Improve The Fully Mechanized Gaving Working Face Initial Mining Of Coal Recovery Rate Of Pre-splitting Blasting Method And Its Effect Analysis

The key of fully mechanized caving technology in the applications is coal recovery rate, and initial mining losses are the most important loss in the fully mechanized caving mining working face. For hard roof, if the roof can collapse in time, it can weaken the initial impact load on the bracket and avoid the gas transfinite and mine pressure resulting from the sudden collapse of most part of the roof, in the end, it can ensure the safety production during the initial mining. Doing the pre-slitting blasting by drilling a hole through the roof behind the open cut eye frame is a way to improve the early mining coal recovery rate, and it is of great significance for improving top coal recovery rate in the caving initial mining. In this paper, the author will probe into the main problems of this method.(1) By theoretical calculation of the main parameters of the deep hole pre-splitting blasting, this paper makes a blasting proposal for the3407working face of Tang An Mine. In the proposal, the explosive will be the third class emulsion explosive for the mines, and the explosive roll diameter is60mm, hole diameter is75mm, blast hole spacing is3.5m, vertical depth is12m, elevation angle of blast hole is45°to75°, borehole depth is12.5m to17m, continuous decoupling charge, and decoupling coefficient is1.25, the amount of explosives of each blast hole is33kg, one charge, each detonating leads to three blast holes.(2) During initial mining, the way of deep hole pre-slitting blasting is used for the roof cutting. Therefore, the roof structure will become cantilever structure instead of clamped-end beam structure; the step pitch of cantilever structure is smaller than that of the clamped-end beam structure. In this way, it can greatly reduce the step pitch of initial pressure, and in the end ensure the safety production during the early mining.(3) This paper uses the LS-DYNA2D software to simulate the blasting situation of the single hole and three holes respectively of3407working face of Tang An Mine. Through this, there is a visual picture of the blasting stress wave propagation in the rock, and there is also the development process of the rock crack at different moments, therefore it verifies the rationality of3.5m blast hole spacing.(4) This paper uses the UDEC Software to simulate the roof breaking down of both no-cutting and blasting cutting of3407working face of Tang An Mine. When the working face is not cut, the immediate roof collapsing step is12m31.2m; after cutting the roof, the immediate roof collapsing step is7.2m, and the basic roof collapsing step is21.6m. The comparison shows that the immediate roof collapsing step is shortened for4.8m, and the basic roof collapsing step is shortened for9.6m, and there is a significant reduction of the basic roof collapsing step pitch after the roof cutting.(5) The vertical stress of blasting roof cutting increases faster than that of no-cut, and generally the vertical stress after the roof cutting is slightly larger than that of no-cut. All these can accelerate the roof collapse in advance; therefore shorten the initial pressure step pitch. The extent of the damage of top coal after the roof cutting is higher than that of no-cut, so that the top coal can be fully broken and in the end the top coal recovery rate can be improved.(6) The pressure Data of3405working face of Tang An Mine shows:the collapsing step pitch of the immediate roof is13.2m and that of the basic roof is32m. This is basically similar with that of the simulated working face3407, which proves the rationality of the simulation of3407working face.(7) If the deep hole pre-slitting blasting for roof cutting is applied on3407working face of Tang An Mine, the basic roof collapsing step pitch is expected to shorten for9.6m, and this means5600t more tons of coal could be exploited. The coal recovery rate will increase by14%during initial mining.