Abstract
Overburden conditions consisting of ultrathick and hard stratum (UTHS) are widespread in China and other countries, but existing surface subsidence prediction methods ignore the strong impact of UTHS on surface subsidence. They are thus not applicable for surface subsidence prediction for coal mining with the presence of UTHS. We conducted actual measurements of surface and UTHS subsidence in the Tingnan Coal Mine. The results showed that under the UTHS mining condition, the required gob dimension is much larger than the empirical value when the surface reaches sufficient mining and that the actual measured maximum value of surface subsidence is much smaller than the empirical value. The UTHS subsidence is approximately equal to the surface subsidence. The movement of UTHS has a strong impact on surface subsidence and has a controlling function for it. It was proposed that surface subsidence could be approximately predicted by calculating the UTHS subsidence. The UTHS movement characteristics were studied using Winkler’s theory of beams on an elastic foundation, the subsidence prediction equation of the main sections in the strike and dip directions was obtained under different mining dimensions, and the subsidence prediction equation of any arbitrary cross section parallel to the two main sections was established. Then, the surface subsidence prediction method for coal mining with the presence of UTHS was developed, and the influences of UTHS thickness, strength, and layer position on the surface subsidence were discussed. The Tingnan Coal Mine was taken as an example, and the subsidence curves of the strike and dip main sections were calculated using different mining dimensions. Subsequently, the surface subsidence after the mining of working faces 204, 205, 206, and 207, respectively, was predicted, and the prediction method was verified by comparing the results with the measured surface subsidence results of working faces 204, 205, and 206.
Highlights
Coal mining inevitably leads to movement of overburden strata and surface subsidence, and surface subsidence can result in massive lowering of the surface, damage to construction works, geological disasters, and damage to farmland, which have strong impacts on the ecological environment and the normal production of human society [1,2,3,4,5,6]
(4) When neither of them reaches sufficient mining, the ultrathick and hard stratum (UTHS) deflection curve equation of main section I can still be calculated through equation (9), but the equation needs to be multiplied by a coefficient, λΙΙ, which is shown in equation (17). e subsidence of main section II can still be calculated through equation (11), but this equation needs to be multiplied by a coefficient, λΙ, which is shown in equation (16)
We investigated the influences of UTHS thickness, strength, and layer position changes on the surface subsidence of main section I when main section II of the Tingnan Coal Mine reaches sufficient mining with the mining dimension of main section I of L1 660 m using the proposed prediction method
Summary
Coal mining inevitably leads to movement of overburden strata and surface subsidence, and surface subsidence can result in massive lowering of the surface, damage to construction works, geological disasters, and damage to farmland, which have strong impacts on the ecological environment and the normal production of human society [1,2,3,4,5,6]. When the overburden strata includes UTHS, considering the overburden strata as a homogenous medium is obviously an oversimplification of the overburden condition, which ignores the control function of UTHS on surface subsidence It does not relate surface subsidence with the movement of UTHS and does not consider the strong influence of the characteristics of movement of UTHS on surface subsidence. A surface subsidence prediction method for coal mining with the presence of UTHS must consider the control function of UTHS on surface subsidence. We studied the UTHS movement characteristics using Winkler’s theory of beams on an elastic foundation, developed a surface subsidence prediction method for coal mining with the presence of UTHS, and evaluated the influences of UTHS thickness, strength, and layer position on surface subsidence. We took the Tingnan Coal Mine as an example and calculated the subsidence curves of strike and dip main sections with different mining dimensions. en, we predicted the surface subsidence after the mining of the 204, 204 + 205, 204 + 205 + 206, and 204 + 205 + 206 + 207 working surfaces and verified the accuracy of the predicted results using the actual measurement results of surface subsidence of the 204, 204 + 205, and 204 + 205 + 206 working surfaces
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