Abstract
Horizontal sublevel caving is the unique way to mine the steep and extra thick coal seams. We aim to determine reasonable height of horizontal subsection, which is crucial to ensure the output and safety of mining. For this aim, a theoretical model is established to determine the theoretical solution of elastic stress distribution in deeply inclined coal seam, and first principal stress expression is derived. And on this basis, related factors affecting the top coal caving property and key delayed-action areas are investigated. The results show that there are four zones in top coal, which are tensile failure zone (TFZ), tensile damage zone (TDZ), elastic zone (EZ), and compression-shear damage zone (CSDZ). The elevation of sublevel height cannot increase the release of top coal. It is necessary to determine the key region of affecting the top coal caving. The key delayed-action region (KDAR) consists of EZ and TFZ in top coal; the EZ and TFZ are type I and II KDAR, respectively, and type I is the key area of weakening top coal. In order to effectively weaken KDAR, opening coal channel of core region, and especially effectively obstructing the continuous moving upward of top coal caving arch structure with the help of weakening top coal body in type I KDAR, would promote caving property of top coal and improve the working face extraction rate.
Highlights
E method only relied on compression of mine and effect of support would not make sure the top coal can be effectively mining [18, 19]
Elastic solution of stress distribution is analysed based on top coal mechanical model, and first principal stress expression is derived
The most dangerous situation of top coal mining is that when the coal breaking effect by support is finished, the stable top coal structure is formed in upper part of top coal, which will generate separation between the loose coal and upper top coal
Summary
Considering the top coal is deformation body and stress boundary conditions, σx, σy, and τxy, should be independent. From formulas (5) and (6), the deformation potential energy expression represented by stress function is as follows:. Considering the stress and displacement boundary conditions of coal body, take stress variation equation as follows: zU. Formula (16) is the first principal stress expression at any point of the parallelogram top coal body. E analysis of formula (16) shows that the first principal stress in the top coal is related to the load intensity q, coal seam dip angle α, sublevel height h, and the working face length 2a, in which only the load intensity q is linear with the first principal stress, and the rest are nonlinear relations with it. From the perspective of top coal caving, the researchers should pay attention to the falling height of the top coal. erefore, the researchers choose the point which is 5 m with the lower boundary of top coal from y axis to study the influence of the relevant factors on the first principal stress
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