The tunnel of a hydropower plant that collapsed last week and trapped 12 workers for 82 hours before they were rescued in the Central Highlands province of Lam Dong has been built on a weak foundation, its investor admitted.

>> 12 Vietnamese workers trapped in collapsed tunnel get out safely

Vo Nhat Thang, chairman of the Long Hoi Hydropower Joint Stock Company, the investor of the $22 million Da Dang-Da Chomo hydropower plant, made the admission at a meeting held on Monday to review the rescue mission that led to the safe removal of 12 workers from the collapsed tunnel on December 19. Thang’s statement came while an investigation is being conducted by competent agencies to identify the cause of the accident. The first investor of the plant was the Lung Lo Construction Corporation, which was later replaced by Long Hoi, which then engaged Vinavico – a builder of underground works – in constructing the tunnel, Thang said. “During construction, ground subsidence occurred and caused soil and sand to be swept by underground water into the tunnel while Vinavico failed to tackle the problem” Thang said. Long Hoi finally decided to stop the construction by Vinavico and the tunnel had been suspended for ten months prior to Song Da 10 Joint Stock Company taking over the building work, not long before the collapse, Thang said. Thang added that the accident was spurred by vibrations caused by machines that were brought into the tunnel and by month-long rains that had weakened the structure.  Le Quang Hung, Deputy Minister of Construction, said that the construction of the plant has been going on for more than 10 years, so construction quality regulations applied during different time periods should be considered to determine the responsibility of each relevant contractor. Based on the examination of the scene, it is certain that the tunnel had suffered from structural problems before it collapsed, Hung said. “The collapse could have been caused by complicated geographical conditions, poor design, or unqualified construction…," Hung said  Competent agencies have suspended the building of the tunnel pending investigation into the confirmed cause of the collapse, Hung added.  On Sunday, the Ministry of Construction sent a report to the government about the tunnel collapse and proposed that the Prime Minister set up a verification team chaired by the ministry in conjunction with relevant other agencies, Hung said. The 12 workers were isolated after a 20-meter long section of the tunnel in Lac Duong District collapsed at 7:15 am on Tuesday last week. The tunnel is designed to be 700 meters long, 600 meters of which had been completed before the collapse occurred about 500 meters from the opening of the structure.

The rescue effort was hindered by bad weather and the complicated geology of the site, amid fears the workers might not survive after battles to provide them with oxygen and drain water rising inside the collapsed tunnel section. Rescuers managed to drill holes to put pipes through them so that food, milk, and water could be pumped to the workers. They also succeeded in digging two underground passageways from both sides of the collapsed tunnel to gain access to the workers.

During the digging, rescuers had to use explosives to destroy large pieces of rock that blocked the way leading to the group.

Finally, the passageway on the left side reached the area where the workers had been trapped, opening a way to get them out on December 19 afternoon.

The victims were then taken to the Lam Dong General Hospital, and after several days of care all of them recovered and were discharged on Monday.

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