The Ministry of Land, Infrastructure and Transport on the morning of the 3rd announced measures to prevent a recurrence, including stronger design and construction oversight and supplements to underground safety assessments, in relation to the ground subsidence accident in Myeongil-dong, Gangdong District, Seoul, at the Government Complex Sejong.
The Ministry of Land, Infrastructure and Transport, based on proposals from the Central Underground Accident Investigation Committee, drew up institutional improvement measures to prevent similar accidents from recurring by combining internal reviews and opinions from related agencies.
First, by revising the geotechnical investigation design standards (KDS), it will establish investigation standards for non-open-cut urban tunnel projects and strengthen existing geotechnical investigation standards for tunnel work, such as recommending that investigation intervals be within 50 meters for tunnel construction in deep weathered zones in urban areas. It also plans to revise the standard manual for underground safety assessment to subdivide and manage action guidelines related to cumulative groundwater level drawdown to prevent rapid changes in groundwater levels.
In addition, it plans to enhance the effectiveness of inspections of underground utilities by specifying the timing of geophysical surveys during excavation work. The underground development project owner will be explicitly required in the standard manual for underground safety assessment to conduct geophysical surveys of underground utilities near the construction site before excavation and within three months after backfilling, and the administrator of underground utilities will have to shorten the survey cycle near their facilities according to subsidence risk by revising the enforcement rules of the Special Act on Underground Safety Management.
In addition, when constructing tunnels in deep weathered zones in urban areas, if underground utilities such as water and sewer lines exist above, it will recommend applying reinforced tunnel strengthening methods, and it will also consider activating an online evaluation system when face analysis is difficult.
Separate from the activities of the Central Underground Accident Investigation Committee, the Ministry of Land, Infrastructure and Transport and the Seoul Regional Land Management Office conducted a special inspection in April of the construction site for Section 1 of Phase 4 of the Seoul Subway Line 9 extension, where the accident occurred, together with the Korea Authority of Land & Infrastructure Safety (KALIS) and private experts.
These agencies uncovered three cases of supplemental underground safety management, including reinforcement of sections without struts, periodic inspections of soil tunnel sections, and reexamination of tunnel stability in the accident section, and requested action from the Seoul Metropolitan Government. For two cases of inadequate construction safety management concerning the slope of the berm at the bottom of the retaining wall and the overlap length of the connection part of the falling object safety net, they issued on-site correction orders and confirmed completion of the measures.
The Ministry of Land, Infrastructure and Transport will immediately notify related ministries, local governments, and other related agencies of the investigation results of the Central Underground Accident Investigation Committee to strengthen on-site safety management to prevent similar accidents from recurring, and will take steps to ensure administrative dispositions and investigations proceed swiftly.