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Author: Admin | 2025-04-28
In the Tieer mining area are medium–hard rock strata, so the formula for calculating the height of the falling zone is selected:hm=100M0.49M+19.12±4.71(2)The crack belt calculation formula is as follows:hm=100M0.26M+6.88±11.49(3)where M is the thickness of the coal seam, and the ranges of the falling zone and crack belt are calculated. According to the above discussion and analysis, the structure diagram of the whole section of coal seam 9 to the surface is drawn, as shown in Figure 14. Finally, the results or rules of three kinds of experiments are compared and studied, and the relevant conclusions of the movement pattern of overburden and the form of development of separation space after mining of a thick coal seam are obtained.(1) With the advance of the working face, separation is generated from the bottom to the top. The time of separation existence is negatively correlated with the depth of the upper rock strata and positively correlated with the strength factor. The expansion of the separation space has a certain temporal effect, that is, it generally takes 20–30 days for the separation to reach its maximum from initiation, which is equivalent to the working face advancing 70–100 m, and the corresponding horizon height is 200 m.(2) If the lithologies of adjacent rock strata are similar, the thickness of the upper rock strata is larger than the thickness of the lower rock strata, and it also produces separation. The separation has a strong sensitivity to the thickness of the rock strata. The difference in the bending stiffness between two adjacent rock strata is the key to the occurrence of separation. The bottom surface of the thick and hard rock strata is undoubtedly the location of separation.(3) In the two stages of working face mining, the amount of separation in the separation zone is significantly different. In the first stage, the separation can generally reach 0.31 times the mining thickness of the coal seam, and the maximum can reach 0.58 times the mining thickness; in the second stage, the width of the separation seam is narrow, and the separation is small. With the fracturing of the overburden, the separation seam closes quickly.(4) Separation gradually develops from bottom to top. The lowermost separation tends to close with the emergence of the upper separation. For medium–hard strata and medium–thick coal seam mining, when the advancing distance reaches approximately 1/3 of the mining depth, separation above the fracture zone
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