Research On Movement And Deformation Rules Of Rock Strata Between Coal Seams In Caving Method Upward Mining Of Left-Over Coal With Numerical Simulation

The structure, movement and deformation of rock strata between coal seams are the key factor of the feasibility study in upper mining and working on control measure. Original theory and traditional methods base the feasibility of upper mining mostly on the vertical spacing of coal seams, but not dynamic process of upper mining. Consequently, we should strengthen the study on the movement and deformation of the rock strata between coal seams, only in this way can intrinsic process of upward mining be completely described, and on this basis, the feasibility of upward mining can be judged further, and the control measure can be formulated more fully.In this paper, the model is established on the practical mining. Considering the initial stress field formed by the weight load, the upward mining is simulated by numerical simulation software. The monitory points are set up to monitor the movement and stress in model. Based on the results of numerical simulation, the control layer forms a beam structure which is supported by rock strata, and along which the stress deliver as a arch, and under which the stress is smaller, the rock strata separates with the control layer. At the beginning of upward, the stress in outside stress arch feet is bore by new beam structure forms over the roof of upper coal, and it makes the stress concentrate in the front of the upper coal face, and move with the upper coal face. The stress is supported by stress arch which move forward too, and transferred to the arch feet. In the process of upward mining, the control layer moves down under the stress, contrary, the lower rock stratum move under dead weight and horizontal stress. After the vertical stress move forward, the control layer turn to horizontal migration, and occur opposite dislocations with lower lay and coincidental dislocations with upper lay horizontal. The bed separations enlarge more. After upward mining, the diffuse indications of rock stratum under control layer diminish. The maximum displacement increment points of the control layer move forward, and the maximum displacement increment of the control layer is least from beginning to end.On the basis of study above, through the research of different models which are created by changing the group of the rock strata between coal seams, the stress of control layer and upper layer is bigger, but movement is lesser when there is control layer in the rock strata between coal seams, contrary, when there is no control layer, the movement of rock stratum increased obviously, and is 3～4 times when there is control layer.For further details, the transient electromagnetic method is used to prospect the situation of goaf and integrality of the rock strata between coal seams. Before upward mining, the lower goaf exist high resistance, but the control layer and surrounding rock show lower resistance because the structure of which is whole in the main. After upward mining, the rock strata between coal seams appear varying degrees of fracture in part, but the resistance of it in most part is lower than which of goaf. There is no wide range of collapse in control layer.As the results of drilling and tunnel detection, there is mining fissure under control layer which remain macroscopical completeness. There is separation between layers. Upper coal become loose because of leaving stress. The rock stratums appear as a basin in the middle of lower goaf. In the process of upward mining, there is no wide range of collapse and violent pressure stress at the mining face. The results of drilling agree with the results of mathematical model and practical mining.