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maedchenhosen t1_j5de95z wrote

Reply to comment by SierraVictoriaCharli in TIL that the California St. Francis Dam disaster of 1928, a midnight-hour 120' wave that killed 431 sleeping people and wiped out giant sections of land more than 50 miles west to Ventura, was caused by the dam having been built on a fault zone (in addition to the dam's retention of water). by atrailofdisasters

Can you point me to where it says they built on gypsum deposits? I can’t seem to find it and thought the issue was they built on schist.

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SierraVictoriaCharli t1_j5f0lx5 wrote

https://en.wikipedia.org/wiki/St._Francis_Dam references to gypsum begin five paragraphs down in planning and design, noted on the eastern abutment. Then more in the discussions of the various failure modes as one of the investigations faulted upthrust on the eastern abutment. The western abutment is also listed as having veins of talc which is just as bad if not worse.

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maedchenhosen t1_j5f6cpe wrote

Thank you! Small veins of gypsum and talc certainly wouldn’t help (and you’re right, talc is slippery and probably worse than gypsum). I’ve been to the site and the schist is clearly very friable at least at the surface. Thanks for expanding my knowledge on the site :)

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SierraVictoriaCharli t1_j5rh412 wrote

Thank you for sharing your experience of the site; Mastery is running out of ways of making mistakes, the true and best masters learn from others' mistakes. The St. Francis Dam was a wonderful theory. Engineering is the joke; what is the difference between theory and practice? well in theory nothing; now prove it.

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