In order to explore the evolution mechanism of water and mud inrush, based on the fluid-solid coupling similarity theory and a large number of matching tests, fault similar materials with mountain sand, gravel, and red clay as raw materials and surrounding similar rock materials with mountain sand, red clay, cement, and water as raw materials are developed. Similar materials’ physical and mechanical properties and hydraulic properties with different ratios are tested and analyzed. The results show that the red clay content influences the mechanical properties of similar materials and their hydraulic properties, and the gravel substrate mainly influences the fault permeability coefficient. Similar material can be adjusted within a certain range of mechanical parameters. The material is simple and suitable for developing similar materials for different low and medium strength rock masses. Finally, a similar material was used in a model test of the tunnel fault fracture zone to reveal the mechanism of water and mud bursts in the tunnel. The study results can be used as a reference for the development of similar materials for tunnel fracture zone surrounding rocks.

The shear strength parameters of conglomerate soils are crucial to the stability analysis of foundation support when excavating and supporting ultra-deep foundation pits in the highland alluvial lacustrine layer. The difference in water content of conglomerate soils in different regions will directly affect the values of shear strength parameters. At the same time, more research on the shear strength of conglomerate soils under different water contents is required. In this study, a series of large-scale direct shear tests were carried out on the round gravel soil in the plateau alluvial-lacustrine deposit, and the round gravel soil’s shear strength curves under natural and saturated conditions and water content were obtained. The influence of different water content on the shear strength characteristics of the round gravel soil was discussed, and the shear strength parameters of the round gravel soil with different water content were used in the numerical simulation of ultra-deep foundation pit excavation and support. The stress and deformation laws of the foundation pit support were analyzed. The results show that the peak strength of the round gravel soil in the natural water content state appears between 30% and 45% of the shear displacement, while the peak strength in the saturated water content state appears around 45–55% of the shear displacement. The shear strength tends to be stable or slightly weakened with the increase of the shear displacement. The angle of internal friction and cohesion of round gravel soil in the natural water content state is greater than those in the saturated water content state. The simulation of the foundation excavation support shows that the shear strength parameter of the round gravel soil influences the force deformation of the support structure. The higher the water content of the round gravel soil, the more the shear strength parameter affects the soil displacement. The research results can provide some reference for optimizing project design parameters.

In order to study the evolution process, damage characteristics, and occurrence mechanism of water and mud inrush disaster in deep tunnel fault zone with infiltration instability under complex conditions, a set of the three-dimensional physical model test systems of water and mud inrush flow-solid coupling in tunnel fault zones is developed. The system mainly comprises a rigid test frame, ground stress loading system, hydraulic loading system, multiple information monitoring and acquisition system, and mud and water protrusion recovery system. The system’s main features are that it can meet the model’s simulation of the ground stress field, water pressure, and other complex environments subjected to ground stress, and water pressure gradients can be controlled. The system is characterized by high rigidity, high-pressure strength, visualization, good sealing, and expandability. Taking the water fault zone of a well in the Dazhu Mountain Tunnel of the Darui Railway as the research object, the new fault zone and surrounding rock similar materials applicable to the flow-solid coupling model test are designed using the self-developed flow-solid coupling similar materials. The system is used for model tests to reveal the spatial and temporal changes of the surrounding rock stress field and seepage field during the tunnel excavation process. The test results show that the system is stable and reliable, and the research method and results are of guiding significance to the research of the same type of underground engineering.

No abstract

No abstract