## 5 Result
### Analysis of the Soil's Inclined Stratification Parameters  
Figures 7 and 8 present the critical support pressure for inclined layered soils under varying strike angles and dip angles in three different hydraulic conditions. These conditions reflect the influence of water movement within unsaturated soils on the stability of the tunnel face. The normalized depth ratios in the two figures differ: Figure 7 corresponds to \(d_{t}/D=-0.1\), indicating that the soil layer interface intersects the tunnel face, whereas Figure 8 corresponds to \(d_{t}/D=0.1\), where the interface is located above the tunnel face. In Figure 7, the intersection of the soil layer interface with the tunnel face results in greater variability in critical support pressure across the range of strike angles. The destabilizing effects of inclined stratification are more pronounced, particularly under infiltration conditions, where seepage forces significantly increase the required support pressure, especially for steeper dip angles. The no-flow condition shows the lowest critical support pressure across all strike and dip angles, as no additional destabilizing forces are present. Evaporation introduces moderate destabilizing effects, with support pressures slightly higher than the static condition but lower than infiltration. In contrast, Figure 8 shows a less pronounced variation in critical support pressure, as the soil layer interface is positioned above the tunnel face. This configuration allows the upper soil layer to exert a stabilizing influence, reducing the overall destabilizing impact of stratification and seepage forces. While the trends across strike and dip angles remain consistent with those in Figure 7, the magnitude of the critical support pressure is generally lower for all conditions. Infiltration continues to exhibit the highest support pressure requirements, particularly for steeper dip angles, while no-flow and evaporation conditions maintain similar relative behavior. Figure 7: Critical support pressure for inclined layered soils versus different strike \(a_{\rm h}\) with a series of dip \(a_{\rm v}\) under three kinds of unsaturated seepage conditions at \(d_{l}/D=-0.1\). (**a**) clay-loess, no flow. (**b**) clay-loess, evaporation. (**c**) clay-loess, infiltration. (**d**) silt-loess, no flow. (**e**) silt-loess, evaporation. (**f**) silt-loess, infiltration. The comparison between Figures 7 and 8 highlights the significant impact of the relative position of the soil layer interface on tunnel stability. When the interface intersects the tunnel face, the critical support pressure is more sensitive to stratification geometry and hydraulic conditions, reflecting greater instability. Conversely, when the interface is above the tunnel face, the stabilizing effects of the upper soil layer mitigate these influences,  
Figure 8: Critical support pressure for inclined layered soils versus different strike \(\alpha_{\text{h}}\) with a series of dip \(\alpha_{\text{v}}\) under three kinds of unsaturated seepage conditions at \(d_{t}/D=0.1\). (**a**) clay-loess, no flow. (**b**) clay-loess, evaporation. (**c**) clay-loess, infiltration. (**d**) silt-loess, no flow. (**e**) silt-loess, evaporation. (**f**) silt-loess, infiltration. leading to lower and more uniform support pressure requirements. These findings underscore the importance of accurately accounting for the position of the soil layer interface and hydraulic conditions when designing support systems for tunnels in inclined layered soils. The grey relational analysis method is adopted to further analyze the degree of correlation between various dip \(\alpha_{\rm v}\) under different conditions in different layered soils and among different strike \(\alpha_{\rm h}\) on the stability of the tunnel face. The reference sequence consists of the 17 incrementing numerical values of the strike \(\alpha_{\rm h}\), and the corresponding critical support force results serve as the primary sequence.