Seosomun overpass demolished; road to reopen Saturday

Demolition of the Seosomun overpass — which caused casualties when part of the structure collapsed during removal — has been completed, and the road beneath it will reopen to traffic.

The Seoul Metropolitan Government announced Friday that it finished tearing down the Seosomun overpass on Sunday and, following a joint inspection with the Ministry of Land, Infrastructure and Transport, the Korea National Railway and Korail, will fully reopen Seosomun-ro — from the Arisu Headquarters intersection to the Korean National Police Agency intersection — at midnight Saturday.

After the accident during demolition, the city overhauled its removal plan following expert consultations and safety reviews. Deck removal within the railway protection zone was completed May 29, and pier demolition was finished Sunday. Road and railway facility cleanup around the site is scheduled for completion by the end of July. Full construction of a new Seosomun overpass will begin Aug. 1, with a target opening date of March 2029. The main construction work is expected to cost about 33.7 billion won ($22.4 million).

The railway lines running beneath the overpass — including the Gyeongui-Jungang Line — carry more than 600 train services a day. The decision to build a new elevated road was made to relieve chronic traffic congestion along Seosomun-ro by creating a grade-separated crossing over the tracks.

The new Seosomun overpass will stretch 570 meters and carry four lanes of traffic, built with the latest construction technology. The span between piers will be widened from the current 28 meters to a maximum of 45 meters, cutting the number of piers from 18 to 7. Reducing the pier count minimizes interference with railway infrastructure and improves long-term maintenance efficiency.

The clearance height beneath the overpass in the railway crossing section will also be raised from 6.9 meters to 8.7 meters, easing the sense of constriction below and improving driver visibility. To ensure both constructability and safety, the city will use steel plate girders — fabricated by joining steel plates — instead of the prestressed concrete girders used previously. Steel plate girders are better suited to long spans and urban construction, allowing safe and efficient work even in confined spaces.

For the foundation work to set the new piers, the city will use a sacrificial steel casing combined with a reverse circulation drill pile method. This technique involves inserting a rigid steel casing into the excavation to stabilize the walls before filling with concrete, minimizing the impact on the adjacent subway tunnel and enabling stable construction.

The city used ground-penetrating radar surveys and precision measurements to accurately map the positions of subway tracks and major underground utilities, then fine-tuned pier placement to minimize interference. It also plans to reinforce the interior of the subway tunnel — completed 43 years ago — before setting the piers, to ensure the tunnel's structural safety.

During construction, 76 automated monitoring instruments of six types — including crack gauges and convergence meters — will be installed at key points inside the tunnel to track minute structural movements in real time.

Given the constrained urban work environment and the need to prioritize the safety of nearby subway and railway infrastructure, the target opening date has been pushed back one year, from March 2028 to March 2029.

"We have taken the accident during demolition as a hard lesson and have comprehensively strengthened safety management across every phase of the new construction," said Im Chun-geun, head of the Seoul Metropolitan Government's Urban Infrastructure Headquarters. "We ask for the public's understanding regarding unavoidable traffic disruptions during construction, and we will complete the project to the strictest safety standards so that citizens can trust and feel confident in the work."