Simulation Study on Stress Distribution and Failure Characteristics of Soft-hard-soft Interbedded Composite Floor in Deep Seam Mining

Take Hengyuan Coal Mine II 633 working face as the engineering geological background, a three-dimensional calculation model was established by FLAC^3D 5.0 to study the stress, displacement and the plastic zone variation of the floor under the condition of deep mining. The results show that: in the process of advancing the working face, the coal seam floor has experienced the repeated destruction of concentrated stress compression - floor uplift and pressure relief - roof caving and recompression. The stress variation curve shows an “M” shape, the maximum stress concentration coefficient is 1.74, the roof of the goaf falls behind, the stress of the floor is gradually restored to about 0.75 to 0.8 times of the original rock stress, and the displacement curve is “serrated”. The maximum downward displacement is about -6.5 cm, the maximum floor heave is +16.4 cm, the longer the length of the working face is, the greater the span of the floor heave; the maximum development depth of the plastic zone in the floor of the working face is 12 m, and the development range is gradually expanded, and the accuracy and reliability of the simulation results can be obtained by comparing the results of the empirical formula.