Effects of Basal Reinforcement Methods and Spatial Parameters on Deformation Control of Asymmetric Shared-Wall Excavations in Soft Soil

Deep excavation in soft soil readily induces lateral displacement of retaining structures and basal heave, posing serious threats to adjacent underground structures and the surrounding environment. Basal reinforcement is a key measure for improving excavation stability and controlling deformation; however, systematic comparative studies on multiple reinforcement methods and their spatial parameters in complex asymmetric shared-wall excavations remain scarce. Based on the Tianjin Binhai International Airport Integrated Transportation Hub project, a three-dimensional coupled numerical model of the “soil–Z2 excavation–existing M2 metro station” interaction was established using PLAXIS 3D. The effects of reinforcement depth, width, and area replacement ratio on diaphragm wall deformation, ground settlement, and base slab vertical deformation were quantified for four methods: strip, grid, full-area, and skirt reinforcement. All methods exhibit a pronounced critical depth threshold: the effective depth limits are 0.4H for strip, grid, and skirt reinforcement and 0.5H for full-area reinforcement, beyond which engineering benefit decreases substantially. Reinforcement width shows a marginal diminishing effect and should not be treated as the primary controlling parameter. Under the same area replacement ratio, skirt reinforcement leads to significant conical heave in the central excavation base, whereas strip reinforcement provides the best full-profile deformation control. Under the same total reinforcement volume, full-area reinforcement achieves the best performance across all deformation indices through uniform full-coverage constraint of the excavation base soil. This study elucidates the asymmetric deformation control mechanisms of shared-wall excavations and provides theoretical guidance for reinforcement scheme optimization in similar soft soil projects.