The independent forensic team (IFT) investigating the May 19, 2020, failures of the Edenville and Sanford dams in the U.S. state of Michigan released an interim forensic report, which includes findings to date on the physical mechanisms of the dam failures.
According to the report, “In the IFT’s opinion, the most plausible principal mechanism for the failure of Edenville Dam, with strong evidence, is statis liquefaction (flow) instability of saturated, loose sands in the downstream section of the embankment.”
“This failure mechanism has been rare, but not unprecedented, for water storage dams, and water storage dam engineers have not typically considered it,” the report said.
“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, and (d) a reasonably close match of a simplified kinetic analysis with the characteristics of the failure shown in the dam failure video.”
The IFT also said the failure of Sanford Dam was the result of embankment overtopping. “The breach outflows from Wixom Lake after the failure of Edenville Dam caused the water level in Sanford Lake to rise more quickly than could be accommodated by the spillways at Sanford Dam. As the lake level rose above the crest of the fuse plug spillway at about 7:20 p.m., the fuse plug began to erode and provide additional spillway capacity. However, the combined capacity of the fuse plug spillway and the gated spillway was not sufficient to prevent the lake level from reaching the embankment dam crest elevation at about 7:46 p.m., a little more than 2 hours after the failure of Edenville Dam. As the lake level continued to rise, water flowed over the Sanford embankment crest and down the downstream slope, and the embankment eroded, creating a breach of the embankment.”
In August 2020, the Federal Energy Regulatory Commission (FERC) engaged the five-member IFT to investigate the failure of the Edenville and Sanford Dams in central Michigan. At this time, the IFT has essentially completed its evaluation of the physical mechanisms of the dam failures, but the evaluation of the human factors is still in progress. Although the IFT’s work will not be completed and its final report will not be issued for several months, the IFT wanted to share its findings regarding the physical mechanisms of the dam failures with the profession and the public.