The Gentle-dipping And Medium-thickness Phosphate Ore Body' Undergroud Mining Stope Strata Behaviors And The Overlying Strata' Failure Law

This dissertation takes the sixth pit west mining area as the research object, which belongs to Linhua mining company in Yunnan province. A comprehensive research method, including similar material simulation experiment and numerical simulation method (discrete element program UDEC2D) was used to analyze the feasibility that using improved no-pillar sublevel caving method to mine the gentle-dipping and medium-thickness phosphate orebody, then, the deformation and failure laws of the roof region'surrounding rock, and the surface subsidence rule are obtained. The research results can be used for reference for the study of the similar nonmetal deposit's mining process. The main research work and achieved results of this dissertation are as follow:(1) Through the measurement of the rock's physical and mechanical properties in the sixth pit west mining area, the physical and mechanical properties of all kinds of rock distributed in the whole mining region are obtained.(2) According to the existed undergroud mining method, combining with the mine's actual situation, a new mining method, which is no-pillar sublevel caving method added recovery accesses is proposed.(3) Combining the ore's occurrence conditions, tratum structure and mining process of the sixth pit west mining area, based on the similarity theory, a similar simulation experiment was used to study the feasibility that using improved no-pillar sublevel caving method to mine the gentle-dipping and medium-thickness phosphate orebody. The similar simulation experiment results show that the deformation of the overlying strata originates from the mined-out area's direct roof, and gradually develops to the deep of the strate,and then, irregular'stepladder'caving zone is formed in the mined-out area. The maximum gound settlement is located at the above of the phosphorus orebody, and gradually decreases toward the both sides. With the enter route's propulsion, the maximum subsidence location gradually moves toward the propulsion's direction.(4) Based on the discrete element theory, the numerical simulation method (discrete element program UDEC2D) was used to study the mining process in the sixth phosphate rock pit west mining area. The surrounding rock's stress and deformation characteristics, and the variation of abutment pressure are obtained. The numerical results show that the displacement of the overlying strata is nonlinear, and it gets smaller with the increase of the roof height. After the excavation of the undergroud phosphate rock, the roof support pressure concentration region is formed in the pre and post of the stope roof, also, the pressure unloading area is formed in the roof region above the mined-out area. It shows that the numerical results agree well with the similar simulation experiment data through comparison.