Deeper Transportation Network, Increased Ground Subsidence... Proper Cause Analysis Needed [New Transportation Refugee Report] 16

"Expanding transportation infrastructure inevitably requires going underground. Sinkholes are a resulting problem. In the future, underground excavation projects will accelerate the formation of sinkholes. Rather than focusing on the phenomenon itself, it is more important to identify vulnerable areas first."

Ho Lee, chairman of the Korea Underground Safety Association, is introducing a ground subsidence risk prediction map at the association office in Munjeong-dong, Songpa-gu. Photo by Jinju Han

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As Seoul's transportation network expands, the floating population increases, and with high-density and underground development, public awareness of safety is rising day by day. As large-scale excavation projects become more frequent, both the frequency and types of ground subsidence accidents are diversifying. Experts point out that precise cause analysis and thorough pre-assessment must be properly implemented.

On July 31, Lee Ho, president of the Korea Underground Safety Association, was interviewed at the association's office in Munjeong-dong, Songpa-gu, Seoul. Lee stated, "From 2018 to the present, there have been 139 cases of ground subsidence accidents in Seoul involving areas of at least 1㎡, but the number of times the Central Underground Accident Investigation Committee was convened is very few," adding, "Accidents that did not involve casualties or did not attract media attention often go uninvestigated." Lee became president of the association in September 2023 and also serves as CEO of ACE ENG. He has also served as vice president of the Korean Tunneling and Underground Space Association and vice president of the Geotechnical and Foundation Engineering Society.

Lee emphasized, "We need to investigate dangerous areas, fill any cavities, and when construction of buildings or underground transportation networks is planned, we must inspect buried utilities such as water and sewage pipes to ensure there are no problems before starting construction. Most major accidents at construction sites occur during the construction process, so shortcomings in safety must be disclosed and we need to start from scratch."

His argument that the risk level of ground subsidence should be made public and that measures should be established to minimize potential damage during construction is based on the same rationale. After the sinkhole accident in Myeongil-dong in March, the association compiled a "Ground Subsidence Risk Prediction Map" for Seoul's 25 districts and 426 administrative neighborhoods, using information from 15 experts with over 30 years of experience and publicly available data. By comprehensively analyzing ground and groundwater characteristics, subway distribution, ground subsidence history, and the distribution of aging buildings, they classified risk levels into five categories and even marked locations where cavities have occurred. After this data was published, the association received an official request from the Seoul Metropolitan Government to refrain from releasing the map, citing concerns that it could cause public anxiety.

Lee pointed out, "Even if nothing is done, underground utilities deteriorate and cause sinkholes, but when excavation is conducted nearby, the process is accelerated. We need to reconsider whether the main culprit is underground utilities or surrounding development," adding, "Rather than simply identifying the aging of underground utilities as the sole cause, we need to create detailed maps of high-risk areas to examine exactly 'where the problems lie'." The association also plans to release risk maps for the six major metropolitan cities.

He also emphasized the need to lower the threshold for utilizing platforms that reflect ground subsidence accident data and ground-penetrating radar (GPR) survey results. He said, "In the case of JIS, more than 10,000 underground safety assessment reports are included, but they are saved as PDF files, and only the project owner can access the information. No one else has access rights," adding, "Information needs to be accumulated in one place, but it is regrettable that the government and local governments are operating platforms independently and simultaneously."

Seoul Ground Subsidence Risk Prediction Map created by the Korea Underground Safety Association using public data and the expertise of 15 specialists. Provided by Korea Underground Safety Association

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