Seoul’s Underground Infrastructure Raises Ground Stability Concerns

Seoul’s recent sinkholes have raised public safety concerns and questions on how existing and future underground infrastructure affects such events. 

On March 25th, as you can see in the following video, a biker was swallowed by a 20m-wide and 20m-deep sinkhole while driving on a Seoul street. His body was found the next day 50m away from the sinkhole.

Based on Ministry of Land, Infrastructure and Transport data, out of 867 reported subsidence incidents throughout South Korea between 2020 and 2024, 45.4% of them were attributed to sewer pipe damage.  Furthermore, Seoul district-level data reveals that Seoul’s city center and popular areas have 50-year-old sewer pipelines on a scale between 45.5% and 53.5%. The opposition Democratic Party of Korea revealed recently that 30% of Seoul’s sewer pipelines are over 50-year-old.

With an available budget of 200 billion won ($140 million) for maintenance, up to last month, Seoul was trying to keep up with sewer pipelines deterioration. As a preventive measure, GPR systems are being used to detect anomalies. However, these systems are effective up to 2m underground.

The Seoul Metropolitan Government announced on April 27^th that they will install a bat-shaped column sensor at a 20m depth. The new system will be able to detect underground changes in layers within a 50m radius. Although it seems like a more effective solution, the new system cannot be transferred around the city, like GPR systems, but needs to be installed to a specific location. This is why it has been decided to be installed next to large construction sites and at the same time expand GPR surveys by almost doubling the vehicle-mounted GPR units. 

To support these efforts, an additional 2.27 billion won ($2.08 million) has been allocated by the central government, while the available budget for maintenance is also doubled to 400 billion won to achieve upgrades of 200 kilometers sewer pipelines per year. 

Officials are also expected to create and publish a geotechnical property map of large excavation project areas. While there is a public demand for officials to publish an area risk map, this has not been published due to fear of affecting real estate prices in these areas. Privately generated maps have emerged online to fill in this gap.

Besides aging infrastructure, the city is also facing ground stability concerns due to the rise of the underground retail market and the ongoing tunnel works. Over the decades, due to limited space and increased demand, developers turned to underground space to meet commercial demand. As a result, Seoul’s underground market network has now become a vital element of everyday urban life, where at many major subway stations people can have their meal, shop and even visit a clinic without stepping over ground.

This inevitable increase in underground facilities has raised concerns about the increased overall structural load placed on the ground below and the possibility of disrupting natural flow of groundwater.

Concerns on poor construction management, such as improper excavation, inadequate soil stabilization or poor backfilling were also raised due to a subway tunnel collapse, south of Seoul. Anomalies were sensed shortly before the incident and immediate traffic control measures managed to prevent possible casualties.

Despite these significant events, it is worth mentioning that according to official data, annual occurrences of landslides to the city of Seoul seem to be decreasing over the years.