Seoul overpass collapsed during inspection of deflected section, city gov't says

Police and officials from the Seoul Metropolitan Government investigate the collapse of the Seosomun overpass in Seoul, Wednesday. Yonhap

Workers on the Seosomun overpass had already detected a dangerous deflection in the structure hours before it collapsed, but continued to work on the span rather than leave the site, the Seoul Metropolitan Government said Wednesday in its first detailed account of the accident.

According to Lim Choon-keun, head of the city government's infrastructure bureau, workers began cutting the S9 slab — the ninth deck segment spanning the railway — of the 60-year-old overpass at around 1:30 a.m. Tuesday. Roughly an hour later, they detected a deflection of about 29 millimeters between two girders and halted the operation.

By midafternoon, as engineers and officials were back on the span to inspect the damage and discuss whether to shut down road and rail traffic below. At 2:33 p.m., without warning, a 15-meter section collapsed onto the tracks, killing three people and seriously injuring three others.

Asked why the workers were sent onto a section that had already shown dangerous signs, the official said it was probably difficult to assess the damage from outside.

“To check the condition of the girder, the workers may have determined that someone had to go under the slab,” Lim said.

Lim Choon-keun, head of the city government’s infrastructure bureau, speaks during a press briefing at City Hall in Seoul, Wednesday. Newsis

When asked why the city government did not close the road and rail line once the overnight deflection was detected, the official said the afternoon inspection was meant to determine whether such a shutdown was actually necessary.

Lim noted that earlier design reviews had found no significant issues with the structural stability of the girders under the chosen demolition method.

Demolition work at the site is now frozen under a stop-work order issued by the Ministry of Employment and Labor. The ministry is currently reviewing the resumption plan, submitted by the city earlier that day. If the plan is approved, city officials estimate it will take about 40 hours of continuous work to dismantle the damaged span and clear scaffolding.

Police and prosecutors are now moving to determine whether that assessment and the procedures that followed were sound. According to the Seoul Metropolitan Police Agency, its investigation unit has obtained key documents from the city government. These papers are believed to contain information about the safety rules and procedures that were supposed to govern the demolition of the overpass.

In collaboration with forensic experts, investigators are trying to find out whether the rules were properly followed during the demolition work. Meanwhile, the Seoul Western District Prosecutors’ Office has launched a dedicated task force to handle the case, made up of 10 members, including four prosecutors from its department specializing in industrial accidents.

The overpass spans a railway connecting Seoul Station and a train depot in Goyang, Gyeonggi Province, and the collapse disrupted rail services across the network. According to KORAIL, overall train operations on Wednesday decreased to 80.8 percent of the normal schedule, with 552 of 683 services running and 131 trains canceled as a result of the incident. Amid the continuing disruption, the government said it aims to finish repairs to the damaged railway infrastructure as soon as this week.

The collapse has also thrown the Seoul mayoral race into uncertainty. Both Oh Se-hoon of the People Power Party and his main rival, Chong Won-o, of the Democratic Party of Korea, suspended campaign activities, canceling street rallies and daily morning briefings.

Oh, the incumbent mayor seeking reelection, wrote on Facebook that he had asked relevant agencies “to thoroughly determine the exact cause of this accident and take every necessary measure so that such a loss of life never happens again.” He also urged officials to “carefully examine support measures for the bereaved families.”

Chong has likewise instructed his team to tread carefully. He reportedly told campaign staff not to link the accident to the election or use it to attack opponents while the cause remains unclear and the recovery effort is still underway.