"Warning Signs Like Cracked Walls, Ground Sinks Even After Repairs to Human Depth"... Fear Beneath Seoul's Feet [New Transportation Refugee Report] 15

The Future of Seoul - The Future of Transportation
'Safety' Overlooked in Overcrowded Urban Development
28 Cases of Ground Subsidence in Seoul This Year
Already Surpassing Last Year’s Total of 17
Frequent Incidents Near Construction Sites Due to Water Pipe Leaks
Impact of Urban Subway and Road Development Projects
Neglect of Underground Safety Assessments Due to Cost Issues

"There were warning signs even before the sinkhole appeared, such as cracks forming in the walls. The spot that was first repaired sank again, and it was deeper than a person’s height. There are also many cracks in the old multi-family buildings nearby, which makes us anxious," said the representative of A Realty in Imun-dong.

On the 30th of last month, at the site of the ground subsidence accident near Sinimun Station in Imun-dong, Dongdaemun-gu, a fence restricting access has been installed, and a banner urging the establishment of relocation measures is hung. Photo by Jinju Han

Urban development has made citizens feel uneasy about the ground beneath their feet. It has not only caused inconvenience in daily movement but also affected the expansion of transportation infrastructure. The overcrowding of cities has accelerated underground development, but weakened ground conditions are now threatening both safety and property. Experts say that 'safety' must be the first topic of discussion in the current urban planning process, including transportation infrastructure.

On July 23, a ground subsidence accident occurred near the construction site of the Imun 2-dong Complex Government Building and Public Parking Lot, in front of Exit 1 of Sinimun Station on Subway Line 1. When visiting the site a week later, on July 30, access to a two-story commercial building nearby was restricted, and store fixtures from closed businesses were placed outside. Residents had hung banners reading, "Prepare relocation measures and proceed with construction. We can't live here because it's too dangerous." Residents passing by the pedestrian walkway right next to the construction site looked around anxiously. A resident in his 60s living in Imun-dong said, "I want the commercial building, which could collapse at any time, to be demolished quickly so that we can get around safely. There are a lot of complaints because there are no relocation measures in place."

Residents said there were warning signs such as cracks in buildings and the ground near the construction site, and although they reported these several times to the district office, no action was taken. The first sinkhole that appeared measured 1.2 meters wide and long, and 0.8 meters deep. After the contractor temporarily repaired this sinkhole, it sank again. The second sinkhole was even larger, measuring 2.5 meters wide, 5 meters long, and 2.5 meters deep. Merchants and residents in buildings adjacent to the ground subsidence site have temporarily evacuated nearby. The Dongdaemun-gu office stated, "We are conducting an emergency precision safety inspection on eight buildings adjacent to the construction site and will respond according to the inspection results." A Seoul city official also said, "For safety reasons, we are restricting traffic on the back road at the accident site. Several possible causes have been suggested, but we need to identify the cause in order to establish measures to prevent recurrence."

Experts also pointed out that licensing agencies must take responsibility for management. Park Myungki, a professor from the Korea Industrial Safety Professors Association, said, "Sinkholes occurred in both Imun-dong and Yeonhui-dong last year after it rained, and both areas have weak ground and nearby construction sites in common. When the geological condition is poor, the risk of sinkholes is higher. Measures should be taken during construction permitting or building, but the licensing agencies are not involved at all. When carrying out construction, it is necessary to check the amount of groundwater and soil, but this is not being done properly," he said.

Seoul Ground Subsidence Incidents Surge Compared to Last Year

Seoul has many large construction sites, and during the summer, heat waves and heavy rain occur one after another, making ground subsidence more frequent. In July alone, there were six ground subsidence accidents in Seoul. According to the Underground Safety Information System of the Ministry of Land, Infrastructure and Transport, there have been a total of 28 ground subsidence accidents in Seoul from January to July this year. The number of accidents in these seven months has already surpassed last year’s total of 17. Looking at the causes of last year’s ground subsidence accidents: there were eight cases due to damage to water and sewage pipes, two due to poor excavation work, two due to poor compaction (backfilling), one due to damage to other buried objects, and four due to other reasons. From 2015 to last year, there were 2,119 ground subsidence accidents nationwide over ten years, with 228 of them (10.8%) occurring in Seoul.

The causes of ground subsidence are varied. It can occur when underground water flow changes and cavities form, when old water and sewage pipes leak, or when weak ground is not sufficiently compacted. In urban areas, ground subsidence is often caused by underground development projects that create large-scale facilities such as subways, roads, or commercial buildings underground. Near construction sites where underground development is underway, even a small impact can cause the ground surface to collapse instantly, making it harder to detect risks in advance. Ground stability can also be weakened near underground facilities where excavation is ongoing or has just been completed, resulting in subsidence. Underground water also flows from higher to lower areas; if too much groundwater is pumped out, cavities can appear in the soil, causing subsidence. Ground subsidence typically occurs most frequently in July and August, but with climate change causing more frequent heavy rains, rainwater rapidly flows underground, increasing the frequency of ground subsidence.

Many Cases of Avoiding Underground Safety Assessments

As underground development projects have increased, laws to assess underground safety have been implemented, but limitations remain. According to the Special Act on Underground Safety, which came into effect in 2018, an underground safety assessment is required for excavation deeper than 20 meters, and a small-scale underground safety assessment is required for excavation between 10 and 20 meters deep. Projects less than 10 meters deep are not subject to assessment. The Imun-dong construction site is building a structure with two basement levels and five above-ground floors, and although some areas exceeded 10 meters in depth and underwent a small-scale underground safety assessment, a sinkhole accident still occurred. Clients and contractors often neglect geological or ground investigations due to budget or time constraints. Even after a safety assessment, it is common to switch to unsafe construction methods to shorten the construction period.

An Hongseop, professor emeritus at Kunsan National University, said, "If continuous monitoring is conducted during construction, it is possible to know whether ground subsidence will occur, but accidents still happen due to lack of attention. It is difficult to set uniform regulations, and when it is necessary to establish construction methods and countermeasures suitable for the geology and groundwater level, the costs can be substantial. Since the Underground Safety Act was enacted, the safety assessment period alone usually takes four to six months, so some projects avoid digging basements altogether and build above ground instead," he explained.

Professor Park also pointed out, "From early warning signs such as asphalt cracks, sunken sidewalks, or gaps, we need professionals who can assess the local geology and groundwater conditions. In large cities where major underground development projects are underway, sudden ground subsidence can occur on roads or sidewalks used daily by many citizens, so it is urgent to prepare measures to ensure public safety."