Abstract
Advances in coal mining technology and an increase in coal output are resulting in increasingly challenging conditions being encountered at coal seams. This is particularly so at thin coal seams, where a large number of hard rock layers known as gangue are often present, which seriously affect the normal operation of the shearer and reduce coal output. Therefore, the effective weakening of hard gangue layers in a coal seam is crucial to ensure that the shearer operates effectively and that coal output is maximized. In this paper, the weakening effect of deep-hole presplitting blasting technology on the hard gangue layer in a coal seam is studied via a similar simulation. Four test schemes are designed: (1) A blasting hole spacing of 200 mm with the holes offset vertically. (2) A blast hole spacing of 300 mm with the holes offset vertically. (3) A blast hole spacing of 200 mm with the holes parallel to the gangue layer. (4) A blasting hole spacing of 200 mm with the holes offset vertically and initiation of interval blasting. The effect of the different blasting hole spacings and arrangements and different detonation methods on the weakening of coal seam clamping by gangue is studied, and the best configuration is identified. This improves the effect of weakening the coal gangue layer by deep-hole presplitting blasting.
Highlights
Intensive coal production is causing mining operations to move to coal seams under increasingly adverse environmental conditions, significantly increasing the difficulty of coal mining [1, 2]
Strain brick #1 is located in the gangue layer near the blast hole, for which observation and analysis indicate that it is mainly affected by the blast stress wave and the strain produced by fissures around the blasting hole
More obvious stress concentration arises here due to the tangential stress caused by the superposition of the stress waves from the two blasting holes. e results show that the maximum principal stresses at both strain bricks are far greater than the 6 MPa compressive strength of the gangue layer and are able to play a role in weakening it; the maximum principal strain at strain brick #2 is about 3 times than that at strain brick #1
Summary
Intensive coal production is causing mining operations to move to coal seams under increasingly adverse environmental conditions, significantly increasing the difficulty of coal mining [1, 2]. Deep-hole presplitting blasting technology, which can be used to enhance the permeability of a coal seam to promote gas extraction [6,7,8,9,10,11,12], can be used to control hard interlayers in the coal seam [13, 14] Carrying out this type of blasting in the working face can precrack the gangue in the coal body into small blocks, destroying its integrity and making it looser, and so reduce resistance to the shearer during coal cutting and ensure the smooth progress of mining [15, 16]. Deep-hole presplitting blasting is carried out in similar simulation tests that vary the spacing of the blasting holes and the mode of initiation and the blasting parameters are optimized to improve the weakening effect of deep-hole presplitting blasting on coal seam gangue layers
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