**Poor Management Revealed in Busan City Audit Results…“Cannot Blame Heavy Rain Alone for the Accident”**
– Shoddy installation of earth-retaining walls and substandard water barrier works… Drainage connections poorly constructed
– “Failures in Construction and Supervision”… Busan City promises to strengthen safety management measures
In September last year, a sinkhole swallowed a drainage support vehicle and a 5-ton truck on a street in Sasang-gu, Busan, as provided by the Busan Fire and Disaster Headquarters.
Busan = Reporter Lee Seung-ryun
The sinkhole (ground subsidence) accident that occurred at the entrance of section 2 of the Sasang-Hadan line construction site of the Busan Urban Railway last September was confirmed to have been caused not only by heavy rain but also by poor management during the construction process.
The Busan City Audit Committee conducted a special inspection of the ‘Busan Urban Railway Sasang-Hadan Line Construction Project’ from October 21 to November 15 last year and disclosed the audit results on the 22nd.
The audit committee issued a total of 33 personnel actions, including 2 corrective actions, 4 cautionary actions, and 4 notifications, along with 11 reprimands and 22 warnings. They also ordered a reduction of 1.159 billion KRW from the construction costs. It informed the Busan Transportation Corporation to impose penalty points on the construction and management companies for their errors.
Earlier, around 8:50 a.m. on September 21 last year, a sinkhole measuring 10 meters wide, 5 meters long, and 8 meters deep occurred on Hakjang-dong Road in Sasang-gu, causing a firefighting drainage support vehicle and a 5-ton truck to sink. The audit committee attributed the incident to significant rainfall measuring 379mm. However, factors such as improper execution of the ‘water barrier construction,’ inadequate stabilization of ‘earth-retaining walls’ intended to prevent soil collapse, and poor connection of drainage channels were also identified as significant internal issues contributing to the incident.
During the rainstorm, the U-shaped ‘side drainage,’ meant for water runoff, broke, causing water to seep into the surrounding ground. This led the wooden ‘earth-retaining walls’ installed underground to collapse progressively, resulting in more extensive ground subsidence.
The audit revealed that the managing firm allowed the subcontractor to proceed with water barrier construction without conducting quality tests as per the regulations. Consequently, water and soil seeped underground, complicating excavation and destabilizing the ground.
Despite construction delays, the project owner, Busan Transportation Corporation, instructed the construction firm to speed up progress. However, they did not adequately inspect whether effective strategies were developed and implemented. Issues like difficulty in deploying new construction methods and securing additional budgets were not reported to supervisors, despite problems in project execution.
The construction firm and managing institution failed to properly assess the quality of ‘water barrier construction,’ and the installation of the ‘earth-retaining walls’ was inadequately executed. Essential elements, like ‘thumb piles’ for reinforcement, were not installed, and necessary design drawings for the expanded section (‘widening section’) were neither drafted nor reviewed, leading to improper execution. Faulty fabrication of drainage connection parts impeded water flow.
Due to these shortcomings, the audit committee issued reprimands and cautions to those involved and announced penalty points for the construction and management companies.
Furthermore, the audit revealed that the water barrier’s effectiveness, deteriorated with over three years since its completion, contributed to the problem. Despite the poor permeability coefficient values that measure how well water is blocked by barrier materials, construction continued without adequate review.
There were lapses in including water barrier designs up to 1.5 meters below temporary steel plates covering the construction site for foot traffic and secure fixation of the earth-retaining walls. ‘Thumb piles’ were omitted, and such defects were noted.
Besides these, failures by the safety management technician in fulfilling their responsibilities, poor documentation of the post-construction environmental impact report, and the necessity for improved design and construction methods were highlighted.
Issues in concrete quantity overestimation and material redundancy in the vehicle depot (where trains are parked and repaired), payment for poorly adjusted construction costs in tunnel auxiliary works, and neglected deadlines in construction progress without analysis or catch-up plans were detailed.
Yoon Hee-yeon, the chairman of the Busan City Audit Committee, stated, “The audit findings revealed that the ground subsidence accident was not solely caused by rain but also resulted from inadequate construction and safety management by the building firm and management company, along with inadequate oversight by Busan Transportation Corporation.” He further emphasized, “This audit serves as a catalyst for the city to boost its safety management system, aiming to prevent similar accidents in the future.”