Study On The Effect Of The Main Key Stratum On The Abutment Pressure

Distribution of abutment pressure will have direct influence on coal mine engineering problems, such as working face roadway support in advance, coal and gas outburst and rock burst. In order to obtain the distribution of abutment pressure ahead of working face, numerical simulation, theoretical calculation and mathematical methods were used comprehensively. The characteristic of the main key stratum’s influence on the abutment pressure ahead of the working surface was studied, and the assessment indicator of its impact degree was obtained. And the mechanical model was established to analyze the influence mechanism. The variation rules of main key stratum’s influence on the abutment pressure along with its thickness and layers were also studied and the condition that when main key stratum would influence the abutment pressure was obtained, and the corresponding prediction model was established. Finally, the prediction model was applied combined with Haizi coal mine in Huaibei. The following results have been achieved.(1) Through UDEC simulation, it is found that under the influence of the main key stratum, the peak concentration coefficient of abutment pressure decreases, however, the effect scope of the abutment pressure increases, and the abutment pressure decays much more slowly after the peak. The average absolute deviation is selected as the assessment indicator of main key stratum’s impact degree, and it is defined that the indicator reaching 0.05 means main key stratum having influence on the abutment pressure. When mining width is less than the critical mining width, the main key stratum has no effect on the abutment pressure; with the mining width increasing, the influence degree increases gradually and reaches the maximum value before the first breaking of the main key stratum, then fluctuates with the periodic breaking of the main key stratum.(2) Using the mechanics calculation model of elastic foundation beam and wedge of elastic mechanics, the stress of main key stratum transferred to the coal seam is solved. And the mechanism of influence on abutment pressure is that the bending stiffness of the main key stratum is bigger than the soft rock, and the subsidence of pivot point with the same mining width is less than the soft rock, however, the deflection scope is greater than the soft rock, in result, the stress of the main key stratum on the rock below exhibits the characteristics referred to above after transferred to the coal seam.(3) Through numerical simulation and theoretical calculation, the variation rules of the main key stratum’s effect on abutment pressure with its layer and thickness is studied. When the other conditions are the same, the more the main key stratum is far from the coal seam, and the greater the thickness of the main key stratum is, then the smaller the peak concentration coefficient of abutment pressure is, and the greater the effect scope is. The maximum degree of the main key stratum’s effect increases with the thickness of the main key stratum, and decreases with the distance to coal seam. When the distance from the main key stratum to coal seam is greater than the critical layer, the main key stratum has no longer influence on the abutment pressure.(4) Based on the results of numerical simulation, the predict model of the main key stratum’s effect on abutment pressure is developed using mathematical analysis method of linear regression. With the model applied to the II102 mining area of Haizi coal mine in Huaibei, it is concluded that the effect scope under the overburden rock condition reaches up to 294.8m. In result, II1026 conveyor roadway is in the stress concentration area after II1024 working face was mined. This explains the reason why dynamic disaster occurred at conveyor roadway of II1026 working face.