New report blames "rare, but not unprecedented" cause for Edenville Dam failure
An independent forensic team made up of members of the Association of State Dam Safety Officials has delivered its interim report Investigation of Failures at Edenville and Sanford Dams.
The dam failures contributed to a 500-year flood event in Gladwin and Midland counties that forced the evacuation of more than 10,000 people from their homes. The flooding caused tens of millions of dollars of damage to homes, businesses and local infrastructure.
The interim report blames the Edenville Dam’s catastrophic collapse on a phenomenon called “static liquefaction instability.”
This failure mechanism has been rare, but not unprecedented, for water storage dams, and water storage dam engineers have not typically considered it. It has generally been assumed by geotechnical engineers that, under loading conditions other than earthquakes, water will be able to flow in and out of sands and their strength will be defined by the drained shear strength, regardless of the density of the sand – i.e., there will be no dramatic strength reduction as occurs in static liquefaction.
The conclusion regarding static liquefaction at Edenville Dam is supported by:
(a) the accelerations and velocities of the failing soil mass evident in the dam failure video
(b) strong evidence of loose, uniform fine sand in the embankment
(c) strength loss behavior exhibited in laboratory tests on loose specimens of uniform sand collected from the breach remnant
(d) a reasonably close match of a simplified kinetic analysis with the characteristics of the failure shown in the dam failure video.
The report concludes the saturated, loose sand in a section of the dam’s embankment gave way and that led flood waters to over top the Sanford Dam downstream.
A future report will address the human factors that led to the dam failures.
Hugh McDiarmid Jr. is the spokesman for the Michigan Department of Energy, Great Lakes and Environment.
“We are waiting for the full report,” says McDiarmid Jr. “But...we will be reviewing the findings to see how we might apply them to Michigan to make the state’s dam safety program stronger.”