Study On Movement Laws Of Overlying Strata And Its Control Of Extra-thick Coal Seam Mining In Xinjiang Region

According to the occurrence characteristics and geological features of extra-thickcoal seam in Xinjiang region, situ survey, numerical simulation, physical simulationand theoretical analysis were undertaken to study the overlying strata movement lawsand its control technology of extra-thick coal seam mining. This study will pay anactive role in theoretic references to efficiency and safety mining of extra-thick coalsea.Main achievements of this dissertation have been displayed as follows:（1）Occurrence conditions of extra-thick coal seam in Xinjiang region wasapplicable classified, and based on this the overlying strata movement laws indifferent types of extra-thick coal seam were analyzed and contrasted.“Fracture-Hinged stable-Unstable-Fracture again” variations of overlying stratacaused by different mining height were proposed and confirmed, and the generationmechanisms of overlying strata in different compositions were revealed.（2）Physical simulation and numerical simulation experiment results show thatextra-thick coal seam mining causes a significant increase in goaf space, and miningdisturbance influence scope has spread to a large range, which lead to more space ofoverlying strata movement, and could easily cause a wide range structural instabilityof overlying strata. Overlying strata fissures development, surface subsidence, andstress concentration of extra-thick coal seam mining are controlled by the structuralstability of key strata rocks. When the structural instability of key strata occurs,hinged stable structure cannot be reformed in the subsequent mining process. Part ofoverlying strata blocks will break again in the slicing mining of extra-thick coal seam.（3）According to key stratum theory of strata control, the overall structuralmechanical models of key strata were constructed to analyze the stability of key strata.Based on the stability of key strata, key areas of roof control were identified inextra-thick coal seam mining. The critical thickness concept of extra-thick coal seammining had been put forward, and used as the forecast index for key layer structuralstability during coalface mining process, and the critical value of extra-thick coalseam thickness for judging key layer structural stability had been preliminarilydetermined.（4）Secondary break mechanism of overlying strata blocks was revealed. Understatic loading, the secondary fracture mode of overlying strata block was tensile fracture, when block formed a cantilever structure after instability, and overlyingstrata blocks secondary breaking mainly occurred in the collision course with otherblocks under impact loading. Mechanical model of overlying strata secondarybreaking were respectively constructed under the conditions of static loading andimpact loading, and secondary rupture discriminants of strata blocks in differentfactors were formulated.（5）“support-surrounding rock” of extra-thick coal seam mining had beenmechanical analyzed under the condition of different overlying strata structures, andsupporting resistance of controlling roof structure instability had been calculated,which achieved good comprehensive application results. The central role of overlyingstrata thickness and working face length in “support-surrounding rock” relationshipswas revealed. Using the condition whether the support could control the roof or not asjudgment criterion, full mining critical condition of extra-thick coal seam wasobtained.