Safety Mining Of The Lower Layer Of Ultra Thick Coal Seam Under The Super Thick Sandstone Aquifer

The lower slicing mining of extra thick coal seam is affected by the broken gangue and left coal pillar in the goaf of upper slicing.The results show that the stress distribution characteristics are different from that of the conventional mining face,which affects the layout of the lower sliced working face and roadway,and the mining of the lower sliced working face is easy to induce the secondary development of water flowing fissures in the overlying strata,which may lead to the overlying aquifer.In view of the above problems,this paper adopts the comprehensive research methods of theoretical analysis,laboratory test and numerical calculation to study the stress distribution and failure c haracteristics of the lower layer after the upper layer mining in the extra thick coal seam,and optimize the mining layout.On this basis,aiming at the situation of thick sandstone aquifer in the overburden of Chenjiashan coal seam,this paper studies the secondary development law of water flowing fissures in the overburden after mining in the lower slicing working face,and analyzes the risk of roof water inrush.The main research results are as follows.(1)This paper analyzes the roof structure characteristics of the lower layer after the upper layer mining in the extra thick coal seam,establishes the mechanical model of "left coal pillar broken gangue in the goaf",determines the bearing characteristics of the broken gangue and left coal pillar in the goaf,and gives the stress expression of the lower layer after the upper layer mining.(2)The creep parameters of the remaining coal pillar are determined,and the distribution characteristics of the vertical stress,horizontal stress and shear stress of the lower layer are analyzed,which are symmetrical with the center of the coal pillar.The stress concentration factor of the lower layer gradually decreases with the increase of the distance from the coal pillar.(3)This paper studies the failure range of the lower slice after the upper slice mining in the extra thick coal seam,analyzes the stress distribution law and stability of the coal pillar in the lower slice section under the conditions of the inner,outer,overlapping and dislocation layout of the mining roadway,and determines the outer staggered layout scheme of the lower slice working face.(4)This paper studies the secondary development law of water flowing fractures in overlying strata in the lower slicing working face of extra thick coal seam,analyzes the water inrush risk of overlying thick sandstone aquifer,and determines the control method of combined drainage(drainage)of old empty water and roof sandstone water damage wells and other methods as supplement.There are 70 figures,9 tables and 117 references in this thesis.