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采用数值分析的方法,建立了保护煤层开采厚度、被保护煤层赋存厚度及层间岩性对上保护层开采保护效果影响的计算模型。结果表明,当上保护煤层开采厚度增加但小于下部被保护煤层赋存厚度,或者上保护煤层开采厚度不变而被保护煤层赋存厚度增加时,保护效果逐渐增加;但当上保护煤层开采厚度大于被保护煤层赋存厚度时,保护效果基本一致。同时,当上保护煤层与下部被保护煤层间的岩层岩性越硬时,被保护煤层煤体单元的塑性变形量和应力减小量越小,保护效果越差。在实体煤岩内,岩性差异大的区域内水平应力降也较大。采空区下方不均衡分布的垂直应力的垂向挤压与水平应力的横向剪切作用,是底板煤岩体单元发生偏心失稳进而产生塑性变形和破坏的重要原因。
Numerical calculation method was used to establish the calculation model to protect the thickness of coal seam mining, the thickness of coal seam under protection and the influence of interlayer lithology on the mining protective effect of upper protective layer. The results show that the protective effect increases gradually when the thickness of the upper protective coal seam increases but is less than the thickness of the lower protected coal seam or the thickness of the upper protective seam increases and the deposit thickness of the protected coal seam increases. However, when the upper protective coal seam thickness Greater than the thickness of the coal seam is protected, the protection effect is basically the same. In the meantime, when the lithology of the rock formation between the upper protective coal seam and the lower protected coal seam is harder, the smaller the amount of plastic deformation and the decrease of the stress of the coal seam unit under protection, the poorer the protection effect is. Within the real coal rock, the horizontal stress drop is also larger in the area with big difference in lithology. The vertical extrusion of vertical stress and the horizontal shear of horizontal stress under the unevenly distributed goaf are the important reasons for the occurrence of plastic deformation and failure due to eccentric instability of the coal and rock mass unit in the floor.