Rainfall infiltration is the primary factor that induces landslides. In this paper, discrete element software (PFC^3D) was used to establish a novel rainfall infiltration model, which integrates water transfer, intensity decay and seepage force into the calculation of the moisture field. By applying this model to the rainfall infiltration analysis of a road slope in Nanping City, Fujian Province, China, the distribution law of water content, the functional relationship between shear strength and water content, and the calculation of permeability at different times can be obtained. The model was verified by comparing simulated results of water content with field monitoring data. The simulation error of water content is lower than 10%. Furthermore, this model application was validated by reproducing the pressure variation of the retaining wall on 12 May 2022. To obtain the accuracy of this model application, it was compared with saturated water content model and seepage force model. The comparison results of the three models showed that the simulation results of this model are best matching with the observation data. Moreover, the verification and validation indicate that our proposed model can be used to effectively analyze the rainfall infiltration of road slope.

In order to study the stability of rock layers and the change in volumetric water content at different stages of mining under an environment of heavy rainfall, a self-developed large-scale open-pit-to-underground-mining similar physical model was used, and the intensity of continuous rainfall was set at 40 mm/h. The results of this study show that fissures accelerated the instability of rock strata, and when spreading to different rock strata, they were prone to form subsidence cracks and produce collapse zones. The volumetric water content is closely related to the stability of the rock formation. An ‘arch-shaped collapse zone’ was formed in an interval of (0.9~1.8 m), and a convex spreading zone of volumetric water content was formed in an interval of (1.2~1.6 m). The infiltration line shows different diffusion patterns in different mining stages. In the early stage of mining, the volumetric water content infiltration line is roughly parallel to the slope; in the middle stage of mining, the infiltration line diffuses parallel to the two ends of the interface with the slope and diffuses convexly in the middle; in the late stage of mining, the infiltration line shows a pattern of rapid diffusion in the lower area, rapid diffusion in the middle area, and slow diffusion in the middle area. Therefore, in the process of the mining stage, it is necessary to focus on mining area fissure changes and monitor the point water content for sudden changes and other indicators. This study has certain guiding significance for safe production.

The exploitation and utilization of coal resources are closely related to sustainable social and economic development. To uncover the deformation and seepage patterns of coal on the mining process, this study devised a new stress program with simultaneous changes in axial and confining pressures, then performed coal seepage experiments at various gas pressures. The results show that the residual deformation exhibited a stepwise change, the relative residual deformation at the same level decreased gradually, and the increase in gas pressure led to a reduction in residual deformation. In each stress grade, the absolute permeability damage rate increased gradually, while the relative permeability damage rate decreased with the number of cycles, and the growth of gas pressure could decrease the permeability damage rate. The higher gas pressure led to a lower average energy dissipation ratio at each stress level and increased the rate of growth of elastic energy before destruction of the specimens. A higher gas pressure led to a quicker rate of change in damage variables at high stress levels. The findings have implications for the effective mining and sustainable development of coal resources.

With the continuous expansion of the depth and scale of mining, the mined-out area poses a major threat to the safety of mine production, the surrounding environment, and the lives of residents. Because of the potential safety hazards caused by the large-scale collapse of the mined-out area of metal mines, a treatment plan was formulated in combination with the actual geological conditions of the mined-out area under a metal mine in Henan Province. Through the comparative analysis of the treatment scheme, the blasting caving method is preliminarily selected to control the mined-out area. Considering that the roof of the mined-out area of the mine is strong and the area of the mined-out area is large, an optimized blasting caving method—Underground induced caving and roof cutting technique scheme. Considering the influence of geological conditions and surrounding rock, Flac3D was used for numerical simulation calculation, and the design of the Underground induced caving and roof cutting technique scheme and blasting operation was formulated. By canceling the pressure relief skylight project, unnecessary engineering expenditure is avoided, and the investment structure of the project is optimized. Through the on-site blasting practice, the roof of the mined-out area gradually collapses, and the precise damage induction of the roof of the mined-out area is realized. Finally, a stable waste rock overburden is formed, which effectively prevents the occurrence of sudden roof caving and significantly reduces the risk of mine safety production. It provides technical ideas and practical experience for the treatment of mined-out areas under similar geological conditions.