In the bustling world of urban infrastructure, the construction of new metro lines often involves navigating complex underground landscapes, where new tunnels must pass beneath existing ones with mere inches to spare. This delicate dance of engineering is fraught with risks, including deformation and even collapse of the existing tunnels. A recent study, led by ZHAO Yao of the Kunming Railway Construction Company of China Railway No. 8 Engineering Group Co. Ltd., delves into the critical factors influencing tunnel deformation in such high-stakes scenarios, offering insights that could revolutionize how we approach these challenges.
The research, published in ‘Chengshi guidao jiaotong yanjiu’ (Urban Rail Transit Research), focuses on the construction of the Qingdao North Station-Cangkou Station interval on Qingdao Metro Line 8. Here, a new tunnel is being built to obliquely under-pass an existing operational tunnel on Line 3, with an extremely small clearance. The study employs advanced finite element simulation using ABAQUS software to model the excavation process and analyze the impact of key factors on tunnel deformation.
One of the most striking findings is the significant difference in deformation control between full-face excavation and bench excavation methods. “Compared to the full-face excavation method, the bench excavation method would increase the maximum vertical displacement and horizontal displacement of existing tunnel by 24%,” ZHAO explains. This stark difference underscores the importance of choosing the right excavation method to minimize risks.
The study also highlights the critical role of excavation step length and surrounding rock conditions. As the step length increases from 0.5 m to 1.5 m, vertical displacement increases by 13% and horizontal displacement by 28%. Moreover, when the surrounding rock grade deteriorates from Grade III to Grade V, vertical displacement surges by a staggering 302% and horizontal displacement by 205%. These findings emphasize the need for meticulous planning and execution in such projects.
For the energy sector, the implications are profound. Many energy infrastructure projects, such as pipelines and power tunnels, often require new constructions to pass beneath existing ones. The insights from this research could inform better practices in these sectors, ensuring the safety and longevity of existing infrastructure while facilitating the development of new energy projects.
Looking ahead, this research could shape future developments in tunnel engineering by providing a robust framework for analyzing and mitigating deformation risks. As cities continue to expand and evolve, the ability to build new infrastructure without compromising existing systems will be crucial. By prioritizing full-face excavation methods, minimizing step lengths, and ensuring favorable surrounding rock conditions, engineers can mitigate stress and deformation in existing tunnels, paving the way for safer and more efficient urban development.
The study, published in ‘Urban Rail Transit Research’, offers a comprehensive analysis that could guide future projects, ensuring that the delicate balance between innovation and safety is maintained. As we continue to push the boundaries of what’s possible in urban infrastructure, research like this will be instrumental in shaping a safer, more efficient future.