## 2 Case Background
### Analogical Analysis of Water-Rich Loess Tunnel Project  
Analogical analysis of engineering projects can provide precise and efficient solutions to targeted problems. By conducting a comprehensive analogical analysis of various aspects, such as the characteristics of water-rich loess tunnel surrounding rock, water-rich conditions, types of water-rich surrounding rock, excavation and construction challenges in water-rich sections, and disaster control techniques, we can find scientific and effective solutions to engineering problems encountered in the implementation of projects. Additionally, it can provide new ideas for the development of new technologies. Therefore, through the literature research, an analogical analysis was conducted on 16 water-rich loess tunnels that have been constructed in the arid inland basins of northwest China and the loess plateau region in central China [27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41]. The analysis covered aspects such as geological conditions, characteristics of surrounding rock, types of water-rich surrounding rock, excavation methods for water-rich sections, support measures, construction difficulties, and engineering disaster control techniques. The detailed analogy analysis is shown in Table 1 of Appendix A. The experience from investigating and conducting comparative analyses of 16 tunnel projects in water-rich loess indicates that the following issues need to be paid attention to during the construction of tunnels in water-rich loess:  
(1) Water has a significant impact on the stability of the surrounding rock of loess tunnels. The engineering properties of the surrounding rock of loess tunnels are closely related to the water-rich state of the loess. When the moisture content increases, the strength and stiffness of the loess decrease significantly, and the attenuation of the cohesion index is stronger than that of the internal friction angle. Influenced by the dual stratigraphic  
Figure 3: A series of engineering disasters encountered during the construction of the Tuanjie Tunnel. structure of soft upper and hard lower layers, excavation disturbance, and surface infiltration, water-rich Ioess tunnels can be classified into three types: naturally water-rich, excavation-disturbed water-rich, and surface infiltration water-rich. Therefore, taking necessary precipitation or water-stopping measures according to the water-rich type of the Ioess surrounding rock during the investigation, design, and construction of water-rich Ioess tunnels is the primary issue to ensure the stability of the surrounding rock and safe construction. (2) The softening of the surrounding rock at the base or arch foot is the main cause of large deformations of the surrounding rock, lining cracks, collapses, and roof falls. After tunnel excavation, the moisture in the surrounding rock migrates towards the excavation face, accumulates at the arch foot or base, and may cause water seepage or even flowing water in severe cases. This softens the arch foot, leading to overall settlement and deformation of the upper lining. If not addressed promptly, it can result in large-scale deformations of the surrounding rock, causing the lining to bear significant pressure and potentially leading to cracking, intrusion, or collapse of the support structure. Therefore, ensuring the bearing capacity of the arch foot during the construction of water-rich Ioess tunnels is a crucial issue for ensuring the stability of the surrounding rock and safe construction. (3) Deep hole precipitation, pre-reinforcement of surrounding rock, and reinforcement of support measures are important measures to ensure the stability of surrounding rock. For shallow water-rich Ioess tunnels, support measures should focus on controlling overall settlement and deformation and preventing collapses and roof falls.