This study presents stability analyses and a cable bolt support design for a typical deep large-span stope (1-1# stope) at the Hongtoushan mine in China, using an integrated empirical and numerical method. Detailed field work including quantification of joint distribution and surface quality, along with laboratory test on intact rock samples, were performed to obtain the geotechnical properties of rock masses. The rock mass of the 1-1# stope was characterized by rock mass rating (RMR), rock mass quality (Q), and geological strength index (GSI), and then the modulus, peak strength, cohesive strength, and internal friction angle of the rock mass were estimated. The stability of the stope was then evaluated by empirical (RMR, stability graph) and numerical approaches (limit equilibrium analyses with UNWEDGE and stress-strain analyses with FLAC3D), considering of the effects of rock mass quality, induced stress, and large-span. A cable bolt support system obtained from the empirical method, was then further analyzed using the FLAC3D and UNWEDGE codes. The results show that the maximum plastic zone thickness and vertical displacement at the stope roof decrease significantly and the safety factor of the unstable wedge block increases significantly after installing the cable bolt support systems recommended by the empirical method. Therefore, it is suggested that an integrated empirical and numerical method is used to obtain quantitative stability assessment and optimum cable bolt support design for deep large-span stope roofs.

The Yangjiacun coal mine, located in western China, exhibits distinctive characteristics, such as its shallow depth, thick bedrock, thin loose layer, and unique roof strata breaking movement. In this research, a comprehensive analysis of previous exploration data, subsequent mechanical testing, key stratum theory, natural equilibrium arch theory, and simulation tests and numerical simulations has been conducted to investigate the failure behavior of the overlying rock strata in the Yangjiacun Coal Mine. Specifically, the load‐bearing capacity of the key stratum structure in the bedrock and the morphological properties of the arch‐beam structure have been thoroughly examined. A mechanical model of the roof rock arch‐beam structure has been established, and an analytical formula for the limit size and stability criterion of the arch‐beam structure has been derived. The mining‐induced rock arch‐beam structure plays a crucial role in transferring the load of the upper strata to the surrounding goaf, thereby preventing subsidence and deformation of the overlying strata. However, the arch‐beam structure periodically experiences instability during the advancement of the working face, gradually progressing towards the upper layer until the main key stratum is breached and the arch‐beam structure collapses. Based on the characteristics of weathered rock and the arch‐beam failure model in the Yangjiacun Coal Mine, quantitative backfilling mining methods have been proposed to either compensate for the mining void created by coal extraction or limit the size of exposed key strata through strip mining, ensuring the stability of the R6 key stratum. This study represents a significant contribution to understanding the intricate failure behavior of overlying rock strata in coal mines and provides a valuable framework for the responsible and efficient extraction of coal resources in similar environments.

The massive emission of low concentrations (≤0.5%) of methane (CH₄) from ventilation roadways results in resource waste and environmental pollution. To mitigate these emissions, an enrichment tower for low-concentration methane is designed, and segregation and non-segregation experiments are conducted. The results reveal that stable concentrations of methane under segregation and non-segregation states in the enrichment tower gradually increase with height, with a maximum methane concentration of 0.64% and 0.54%, respectively. This shows that the methane enrichment effect in free diffusion conditions is more significant under the segregation state than under the non-segregation state. The stable concentration of methane in the middle and upper sections of the enrichment tower shows an increasing trend. However, the stable concentration of methane in the lower section of the enrichment tower has an increasing trend (less than 0.50%). According to the methane molecule Boltzmann distribution law, methane concentration enrichment decreases with height, and the conversion of the methane from the segregated to non-segregated is irreversible. Consequently, industrial applications of methane enrichment from buoyant forces are not feasible for low concentrations of methane.

The failure of surrounding rock in deep hard rock roadway is closely related to mining disturbance. In this study, the 13# stope ramp of −767 m level (at a buried depth of 1,197 m) at Hongtoushan copper mine was taken as the engineering background, a comprehensive analysis method of numerical analysis and borehole detection was put forward, and the evolution law of fracture depth of the ramp surrounding rock under the mining influence was obtained. The results show that the maximum tangential stress and fracture depth of the ramp surrounding rock on both sidewalls increase slowly at the initial mining stage. When the ore body above the ramp is mined, the maximum tangential stress and fracture depth of the ramp surrounding rock on both sidewalls increase rapidly, and the two parameters are positively correlated. Based on this, the ratio of the maximum tangential stress of the surrounding rock to the uniaxial compressive strength of intact rock (σ_θmax/σ_c) and the equivalent radius (a) of the roadway were used as parameters, and an equation for the fracture depth of the roadway surrounding rock was proposed. Through the case analysis, the results show that the proposed equation of fracture depth of the roadway surrounding rock has good prediction accuracy. This study enriches the research on the stability and failure mechanism of the roadway surrounding rock under the mining disturbance, and provides new basis for the support design of mining roadways.

The safe and efficient extraction of ore bodies under buildings contributes to the continued exploitation and utilization of mineral resources. To effectively reduce the mining-induced disturbance caused to surface buildings, the Vertical Crater Retreat (VCR) delayed backfilling method was applied at the Wuji iron mine according to mining theory and engineering experience, and the surface deformation under buildings was investigated through numerical simulation and on-site monitoring. The results show that stress concentration occurs at the top of the ore body and in surrounding rocks between ore veins, and the direction of the principal stress coincides with that of the main bearing capacity of the rock mass. With the increasing distance between the surrounding rock and the ore body, the stress disturbance in the surrounding rock attenuates gradually. The surface subsidence and deformation caused by ore mining exhibits the same northwest trend as the strike of the ore body, and the surface deformation in the X direction is greater than that in the Y direction. The surface deformation of the mining area near the 1# air shaft, Wuji village, steam autoclave workshop of the brick factory, and 1# substation is relatively large, while the surface subsidence, horizontal deformation, inclination, and curvature are all smaller than the critical values allowed for buildings and structures. This research provides a theoretical basis and engineering guidance for the prevention and control of surface deformation during mining under buildings and structures.