Structural Response and Preservation of Historic Buildings Adjacent to Oversized Deep Excavation

A super-large-scale foundation pit (74,000 m(2) in plane) adjacent to an existing historic building on three sides was constructed by the technique of a deep foundation pit group in downtown Shanghai, China. Through extensive and long-term field monitoring, this study investigated structural responses of the building during the construction process as well as effectiveness of corresponding protective measures on controlling the deformation of foundation pit and building settlement. The analysis of field data indicated that by taking advantage of the construction technology of the foundation pit group, the wall deflection close to the protection building was controlled within 0.09% final excavation depth, which was less than the limit of relevant specifications. The control effect of prestressed steel support on wall deflection did not surpass that of reinforced concrete supports when the excavation depth was less than 12 m but rose significantly after the excavation entered the soft clay layer. The construction of diaphragm wall panels resulted in significant settlement of the historic building. However, more importantly, the lateral stress relief of soils on both sides of it caused by trenching would lead to hogging deformation of the bearing wall and horizontal tensile stress in the building's foundation, which aggravated the crack propagation and structural damage. Underpinning for the historic building was verified to be an effective method to resist the impact of ground movement caused by the excavation in soft soils. The maximum settlement of the historic building during the excavation stages stabilized between 10 and 18 mm, accounting for 20%-40% of the total settlement, far less than the settlement of ground surface around the building. (c) 2021 American Society of Civil Engineers.