In order to explore the development characteristics of overlying strata cracks and"two zones"under the geological conditions of deep-buried and extremely thick coal seam,taking Zhundong No.2 Mine as the engineering background,the method of combining numerical simulation and physical similarity simulation is adopted to reveal the evolution law and prop-agation mechanism of overlying strata cracks in fully mechanized top-coal caving face in extremely thick coal seam,and the development height of"two zones"is determined.The results show that the overlying strata fracture field is trapezoidal,and the cracks in the caving zone are interconnected and crossed to form a complex fracture network.Local tensile stress concen-tration leads to contact fracture-initiated micro-cracks,and with the increase of working face advancing distance,micro-cracks gradually expand and connect with each other.On the surface of similar simulation results,the development of overly-ing strata fractures tends to be higher with the increase of mining space,and the evolution process of fractures in the strike direction is"initiation-opening-increasing-decreasing-closing".The maximum heights of the caving zone obtained by similar simulation and numerical simulation are 92 m and 96 m,respectively,and the fracture zone develops to the surface.The de-velopment laws of the two zones obtained by the two research methods are basically the same.
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