Tunnel building at a 23-MW hydroelectric power plant being constructed on the Da Dang River in the province of Lam Dong, Vietnam, is suspended pending investigation into the confirmed cause of a tunnel collapse at the site on Dec. 16.
The mishap at the US$22.4 million Da Dang-Da Chomo hydropower plant trapped 12 workers for three days, according to local news sources. All of the workers were rescued Dec. 19 from a 20-meter-long section of the tunnel, designed to be 700-meters-long, which collapsed, as the passageway was nearly complete.
There are no reports of serious injury or deaths from the accident.
About 600 meters of the tunnel was completed before the collapse, which occurred about 500 meters from the opening of the structure.
Vo Nhat Thang is chairman of Long Hoi Hydropower Joint Stock Co., a company that is a major investor for the project. Thang reportedly said, “During construction, ground subsidence occurred and caused soil and sand to be swept by underground water into the tunnel while [underground construction] failed to tackle the problem.”
According to published reports, the plant has been being built for more than 10 years. During that time conditions have changed in building code requirements, contractors and geological conditions at the site.
Based on the examination of the scene, it is certain that the tunnel had suffered from structural problems before it collapsed, said Le Quang Hung, deputy Minister of Construction.
“The collapse could have been caused by complicated geographical conditions, poor design, or unqualified construction," Hung said.
No timetable is available for construction at the site to resume, but Da Dong-Da Chromo is expected to provide 109.27 million kWh per year when it begins generating electricity.