## 3 Analysis of Test Data
### Analysis of Lining Stress Results
The construction of the entire upper guide tunnel for the second ring tunnel leads to increased stress values at various points. Specifically, the arch top, left arch waist, right arch waist, left upper diaphragm wall, and right upper diaphragm wall experience increases to 6.690 kPa, 8.894 kPa, 6.973 kPa, 12.405 kPa, and 10.663 kPa, respectively. Concurrently, the stress values of the left lower diaphragm wall and right lower diaphragm wall decrease to 7.287 kPa and 9.834 kPa. This shift suggests that stresses on the second ring support structure are transferred to the first ring, resulting in heightened stress on the upper structure of the first ring. Simultaneously, the lower structure of the second ring, which has not been applied yet, exhibits non-uniform stress distribution and force transmission,  
Figure 13: The time-history curve of lining stress in the first group of the test. (**a**) Stress time curve of the lining of the vault and the base of the arch. (**b**) Stress time curve of arch waist lining. (**c**) Stress time-course curve of footing lining. (**d**) Stress time curve of the left diaphragm wall lining. (**e**) Stress time-curve of the right-central diaphragm wall lining. (**f**) Temporary back arch lining stress time curve. leading to upward stress concentration and a reduction in stresses on the lower support structure. Following the excavation of the second ring's lower guide hole, lining stresses re-center to the lower support structure. Stress values for the arch waist, upper left center diaphragm wall, and upper right center diaphragm wall decrease, while those for the arch foot, arch bottom, lower left center diaphragm wall, lower right center diaphragm wall, and superelevation arch increase. The stress pattern of the support structure in the third ring section excavation mirrors that of the second ring, albeit with a smaller overall impact due to the increased distance from the first ring. The stress values of the first ring's support structure fluctuate up and down. Upon the completion of all guide hole excavations, the lower left and lower right diaphragm walls bear the highest stresses at 11.932 kPa and 11.841 kPa, respectively. They are followed by the upper left and right diaphragm walls at 8.536 kPa and 10.626 kPa, and then the arch roof at 7.568 kPa. The stress values for the arch top follow at 7.568 kPa, with the left and right arch waist stresses at 5.897 kPa and 7.415 kPa, respectively. Finally, the stress values for the left and right foot of the arch, the left and right superelevation arches, and the bottom of the arch show minimal differences, maintaining values near 3.503 kPa. This analysis reveals that the primary stress-bearing positions in the double sidewall tunnel are the diaphragm wall, arch top, and lining at the arch waist. The diaphragm wall handles the vertical load imposed by the overlying surrounding rock, while the vault and arch waist bear and transfer the vertical and horizontal loads from the surrounding rock. Monitoring the arch footing, positioned horizontally at the corner of the side wall, is crucial, as per the stress transfer principles mentioned above. Stress concentration is expected in the vertical arch footing of the side wall, making it a significant stress point in the supporting structure. Conversely, stresses in the horizontal arches, foot arch bottom, and temporary elevation arches are relatively small. Upon the removal of temporary support, the stresses initially borne by the diaphragm wall and temporary elevated arch are transferred to the initial support, resulting in an increase in the stress values of the initial support. Following the removal of the temporary support from the first ring, the stresses on the diaphragm wall and temporary support shift to be supported by the initial support of the first ring and the temporary support of the second ring. The temporary support of the second ring contributes to the support capacity, causing a minor increase in the stress value of the initial support of the first ring.