Abstract
The main shaft and auxiliary shaft in the Guotun Coal Mine underwent large deflections, with deflection values of 359 mm and 322 mm, respectively. These two deflections represent the first occurrence of such large vertical shaft deviations in the soil strata in China. The deflection problem has seriously affected the hoisting safety and lining safety and has become a serious impediment to the sustainable production of mines. Therefore, the deflection mechanism must be determined. For this purpose, based on mining subsidence theory, the spatial probability integral method and a more accurate time function were used to establish a model, called 3D dynamic prediction model, for predicting the shaft movement. The formulas for calculating the lining stress caused by coal mining were based on established models. With measured shaft deflection data, the prediction parameters for deep soil strata were calculated on the basis of an inversion analysis. A comparative analysis of measured and calculated deflection values revealed that the reason for shaft deflection in Guotun Coal Mine is the insufficient size of the protection coal pillar (PCP); namely, the design parameters of the PCP in current codes are not applicable to the deep soil strata. As a result, under the asymmetric mining conditions, mining causes the shaft to deflect without damage and under the symmetric mining conditions, mining causes the lining to fracture. The results have an extremely important significance for the prevention and control of shaft deflection, for the rational design of PCP, and for the sustainability of mine production.
Highlights
Since 2002, China has built 71 shafts with soil thickness over 400 m, and 86% of these shafts have a soil thickness greater than half of their depths (Figure 1). e shaft is regarded as the throat of a mine, and its safety concerns the survival and sustainability of the entire mine
To further verify the feasibility of the prediction parameters, the auxiliary shaft was taken as a case. e horizontal displacements of the auxiliary shaft were expressed by ua. e theoretical values and the measured values in 2015 and 2017 are shown in Figure 10. e errors in two times were only approximately 7% and 2% of the measured values at the shaft head, respectively, which indicated that the calculation results were still highly reliable considering the measurement error and the difference between the main shaft and auxiliary shaft
The theoretical and measured values, the following conclusions were obtained: (1) e shaft de ection mechanism in deep soil strata was as follows: under the conditions of asymmetric mining, the mining caused the soil around the shaft to produce di erent displacement magnitudes at di erent depths, resulting in the vertical and horizontal displacements of the shaft within the range of mining in uence
Summary
Since 2002, China has built 71 shafts with soil thickness over 400 m, and 86% of these shafts have a soil thickness greater than half of their depths (Figure 1). e shaft is regarded as the throat of a mine, and its safety concerns the survival and sustainability of the entire mine. Based on the above analysis, mining subsidence theory was used to clarify the shaft deflection mechanism in deep soil strata. E key to the probability integral method is the solution of prediction parameters For this purpose, Guo et al [11] obtained more precise results by applying the theory of artificial neural network to this method, Zhang et al [12] provided a highly effective method based on least squares support vector machine theory, and Han et al [13] calculated the parameters that are suitable for deep soil strata by a back analysis. Combined with the probability integral method, a 3D dynamic prediction model was established to reveal the shaft deflection mechanism and to analyse the lining safety in deep soil strata. By comparing and analysing the theoretical and measured horizontal displacement values, the feasibility of the model was proved and the shaft deflection mechanism was clarified. e results in this paper are of great significance to the sustainability of mine production
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