## 1 Introduction  
The South-to-North Water Diversion Project (SNWDP) aims to optimize the temporal and spatial allocation of water resources in China. As a national strategic project, it safeguards China's land management and sustainable development. Canal engineering is an integral part of SNWDP, and its seepage failure involves complicated hydraulic problems, particularly in some deep excavated sections, due to the high groundwater level, complex geological conditions, soil consolidation and deformation, and rainfall or channel infiltration [1]. The seepage-stress coupling may occur between the concrete lining and the foundation, damaging the lining plate. If the damage persists, the water from the canal will keep into the soil of the canal more quickly, altering the seepage field and causing structural damage between the soil of the canal, the concrete lining, and the seepage field [2]. Therefore, scholars at home and abroad are all concerned about the SNWDP's service life and performance evolution in long-term operation, for it matters to water delivery safety and further affects the people's living conditions, social and economic development, and environmental protection [3]. The Xichuan Section is the first section of the main channel of the SNWDP Middle Route, classified into Class I project according to the engineering grade, so its safe running is of great significance. A seepage/stress-damage (SSD) coupling theory was proposed, and a finite element model of a deep excavated canal in the SNWDP Xichuan Section was established in the same scale as its actual design drawings. Even the materials used and the surrounding environment were the same as the actual situation. First, the SSD coupling theory proposed in this paper needs a stable seepage field, on which a lot of research has been performed. For example, [PERSON] et al. [4] used the strength reduction method to establish a seepage-stress coupled numerical model. They discussed the impact of various factors on the slope stability under different working conditions and concluded that the groundwater and rainfall infiltration have the most considerable effect on slope stability. In southern Jiangxi province, [PERSON] et al. [5] investigated the failure modes of granite residual soil slopes and employed normal soil material parameters to analyze precipitation infiltration under three operating situations. They discovered that the wet front's depth and slope coefficient have varied over time. [PERSON] et al. [6] studied the spatial-temporal characteristics of water movement on fractured soil slopes under rainfall conditions. They investigated the mechanism of fractured slope instability as a function of soil saturation variations and discovered that matrix suction is the primary driver of overall instability. [PERSON] et al. [7] analyzed the stability of hydraulic landslides with different permeability coefficients under fluctuating reservoir water levels and rainstorm conditions. They found that due to heavy rains, the stability of the landslide was considerably reduced, and the coefficient of stability increased with increased permeability. [PERSON] et al. [8] analyzed and compared water pressure and pore pressure data from hydraulic wells to observe the influence of seepage changes. [PERSON] et al. [9]. analyze the sudden pipeline crash of a specific project and derive its evolution process. [PERSON] et al. [10] proposed an innovative permeability evolution equation. They found that the seepage pressure will continuously intensify fracture propagation and penetration in the rock mass due to the time effect of permeability and failure. [PERSON] et al. [11] used pore pressure as a controlled condition to analyze the rainfall infiltration and seepage on slopes under different rainfall intensities. They obtained the relationship between the rainfall intensity and the actual infiltration rate.