Progressive deformation and reinforcement control of a mountain slope under sequential excavation of multiple underground openings

Sequential excavation of multiple underground openings in steep slopes can reactivate previously disturbed ground and adversely affect tunnel support and slope stability. This study investigates disturbance-zone evolution and reinforcement effects in a mountain slope containing two tunnel anchorages and a main tunnel. A three-dimensional finite difference model was developed to simulate anchorage excavation followed by main tunnel excavation. The simulated displacement trends were generally consistent with the measured trends. Seven numerical cases were compared in terms of deformation, shear localization, primary-support safety, and global slope stability. The results indicate that anchorage excavation generated localized shear deformation and yielded zones, which underwent further deformation during main tunnel excavation, with increased connectivity of shear deformation and plastic yielding among the openings and toward the slope surface. Compared with conventional support, integrated tunnel reinforcement reduced the maximum system displacement from 94.2 to 40.3 mm (57.2%) and increased the minimum primary-support safety factor from 0.61 to 1.10. For the reinforcement arrangement examined, omitting prestressed bolts caused the greatest deterioration among the component-omission cases, increasing the peak displacement at tunnel monitoring points from approximately 39 to 46 mm and reducing the minimum support safety factor to 0.98. Adding the field-designed left- and right-side anti-slide pile configurations increased the global slope safety factor from 1.20 to 1.32 and 1.28, respectively. Among these configurations, the left-side piles more effectively reduced the continuity of the potential shear-deformation pathway toward the lower slope surface. These findings highlight the role of inherited excavation disturbance in subsequent slope deformation and the importance of coordinating tunnel reinforcement and pile placement with the spatial development of disturbance zones.