Determining the cause of the incident
On the afternoon of February 21, the Hanoi Urban Railway Management Board (MRB) had official information on the cause and measures to handle the phenomenon of tunnel excavation sprayed on the ground during the tunnel drilling process using a TBM excavator, at the underground section of the Hanoi City Metro pilot project, the Nhon - Hanoi Railway Station section (Nhon - Hanoi Railway Station metro).
Accordingly, during the excavation process of the TBM 1 machine, the tunnel excavation was done from the drainage culvert in the area of Lane 7 Giang Van Minh (Ba Dinh District).
The incident was determined and immediately reported by the contractor's staff assigned to supervise the area.
Upon receiving the report, the Investor, MRB, worked with Systra consultants, Hyundai - Ghella contractors and local authorities (Kim Ma ward) to inspect the scene to coordinate handling according to the response plan.
Up to now, the Project has determined that one of the reasons for the above incident is that underground wells still exist, old drainage culverts are no longer used, creating a path for tunnel boring additions to the ground.
During the drilling process, the tunnel drilling accessories are sprayed with pressure to stabilize the soil in front of the peach mirror. When encountering holes, tunnel drilling additives combining water and fine materials in the soil will follow these holes to the ground.
MRB also affirmed that this is a common phenomenon in the construction of urban tunnel drilling works using TBM technology to balance soil pressure (EPB).
"Construction under soil conditions always has many unpredictable problems. Although the project has conducted a thorough survey along the route and worked specifically with local houses and authorities where the tunnel passes through to collect data, in reality, there is still incomplete information because the owners have changed and the houses have been rebuilt many times.
However, we affirm that the houses on the tunnel are being monitored continuously and are all within the safety threshold. This phenomenon may continue to occur, but we have developed a response plan in advance and are making efforts to speed up the processing progress to ensure environmental sanitation and people's lives," said Mr. Salvatore La Valle - Head of TBM Engineering Group.
Non-toxic solutions
According to Mr. Sergei Papin - Head of the Systra Consulting Tunnel Engineering (France), the material sprayed on the ground in the above incident was a mixture of mud, water and tunnel digging additives.
"In which, tunnel excavation additives are completely harmless, environmentally friendly, meet European standards and have undergone strict inspections and approvals of the Project," Mr. Sergei Papin shared.
On behalf of the investor, Mr. Nguyen Ba Son - Deputy Head of the Hanoi Urban Railway Management Board, along with the Consulting team and contractors, apologized to the people for the inconveniences during the construction process, hoping to receive sympathy and cooperation from the people in the project area.
According to Mr. Son, the project always puts safety first, has been strictly implementing safety measures during the construction process, complying with the project's technical standards and current legal regulations.
"MRB has directed Systra Consulting and the Huyndai - Ghella Contractor Joint Venture to continue surveying, assessing the causes and providing solutions to minimize the occurrence of similar situations as well as the impact on people", Mr. Nguyen Ba Son - Deputy Head of the Hanoi Urban Railway Management Board shared.
Mr. Son also affirmed that the above phenomenon did not affect the structure of the project nor caused any human casualties. TBM 1 has so far dug 1.2km and is still continuing construction at an average speed of 10-12m/day.
Currently, the work to fix the problem and clean up the environment is being urgently carried out.
