Active displacement control of bridge piers adjacent to an open-cut foundation pits in offshore complex geological conditions

With the rapid development of infrastructure construction in complex geological environments such as offshore artificial islands, deformation coordination control of existing bridges adjacent to open-cut tunnel excavation has become increasingly challenging. The traditional passive axial-force control methods rely on preset structural stiffness to resist earth pressure, cannot adapt dynamically to construction-induced disturbances, which may result in support systems overloading and potential risks to expressway operation. To address these issues, this study investigates undercrossing project of the main tunnel at the East Artificial Island of Shenzhen-Zhongshan Link beneath the existing Yanjiang Expressway Bridge. A numerical model of the excavation process was established using Plaxis finite-element software to analyze the evolution patterns of retaining structure deformation and bridge pier displacement under conditions without active control. Subsequently, an active axial-force control technology was then incorporated into simulation, and comparative analysis with field monitoring data was conducted to evaluate the effectiveness of the active control system in mitigating foundation pit deformation. Results indicate that during excavation, the lateral displacement of the retaining structure exhibits a "bulging" profile with larger deformation in the middle and smaller deformation near both ends, and the position of maximum displacement gradually shifts downward as excavation proceeds. The lateral displacement of bridge piers exceeded the allowable engineering limits under passive control conditions. After deploying a servo steel-strut system for active control, the maximum horizontal displacements of the retaining structure and bridge piers were reduced by 42.34% and 52.8%, respectively, compared with the uncontrolled conditions. Numerical simulations aligned well with field measurements, confirming the effectiveness of active axial-force control. These findings provide a useful reference for the implementation of active control technologies in foundation pit construction and monitoring within offshore complex strata.