The pressure relief of coal pillars in close-distance multi-coal seam goaf is a complex engineering problem with the characteristics of “dynamic mine pressure”. Hence, this paper studies such problems. First, the influence factors of the coal pillar in the goaf on the mine pressure of the mining face of the lower coal seam under this condition were theoretically analyzed, and it was concluded that vertical stress is the most important element, followed by horizontal stress. Next, a physical similarity simulation experiment was designed to study the stress distribution law of the coal pillar floor in the goaf before and after pressure release and the damage depth. Finally, a technology and monitoring method for coal pillar blasting pressure alleviation in goaf were introduced and implemented in engineering practice. After the pressure is alleviated, the surrounding rock stress of the lower coal seam mining face is redistributed, and the vertical stress is decreased by 20%. The adjacent rock’s deformation is improved. This technology’s cost and safety advantages are extraordinary and helpful for mining coal seams over close distances.
This paper focuses on the failure mechanism of a water-resisting soil layer with both coal excavation and seepage effect. Being taken the simulation principle of fluid-solid coupling as the research basis, we have established a new kind of experimental material for fluid-solid physical simulation (FPS). The material adopts river sand and clay as the aggregates, besides engine oil and low-temperature grease that are used as the gelatinizing agents. According to the relevant property testing on the experimental material, the mechanical parameters and seepage parameters of the material totally match the parameters of the soil layer, which satisfy requirements of the fluid-solid coupling experiment. Simultaneously, we have solved abundant material property problems, such as the material disintegration with water and visuality of water seepage in the simulation. Next, we have built up the FPS model to simulate coal excavation under water-bearing strata with the specific material. The results indicated that in the FPS, movement and failure mechanism of the water-resisting soil layer agree with the in-situ monitoring results. In addition, the revolution law of a mining-induced crack is also fitting the actual data. The mechanism of submarine seepage and its parameters on the material and the prototype are similar. All research results would be necessary for controlling mining-induced destroying of clay water-resisting property. Meanwhile, the model demonstrates that selection of the material and coupling parameters is valid. Finally, we can alter the material matching to obtain the layer materials with various characteristics, which would be applied in extensive experiments for studying soil layer failure and seepage simulation.
The development law of mining cracks in shallow coal seams under gully topography was used as the research base to analyze the development characteristics of mining cracks in the 5-2 coal mining face of Anshan Coal Mine, and the weak strength was established. The basic top force model under the action of the overburden is the “nonuniformly distributed load beam” structure model. Through similar simulation research and theoretical calculation analysis, the fracture development law of the working face passing through the valley is studied. Based on the mechanical analysis of the beam structure with nonuniform load, the discriminant conditions of the stability of the bearing structure of the bedrock are derived, the calculation formulas of the parameters such as the pressure, shear force, and the ultimate span of the basic roof at both ends are determined, the influence law of the thickness and slope change of the weak strength overburden on the mining crack spacing is revealed, and the influence of the slope of the weak strength overburden on the weighting step distance on the beam with nonuniform load is obtained. The phenomenon is that the burial depth has a great influence on the step distance of weighting. The practice shows that the distance between the mining-induced fractures determined by the nonuniformly distributed load beam model and the periodic weighting step, the height of fracture development, and the buried depth are approximately the same; the mining-induced fractures in the overburden develop and evolve periodically with the failure and instability of the bedrock. The research results will clarify the development mechanism of surface cracks in the gully mining area, which is of great significance to reduce terrain disasters.
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