2020 Michigan Dam Failures: Forensic Report

While we're on the subject of dam failures... Michigan Dam Failures Caused by Rapid Liquefaction of Downstream Sand Embankments | 2021-09-14 | Engineering News-Record

First, let's refresh your memory.

The Edenville and Sanford Dams along the Tittabawassee River in north central Michigan failed on May 19, 2020, after two days of heavy rain, resulting in flooding and property damage.

There was an ongoing dispute between the dams owner, the federal government (in the form of the regulating body) with some interaction with the local community. Oh, and the state environmental agency was also involved, if memory serves me.

An interim report from the Association of State Dam Safety Officials reports that a clear factor in the failures of two dams built in the 1920s was static liquefaction (flow) instability of saturated, loose sands in the downstream section of their embankments. [SNIP]

Static liquefaction has rarely been observed in dam failures and is more commonly associated with earthquakes, according to the forensic team. It occurs when the mobilized shear strength in saturated, loose sand decreases rapidly to values significantly less than the applied static shear stresses, resulting in a force imbalance. The sand quickly liquefied, became mud and then accelerated the velocity of the already fast-moving water with its mass.

There is more at the link above. The complete interium report can be found at the following link: INVESTIGATION OF FAILURES OF EDENVILLE AND SANFORD DAMS. It is a 42 page PDF, so you may not want to download it to your phone. It does contain a number of photos of the dam at various points leading up to the failure, and as the failure unfolded.