Insufficient supports, flawed formworks cause of Muskrat Falls collapse

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Insufficient supports, flawed formworks cause of Muskrat Falls collapse

An investigation into the collapse of formworks, causing an avalanche of concrete at the Muskrat Falls hydroelectric project in Labrador last year has blamed deficiencies in the shoring system.

As well, there were issues with the integrity of the wooden formwork, Nalcor said in a news release Monday.

The Crown corporation hired aDB, a structural engineering consultant, to work with contractor Astaldi to figure out what happened on May 29, 2016.

About 500 cubic metres of wet concrete collapsed at the construction site for the powerhouse portion of the Muskrat Falls project, in what Nalcor called a "catastrophic" formwork failure.

Because the forms that collapsed were buried under hardened cement, the investigators had to examine other draft tubes for clues.

They found that the formwork displayed evidence of exposure to high humidity, rain and snow and signs that wood had been submerged in water for a long period — for example, fungus and mushrooms growing on lumber.

There were also gaps between lumber joints, signs that wood had been damaged and insufficient bracing to align steel beams.

The draft tube formwork is a temporary structure, or mould, used to install concrete for the permanent draft tubes of the powerhouse.

Nalcor said the contributing factors identified by the consultants have been addressed.

All four draft tubes have since been completed and the temporary formwork is being removed.

'We all went down in seconds'

Statements from 14 workers who were on site during the collapse described loud noises, including cracks and pops.

"Everything went extremely fast, we all went down in seconds," said one worker, quoted in the report.

"Heard a pop, then crashing sounds, and was sucked into a big hole." 

Five workers fell into the collapsed area. One was sent to hospital.

The consultant's report said the construction crew should have noticed the quality problems with materials and the water damage to the formwork and flagged it as a safety concern.

Workers should be encouraged to speak up "about the smallest of issues" the report said, calling for an onsite safety leadership program.

"Nalcor's Number One priority is the safety of workers and the public. We encourage all workers and contractors to report any safety issues or concerns to us," Stan Marshall, Nalcor's CEO and president, said in a media release Monday.

The full findings of aDB's report are available online.