Evolution and stability mechanics analysis of the elliptical stress arch structure in the surrounding rocks of the underground mining area.

After coal extraction in underground mining, progressive fracturing occurs in both roof and floor strata, resulting in stress redistribution within these rock layers. Considering the fractures in the strata at roof and floor, an elliptical stress arch was introduced. This concept analyzed how the shape and structure of this arch evolved when mining progressed, as well as the evolution law of the strata at roof and floor fractured. Research results are as follows. (1) The elliptical stress arch bore most of the load on the surrounding rocks of the mining site, and the front and rear arch springing moved forward with the mining face. The surrounding rocks of the mining site redistributed stress, which formed tensile stress in the areas near the arch top and base. The stratum underwent active fracture and was compressed in its movement direction. Compressive stress was formed to clamp unbroken strata in the area far away from the arch top and base. Strata were passively broken along the arch trajectory due to their self-weight load, the compressive load of active-fracture strata, and the clamping effect of the compressive stress around the stress arch. (2) Unbroken hard strata inside the elliptical stress arch formed a cantilever beam. A hinged rock beam was formed after hard strata broke. Soft strata acted on lower strata in the form of loads. The support structures at the working face and the coal wall carried the weight of strata, which was transmitted through cantilever beams or hinged rock beams at roof and floor. The passive fracture of the cantilever beam and the instability of the hinged rock beam directly affected the stability of the working face support and coal wall. (3) The analysis focused on how the lengths of the long and short axes and the coordinates of the center of the elliptical stress arch changed as the working face advanced. The theory of composite beams was used to determine strata, rock loads, fracture distances, and fracture sequences of hard strata at the roof and floor of the elliptical stress arch. The stability at the roof and floor of the hinged rock beam was obtained using the criteria for compression deformation instability and sliding instability of the hinged rock beam. The research results can provide support for calculating the resistance of the working face support, the load borne by the coal wall, and the width of the plastic zone of the coal wall. Besides, they offer a theoretical basis for analyzing the stress of the working face support and the stability of the coal wall in the mining area, as well as production practice.