In the heart of Qingdao, a critical metro station project is underway, pushing the boundaries of construction technology in challenging soil-rock composite strata. The deep foundation pit construction, a complex endeavor, has been the focus of a recent study led by SUN Chao from China Railway Fourth Bureau Group Co., Ltd., published in ‘Chengshi guidao jiaotong yanjiu’ (Urban Rail Transit Research). The research delves into the stress characteristics of anchor cables and excavation-induced deformation, offering insights that could reshape how we approach similar projects in the future.
The study highlights a pressing issue: prestress loss in anchor cables. “Within just five days, we observed a prestress loss exceeding 10% of the lock-in value,” reveals SUN Chao. This short-term loss, higher than expected, underscores the need for vigilant monitoring and adaptive management strategies. The implications are significant, particularly for the energy sector, where deep excavations are often necessary for infrastructure development.
Using non-destructive testing methods, the research team tracked the evolution of anchor cable prestress, both short and long-term. They found that over 75% of the anchor cables passed the initial tensioning acceptance criteria, but the subsequent prestress loss posed a challenge. To mitigate this, the team employed FLAC3D software to develop a 3D foundation pit-stratum model, analyzing the displacement of retaining piles and the distribution of plastic zones under prestress loss conditions.
The results were eye-opening. Under low anchor cable prestress, wide and extensive plastic zones developed on both sides of the foundation pit, increasing the risk of surrounding rock deformation. However, the installation of steel struts proved to be a game-changer. “The steel struts shared part of the active earth pressure and altered the horizontal displacement distribution of the retaining piles,” explains SUN Chao. This reinforcement measure effectively controlled the deformation of the surrounding rock, demonstrating the potential for innovative support systems in similar projects.
The study’s findings have commercial implications for the energy sector, where deep excavations are common. By understanding and managing prestress loss in anchor cables, construction firms can minimize risks, reduce costs, and enhance the safety of their projects. The research also underscores the importance of real-time monitoring and adaptive management, paving the way for smarter, more resilient construction practices.
As the metro station project in Qingdao progresses, the insights gained from this study will undoubtedly shape future developments in the field. By embracing innovative technologies and adaptive strategies, the construction industry can overcome the challenges posed by complex strata, ensuring the safe and efficient development of critical infrastructure.