Mechanical structure and seepage stability of confined floor response to longwall mining of inclined coal seam

Abstract

The floor of inclined coal seams during mining is prone to seepage instability, resulting in water loss and even water inrush. The production of inclined coal seams occupies a certain proportion in China. Therefore, it is necessary to carry out the research on the floor structure stability in response to underground mining. Firstly, a four-side solid support inclined laminate model was established by analyzing the stress state and deformation failure law of inclined floor under the action of bidirectional linear load. Then, by studying the relationship between permeability coefficient and deformation, the method and conditions for determining seepage stability are obtained, and the influencing factors and sensitivity of water protection mining in inclined coal seams are determined through engineering cases. The inclined floor deflection curve is not symmetrical; the maximum deflection of the inclined coal seam floor is located at a distance of 0.5864 times the length of the working face in the middle and lower part of the working face, and at a distance of 0.5864 times the advance distance of the working face in the advancing direction. Through an orthogonal experimental analysis, the significance order of the factors affecting the deflection of the bottom plate is as follows: working face length > water pressure > advance distance > dip angle. The boundary of the upper layer in the laminated plate is a compressive stress area, while the middle layer is a tensile stress area. The opposite is true for the middle and lower layers, where shear stress is concentrated in different regions. The maximum stress values in the lower area of the working face are greater than those in the upper area, showing an obvious asymmetry. Finally, the evaluation indicators and stability conditions for seepage stability were determined: the ratio of the ultimate permeability coefficient (K_li) to the equivalent permeability coefficient (K_eq) should not be less than 1, that is, K_li/K_eq≥1. The significance of the factors affecting seepage stability is as follows: water pressure>working face length>dip angle, which can provide guidance for water protection mining in similar mines.

Keywords

laminate model / inclined coal seam / structure stability / seepage stability / equivalent permeability coefficient / orthogonal design / significance analysis

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