Coal pillar pre-blasting project of Hanjiawan coal mine when fully mechanized working face passes through the upper coal room and pillar goaf
1. Introduction
Shendong mining area, a typical area of close distance between shallow seams，has turned into the mining of the second coal seam step by step. Due to the coal pillars left in the upper first coal seam, many support crushing accidents have happened in the mining of the lower second seam while the working face is out of the upper coal pillar in the area 5m away from the coal pillar boundary. Violent weighing phenomenon occurred in the accidents, such as sharp and huge shrinkage length of support plunger in 1~2 minutes. According to incomplete statistics, 7 similar cases have happened since 2007, which had caused nearly the economic loses of one million RMB yuan and had been threatening the safe and efficient production of the coal mines in the mining area. So, how to insure the safety during mining out of the upper coal pillar is a significant technical problem.
Picture of the crushing support in No. 22103 working face of Daliuta coal mine
2. Treatment solution
Creative control technology was put forward, that is to drill some super deep upward holes from the both sides of the lower coal fully mechanized working face, these holes penetrate the interlayer strata and upper coal remained concentrated coal pillar and its immediate roof with designed depth, pre-blast remained concentrated coal pillar of the upper coal and its immediate roof, the technical principle is shown in the schematic diagram.
Technical schematic diagram
3. Construction situation
In order to prevent the support crushing disaster, a technique is presented for pressure relieve blasting of concentrated coal pillars with the super long upward hole through analysis of the theory of disaster prevention by pressure relief and loosening blasting with super long upward holes. Three technical difficulties have been solved through field practices and some experiments. First, an explosive charging device was developed by ourselves for quick explosive charging even to 110m hole depth with the angle to 30°. Second, the optimal spacing of blasting holes was found through theoretical calculation. Third, the safe detonation and elimination of plugging of the super long upward hole was achieved through the explosive test and the setting property test of cement-silicate grouting.
Detonation test in an open pit
4. Achieved accomplishment
Aimed at evaluation of the control effect, one comprehensive evaluation technology was put forward, it includes the micro seismic monitoring technique, seismic wave CT technology, surface movement observation and mine pressure monitoring. The successful blasting of the concentrated coal pillars in two working faces proved that the technology has engineering reference and application significance.
Figure 1 Distribution of micro-seismic monitoring seismic events in working face 3302
Figure 2 Total energy release of seismic events in working face 3302
Figure 3 The wave velocity difference distribution of the seismic computed tomography before and after blast
Figure 4 Settlement deformation of surface before mining in the blast area
Figure 5 The display of mine stress when mining in the blast area
5. FAQ
Q1: How to ensure these holes drilled to the designed location?
A: In order to ensure these holes drilled to the designed location, we use directional drilling machine manufactured by our company, acquired good result.
Q2: How many tons of explosive need to blast one fully mechanized working face?
A: Commonly it depends on the types of explosives, the amount of boreholes, we used 4.5 tons of water gel explosive for one fully mechanized working face.
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