Independent investigation finds foundation of earthen dam failed because of unstable underlying layers
An independent investigation has determined the breach of the Mount Polley mine tailings dam in B.C. was caused by a failure to detect a weak layer in its foundation, likening the massive embankment to a “loaded gun.”
The report, which was released on Friday morning in Victoria, said the design failed to take into account the complexity of the instability of underlying glacial and pre-glacial layers under the retaining wall.
But the authors, geotechnicians Norbert Morganstern and Steve Vick, did not blame provincial inspectors for not detecting the problem beforehand.
The investigators said the dam was built on a weak layer of glacial deposits that was undetected at the time, making the dam like a ‘loaded gun.”
They said the construction of a steep slope in the embankment as the dam was raised was “like pulling the trigger,” causing the failure last summer.
They also concluded that massive volume of water in the tailings dam did not cause the dam to fail, but it did result in more tailings being released when it did breach.
Just eight days before the dam failed, a plan was approved to raise the dam further, but on the condition that a buttressing wall was put in place and the slope decreased, they said.
The investigators also made several recommendations to improve the safety of tailings dams, including updating the way they are designed, monitored and regulated in B.C.
…click on the above link to read the rest of the article…
