Study on the law of surface subsidence in layered mining of thick coal seam with medium hard roof.

In this study, the change law of the surface subsidence coefficient under the condition of thick coal seam layered mining was investigated. The study is based on the measured subsidence data of the 1210-working face of the Mengba mine surface mobile observation station after the first- and second-layer mining. UDEC numerical simulation software was used to simulate the variation of surface subsidence coefficient after the first, second, third, fourth, fifth-, and sixth-layer mining when the thickness of slicing mining is 5 m. The maximum relative error between the simulated result and the measured result of the subsidence coefficient q is 2.7%, which further verifies the correctness of the established model. Moreover, the simulation results show that with the increase of the cumulative mining thickness, the subsidence coefficient q of the surface presents a segmented characteristic. When the cumulative mining thickness does not reach 25 m, the subsidence coefficient of the surface gradually increases with the increase of the mining thickness. On the other hand, when the cumulative mining thickness reaches 25 m, the subsidence coefficient of the surface will tend to a constant value and no longer change with the increase of the mining thickness. Finally, the calculation formula between the surface subsidence coefficient and the cumulative mining thickness of layered mining under the condition of medium hard roof is fitted, which provides a parameter basis for coal seam mining with similar geological conditions.