## 1 Introduction  
Since the beginning of the 21 st century, China's transportation infrastructure has developed rapidly, with transportation networks expanding from plain and hilly areas into complex and challenging mountainous regions. This expansion has led to increasingly complex geological conditions along transportation routes, resulting in a gradual increase in the proportion of bridges and tunnels. According to statistics, by the end of 2023, the total length of operational transportation tunnels in China was approximately 57,421 km, including 23,508 km/18,573 tunnels for railways, 26,784 km/24,850 tunnels for highways, and 7129 km of subway tunnels [1, 2]. Meanwhile, the distribution area of loess in China is approximately 640,000 km\({}^{2}\), accounting for about 6.6% of the country's land area. The Loess Plateau, characterized by its intricate gullies, rolling hills, and complex geological environment, poses a series of technical challenges for the design and construction of loess tunnels. Unlike unsaturated loess tunnels, due to factors such as naturally occurring soft and hard interlayered strata, surface infiltration, and excavation disturbances, the surrounding loess rock in tunnels often exhibits a water-saturated state, resulting in almost complete loss of its bearing capacity. This poses a serious threat to the stability of the surrounding rock and the safety of tunnel structures. To reasonably address these tunnel engineering challenges in loess areas, researchers have conducted extensive studies on various aspects such as the geological characteristics of loess tunnels [3; 4; 5], engineering properties [6; 7; 8], excavation methods, and support measures [9; 10; 11; 12], making significant contributions to supporting tunnel construction in loess regions. Due to the typical regional sedimentary sorting phenomenon of Chinese loess, there are distinct differences in geological and engineering characteristics between the loess in the arid inland basins of the northwest, the loess plateau in central China, and the hilly regions at the foot of mountains in the east. These differences result in notable regional characteristics in geological conditions, water-rich conditions, and the selection of excavation and support measures for loess tunnel projects. [PERSON] et al. [13; 14; 15], taking the Q\({}_{2}\) loess tunnel with a soft plastic interlayer in the Yinchuan-Xi'an High-Speed Railway as an example, used experimental analysis and numerical simulation to study the mechanical and permeability properties of soft plastic loess surrounding rock, as well as excavation and support engineering measures. Through the literature review and engineering analogy analysis, [PERSON] et al. [16] pointed out that water-rich loess tunnels mainly exhibit three types: naturally water-rich, excavation-induced water-rich, and rainfall infiltration-induced water-rich, and that targeted construction strategies should be adopted based on different water-rich types. [PERSON] et al. [17] revealed the effects of technical measures such as excavation methods, advanced pipe roof support, and advanced small pipe grouting on displacement and deformation control in shallow-buried loess tunnels, indicating that advanced pipe roof support is better than small pipe grouting support in controlling surface settlement and displacement. [PERSON] et al. [18] conducted research on the mechanical response and spatiotemporal distribution of support structures in naturally water-rich deep-buried loess tunnels through field monitoring, pointing out that tunnel surrounding rock displacement exhibits significant spatiotemporal effects and its deformation roughly undergoes three stages: rapid deformation, continuous deformation, and slow deformation, with the water-rich environment accelerating the early deformation of the surrounding rock. [PERSON] et al.