## 3 Analysis of Test Data
### Analysis of Surrounding Rock Stress Results
The peripheral rock at the foot of the arch, situated below the lower left guide hole, exhibits an overall gradual increase in stress values. The peripheral rock stress value reaches 10.033 kPa upon the completion of all guide hole excavations and further increases to 10.601 kPa after the removal of all temporary supports. Additionally, the peripheral rock at the bottom of the arch undergoes a stress release after the excavation of the middle-lower 1 guide hole and middle-lower 2 guide holes. The stress value reduces to 7.458 kPa following the excavation of the middle-lower 1 guide hole and further decreases to 7.098 kPa after the excavation of the middle-lower 2 guide hole. Subsequent excavation of the middle and lower 2 guide holes leads to a decrease in stress values from 10.886 kPa to 7.458 kPa and from 7.786 kPa to 7.098 kPa, respectively. The remaining guide hole excavations result in a gradual increase in stress values. Upon the completion of all guide hole excavations, the stress value of the surrounding rock settles at 7.572 kPa. After removing all temporary supports, the stress value of the entire structure reaches 8.381 kPa. The observed stress change patterns in the surrounding rock reveal that, following guide hole excavation, the area near the excavation zone experiences deformation toward the excavated chamber due to the release of constraints. During this deformation process, a portion of the energy is released, leading to a reduction in compressive stress. The diminished energy is then transferred to the surrounding geotechnical body, resulting in the redistribution of stress within the surrounding rock. Upon the application of the support structure, it generates resistance against the movement of the rock body, establishing corresponding constraints. Consequently, the deformation of the surrounding rock gradually weakens until a new balance is achieved between the surrounding rock and the  
Figure 11: The time-history curve of surrounding rock stress in the first group of the test. (**a**) Stress time curve of the surrounding rock at the top and bottom of the arch. (**b**) Stress time curve of the surrounding rock at the arch shoulder. (**c**) Stress time-course curve of the perimeter rock at the arch girdle. (**d**) Stress time curve of the surrounding rock at the foot of the arch. support structure. Upon the removal of the diaphragm wall providing vertical support and the temporarily elevated arch providing horizontal support, the joint between the initial support and the temporary support undergoes inward shrinkage and deformation due to the lack of support. In this scenario, the nearby surrounding rock temporarily forms a critical surface, leading to a reduction in stress values that are then transferred to the surrounding area. The specific data on surrounding rock stress in the second group of tests are presented in Figure 12. It is evident from the figure that, due to the different excavation sequences in the second group of tests, the temporal changes in perimeter rock stress at each point differ from those in the first group. Nonetheless, the overall pattern remains consistent. The perimeter rock stress is primarily influenced by the excavation of adjacent guide holes, causing a decrease in stress values near the excavation area and an increase in neighboring perimeter rock stress values. The construction of guide holes at a greater distance has a lesser impact on perimeter rock stress values. To gauge the degree of disturbance of excavation on the surrounding rock, average stress change values were calculated. A larger value indicates a greater disturbance caused by excavation. The average stress change values at the top of the arch, the left and right arch shoulders, the left and right arch waist, the left arch foot, and the bottom of the arch are smaller in the second group by 2.81%, \(-\)9.66%, 12.25%, 23.59%, 38.35%, 22.04%, and 16.76%, respectively, compared to the first group. This suggests that the left and right excavation methods result in less disturbance to the surrounding rock.