▲ The Seosomun Overpass is being demolished on May 29, following an accident that resulted in 6 casualties due to a partial structural collapse.
With the demolition of the Seosomun Overpass—which saw a partial collapse of its deck in May, resulting in 6 casualties—now complete, traffic under the overpass and in the surrounding area, which had been partially restricted, will fully resume starting at midnight tomorrow (July 11).
The Seoul Metropolitan Government announced, "We finished the demolition work on July 5 and have since completed joint inspections with the Ministry of Land, Infrastructure and Transport, the Korea National Railway, and Korea Railroad Corporation (KORAIL)."
The Seosomun Overpass project was halted on May 26 after a girder sank during demolition work. Later that afternoon, a portion of the slab collapsed during an on-site safety inspection, killing 3 construction workers and injuring 3 public officials.
Following the incident, the city completely re-established its demolition plan after consulting with experts and conducting safety reviews, subsequently proceeding with the removal of the remaining structures.
After finishing the removal of the deck on May 29, the city recently completed the demolition of the bridge piers as well.
As planned, the city will construct a new overpass on the site where the old one stood.
The city plans to finish clearing the site and organizing surrounding roads and railway facilities by the end of this month, begin construction of the new overpass early next month, and open it in March 2029.
The new Seosomun Overpass will have a total length of 570 meters (335 meters for the bridge and 235 meters for retaining walls) and will feature 4 lanes in both directions.
By applying the latest construction technology, the distance between bridge piers (span length) will be increased to a maximum of 45 meters, up from the previous 28 meters, and the number of piers will be reduced from 18 to 7.
The city explained that the height under the overpass where the railway passes will be 8.7 meters, higher than the previous 6.9 meters, to reduce the sense of confinement under the structure.
To ensure safety and construction efficiency, the girders that support the bridge deck will also be changed.
While the previous structure used "prestressed concrete girders," which contain steel wires inside concrete, the new overpass will use "steel plate girders" made by joining steel plates together.
The city stated that steel plate girders are lighter in self-weight and easier to install, allowing for a reduction in the number of piers and enabling safe and efficient construction even in limited working environments.
Furthermore, for the foundation work to set the piers, the city will apply the "Sacrificial Steel Pipe + Reverse Circulation Drilling (RCD)" method, which involves inserting a sturdy steel pipe to fix the wall before filling it with concrete during excavation.
This method was chosen to minimize the impact on the adjacent subway tunnel, considering that the distance between the new overpass piers and the subway tunnel is as close as 3.8 meters in some areas.
The city explained, "This new overpass construction is being carried out in an environment completely opposite to the past, so we have placed a unique emphasis on safety. In the past, the overpass was installed first and then Subway Line 2 was built underneath, but this time, we must place a new overpass over the currently operating Line 2."
Accordingly, the city identified the location of underground facilities through Ground Penetrating Radar (GPR) surveys and precise measurements to adjust pier locations and minimize interference. It also plans to secure safety by reinforcing the interior of the tunnel before setting the piers.
During construction, 76 automated monitoring devices of 6 types, including crack gauges and convergence meters, will be installed at key points in the tunnel to monitor minute movements of the structure, and inspections will continue for more than 6 months after construction is completed.
Regarding the reason for delaying the opening date, which was initially planned for March next year, by one year, the city explained, "We prioritized the safety of the extremely limited urban work environment and nearby facilities such as subways and railways. To minimize inconvenience to citizens, we decided to focus on a 'perfect and complete opening' rather than shortening the construction period."
As the new overpass construction must cross over the Gyeongui-Jungang Line railway, work can only be conducted during late-night hours from 1:30 AM to 4:30 AM.
Lim Chun-geun, Head of the Seoul Metropolitan Government's Infrastructure Headquarters, said, "Taking the accident that occurred during the overpass demolition as a lesson, we have completely strengthened the safety management system for the entire process of the new construction." He added, "We ask for the broad understanding of citizens regarding the inevitable traffic inconvenience during the construction period, and we will safely complete the construction based on thorough prior consultation and strengthened safety standards so that citizens can trust and feel at ease."
(Photo: Yonhap News)
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