## 5 Long-Term Deformation Predictions for the Jinping Auxiliary Tunnel Expansion Project
### Numerical Simulation Results and Analysis  
Given that the Jinping auxiliary tunnel and CJPL-II share the same lithology and strata, the elastic parameters of the rock mass reinforced by rock bolts and concrete are adopted from studies on CJPL-II [43]: an elastic modulus \(E=12.66\) GPa and a Poisson's ratio \(v=0.27\). Due to limited data on the time-dependent deformation parameters for the expansion zone, this study inversely calibrates these parameters using field monitoring data for CJPL-II. CJPL-II is situated on a north-south-trending anticline. Monitoring using an embedded multi-point displacement meter reveals that the deformation of the surrounding rock in the anticline core (at the B1 and B2 laboratories) reaches up to 60 mm, while the deformation in the anticline limbs is smaller (\(\leq\)16 mm) [39]. Based on the structural similarity between the auxiliary tunnel and the laboratories on the anticline limb, the deformation parameters from the limb areas [39] are applied to simulating the auxiliary tunnel's expansion. The numerical results align closely with field monitoring data [39; 43] on both the creep trends and magnitudes (Figure 13), validating the rationality of the inverse parameter selection. Following parameter validation, the long-term mechanical behavior of the auxiliary tunnel is simulated. The key steps of the numerical workflow simulating the Jinping auxiliary tunnel are as follows:  
Step 1: Fix the horizontal displacements at the model's sides and the vertical displacements at the base, and apply in situ stress gradients and seepage pressure to achieve initial equilibrium;  
Step 2: Compute the creep equilibrium under initial stress;  
Step 3: Simulate the initial tunnel excavation and the subsequent 12-year operational creep;  
Step 4: Simulate the expansion excavation and predict the 3-year post-expansion deformation. The vertical stress distributions before and after the expansion of the Jinping auxiliary tunnel are shown in Figure 14. The results indicate that the expansion project significantly disrupted the tunnel's stress equilibrium. Prior to expansion, stress was concentrated primarily at the tunnel's shoulders and base. The stress state on the right sidewall remained consistent during the post-expansion stage with the pre-expansion conditions, whereas a pronounced stress concentration occurred in the expanded section of the left sidewall. The maximum stress magnitude increased from 135 MPa to 203 MPa, indicating elevated rockburst risks at the top and base of the left sidewall. These areas require prioritized monitoring. Furthermore, a statistical analysis of the maximum principal stress contours revealed an increase from 138 MPa to 215 MPa in the expanded section. According to the existing study [12], the long-term strength of the surrounding rock at a 2400 m depth is approximately 192 MPa. Consequently, stress concentrations at the left sidewall's top and  
Figure 13: A comparison of the simulated and monitored deformation in the Jinping Underground Laboratory sidewalls [39]. base are likely to exceed this threshold, potentially triggering localized plastic deformation or creep failure. Enhanced support measures are therefore recommended in these zones. Figure 15 illustrates the evolution of the vertical strain before and after tunnel expansion. Its expansion also altered the original strain state of the surrounding rock. Post-expansion, both the magnitude and extent of the strain increased significantly compared to those under pre-expansion conditions. The deformation gradually intensified over time, stabilizing 120-180 days after the completion of the expansion. The stability of the surrounding rock was maintained within three years post-expansion, with no significant increase in deformation. Notably, the highest strain magnitudes occurred at the top and base of the left sidewall, aligning with the stress distribution patterns and further confirming the instability risks in these regions.