Seoul City said on the 10th that traffic under and around the Seosomun overpass will fully resume from 12 a.m. on the 11th. It comes one month after a deck collapsed during demolition work early on May 26, killing three people and injuring three.
Seoul City said it finished demolishing the Seosomun overpass on the 5th and then underwent a joint inspection with the Ministry of Land, Infrastructure and Transport, Korea National Railway, and Korea Railroad Corporation (KORAIL).
As planned, a new overpass will be built where the old one was demolished. By the end of this month, it will finish tidying the site and maintaining nearby roads and railway facilities, and from the 1st of next month it will begin construction of the new overpass. Opening is scheduled for March 2029.
The new Seosomun overpass will be 570 meters long in total (a 335-meter bridge and a 235-meter retaining wall), with four lanes in both directions. The maximum span between bridge piers will be extended from 28 meters to up to 45 meters. The number of piers will be reduced from 18 to seven. The clearance under the overpass where the railway runs will be built to 8.7 meters, higher than the previous 6.9 meters.
The girders that support the bridge deck will also be changed. Previously, they were prestressed concrete girders with steel tendons embedded in concrete. The new overpass will use steel plate girders made by joining steel plates. They are lighter and easier to build.
The new overpass construction takes into account that conditions are entirely different from when the former overpass was built. In the past, the overpass was installed first and then Subway Line 2 was bored underneath. This time, the overpass must be set over an already operating Line 2. The distance between the new overpass piers and the subway tunnel is as little as 3.8 meters at the closest point.
For the foundation work to erect the piers, it will apply the sacrificial steel casing plus reverse circulation drill (RCD) cast-in-place pile method, which inserts a rigid steel casing in advance to fix the wall when excavating and then fills it with concrete. The method minimizes the impact on the subway tunnel.
Work is only possible for three hours late at night, from 1:30 a.m. to 4:30 a.m., when trains are not running. That is because the new overpass will span over the Gyeongui-Jungang Line railway.
Im Chun-geun, head of Seoul City's Infrastructure Headquarters, said, "We have significantly strengthened the safety management system throughout the entire new construction process, taking as a lesson the accident that occurred during the overpass demolition," and added, "We ask for citizens' generous understanding of the unavoidable traffic inconvenience during the construction period."