A large-scale foundation pit with an area of 39,677 m2 (B2) was excavated to the south of an existing 25,720 m2 Chengdu Universal Trade Plaza (CDUTP) foundation pit (B1) in Chengdu, China. The purpose of this manuscript was to investigate the deformation characteristics of B2 and compare the difference of deformation characteristics between foundation pits B1 and B2. Direct monitoring results of foundation pit B2 were comprehensively investigated and compared with that observed in B1, which include lateral movement, column movement, stress in the columns, and axis force in the anchor cable. Additionally, a strategic approach to mitigate potential extensive lateral deformation was introduced. The monitored results for B2 revealed that the deflection and vertical movement of the columns were comparatively smaller than the reported lower boundaries. The maximum excavation-induced lateral column deflection exhibited a notable 35% reduction in comparison to the lateral deflection observed in the new excavation. However, vertical column movements were approximately twice as pronounced as those in B1. Furthermore, the installation of temporary columns with anchor cables in front of permanent columns proved effective in limiting the vertical deformation during excavation in close proximity to the permanent columns. This research provides valuable insights into the documentation of large-size excavations in soft soil, along with corresponding mitigation approaches.

This research aims to comprehensively study the deformation characteristics of an excavation pit of 7,600 m2 (117 m long, 65 m wide and 20.8 m deep) in soft clay in Shanghai, China. The deformation characteristics of the mixing pile in both the vertical and lateral directions, ground surface movement, and surface displacement in the adjacent tunnels were comprehensively investigated. The results indicated that the maximum lateral deflection was approximately 85 mm at the end of the excavation and that the maximum lateral displacement, delta hm, was in the range between 0.12%He and 0.41%He. The factor of safety of the excavation was approximately 1.6, which was larger than that of most reported sites in Shanghai. The relationship between heaving and excavation depth was strong between 0.0047%He and 0.056%He, and a relatively large settlement was observed at a distance of approximately 0.2He-0.3He. The tunnel surface of the eastbound line deformed upward and inward with a maximum horizontal convergence of 4 mm. A multilayer regression model was also validated, showing a maximum discrepancy of 26.5 mm. This research provides a valuable historical case for the documentation of the deformation characteristics of excavation pits close to existing foundation pits and tunnels.