The Hanoi Metropolitan Railway Management Board (MRB) has issued an official statement regarding the unexpected surge of tunnel excavation additives to the surface, which spilled into Alley 7 on Giang Van Minh Street.

The incident occurred at 4:00 PM today during the underground construction of the Nhon - Hanoi Station metro line. While tunneling, additives used in the excavation process unexpectedly surfaced in the Kim Ma area, causing material to flow into a residential alley.

Following an on-site inspection, MRB, alongside consultants and contractors, initially determined that the likely cause was the existence of old, unused wells or drainage pipes underground, which created pathways for the excavation additive to rise to the surface.

MRB representatives explained that prior to tunnel boring, consultants and contractors had conducted surveys along the metro route. However, due to changes in property ownership over time, some underground structures, such as old wells or boreholes from previous construction projects, were not fully documented. As a result, there were gaps in data regarding underground conditions.

During tunneling, excavation additives are injected under pressure to stabilize the soil at the tunnel face. If the additive encounters open voids, such as old wells or boreholes, it can escape to the surface.

MRB assured that this phenomenon was short-lived and stopped immediately after the tunnel boring machine (TBM) passed through and installed the tunnel lining. The agency emphasized that such occurrences are common in urban tunneling projects and do not pose structural risks.

Upon detecting the issue, the project’s management team promptly instructed contractors to mobilize equipment and personnel to resolve the situation. The response included extracting the additive, cleaning affected areas, and ensuring environmental safety.

Lee Young Kyeong, Deputy Project Director of the Hyundai & Ghella consortium, stated: "This is a technically anticipated situation during tunnel boring and was immediately controlled. We are committed to complying with all technical and safety standards while maintaining close coordination with the project owner and relevant agencies to ensure safe and efficient construction."

MRB reaffirmed that the incident did not compromise the structural integrity of the metro project and caused no harm to people or property. The board is now working closely with relevant units to assess the exact cause and implement technical measures to prevent similar occurrences in the future.

N. Huyen