Study On Retaining Safety Coal Pillar Against Sand With Fully Mechanized Caving Under Thick Alluvium And Thin Bedrock

Based on the scene investigation, the laboratory experiment, the theoretical analysis, the similar material simulation and the numerical simulation and the field test and so on, this article has been studied systematically the sedimentary structural features, the ground water dynamics parameter of bottom aquifer, variation characteristic and resistance water function of the bedrock weathering zone, composite structure type and the law of movement and fracture of overburden. The work involved:1. According to the scene investigation, the laboratory analysis test experiment, the water-bearing stratum of loose seam base and the bedrock weathering zone are researched. The result indicates that, the water-bearing stratum of loose seam base is weak～very poor water-bearing stratum with high content of clay minerals and lower porosity, it belongs to the enclosed～half-closed compound water body with consolidation～half-consolidation behavior, poor fluidity and weak ability of vertical permeation; In the bedrock weathering zone, because of the weathering influence, the intensity of the rock reduces greatly, the mineral ingredient have the obvious variation, the clay mineral content has increased, plastic deformation ability enhancement; After absorbing water the volume expansion, the regeneration separates the water ability is stronger.2. According to the similar material simulation and UDEC numerical simulation, the paper analysis the movement and failure law of the first section working face overburden of No.87 mining area. The result indicates that, the caving zone's maximum height is 13.6m with fully mechanized caving under thick alluvium and thin bedrock; Because of the influence of mining activities, the rock has the destruction migration evolution rules, such as, large subsidence, higher moving speed, fast velocity of pressing the crack presses densely, weak water and sand bursting the ability.3. Based on the field test, the caving zone's maximum height is obtained, it is 11.34～15.74m, the caving zone height and coal thickness ratio is 1.44～1.69.Based on study above, the sand-proof pillar is retained 18.1m in the first section of No.87 mining area. This mining method can be taken by other similar mines for reference in china's northanhui mining area.