I never saw a ground squirrel report. I would appreciate it if you can direct me to such.
https://damfailures.org/case-study/oroville-dam-california-2017/
“Over time, chute flows and temperature variations led to progressive deterioration of concrete and corrosion of steel reinforcing bars and anchors in the chute slab, with likely loss of slab strength and anchor capacity. There was likely also some shallow underslab erosion, damage and deterioration of the underdrain system, and some loss of underdrain system effectiveness, which contributed to increased slab uplift forces. The particularly poor foundation conditions at the initial service spillway chute failure location likely contributed to low anchor capacity and shallow underslab erosion.
The seriousness of the weak as-constructed conditions and lack of repair durability was not recognized during numerous inspections and review processes over the half-century history of the project. For example, although the poor foundation conditions at both spillways were well documented in geology reports, these conditions were not properly addressed in the original design and construction, and all subsequent reviews, including FERC five-year reviews and Potential Failure Mode Analyses (PFMAs), mischaracterized the foundation as “good quality rock.”
I don’t recall ever seeing anything about ground squirrels, but I do recall speculation about root intrusion beneath the slab from trees adjacent to the failure area. Those roots may have contributed to failure of the underslab drains and allowed that area beneath the slab to erode.
Remember the pics of the drains in the sidewall not jetting out water like they did in the rest of the spillway.