Abstract
To prevent serious shaft deflection disasters under asymmetric mining conditions, it is urgent to solve the problem of designing shaft protection rock pillar (SPRP) sizes in thick soil and thin rock strata. In this paper, based on the parallel mining model and the perpendicular mining model, a dynamic prediction model that can describe the horizontal movement of the shaft was established by the probability integration method and the Knothe time function. Next, according to the measured data of the shaft deflection in the Guotun Coal Mine, a back analysis was used to calculate the prediction parameters that were suitable for the deep soil strata. Based on the mining model, the variation law of the horizontal deflection displacement of the shaft and SPRP size was obtained. The results showed that the final displacements of the shaft under the two ideal mining models were equal, while the parallel mining model was superior to the perpendicular mining model at the initial stage of mining. The horizontal displacement of the shaft head had a nonlinear negative correlation with the SPRP, and the SPRP size in thick soil and thin rock strata calculated by the parallel mining model was more reasonable. For the Guotun Coal Mine, when the soil movement angle was 57.8% of the actual value, the horizontal displacement of the main shaft head was reduced by 87%. The results have important theoretical and practical value in preventing shaft deflection in thick soil and thin rock strata.
Highlights
Since 2002, a large number of vertical shafts have been built in deep soil strata in China
Mine was 77.8% and 57.8% of the actual movement angle (i.e., 45◦ ), the horizontal displacement of the main shaft head was reduced by about 50% and 87%, respectively
This indicates that the shaft deflection can be effectively attenuated by appropriately reducing the soil movement angle used to design the shaft protection rock pillar (SPRP) in thick soil and thin rock strata
Summary
Since 2002, a large number of vertical shafts have been built in deep soil strata in China. Vertical shafts with soil thicknesses exceeding half the total depth account for 86% of the shafts (see Figure 1). Underground mining activities may cause the shaft to deflect and subside, which significantly affects hoisting safety and poses a great threat to lining safety. The design methods for SPCPs are basically similar, and existing SPCPs are mostly designed by experience or angles. Due to the large size of SPCPs designed by empirical methods, the boundary angle or the movement angle has been used to design SPCPs in European coal mines [1] and is stipulated in existing criteria [2] and manuals [3] in China. Zeenke et al studied the shape and size of SPCPs in the Energies 2019, 12, 2553; doi:10.3390/en12132553 www.mdpi.com/journal/energies
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