ST. Francis Dam Failure

Events leading up

the reservoir rose rose within 5 feet of spillway crest, which made the dam unstable.

a crack could then have developed in the upstream heel

a heel crack, such as the one found right after the failure, would shift the resultant thrust far downstream, making it unstable in overturning.

What was to blame?

Most blamed the failure on hydraulic pipping along the inactive San Francisquito fault beneath the dam's right abutment.

Facts and Figures

420 people died, and 179 of those bodies were never found.

The city of Los Angeles paid out $14 million in damages.

Physics

St. francis dam was arched upstream on a 500 ft radius, but was not designed for arch action.

the arch loads on St. Francis become significant when the reservoir rose to within 11 ft of spillway crest , exceeding 10,000 psf.

then a massive landslide occurred along the dam's left abutment

the landslide involved 1.52 million tons of schist moving against the dam's 271 tons of concrete.

New Designs  

Engineering geologic input on dams became common place in the 1930's

review of all federal dams

increased dam safety legislation in California

state-mandated arbitration hearing for victims of natural disasters

after the st. francis dam failure, the federal government ordered a through safety inspection and review of all their dams.

Work Cited

http://web.mst.edu/~rogersda/st_francis_dam/Impacts%20of%20St.%20Francis%20Dam%20Failure-compressed.pdf

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