A large land subsidence site occurred in the Busan Sasang-Hadan urban subway section 2 on Sep. 2024. /Courtesy of Busan City

An audit has revealed that the ground subsidence that occurred in the 2nd section of Busan's Sasang-Hadan urban subway line in September 2024 was due to the Busan Transportation Corporation's poor management and supervision of construction.

The Busan City Audit Committee announced on the 22nd that findings from a specific audit showed there were deficiencies in quality, safety, and construction management during the excavation process, and illegal matters were also discovered. This audit was conducted from October 21 to November 15 last year, targeting the Busan Transportation Corporation and the Busan City Railway Facilities Department.

The audit committee concluded that the large ground subsidence occurred due to insufficient construction management during the dam construction and temporary earth retention works, combined with the concentrated rainfall amounting to 379 mm. The Construction Project Management Unit confirmed that an unqualified subcontractor conducted the quality tests and compiled the quality test reports without proper verification, allowing the main contractor to proceed with excavation, leading to the outflow of groundwater and soil. Both the main contractor and the Construction Project Management Unit were found to have inadequately managed the quality test results for the dam project and implemented the detailed safety management plan for the temporary earth retention works.

The Busan Transportation Corporation merely instructed the Construction Project Management Unit to formulate and submit measures for the lagging construction progress but failed to properly guide or inspect whether the measures were established and implemented. It was also revealed that the Busan Transportation Corporation neglected oversight by not reporting issues with construction progress to higher authorities, claiming that new construction methods were difficult to apply and securing additional budget was challenging. This contradicts the corporation's claims that the ground subsidence was caused by concentrated rainfall.

The audit committee has demanded 10 administrative actions, 33 personnel actions, and a reduction in design changes amounting to 1.159 billion won from the Busan Transportation Corporation. It has also notified the main contractor and the Construction Project Management Unit to impose penalties for the identified issues.

The Busan Urban Subway Sasang-Hadan Line, totaling 6.9 km with seven stations from Sasang Station on Line 2 to Hadan Station on Line 1, is under construction with the goal of opening by the end of 2026. However, ground subsidence has been occurring around the construction site every time it rains, with three incidents in 2023, eight in 2024, and three occurring this year.