The Influence Of Coal Seam Floor's Rockmass Structure On Mining Effect

Rockmass structure is one of the controlling factors to coal seam floor's stabilization, and it has an important influence on the mining effect of coal seam floor. In order to research the breakage depth and range, the stress change caused by different coal seam floor structure, supply reasonable parameters and advice for coal mine, the following work has been carried out: the mining effect numerical simulation of two coal seam floor types which are integrated horizontal layer structure and coal seam floor that has fault in, the test of physic and mechanical parameters and the structure of coal seam floor in II 614 working face of No.2 Liuqiao coal mine, the mining effect numerical simulation and the quake wave CT test of breakage band in II 614 working face. The influence of coal seam floor's rockmass structure on mining effect and the band division of breakage zone of coal seam floor are analyzed, the main conclusions are as follows:1. The breakage depth is large in the two ends and small in the middle under the mined area. The breakage depth grows as the length of working face grows and the strength of coal seam floor reduces. When the compressive stress comes for the first time, the stress of coal seam floor changes from linear change before mining to nonlinear change after mining, above the stress adjust point is stress decreasing area and below it is increasing area. When the coal seam floor is composed of different kinds of rocks and arranged in different patterns, the breakage depth and stress change will be different, the structure effect is obvious.2. When there is a fault in coal seam floor, the breakage depth will increase and the stress change will be more complicated. The smaller dip angle and the longer length of fault, the larger breakage depth of coal seam floor. Fault zone and its adjacent rockmass are stress concentration areas, they will be easily destroyed. When mining along fault's trend, the fault zone is compressed closer, compared with mining against fault's trend, the coal seam floor is more steadily.3. The coal seam floor of II 614 working face is mainly made up of three sections: the top section is sand stone of integrated block structure, the middle section is silt stone of block structure, the bottom section is mud stone of layer structure. As a whole, the coal floor of II 614 working face is a type of top hard and bottom soft rockmassstructure.4. The results of breakage band CT test shows: the maximal breakage depth is 14.9m. The strong breakage band is from 0m to 9.8m, the disturbance band is from 9.8m to 14.9m.5. The results of numerical simulation shows: the breakage depth in wind lane is 15.22m, which is accordant to the result of field breakage band CT test. So applying numerical simulation to predict the mining effect is feasible.6. The breakage band of coal floor can be divided into to two parts: the strong breakage band and the disturbance band. In the strong breakage band, the rockmass is completely destroyed by shearing action first and then tension action. The crannies link to each other and the rockmass lose its strength and waterproof ability. In the disturbance band, crannies are formed by shearing action in the rockmass, but they are closed and don't link to each other. So the coal seam floor still has certain waterproof ability.