During mining close-distance multi-layer ore bodies,the safety of the lower ore body mining is affected by the stress migration law of the pillar and floor in the goaf of upper ore.In order to investigate the stress transfer law of the floor under the load of pillar group,taking a phosphate rock mine as the research object,based on the theory of semi-infinite space,the load distribution law of the floor of the pillar group was regarded as a periodic square wave,and the cosine function was used to approximate the wave function of the square wave(the stress distribution of the floor of the pillar group),the square wave model of floor stress transfer was established by inverse method.The stress concentration degree of goaf floor and the energy storage-dissipation law of the pillar group were investigated by numerical method under two different constitutive relationships(elastic model and Mohr-Coulomb model).The results show that the more load transferred and elastic energy stored on the pillars in goaf under the elastic constitutive model,the higher the stress concentration of the floor.Under the elastic-plastic constitutive model,the pillar in the central area of the mining area is damaged and the energy is dissipated,and the stress concentration of the floor is small.Under the action of pillar load,there is a large stress concentration within 15 m of the floor,and the stress value is the highest at 3 m below the pillar.The research results provide a reference for the ground pressure control of room-and-pillar mining of close-distance multi-layer ore bodies.
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