In order to explore the catastrophic evolution process for karst cave water inrush in large buried depth and high water pressure tunnels, a model test system was developed, and a similar fluid–solid coupled material was found. A model of the catastrophic evolution of water inrush was developed based on the Xiema Tunnel, and the experimental section was simulated using the finite element method. By analyzing the interaction between groundwater and the surrounding rocks during tunnel excavation, the law of occurrence of water inrush disaster was summarized. The water inrush process of a karst cave containing high-pressure water was divided into three stages: the production of a water flowing fracture, the expansion of the water flowing fracture, and the connection of the water flowing fracture. The main cause of water inrush in karst caves is the penetration and weakening of high-pressure water on the surrounding rock. This effect is becoming more and more obvious as tunnel excavation progresses. The numerical simulation results showed that the outburst prevention thickness of the surrounding rock is 4.5 m, and that of the model test result is 5 m. Thus, the results of the two methods are relatively close to each other. This work is important for studying the impact of groundwater on underground engineering, and it is of great significance to avoid water inrush in tunnels.

The discrete element method (DEM) cannot effectively account for macroscale problems because of its high computational cost and time-consuming nature, especially for fluid–solid coupling problems. Therefore, a spatially scaled-down model, which should be established based on a set of scaling laws, is commonly employed to study the behaviors of the macroscale prototype. In the present study, various basic scaling relationships proposed by previous researchers for a scaled-down model are summarized first, as well as their limitations when they are used for DEM-CFD simulation of fluid–solid coupling problems in saturated and cohesiveless granular soils. Then, a new set of scaling relationships is proposed using a governing equation approach. Finally, a DEM-CFD model is established as an example analysis to study the feasibility and accuracy of the new scaling relationship present in this study for simulating fluid–solid coupling problems in saturated and cohesiveless granular soils. The results are analyzed in comparison with other scaling relationships, and the results indicate that the new set of scaling relationships is more reasonable and accurate than others.

Water inrush is a geological hazard often encountered in tunnel construction. In order to overcome problems encountered when using the existing water-inrush simulation model test, such as single function, low repetition utilization rate, and poor visibility, we developed a multi-type water-inrush model test system. Our test system can be a precursor to large-scale studies, handle multiple types, and perform serialization and visualization. We conducted cavity water-inrush simulation testing using this device, and studied the failure model of aquifuge rock. We reveal the evolution laws of water inrush from the cavity, including the initiation of fracture in the aquifuge rock, the formation of water-inrush channels, and the rupture of the aquifuge rock. By analyzing the seepage pressure changes at the monitoring points of the aquifuge rock, we divided the water-inrush process of the cave into a rack generation stage, a holing-through of fracture and forming of water-inrush channel stage, and a water-inrush stage. Test results show that the system is stable and reliable, only requiring a short test period, and can be used to guide large water-inrush testing and related projects.