The probe was triggered by the discovery that 50 of 80 main columns supporting the GTX platform at the underground fifth floor were built with only one row of main rebar instead of the two rows specified in the design, a shortfall of approximately 2,570 rebars across the affected columns, with up to 36 missing per column.
Contractor Hyundai Engineering & Construction has acknowledged that workers misread the design drawing, interpreting a two-row "two bundle" specification as a single row. The contractor self-detected the error during a quality inspection in November 2025 and reported it to the Seoul Metropolitan Government, but the city did not formally notify the transport ministry until April 29, drawing political criticism over a five-month reporting gap. The probe adds fresh scrutiny to a 1.07 trillion won ($713.2 billion) underground transit complex that has been in planning or construction since 2015 and its completion has already slipped from 2027 to October 2028.
According to the transport ministry, the inspection team includes 12 outside experts from the Korea Authority of Land and Infrastructure Safety, the Korea Railroad Research Institute and the Korea National Railway. The investigators will assess whether construction parties met legal obligations on construction management, safety, quality control and project management. The inspection period runs one month from its first meeting Monday and may be extended. Penalties available to the ministry include demerit points, corrective orders and fines against contractors and supervisors.
The Yeongdong-daero Underground Complex Development project beneath Gangnam, Seoul's heart of fashion and finance, connected to the Samseong Station GTX section, is one of the largest underground infrastructure undertakings in South Korea. The 21 hectare facility runs 1,000 meters from Bongeunsa Station to Samseong Station and reaches 53 meters underground across seven floors, according to the Seoul Metropolitan Government. When complete, it will serve five rail lines — GTX-A, GTX-C, the Wirye-Sinsa line and Subway Lines 2 and 9 — alongside a bus interchange, commercial space and a ground-level park covering the buried roadway.
Construction inspections are distinct from a separate audit the ministry launched on May 15 targeting the Seoul Metropolitan Government and Korea National Railway over delayed reporting of the defects, the ministry said.
The Samseong project's timeline has been repeatedly pushed back. The feasibility study began in 2015 under planning name "Yeongdong-daero Underground Space Complex Development Feasibility Study and Basic Plan." Groundbreaking originally scheduled for November 2020 was delayed to June 30, 2021 after design changes consolidated two separate rail levels into one, requiring fresh permits. The completion target moved from December 2027 to April 2028, and most recently to October 2028.
GTX-A trains will pass through Samseong without stopping until a temporary transit hub opens in June 2027. Full station opening is now scheduled for 2028.
The project is funded by public contribution payments from Hyundai Motor Group's Global Business Center development rather than from tax revenue. Total project cost stands at 1.076 trillion won under the basic plan, according to the Seoul Metropolitan Government.
Construction has been carved into six work zones. Civil engineering work is divided across four zones, with DL E&C, Hyundai E&C and Lotte E&C as principal contractors. Architecture is divided across two zones, with Hyundai E&C and a DL E&C consortium contracted. The 2nd architecture zone failed two bidding rounds before being awarded, contributing to schedule slippage.
The Samseong corridor, dubbed by locals as "highway of hell," concentrates four major construction projects within a single neighborhood. The Hyundai Motor Group GBC tower, the GTX-A Samseong Station, the Yeongdong-daero complex transit center and a separate Yeongdong-daero road undergrounding project run by Daewoo E&C between Bongeunsa Station and Cheongdam-dong are all underway concurrently.
Two subway Line 2 exits at Samseong Station — Exits 5 and 6, the route most heavily used by foot traffic toward COEX — are scheduled to close for construction. Exits 7 and 8 will also close. Permanent replacement exits will open when the complex is finished, with temporary exits to be designated in the interim, the Seoul Metropolitan Government said.
The defect inspection is the second high-profile structural concern to surface at a GTX-A site in recent months. In late March, the ministry confirmed that the central section of GTX-A from Seoul Station to Suseo, originally scheduled to open in June, would be delayed to July or August due to construction coordination issues between the ministry's tunnel work and the Seoul city government's underground complex work. A ministry official said reinforcement methodology for the Samseong defects would be reviewed in consultation with certified institutions this week.
The completion of the Samseong underground complex would mark the convergence point of Seoul's three GTX lines and reshape commuter flows across the metropolitan region. The project's cumulative delays — now spanning 11 years from feasibility study to projected opening — underscore the scale of risk in coordinating multiple rail authorities, a city government and several private contractors on a single underground site.
Copyright ⓒ Aju Press All rights reserved.