Abstract:
There is a type of shallow close distance seams in Western China,which is buried shallow,has thin rock overlying strata and water-bearing sand seam. Under the geological conditions and mining technology of shallow close distance seams,once the water-bearing sand seam is affected by the coal face mining,water and sand pouring disaster will occur,which affects the safety and production of the coal mine. In order to avoid water and sand pouring problems of overlying strata structure in repeat mining of shallow close distance seams,a new theoretical approach is proposed to build up the double-rectangular-hole theoretical model within infinite plane to analyze the evolution rule of overlying strata structure in repeat mining of shallow close distance seams,and carried out similar material simulation. Firstly,based on elastic theory and Schwarz alternating procedure,a theoretical formula of stress field of overlying strata is deducted. Based on this theoretical model,the evolution rule of stress field in overlying strata of upper-lower coal seams and failure range is evaluated. The research results show that the horizontal stress distribution in overlying strata σ
x is X-shaped,the floor and roof of the coal face is under tensile stress. When the intermediate rock is 20 m in thickness,the maximum tensile stress is up to 0.82 MPa,the failure zone is up to 58 m. Compared with the failure zone of 32 m in the mining of single coal seam,the failure zone increases. Secondly,the similar material simulation test results show that,the whole intermediate rock seams fails. Compared with the failure zone of 35 m in the mining of upper coal seam,the lower coal seam induces the increase of the failure zone,up to 61 m,namely,the mining of lower coal seam increases the original failure zone induced by upper coal seam. The similar material simulation tests prove the theoretical approach is good. The research results provide theoretical basis and technical support for the repeat mining of shallow close distance seams in Western China.