Seoul to Resume Line 9 Construction at Myeongil-dong Subsidence Site... "Safety First"

Ground Reinforcement Completed for Phase 4 of Line 9 in Myeongil-dong
Supplementary Design for "Ground Subsidence Zone" Ensures Tunnel Stability
Reflecting Joint Findings with the Ministry of Land, Load Reinforcement Implemented

The Seoul Metropolitan Government has completed ground reinforcement at the construction site for Phase 4 of Line 9 in the Myeongil-dong area of Gangdong-gu, where a ground subsidence accident occurred in March last year, and will resume construction.

On March 26, the Seoul Metropolitan Government announced that it has completed supplementary design work related to the ground subsidence accident in the area and will begin construction on March 31. During the construction period, the city will establish a real-time safety inspection system, conduct daily visual inspections inside the tunnel, perform measurement management twice a day, and carry out GPR (Ground Penetrating Radar) surveys during construction, with a commitment to managing the site with "citizen safety as the top priority."

Location map of the resumption of Line 9 construction in Myeongil-dong, Gangdong-gu. Seoul Metropolitan Government

After jointly investigating the cause of the accident with the Ministry of Land, Infrastructure and Transport, the Seoul Metropolitan Government determined that a discontinuity in the underground deep weathered zone, which was not identified during the design and construction phases, became weakened due to a drop in the groundwater level and sewage pipe leakage, causing it to slip. Additionally, external forces exceeding the design load acted on the tunnel, leading to tunnel collapse and ground subsidence.

Based on these findings, over the past three months, the city has reinforced the stability of the ground and tunnel through detailed inspections of the entire site. This included checking for abnormal leakage around excavation areas, inspecting the condition of sewage facilities (such as sewage pipelines, manholes, and stormwater inlets) around open-cut sections, and conducting electrical resistivity surveys.

Additionally, the city has completed supplementary design work that applies reinforcement methods capable of withstanding maximum external forces and ground pressure during tunnel excavation. To suppress ground deformation and improve structural stability, the plan is to install perforated steel pipes around the tunnel and inject solidifying agents into them, thereby hardening the soil and enhancing ground stability through the "steel pipe reinforcement grouting" method.

Furthermore, before tunnel excavation, the ground from the surface down to below the tunnel will be solidified using grouting, and additional grouting will be densely applied at 0.8-meter intervals to various parts, sidewalls, and the lower section inside the tunnel. The grouting for the tunnel roof ground, previously arranged in two overlapping rows at 5.6 meters, will now be arranged in three overlapping rows at 4 meters, narrowing the spacing. In addition, the steel support structures inside the tunnel, which support it against external forces, will be upgraded from the previous H-100 grade to the thicker and stronger H-150 grade.

To further enhance safety and quality management during construction, the city will also implement continuous CCTV monitoring and manage video records of the work process.

The Seoul Metropolitan Government is actively working to compensate accident victims, including bereaved families, through disaster management funds, citizen safety insurance, and liability insurance for public facilities. Although the investigation concluded that the tunnel construction was not the direct cause of the accident, the city deeply sympathizes with the families of the victims and is working to ensure that construction loss insurance can provide prompt support.

Chunkeun Lim, Director of the Urban Infrastructure Headquarters of the Seoul Metropolitan Government, stated, "Above all, we have decided to resume construction after implementing double and triple checks and sufficiently securing the ground stability of the tunnel so that citizens can safely pass through the construction section. Going forward, we will not only manage all sites in Seoul with 'citizen safety and reassurance' as the top priority, but also ensure that compensation for accident victims is handled as quickly as possible within the institutional framework."

This content was produced with the assistance of AI translation services.