Seoul has urged the Ministry of Land, Infrastructure and Transport to expedite the reinforcement of columns lacking rebar in the underground complex development of Section 3 along Yeongdong-daero. As construction progresses, the effectiveness of reinforcement using steel plates of the same thickness diminishes, with analyses indicating that a maximum thickness of 58mm may be required after the completion of basement level 2.
On September 23, the city announced that it had formally requested the ministry to promptly decide on the reinforcement method. On September 11, Seoul shared the interim results of a detailed safety assessment and external expert consultations with the ministry and the Korea National Railway Authority, urging a swift decision on the reinforcement method and the expedited implementation of non-stop GTX-A service at Samseong Station.
According to the interim results of the urgent detailed safety assessment conducted by Seoul, the current state and safety of the constructed structures have all been rated 'A.' Calculations based on the current state, which includes the construction of the upper slab of basement level 2, showed that the structures meet the allowable strength criteria.
However, experts have analyzed that the later the reinforcement is implemented, the greater the required thickness of the steel plates will be. When steel plates are added to the columns, the new loads applied after installation are shared between the columns and the plates. In contrast, the loads already applied to the columns before the installation cannot be shared by the plates, resulting in diminished reinforcement effectiveness as construction progresses.
For instance, if 22mm thick plates are used, the strength after reinforcement is projected to be 123% of the original design strength immediately after completing basement level 5. However, this percentage is expected to drop to 118% after completing basement level 4, 113% after level 3, and 105% after level 2.
To achieve the reinforcement efficiency level of 120% proposed by the ministry, thicker steel plates will need to be used as construction progresses. Notably, after the completion of basement level 2, a maximum thickness of 58mm has been considered necessary. As the thickness of the plates increases, so does the weight, making on-site installation, including welding, more challenging.
Currently, construction is underway for basement level 3 of the Yeongdong-daero complex development. Seoul has indicated that delays in deciding on the reinforcement method could extend the reinforcement construction period, potentially impacting the overall schedule of the complex development project.
The ministry has stated that further review is necessary before deciding on the reinforcement method. The review of the appropriateness of the column reinforcement, commissioned by the Korea National Railway Authority, is scheduled to continue until December 31, and the government joint inspection period has been extended from July 20 to November 20.
Seoul has expressed its readiness to proceed with the reinforcement work in accordance with whatever method the ministry decides, in addition to its proposed steel plate and epoxy injection method. The city has stated that it is prepared to commence column reinforcement as soon as the ministry makes its decision.
Seoul has also requested the prompt implementation of non-stop GTX-A service at Samseong Station. According to the city, train vibration measurements conducted in May and July recorded maximum vibration speeds of 0.069cm/s and 0.049cm/s, respectively. Compared to the relevant standard of 0.3cm/s, these levels are approximately one-fourth and one-sixth, respectively.
External experts have reportedly concluded that, considering these vibration levels, the non-stop passage of GTX-A trains through Samseong Station can proceed alongside the column reinforcement work. Based on this, Seoul has requested the swift resumption of comprehensive test operations, including trial runs.
The non-stop passage of GTX-A trains through Samseong Station was initially scheduled for implementation in August of this year. Following the discovery of missing rebar in the Yeongdong-daero complex development, Seoul had planned to assess structural safety and complete reinforcement work by July. The city believes that if the reinforcement had proceeded as planned, non-stop passage could have been achieved in August.
Seoul has raised concerns about additional costs arising from delays in deciding on the reinforcement method and resuming comprehensive test operations. The city asserts that costs related to operational losses, which arise from delays in decision-making even after safety has been confirmed, should not be passed on to the city and its citizens.
Seoul has emphasized that, given the confirmed structural safety at the construction stage, the ministry should promptly decide on the reinforcement method and quickly resume comprehensive test operations for the non-stop passage of GTX-A trains at Samseong Station.
* This article has been translated by AI.
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