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Introduction
Steeply inclined coal seams account for about 4 % of China’s total reserves of coal; 80 % of these steeply inclined coal seams exist in southern China, while a few are distributed in northeast and central China (Xie et al. 2007). The goaf formed by the mining of shallow coal seams is often saturated with water due to communication with rivers on the earth’s surface. When lower coal seams are mined, the overlying water-filled strata can cause huge potential safety problems at the working face (Du and Wang 2005). Therefore, when a steeply inclined coal seam is mined under such conditions, barrier pillars must be designed to ensure safe mining, while minimizing coal loss.
Various analytical methods have been developed to determine the appropriate size of barrier and longwall coal pillars for different coal seam conditions (Gale 1996; Gui 1997; Jia et al. 2009; Mark 1992; Tang et al. 2006; Wu et al. 2004), such as when: the exit of key stratum in a steep seam can enlarge the falling range of a pillar, allowing water to more easily to enter the goaf (Li et al. 2012); the coal pillar obviously cannot reduce the height of a permeable fractured zone, and the pillar is subject to plastic failure, which would allow the fracture to connect with an aquifer (Liu et al. 2010); high content of clay minerals will result in weak permeability and regenerated water tightness, and the effective height of water flowing-fractured zone aligns with the caving zone height of overlying strata (Tu et al. 2004). In addition, a method for coal pillar design was developed based on the division of “elastic–plastic-failure” coal pillar zones (Li 2012; Liu and Ding 2001), an empirical method was derived from experience (State Bureau of Coal Industry 2000), and methods have been developed to design pillar layouts for potential variability in strata strength characteristics surrounding a coal seam (Gale 1998). In this paper, we propose a method to define coal pillar design, goaf filling, and grouting for mining a steeply inclined coal seam under overlying strata that contains water, to prevent seepage and ensure safe production in a mine that engages in blasting.
Theoretical Analysis
Analysis of the Appropriate Size of the Barrier Pillar
Up-dip longwall mining...