## 1 Introduction  
With the launch of the \"Western Development\" strategy and the progress of the \"Belt and Road\" initiative, China's tunnel construction has shifted towards the western mountainous areas, characterized by highly complex geological and topographical conditions. Numerous tunnels that are crucial for infrastructure development in sectors such as transportation, hydraulic engineering, hydropower, and underground national defense are currently under construction [1; 2; 3]. Due to the complex geological conditions and the limitations of preliminary explorations, it is challenging to identify all potential risks during the early stages of tunnel construction, leading to frequent occurrences of major geological disasters, including mud and water inrushes. Statistics [4] indicate that fault-type accidents constitute 29% of tunnel-related mud and water inrush disasters. These disasters often caused serious casualties and economic losses, indicating a significant challenge for tunnel construction [5; 6; 7]. Therefore, it is necessary to investigate the mechanism of water and mud inrush and to propose control methods to overcome this challenge. Up to the present, numerous researchers have conducted extensive studies on the mechanisms of mud and water inrush disasters through field and laboratory experiments,theoretical assessments, numerical modeling, and other approaches. [PERSON] et al. [8] introduced an innovative expandable water inrush model experimental system for undersea tunnels, which uncovered the evolution rules of multi-physical fields around faults and the surrounding rock during excavation and water bursting. Focusing on the characteristics of typical faults in China's coal mines, [PERSON] [9] carried out a water inrush model experiment with high hydraulic head pressure, revealing multiple changes in the flow pattern throughout the seepage-erosion evolution. [PERSON] et al. [10] developed a mud and water inrush model experimental system for tunnels in fault fracture zones, showcasing the variations in adjacent rock seepage pressure, displacement, stress-strain, and effluent characteristic parameters during tunnel excavation and upon fault exposure. [PERSON] et al. [11; 12] reported that rock strata around coal faces are generally in a post-failure state or even in a broken state; therefore, the instability and bifurcation of non-Darey flow in rock may lead to water irruption and coal and gas outbursts in coal mines. Using an independently designed seepage testing assembly for variable masses of fractured rock, [PERSON] et al. [13] examined the nonlinear seepage traits for variable masses of fractured mud-stone. The seepage pattern of the mud-stone specimens changed immensely during the course of seepage. For the theoretical and numerical modeling, [PERSON] and [PERSON] [14] developed a flow-stress water inrush model based on the assumption that the permeability variation was mainly caused by rock deformation during water inrush evolution. [PERSON] et al. [15] proposed a numerical groundwater flow model to predict the location and magnitude of tunnel water inflows in a Barcelona subway. [PERSON] et al. [16] and [PERSON] and [PERSON]. [17] developed different numerical models to simulate the water inrush process from a mechanical perspective. These studies have provided a comprehensive theoretical understanding and practical insights, effectively guiding the forecasting and prevention of such disasters in underground constructions. However, these methods fall short when dealing with weathered rock, especially fully weathered rock in fault fracture zones, due to its soil-like behavior. The presence of substantial fine particles and minimal cementation in fully weathered rock makes it prone to water erosion and disintegration. The evolution of such disasters in fault fracture zones is thus influenced by both erosion and seepage. On one hand, erosion of the fine particles caused by water flow leads to an increase in porosity and permeability, as reported by many studies [18; 19; 20].