Ground-level mud surfacing during the Nhổn-Hà Nội metro tunnel construction project on February 20th prompted public concern. The Hà Nội Metro Rail Management Board (MRB) issued a statement detailing the cause and remediation efforts.
Cause of the Incident
According to the MRB’s statement, a key factor in the incident was the presence of pre-existing, neglected, underground wells and drainage pipes. These subterranean structures acted as conduits for the tunnel boring machine (TBM) slurry, allowing water and fine soil particles to rise to the surface as the TBM worked.
The tunnel-boring process utilizes pressurized slurry to stabilize the surrounding soil. When encountering voids or pre-existing openings, this slurry combined with water and soil materials, causing the mud to surface. This phenomenon is common in Earth Pressure Balance (EPB) tunnel-boring methods and typically resolves itself once the TBM passes through the affected area and the tunnel lining is installed.
Slurry Safety
Systra (France) Tunnel Chief Engineer Sergei Papin stated that the surfaced material (a mixture of mud, water, and slurry) is completely harmless and environmentally friendly. The slurry conforms to European standards and has undergone rigorous testing procedures.
Remediation Efforts
The project’s investors swiftly deployed resources to resolve the issue. Six mud-suction trucks, two road-washing machines, and 100 workers are actively remediating the affected areas in accordance with the project’s procedures.
Apology and Safety Commitment
MRB Deputy Director Nguyễn Bá Sơn offered an apology to residents for the inconvenience caused by the construction. The MRB reiterated their commitment to prioritizing safety, adhering to safety protocols, technical standards, and legal regulations. They also instructed Systra and the Hyundai-Ghella joint venture to conduct further surveys and assessments to mitigate the risk of future incidents.
Project Status
The incident caused no injuries or damage to the project’s infrastructure. The 12.5km Nhổn-Hà Nội metro line continues at a rate of approximately 10-12 meters per day. Begun in 2009, the project is anticipated for completion in 2027.
Conclusion
Mud surfacing is an unavoidable aspect of complex infrastructure projects like urban rail lines. MRB’s transparent explanation of the cause and prompt remediation efforts are commendable. Effective collaboration amongst all stakeholders is vital for addressing such incidents while maintaining project timelines.
Reference Materials
- Press release from Hà Nội Metro Rail Management Board (MRB)
