The tunnel collapse that trapped a dozen workers last week below a hydropower plant in the Central Highlands was caused by rotten ceiling beams, the project investor announced on Monday.
Facing Lam Dong Province’s authorities on Monday, the chairman and general director of the Da Dang-Da Chomo hydropower plant’s board of investors apologized for the collapse.
The wooden ceiling molds used during the construction of the tunnel had decayed, causing rocks and concrete to fall, said Vo Nhat Thang, chairman and general director of Long Hoi Electricity Construction and Investment JSC.
“Ongoing rains for more than a month also contributed to the collapse,” Thang said.
He also blamed the area's poor geological integrity for the incident, which happened early on Tuesday (December 16) during a heavy storm. Twelve workers, including a woman, were trapped inside a tunnel as the water rose.
They all were freed at more than 4:30 p.m. on Friday (December 19) by a team of roughly 750 rescue workers.
“The geological formation in this area is very complicated. Two experienced contractors -- Lung Lo and Vinaconex – began work on the tunnel, then quit for this reason,” said Thang, “Later, Song Da 10 JSC insisted it could do the job and we agreed.”
Thang said that Song Da 10 JSC was hired to dig the 700-meter tunnel while another company, Song Da 505, poured concrete over the tunnel's ceiling.
The tunnel was designed to bring water from a dam to the hydropower plant.
Song Da 505’s 12 trapped workers, who were taken to the Lam Dong Province General Hospital after being rescued, were discharged on Monday and Tuesday.
Doan Van Viet, chairman of the provincial People’s Committee, ordered concerned agencies to regularly inspect similar projects and stop work if poor geological integrity is discovered.
Minister of Construction Trinh Dinh Dung has sought government permission to investigate the cause of the tunnel collapse, which gripped the country.
“This accident was complicated. It was linked to problems with the surveying, design, construction, and supervision of the project. For these reasons, we want to lead the probe instead of the provincial authorities,” said Dung.
The US$22 million Da Dang-Da Chomo Hydropower plant, one of dozens planned or under construction in energy-hungry Vietnam, is expected to produce about 110 million kWh annually.
The project’s design consultant is China’s Nanning Hydropower Irrigation Design Institute and the supervisor is Hanoi-based Nhat Thang Consulting JSC.