effects of each random factor on the equivalent permeability coefficient of the fractured area are analyzed.Combined with the in-site meteorological,hydrological and geotechnical parameters of Xinjiang Yili No.4 Mine,the equivalent permeability coefficient of the overlying strata is calculated.The program simulates the Yili No.4 mine as mining progresses.Consistent with the situation that only grasses are renovated every year at the mining area,the simulation shows that the equivalent infiltration situation of the Yili No.4 Mine is at the stage of large-scale vegetation cannot be planted and a large amount of vegetation is degraded.Compared with the actual measurement results of mining water level data,the program calculation error is about 10%.The self-designed "fluid-solid" coupling experimental equipment was used to simulate the in-site mining penetration.With the progress of mining,the height of the fracture zone gradually stabilized When the working face is advanced to 140 m,the height of the fracture zone is approximately 69.3m,and the error from the program simulation result is about 5%.The water level change rate gradually grows.According to the development law of the fissure zone,it can be predicted that the water level will gradually stabilize when the water supply is continuously replenished.