Controlling Mechanism Of Surround Rock Stability In Recovering Room Mining Standing Pillars By Consolidated Solid Backfilling Mining

The room mining method has been used for a long time in the boundary of Shanxi,Shaanxi and Inner Mongolia in China, due to the local economy and technical equipment level. With this mining method, many pillars are left standing underground which leads to a low recovery rate. This will not only contribute to coal resource waste, but also trigger coal fire, mine earthquake and other hazards. Therefore, how to retreat room mining standing pillars has become an urgent problem to be solved. The fully mechanized consolidated backfill mining method, with good control effect on strata movement and little surface subsidence, has offered safe and efficient solution to retreat room mining standing pillars.The thesis comes up the framework and detail method to retreat room mining standing pillars with consolidated solid backfilling mining, the thesis focuses on keeping surround rock stabililty. By incorporating situ research, theory analysis, laboratory experiment,numerical simulation, physical simulation and other research methods, the surrounding rock structure characteristics in mining area using consolidated backfill to retreat pillars and relationships between each component are analyzed. The author studies strata stability control in mining area of retreating room mining standing pillar with backfill mining method and obtains the working face support strength, stress-strain characteristic of backfill material,action mechanism of initial stress on surrounding rock stress distribution and plastic zone development in pillars. The main innovative achievements are as follows:(1) A thin plate on a non-linear elastic foundation model was built. In this model, coal pillars were considered as time-dependent non-linear elastic foundation whose elastic foundation coefficient decreased as time elapsed. The proposed model could be used to reveal the dynamic evolution of the decreasing-failure process of supporting capacity of coal pillars. Furthermore, equations for predicting roof deformation and coal pillar failure was put forward. A criterion for evaluating the time-dependent stability of the pillar-roof system was then given in this study.(2) Retreating room pillar with solid backfill mining is proposed. A non-uniform multi parameter nonlinear elastic foundation model including backfill materials-coal pillar-roof is established. The control formula of basic roof deformation using finite element method is constructed to calculate the critical conditions of coal pillar and roof instability, which gives the mixed ratio of aeolian sand and loess material.(3) Based on the Compaction deformation characteristics of backfill material, physical simulation and ABAQUS numerical simulation are combined to study the pillar deformationand strata movement using caving mining and solid backfill mining. The interaction of coal pillar and backfill material, and roof are analyzed, which reveals the failure law and strata movement of room pillar with solid backfill mining.(4) Engineer design method of retreating room pillar with solid backfill mining is come up, and it provides the design basis for selecting backfill material, working face support strength and initial compressive force. The paper also designs backfill index and surround rock stability monitor and feedback system.