Research On Strata Movement Above Goafs Mined Out By Room And Pillar Method Of Slightly Declined And Medium-bedded Mine Body And The Optimization Of Stopes

Based on room-pillar method, surface settlement, destruction of the environmentand even some casualties may be caused by the change of the stress resulted frommining activities of the slightly declined mine body, so the study of the movement ofoverlying strata is of theoretical significance and practical value. Rock mechanicsexperiments, practical monitoring, theoretical analysis and numerical simulation wereused to study the strata movement above the mined out areas of the second mine bodyat Wenfu phosphate mine. Main contents are described as follows:1) Experiments of saturated and dry rocks were carried on, and mean uniaxialcompress and tensil strength, elastic modulus, and poisson ratio of the rocks from roof,floor and mine body were obtained. The values of cohesion and friction angl werealso pointed out. Based on the indoor experiments, the engineering rock parameterswere obtained via kinds of engineering treatments.2) Based on the analysis of the monitoring data, it can be concluded as follows:firstly, the strata above the mined out areas are more likely to subside largely, anddestructions may occur at the mined out areas. Secondly, settlement of the stratabesides the mined out areas tends to be smaller, but it follows a increasing tendency.Thirdly, little subsidence occur of the strata away from the mined out areas and thestrata tend to be stable as mining goes.3) The roof of the goaf is simplified to be a thin plate which is completedclamped supported. Based on the deformation equation of the plate, the settlement ofroof and surface above the goaf created by room-and-pillar mining is computed. Andthe settlement of the roof at2nd bore of5th shaft is calculated out. The failure modelof the goaf created by room-and-pillar minning is discussed.4) Mining activities were simulated by Flac^3D, based on the rock mechanicalparameters obtain via engineering treatments, and comparison between monitoringand simulating data were implemented to research on the simple law, failure tendencyand modes.5) Parameters of the mining areas were optimized by Flac^3D, the ordinary law of the overlying strata above was obtained, and the optimized parameters are written asfollows:When the thickness of overlying strata is40meters, the span of room is10m,the optimized diameter of pillar is3.4m and the maximum exposed area is90.92m².When the thickness of overlying strata is60meters, the span of room is12m, theoptimized diameter of pillar is4.4m and the maximum exposed area is128.80m².When the thickness of overlying strata is80meters, the span of room is12m, theoptimized diameter of pillar is4.5m and the maximum exposed area is125.91m².