Seoul City: "No Safety Issues Found at Seongsu Bridge Step Gap"…Expert Verification Results Released

Seongsu Bridge Entry Ramp Assessed as "Sound" in Terms of Subsoil Condition

Further Settlement Deemed Unlikely; Step Gap Considered a Common Phenomenon

Proactive Reinforcement and Management to Address Public Concerns; Support for Local Governments

The Seoul Metropolitan Government announced on August 21 that, according to an external expert verification of the step gap at the Seongsu Bridge entry ramp, there are no safety concerns. However, to address public concerns, the city has decided to proactively reinforce and manage the area as a preventive measure.

On July 29, Seoul Mayor Oh Se-hoon listened to explanations from officials during an on-site inspection at the southern end B ramp of Seongsu Bridge in Gangnam District, Seoul, where a step difference occurred. 2026.7.29 [Joint Coverage] Photo by Yonhap News Agency

On the same day, the city released the findings of the "Bridge Connection Safety Advisory Panel," which consists of 11 experts in structures, geotechnics, roadways, and construction. The panel thoroughly examined the results of on-site tests at Seongsu Bridge, geological surveys, changes in ramp level differences over time, environmental factors, and results from a comprehensive survey of all Han River bridges.

The advisory panel conducted detailed analyses of the southern B ramp of Seongsu Bridge, which had been a particular source of worry, as well as the adjacent three lanes. They performed surface wave exploration, dynamic cone penetration tests, boring investigations, and ground-penetrating radar (GPR) surveys.

The results showed that the subsoil beneath the Seongsu Bridge entry ramp is mainly composed of sand backfill and is considered to be of "average or better" strength and quality.

Assessment of historical changes in the ramp step and the current condition of the ground indicated that subsidence occurred primarily during the initial construction period. After more than 20 years since completion, the possibility of further settlement is deemed to be negligible. The investigation also examined nearby factors, such as the construction of GTX-A and changes in the groundwater level, but found no evidence of external factors influencing the step gap.

The main reason identified for the step gap at the interface between the bridge and the entry ramp was the difference in foundation types and resulting settlement. While the bridge is supported by a pile foundation resting on underground bedrock, the entry ramp connected to the bridge has a direct foundation installed on layers of fill and sedimentary soil.

The Seoul Metropolitan Government explained, "Settlement can occur in the entry ramp area due to the weight of the structure itself and vehicle loads. This may result in a height difference at the boundary with the bridge, where little to no settlement occurs."

On the 29th, officials conducted a dynamic cone penetration test on the entrance ramp of Seongsu Bridge in Gangnam-gu, Seoul, to investigate the cause of the ramp step difference. This test was carried out to measure the penetration depth of the test rod and verify the ground strength. Yonhap News Agency 2026.7.29

The city added that such step gaps are a phenomenon that can occur in various bridges both in Korea and abroad, and to ensure drivability, "connection slabs" are installed between the bridge and the entry ramp during the design phase.

A connection slab is a structure that mitigates height differences between the bridge and the entry ramp, preventing cracking and damage to the paved surface and ensuring vehicle drivability. During on-site tests at Seongsu Bridge, the city also confirmed that the connection slab was properly installed by removing some of the pavement for inspection.

A comprehensive survey of Han River bridges found step gaps at 32 entry ramps across 11 bridges. However, no voids (underground empty spaces) were detected, indicating no structural safety issues.

Nonetheless, the Seoul Metropolitan Government has decided to take proactive reinforcement and management measures to address public worry and ensure long-term safety. The city plans to reinforce the subsoil at the southern B ramp of Seongsu Bridge and the B ramp of Olympic Bridge, where step gaps are relatively large, and monitor changes in the ground and step gap continuously. If any section causes inconvenience to drivers due to unevenness, additional pavement may be applied to improve road flatness and drivability as needed.

In addition, the city will support emergency repair and reinforcement budgets to ensure the safety and prompt maintenance of road facilities managed by local district offices.

Choi Jinseok, Director-General of the Seoul Disaster and Safety Office, stated, "Through this investigation, we have confirmed that there are no structural safety issues at the entry ramps of Seongsu Bridge and other Han River bridges. We will reinforce and continuously monitor sections with large step gaps while also addressing public concerns and driving inconvenience, so that citizens can use the bridges with peace of mind."

This content was produced with the assistance of AI translation services.