In urban areas where water-rich soft soils pose significant challenges, the construction of new metro lines can lead to serious concerns regarding the integrity of existing tunnels. Recent research led by MA Xifeng from Nanjing Metro Construction Co., Ltd., sheds light on effective protection measures aimed at mitigating deformation risks during shield tunneling operations. This study, published in the journal Chengshi guidao jiaotong yanjiu, highlights innovative strategies that could reshape construction practices in similar environments.
The research was conducted in the context of Nanjing Metro Line 5, which is set to closely underpass an existing section of Nanjing Metro Line 1. The complexity of this project arises from the delicate balance required to maintain the stability of the existing tunnel while executing the shield tunneling. “In water-rich soft soil areas, the control of deformation is critical to ensure the safety and longevity of metro structures,” MA Xifeng stated, emphasizing the need for robust protective measures.
Utilizing advanced finite element software, MIDAS/GTS NX, the team simulated various construction scenarios to identify potential risks and develop effective countermeasures. The results led to a series of proactive strategies designed to reinforce the existing tunnel prior to construction. These included micro-disturbance grouting, permanent circumferential supports, and the installation of longitudinal tension strips. Such measures are aimed at minimizing deformation and ensuring compliance with stringent deformation control standards.
During the actual construction phase, real-time monitoring of vertical displacement and horizontal convergence of the existing tunnel was implemented. This allowed for immediate adjustments to earth pressure and excavated soil quantities, thereby enhancing the precision of the tunneling process. Techniques such as synchronous grouting and optimized distribution of grouting materials were employed to further mitigate deformation risks.
The post-construction phase also received careful attention. MA noted, “Preparation for potential post-construction settlement is crucial. We ensured that sufficient grouting materials and equipment were readily available to address any issues that arose after tunneling was completed.” This forward-thinking approach not only safeguards the structural integrity of existing tunnels but also streamlines future construction projects by providing a reliable framework for managing similar challenges.
The implications of this research extend beyond the immediate project in Nanjing. As cities around the world continue to expand their metro systems, the methodologies developed here could serve as a blueprint for other urban areas facing similar geological challenges. By prioritizing safety and structural resilience, the construction sector can enhance its reputation while ensuring that public transit systems remain efficient and reliable.
As urban rail transit continues to evolve, insights from this study may lead to a new standard in construction practices, particularly in water-rich soft soil regions. The proactive measures outlined by MA Xifeng and his team not only promise to protect existing infrastructure but also pave the way for future advancements in shield tunneling technology.
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