Understanding the formation mechanism of bed separation in coal seam mining under a karst landform is needed for the prevention and control of roof-separated water damage in such areas. This research used a mine in the northern Guizhou coalfield, China, as a case study, and applied theoretical analysis, numerical simulation, and on-site measurement to develop a circular cave structure model in a key stratum. The dynamic evolution of a separation bed was analyzed from several aspects, including the formation mechanism, development location, the mechanical condition of local karst caves, fracture evolution, and fractal rules. Verification using in situ measurements is presented for the case study mine, and a quantitative evaluation method for water inrush from bed separation and improved fusion weighting is proposed based on a cloud model. The research results indicate the following: (1) Tensile cracks are prone to occur above and below a karst cave, which produce an impact of connectivity on the separated space. (2) When the working face advances to 270 m in coal mining, longitudinal tensile cracks below the karst cave gradually increase and the width of the bed separation crack shrinks to 68.2 m, with a maximum separation layer height of 3.01 m. (3) Based on the cloud model and the improved weighted fusion method, the risk of water inrush in bed separation is judged as “high”. The E_n of the cloud digital features is 0.0622 and the H_e is 0.0307, achieving a quantitative evaluation of water inrush in the separation layer that is consistent with on-site practice, and is highly stable and reliable. This study improves the understanding of the development pattern of bed separation and water inrush risk assessment in coal seam mining under a karst cave landform.

The surface subsidence caused by underground mining is a spatiotemporal process. The impact of mining on surface structures (houses, highways, railways, dikes, etc.) and structures in rock strata (shafts, roadways, chambers, etc.) is a dynamic process. It is necessary to study the dynamic movement law of the surface and overlying strata in the mining process of the working face to predict the extent of the impact of mining on the aforementioned structures. It provides a reference for pre-reinforcement and post-mining treatment. This paper studies the variation of surface dynamic movement based on the survey line above the working face of Peigou Coal Mine. The numerical simulation model of the overlying strata dynamic movement is established to study the dynamic movement law of rock strata with different depths, and the fitting function of surface and overlying strata dynamic movement is determined. Finally, the subsidence velocity prediction function of the major section of the surface and overlying strata in the Peigou Coal Mine is established. The accuracy of this prediction function is demonstrated by contrasting the subsidence and subsidence velocity curves of the surface subsidence basin survey line with the numerical model. In this paper, a numerical simulation method for the dynamic movement of the surface and overlying strata and a function for predicting the subsidence velocity on the strike major section are established, which provides an important theoretical reference for the dynamic protection of the structures on the surface and in the overlying strata.

In order to study the effect of interlayer thickness on the deformation and strength characteristics of interbedded sandstone under load, uniaxial compression and conventional triaxial compression tests were carried out on four interbedded medium-grained sandstone samples with different interlayer thickness, accounting for different proportions of the total height of the sample (5%, 10%, 15%, and 20%). The samples were from the Shendong Mining Area and investigated using an RMT-150C rock mechanics test system. Then the stress–strain curve characteristics, strength characteristics, and failure characteristics of the interbedded medium-grained sandstone with different interlayer thickness were analyzed, and the applicability of Mohr–Coulomb strength criterion and Rocker criterion to interbedded medium-grained sandstone with different interlayer thickness was evaluated. The research results show that, as the thickness of the interlayer gradually increases, the uniaxial compressive strength of the sandstone containing the interlayer first decreases and then increases; as the thickness of the interlayer increases, the elastic modulus of the sandstone containing the interlayer gradually decreases, and the peak strain increases gradually; the thickness of the interlayer has little effect on the triaxial compressive strength of the sandstone containing the interlayer. When the thickness of the interlayer is small, the deviation of the fitted uniaxial compressive strength of the Rocker strength criterion is relatively small, and the applicability is good; the prediction result of the uniaxial compressive strength of the Mohr–Coulomb strength criterion is better; for the tensile strength of the interlayer rock, the Rocker strength criterion has good applicability. The existence of the interlayer hinders the development of medium-grained sandstone cracks, but this effect is weakened with the increasing thickness of the interlayer. The research results are helpful to further reveal the movement law of overlying rocks in Shendong mining area, and provide basic parameters for related research.