In the bustling urban landscapes where underground space is at a premium, the delicate dance between construction and existing infrastructure is more critical than ever. A recent study led by Zhiguo Zhang from the University of Shanghai for Science and Technology and the National University of Singapore sheds light on the complex interactions between deep excavation and operational metro tunnels, offering insights that could reshape how we approach such high-stakes projects.
The research, published in the journal *Underground Space* (which translates to *地下空间* in Chinese), focuses on the often-overlooked issue of soil uplift caused by foundation pit excavation. Traditional methods, which primarily consider stress release, fall short when it comes to large soil uplifts, potentially leading to significant impacts on underlying tunnels. “Current simplified solutions are inadequate for capturing the full picture,” Zhang explains. “Our study introduces a two-stage analysis that better reflects the real-world complexities.”
The study’s innovative approach combines the modified Sagaseta solution with a Pasternak foundation model and a variable stiffness Timoshenko beam to estimate tunnel displacement. This method not only accounts for gravity effects but also incorporates tunnel-soil interaction, providing a more accurate prediction of mechanical behavior. “By integrating these models, we can better understand how tunnels respond to excavation-induced soil movements,” Zhang adds.
The research was put to the test in a real-world scenario: the Jinqiao metro superstructure excavation project in Shanghai. Here, a foundation pit was excavated directly above an existing metro tunnel, making it an ideal case study. The team conducted a three-dimensional numerical simulation to verify the feasibility of their simplified solutions, demonstrating their practical applicability.
The findings have significant implications for the energy sector, particularly in urban areas where underground infrastructure is dense. “Accurate prediction of tunnel response is crucial for ensuring the safety and stability of existing infrastructure during new construction projects,” Zhang notes. “This research provides a more reliable method for assessing these risks, ultimately reducing the potential for costly damages and disruptions.”
Parametric analyses conducted as part of the study revealed that greenfield displacement is highly sensitive to the modified uneven convergence Sagaseta solution. The research also highlighted the importance of considering excavation width, as ignoring this factor can lead to overestimated tunnel displacements under plane strain conditions. Additionally, the study found that equivalent bending and shear stiffness influence corresponding bending and shear tunnel deformations, underscoring the need for a comprehensive approach to tunnel response analysis.
As cities continue to expand and underground space becomes increasingly valuable, the insights from this research will be instrumental in guiding future developments. By adopting more accurate and sophisticated methods for predicting tunnel response, the construction industry can minimize risks and ensure the safe coexistence of new and existing infrastructure. “This work is a step forward in our understanding of these complex interactions,” Zhang concludes. “It paves the way for more informed decision-making in urban construction projects.”