Dynamic Analysis Of Water Inrush From Water-Proof Floor Of Coal Seam With Fault Under Roof Caving Impact

With the continuous reduction of shallow coal resources,the depth of coal mining in China gradually develops to the deep.Under the action of high confined water,high geostress and strong disturbance,dynamic disasters occur frequently in deep coal seam mining.Among them,the disturbance and damage of dynamic loads such as mining pressure and roof collapse to the floor aquifer make the water inrush problem of floor damage in coal seam mining urgent to be solved.According to statistics,the vast majority of water inrush accidents occur under the influence of faults.Therefore,the study of floor water inrush under the influence of faults has important theoretical significance for coal mine safety production.Previous research results are mainly carried out under static conditions,but under dynamic loads,such as large-scale roof collapse and other causes of water inrush caused by water-proof floor rupture are relatively few.In this paper,firstly,based on the focal mechanism solution data of the earthquake in the study area,the distribution characteristics of the regional geostress are inverted.Taking the floor with faults as the research object,the risk of water inrush from the water-proof floor under the impact load of roof collapse and the ground stress is analyzed.The main results are as follows:(1)According to the data of focal mechanism solutions of earthquakes in Lianghuai mining area,the characteristics of tectonic stress field are inverted.It is concluded that the inclination angles of the average principal compressive stress axis and the advocated stress axis of the stress field in the mining area are relatively small,which shows that the present tectonic stress in the area is mainly distributed in the near horizontal direction.This provides a theoretical premise for analyzing the critical water pressure peak of water inrush caused by vibration damage of water-proof floor under different horizontal in-situ stress.?(2)The caving forms of roof in coal seam mining process are systematically studied,which are divided into breaking type and integral type.The mechanical analysis of these two different caving forms is carried out,and the ultimate hanging length and expression of caving are given respectively.The research shows that if the roof is broken,the roof will collapse;if the roof is broken,the roof will collapse as a whole.(3)Using the law of conservation of energy and the theory of incomplete elastic collision,the impact force of the broken and integral roof collapse on the floor is calculated;based on the theory of incomplete elastic collision,the time history equation of the impact load of the whole roof collapse on the floor is deduced,which can be used to simulate and analyze the change of the water pressure of the floor under the roof collapse and to solve the floor burst under different geostress.The critical water pressure of water provides the premise.(4)The bottom water-proof layer under the influence of faults is regarded as a cantilever beam.The calculation model of the cantilever beam under the impact of roof collapse and bottom water pressure is established,and the differential equation of vibration and displacement of the beam is deduced,which lays a theoretical foundation for the subsequent discussion of its failure form.(5)Based on the impact load time-history equation of roof collapse on the floor,FLAC3 D is used to simulate and analyze the change of water pressure of the floor when the roof collapse impacts the water-proof layer of the floor.It is concluded that roof collapse can cause the water pressure of the aquifer to rise rapidly and the risk of water inrush from the floor greatly increases.(6)With the increase of lateral pressure coefficient,the failure mode of water-proof floor with faults under impact load changes from tensile failure to shear failure gradually,reflecting the control effect of horizontal in-situ stress on the failure mode of water-proof floor.(7)The critical water pressure peak value of water inrush from water barrier floor is discussed with the constant change of lateral pressure coefficient.It is concluded that with the increase of lateral pressure coefficient step by step,the critical water pressure peak value of water inrush with tensile failure of fault floor increases gradually,while the critical water pressure peak value of water inrush with shear failure decreases gradually.Figure [21] table [8] reference [81]...