The space structure and scale of mined-out area are dynamical variable using high-sublevel fullymechanized coal caving in steep and thick coal seam. Due to segment pre-blasting, the degree of coal damage and cracks would be increased, and the complexity of the physical-geometric structure and time-space relationship of the mined-out-area would be enhanced. Firstly, the comprehensive analysis of complexity of the B1+2 workings environment and the mining technology character at Weihuliang coal mine, and the blasting parameter optimization, dynamite quantity and blasting effect were also optimized. Then, the pre-blasting was applied successfully in 52m sublevel caving and effective deteriorate coal-seam. Finally, the effect had been detected and verified by RSM-SY5-broken-zone device and YS(B)-optic-borehole-camera. It was obviously indicated that the average-forces of the front and behind support were raising based on field monitoring results. All of these could be used as referencing for the subsequent safe mining to the 102m and 18m sublevel-top-coal caving.


During the top-coal caving, the weakening and the accessibility of the top coal directly determine its fully-breaking and its release safety and efficiency (Xie et al. 1999, Shi et al. 2006, Kang et al. 2004, Chen et al. 2002) The mined-out area caused by using high-sublevel fully-mechanized coal caving in steep and thick coal seam is a spatial structure of varying sizes (or dimensions). Due to the segment pre-blasting, the development of coal damage and cracks, the complexity of the physical-geometric structure, and the time-space relationship of the mined-out all increased (Gao et al. 2001, Wang 2007, Shao et al. 2007). Weihuliang coal mine is a mine of low gas. The +579E2EB1+2 steep seam (from 64° to 69°) is a high level top coal caving workface, which is along the strike direction of the B1+2 coal seam, and there are some coal pillars with different heights, respectively 52m, 102m and 18m. During the mining of the 52m coal pillar, several times of large-scaled dynamic collapse occurred, which led to people hurts caused by some harmful gases which were squeezed into the workface.

To ensure fast and safe caving, segment pre-blasting of the 52m coal pillar must be carried out. Analyzed from some aspects like the complexity of the workface, the optimization of the blasting parameters and the techniques, the amount of explosives, and the blasting effects, the segment pre-blasting was finally successfully implemented at the position where it is 100m ahead of the workface. And this can provide some references of the mining of the follow-up process, which will be done to the 102m coal pillar and the 18m coal pillar.

2.1 Geological conditions and characteristics of in-situ stress

The joints in the B1+2 coal seam are fully developed. The structure of the coal seam is complex, and its roof and floor and loose. The strike direction of the seam is 55°, its dip direction is 325°, its dip angle is from 64° to 69°, and its f-factor is 3.

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