# Research on the Settlement Patterns of Tunnel-Surrounding Rock Under Groundwater Conditions
## 4 Results and Discussion
### Groundwater Action Mechanism Analysis  
Based on the aforementioned analysis, groundwater significantly impacts the stability of tunnel rock masses, primarily due to the complex interactions between groundwater and the surrounding rock mass [42]. For weaker and less stable strata with low conductivity, such as loess and mudstone, the absence of groundwater leads to higher soil strength and stability, characterized by uniform stress distribution, reduced pore water pressure in the surrounding rock mass, and a direct relationship between ground surface settlement and vault settlement, with minimal interrelation between them. In such scenarios, settlements  
Figure 8: Z-direction displacement cloud images of various cross-sections; (**a**) various monitoring cross-sections with groundwater action; (**b**) various monitoring cross-sections without groundwater action.  
predominantly result from unloading effects and surrounding rock deformation due to excavation [43]. Conversely, groundwater presence alters stress distribution within strata via permeation [44], softening the surrounding rock mass [45], thereby reducing its strength and load-bearing capacity and causing structural failure and significantly increased settlements. Furthermore, groundwater raises pore water pressure in the surrounding rock mass [46], leading to greater vault settlements and subsequently destabilizing the ground surface, thereby intensifying ground surface settlements. Thus, groundwater primarily influences ground surface and vault settlements through four mechanisms: (1) permeation effects: groundwater alters stress distribution in surface soil and rock mass via permeation, softening soil and causing structural failure; (2) water pressure changes: groundwater pressure variations directly affect rock mass and soil stress states, inducing deformation and settlements; (3) flow and erosion: groundwater flow may erode surface soil and rock mass, leading to soil loss and structural degradation [47]; (4) water-soil interaction: groundwater alters soil physical properties through interaction, reducing its strength and stability [48].  
Figure 10: Settlement and excavation profile curves for various monitoring cross-sections without groundwater influence; (**a**) vault settlement; (**b**) surface settlement.  
Figure 9: Settlement and excavation profile curves of various monitoring cross-sections under groundwater influence; (**a**) vault settlement; (**b**) surface settlement.  
Figure 11 illustrates a schematic diagram depicting the mechanisms by which groundwater influences surface settlement and vault settlement. The figure primarily focuses on the direct effects of groundwater on both surface and vault settlement, as well as their interdependent relationships.  
Accordingly, the presence of groundwater significantly influences the characteristics of ground settlement and crown settlement during tunnel excavation. When groundwater is present within the tunnel's excavation zone, both the ground settlement and crown settlement exhibit notable increases, with an interrelated relationship between them. Conversely, when the groundwater level lies outside the tunnel's excavation zone, the magnitude of the settlement for both the ground and the crown is relatively small, and the interaction between them is weaker. The mechanism of groundwater action is complex, primarily operating through multiple physical processes, such as permeation, water pressure changes, and flow characteristics, which collectively affect the deformation of the ground and crown. In engineering practice, it is essential to comprehensively consider hydrogeological conditions and tunnel excavation methods. By implementing appropriate groundwater control measures, the influence of groundwater on ground and crown settlement can be effectively minimized.