The incident happened at 4:00 p.m. this afternoon. During the construction of the Nhon - Hanoi Railway Station metro line tunnel project, tunneling additives were sprayed onto the ground in the area of ​​lane 7 Giang Van Minh, Kim Ma.

After the inspection, the investor - Hanoi Urban Railway Management Board (MRB), together with the consultant and contractor, inspected the site and initially determined that the cause could be due to the existence of old wells or drainage pipes underground that created a path for the tunneling additives to flow to the surface. These old wells and drainage pipes are no longer in use.

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Additives were suddenly sprayed onto the ground and spilled into the alley where people lived. Photo: MRB

MRB representative added that according to the project process, before tunneling, the consultant and contractor conducted a survey of the works along the route. However, due to changes in ownership of the works over time, many information were not fully provided, so it was inevitable that there was still a lack of data on underground works such as water wells, residential wells, or geological survey boreholes from previous projects that were not filled.

During the drilling process, tunneling additives are sprayed under pressure to stabilize the soil in front of the excavation face. When encountering open holes such as water wells or boreholes, the tunneling additives will flow up to the ground surface through these voids.

This phenomenon only occurs for a short time and ends immediately after the TBM drills through and installs the tunnel lining. This is a common phenomenon during the construction of urban tunnel boring projects.

Immediately after discovering the incident, the investor directed the consultant and contractor to urgently mobilize equipment and human resources to fix it according to the project's process, including cleaning the drilled mortar and cleaning the surface of the grouted area, ensuring safety and environmental hygiene in its original state.

Mr. Lee Young Kyeong - Deputy Project Director of Hyundai & Ghella Joint Venture affirmed: "The phenomenon of tunneling additives overflowing to the ground surface during the drilling process is a technical situation that was within the plan and was immediately controlled. We are committed to fully complying with technical standards and safety procedures, and will continue to closely coordinate with the investor and related units to ensure the construction process is safe and effective."

MRB commits that the above phenomenon does not affect the structure of the building nor cause any damage to people or property. Currently, MRB is closely coordinating with related units to accurately assess the cause and deploy technical measures to prevent similar incidents in the next phase.