The water inrush from karst collapse column (KCC) is a cascading, vicious cycle disaster caused by geological and mining activities, that can cause serious casualties and property losses. The key to preventing this risk is to study the mechanism of water inrush under confining pressure. Aiming at the investigationg the characteristics of the KCC named X1 in Chensilou mine, a series of methods, including connectivity experiments, water pressure monitoring tests in two side-walls, and numerical simulations based on plastic damage-seepage (PD-S) theory have been developed. The methods are used to test the security of the 2519 mining area, the damage thickness, pore water pressure, and seepage vector in the X1. The results indicate that the X1 has a certain water blocking capacity. In addition, with the decrease of confining pressure and increase of shear stress, deviatoric stress could cause the increase of permeability, the reduction of strength, and the reduction of pore water pressure in KCC. Therefore the increased effective stress in the rock will force the rock to become more fractured. Conversely, the broken rock could cause the change of stress, and further initiate new plastic strains, damage and pore water pressure until a new equilibrium is reached. This cascading water inrush mechanism will contribute to the exploitation of deep coal resources in complex geological and hydrogeological conditions.

The mining of shallow buried and thick coal seams may cause ground settlement, loss of surface water, and even soil desertification in arid–semi-arid climate zones. The key to protecting surface water resources through the technology of separated strata grouting is to study the evolution of the separation space under the key stratum (KS) with the change of strata. Aiming at the section of underground strata characteristics of F6202 and F6208 working faces, similar simulation tests under three typical geological conditions were carried out. Based on the experimental results, a theoretical calculation model was established, and the practice of separation grouting was carried out. The results show that, under the conditions of a thick coal seam with one KS, the structure formed by breaking strata below the KS was relatively unstable, and the separation space was relatively large, which is likely to cause serious ground settlement. More seriously, with the increase of the weakly consolidated layer and coal seam thickness, the increase of the ratio of rock to soil in the weakly consolidated layer, and the decrease of the thickness of the strata below the KS (two KS condition), the separation space was further increased. Based on the above analysis, combined with the real-time feedback data of the grout amount and pressure on hydraulic support, the position of the grouting borehole was determined, and the speed of mining advance was adjusted in time, thus effectively controlling the curvature of the ground settlement, protecting the integrity of the red clay layer near the surface, and consequently protecting water resources.

The water-blocking action of the clay Cenozoic overburden layer is an important factor that affects safety of thin bedrock coal seam mining. The change of thin bedrock thickness has an important influence on the deformation and failure of overlying soil layer. In this work, similarity simulation experiment is used and two indexes of failure height and crack density in soil layer are selected to analyze the influence of thin bedrock thickness on the deformation and failure of overlying soil layer. The experiment results show that the failure height of soil layer increases with the decrease of the bedrock thickness. The change of failure height is small when the bedrock thickness is greater than 30 m (mining thickness is 6 m), while when the bedrock thickness is less than 30 m, the failure height of soil layer increases rapidly with the decrease of the bedrock thickness. The main effect of the decrease of the thin bedrock thickness on the deformation and failure of the overlying soil layer results in the increase of shear/tensile cracks. The shear/tension crack density is 0.04 strip/m when the bedrock thickness is 70 m, while the shear/tension crack density increases to 0.14 strip/m when the bedrock thickness reduced to 20 m.

The water‐blocking properties of the clay layer at the bottom of the Cenozoic overburden in China are an important factor influencing the safety of thin bedrock coal seam mining. Clay has remolding properties that are unlike the nonreversible characteristics of cracks in brittle rock, and failure cracks in clay can reclose or continue to expand under the influence of different external factors. In this work, the soil layer on top of thin bedrock is the research object, and the influences of the particle composition, water content, soil layer thickness, and crack width on the crack development‐closure state of soil layer are analyzed by the orthogonal test method. Visual analysis shows that the order of influence of each factor on the stability of soil layer is the crack width, particle composition, soil layer thickness, and water content. The stability of soil layer decreases with increasing crack width and sand content and decreasing soil layer thickness; in addition, soil layer stability decreases first and then increases with increasing water content. Further variance analysis shows that the crack width and particle composition are key factors that impact the stability of soil layer and that the soil layer thickness has some influence, while the water content has little effect on the stability of soil layer. In addition, the crack will reclose when the sand content in soil is less than 50% and the crack width is less than or equal to 1.0 mm, and the soil layer is prone to further failure when the sand content in soil is more than 50% and the crack width is greater than or equal to 3.0 mm; when the soil layer thickness is 15.0 cm, its stability is better than when the soil layer thickness is 10.0 cm or 5.0 cm.

The previous analytical methods mainly focused on the analysis of orthotropic, transversely isotropic, or even isotropic materials, and little analyses have been conducted on nonorthogonal and extreme anisotropic material properties. In this study, the infinite skew anisotropic plate with an arbitrary-shaped hole are considered. Initially, two local Cartesian coordinate systems are established along the skew orientations in the plate, and the equations for the elastic constants of the material are established according to the transformation formulae under rotation of the coordinate axes. On this basis, the elastic compliance matrix for the skew anisotropic material can be obtained in combination with the engineering constants (Young’s modulus, Poisson’s ratio, and shear modulus). Subsequently, the complex variable method is utilized to derive the analytical solutions for stress along the hole boundary. The elliptical, hexagonal, and square holes perforated in skew anisotropic plates are used as examples, respectively, and the stress distributions along the hole boundary are analyzed for different external loadings. Finally, the theoretical method presented in this paper is verified by means of the Finite Element Analysis of ANSYS software.

A mechanical analysis model was constructed for the clay layer. Using a combined approach of theoretical analysis and numerical simulation, the failure state of this layer during coal seam extraction under thin bedrock conditions was investigated. The findings offer insights for evaluating the water-blocking performance of the Cenozoic clay layer and for preventing water inrush disasters in similar geological settings. The key findings are as follows: (1) The most critical factor governing clay layer failure is the amount of bedrock subsidence following collapse. As the subsidence of the fractured bedrock increases, the suspended section of the overlying clay layer extends, elevating its possibility to shear or tensile failure. (2) Variations in bedrock thickness markedly influence the subsidence of both the bedrock and the clay layer. Consequently, bedrock thickness is a primary determinant of the degree of damage sustained by the clay layer. (3) The minimum bedrock thickness required to prevent failure of the basal clay layer within the Cenozoic overburden ranges from 33 m to 38 m. If the bedrock thickness falls below 33 m, the clay layers will be damaged after coal seam mining, leading to a loss of their water-blocking capacity.