The landslide (sinkhole) accident in Myeongil-dong, Gangdong-gu, Seoul, was found to have occurred when unstable ground that was not discovered during the design and construction phase collapsed due to past tunnel construction and old sewer pipe leaks. The government plans to take administrative action and investigation requests for construction works, etc. based on the accident investigation results.
On the 3rd, the Ministry of Land, Infrastructure, Transport and Tourism revealed the results of an investigation by the Central Underground Accident Investigation Committee on the sinkhole accident that occurred in Myeongil-dong, Gangdong-gu, Seoul in March of this year. Sajowi identified a weak deep weather station discontinuity as the cause of the accident. A deep weathering zone is an area where rocks are weakened by physical and chemical weathering effects deep below the surface of the earth. Sajo-wi explained, “We discovered multiple discontinuous surfaces through field research near the accident site and analysis of drone shooting results,” and “the wedge-shaped block formed by intersecting 3 of these discontinuous surfaces is the decisive cause of ground collapse.”
Tunnel construction carried out at the accident site in the past and leaks from old sewer pipes have also been shown to have an impact on the weakening of the ground at the accident site. According to the Ministry of Justice, the groundwater level at the accident site dropped due to the construction of a tunnel in the 13th section of the Sejong-Pocheon Expressway in the past. As the groundwater level drops, empty spaces are created in the ground, increasing the possibility of subsidence. Old sewer pipes also contributed to the weakening of the ground. Sajowi explained, “The discontinuous surface of the deep weathering platform that was not confirmed during the design and construction phase slipped due to a drop in groundwater level and sewer pipe leaks, and as a result, external forces exceeding the design load acted on the tunnel, causing the tunnel to collapse and ground collapse.” In particular, the old sewer pipe is a place where problems such as cracks and broken joints were pointed out as a result of the 2022 survey, but no repair measures were taken.
The Ministry of Justice proposed measures to prevent recurrence, such as strengthening ground surveys. In the future, the Ministry of Sajo recommended reducing the interval between ground surveys to strengthen design and construction management, constructing non-drainage tunnels (TBM, etc.) in the deep weathering zone of the city, strengthening ground exploration to strengthen the management of underground facilities, and replacing old sewer pipes near excavation works. The Ministry of Land, Infrastructure, and Transport plans to immediately notify relevant agencies such as relevant departments and local governments of the investigation results to strengthen on-site safety management and take administrative action and investigation requests to prevent the recurrence of similar incidents.
