Study On Water Impermeability Property Andits Application Of Typical Soil Layers With Thin Bedrock

When coal seam is mined under the geological conditions of thin bedrock and thick alluvium soil strata,the water-conducting fissure zone result from mining can easily penetrate the thick bedrock,affect aquifer of the strata above,which brings huge threat to mine safety,it also cause the deformation and subsidence of the upper soil layer,resulting in the decrease or even the dewatering of the phreatic water,causing serious damage to the ecological environment.In this thesis,based on the physicomechanical properties of alluvium layer soil,the deformation and failure of thin bedrock,and combined with the geological conditions of Sanyuan coal mine,indoor test,theoretical analysis,and numerical simulations were applied to study the impermeability of thin bedrock thick alluvium strata.The main results are as follows:(1)According to the experiment of physical and mechanical properties of soil,the alluvium strata of Sanyuan mine can divide into three sections: shallow,middle and deep.The soil in deep section is low-compressibility saturated clay,with poor permeability and good resistance to damage,it together with the stable structures formed by bedrock play a role in water-blocking and can be used as good roof aquifuge.(2)Considering the supporting effect of mining broken rock masses on overlying rock masses,a Winkler foundation model with four sides fixed branches was established.The deflection expressions and stress expressions were deduced according to the energy method,The relationship between thin bedrock deflection and the Winkler foundation coefficient,and the variation of the critical load with the advancing distance of the working face are obtained.(3)Based on Protodyakonov's theory,the arching effect of overlying clay layer in coal seam mining was analyzed,and the influence about arch shape affected by the lateral pressure distribution and lateral pressure coefficient was obtained.The distribution of lateral pressure and the magnitude of the lateral pressure coefficient determine the shape of the pressure arch.With the increase of the lateral pressure coefficient,the boundary points of tension and pressure gradually expand outward.(4)The analysis shows that the ultimate bedrock thickness of the clay layer which is not destroyed in the thick alluviumr of the Sanyuan coal mine is about 38 m.This thickness has a reference effect on the water-blocking property of clay layer.The loose aquifer and the surface water in the upper of the 3301 mining face are less affected by the mining influence of the adjacent mining face.It will not cause water in the surface subsidence area above the 3301 mining face to crash into the working area.