Study on evolution law of overburden fracture in fully-mechanized top-coal caving face with large mining height in thick coal seam

Fully mechanized top-coal caving mining with large mining height is easy to form strong strata behavior, and the fracture evolution law of overlying strata is very important for safe production of working face. Taking the 160206 working face of Yangchangwan Coal Mine as the engineering background, the comprehensive research methods of similar simulation test, numerical simulation and theoretical analysis are used to systematically study the overburden fracture process and overburden migration law of the fully mechanized top coal caving working face with large mining height. The research shows that the strata in the water flowing fracture zone show “bench sinking” with the advance of the working face, and the subsidence trend of the same strata along the strike shows “sharp decline - stability (maximum) - rapid rise - stability (minimum)”. The overburden movement field of the working face has evolved from two areas (accelerated subsidence area and slow subsidence area) to three areas (accelerated subsidence area, slow subsidence area and stable area). The evolution of abscission layer and the law of surface subsidence are quantitatively described, and the dynamic subsidence mechanism of the surface and its related factors are deeply analyzed by using theoretical calculation expressions. Combined with the experimental results of similar simulation and numerical simulation, the morphological change characteristics of overburden fracture evolution are proposed: the overburden fracture morphology evolves from “single isosceles trapezoid” to “double isosceles trapezoid”, and the influence area of topsoil layer evolves from “rectangle” to “inverted trapezoid”. The dynamic evolution process of collapse area, separation area, compaction area and fracture enrichment area in overburden is analyzed: The caving zone gradually increases to a certain extent, the height decreases slightly and tends to be stable, the separation zone gradually develops from bottom to top and moves forward with the working face, the separation zone gradually closes to form a compaction zone, and the compaction zone gradually increases and finally remains stable, and the fracture enrichment zone is located at the front and back ends of goaf and moves forward with the working face.