How long are dams like Hoover Dam engineered to last? (2006)

79 点作者 monort超过 9 年前

13 条评论

For those who wanted the answer to the title in these comments, paraphrased it was: with proper maintenance, indefinitely. The "with proper maintenance" phrase should be pointed out to management next time they think something we build should last forever; even these remarkable structures that appear formidably unchanging undergo continuous, hands-on, expert maintenance.There is a tangentially-related Straight Dope thread [1] asking "Is the Hoover Dam concrete still curing?", because if you take the tour (highly recommended for hackers with an affinity for industrial- and megastructure-scale engineering), you will be told "the concrete is still curing!" by the guides.This is apparently not technically precise; someone from the concrete industry please correct me if I'm wrong here. I gathered from a civil engineering page that Hoover Dam's concrete is considered cured, but it is still undergoing the hydration process as long as water is present in the concrete. [2] I think the Hoover Dam guides can be cut some slack for colloquially using the terminology "curing" in light of this technical distinction that most laypeople won't understand.[1] <a href="http://boards.straightdope.com/sdmb/showthread.php?t=258217" rel="nofollow">http://boards.straightdope.com/sdmb/showthread.php?t=258217</a>[2] <a href="http://www.engr.psu.edu/ce/courses/ce584/concrete/library/construction/curing/curing.html" rel="nofollow">http://www.engr.psu.edu/ce/courses/ce584/concrete/library/co...</a>

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Rexxar超过 9 年前

<pre><code> With a small dam the water can sometimes be drained, allowing repairs to be done safely. But imagine trying to drain the Hoover Dam to repair cracks at the bottom--it can't be done </code></pre> I don't understand why they think it's a problem to drain the dam. It's done regularly to check and repair them. (Every 30/40 years, at least in France).Recent video of this in France : <a href="https://www.youtube.com/watch?v=JflFg5un5zg" rel="nofollow">https://www.youtube.com/watch?v=JflFg5un5zg</a>It is this dam, this is not a small one : <a href="https://fr.wikipedia.org/wiki/Barrage_de_Sarrans" rel="nofollow">https://fr.wikipedia.org/wiki/Barrage_de_Sarrans</a>

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_52jq超过 9 年前

By last count (few years old), the number of dams was estimated at ~84,000 (not 76,000). Close, but that numerical discrepancy should point out one thing: it's an estimate. USACE maintains an authoritative database of dams in USA (and also 32 in Puerto Rico and 1 in Guam) and the numbers are always a moving target. Believe at this point they're working with pattern matching and satellite imagery to fine-tune the database. USACE is currently more concerned with inspections near urban populations than cataloging.The write-up is a bit vague and misses one major point: not all of these dams in the U.S. are concrete. Not even close. Here's a construction type breakdown:<pre><code> 70,278 Earth 9,031 (Unknown) 1,446 RCC 1,215 Gravity 724 Concrete 455 Other 420 Rockfill 201 Masonry 136 Buttress 103 Arch 58 Stone 51 Timber Crib 16 Multi-Arch </code></pre> Only 847 of those dams are tailings dams, used for industrial processing. More than 0, but less than 84,000. Of those, none are listed as concrete (730 Earth, 61 Unknown, 43 Other, 13 Rockfill).

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TheCapn超过 9 年前

Anecdotal story: This summer I was out at a Dam spillway installing some of my systems and got talking with the operator out there. He was commenting about the engineering of the facility and how impressive it was for the age it was built (50+ years ago) in comparison to the modern dam my government was currently building and all the lawsuits and issues its has even before opening. To him, at least, and I'd agree from his comments, business got too involved with engineering. They started running too many cost estimates and too many lowest-bidder contracts instead of building things for a century plus lifetime.Shame to see that. I hope that our engineers continue to fight for proper surveys and designs rather than a race to the bottom.

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jacquesm超过 9 年前

The Hoover Dam hasn't even properly set yet!Curing is an exponentially decreasing process, there will always be a little bit more concrete that still needs to cure, much like radioactivity half-life.The Hoover Dam is quite an interesting piece of civil engineering, it broke ground in many ways other than the physical one.Tons of interesting stuff here:<a href="http://www.usbr.gov/lc/hooverdam/history/essays/concrete.html" rel="nofollow">http://www.usbr.gov/lc/hooverdam/history/essays/concrete.htm...</a>Concrete, while on the surface very boring is actually a super interesting engineering material.Another interesting tidbit: for the longest time the dam was actively cooled to whisk away the heat from the curing concrete (concrete curing is an exothermic process).

cc438超过 9 年前

The threat posed by small dams and their short designed life expectancy was demonstrated in dramatic fashion earlier this year. The historic flooding that impacted South Carolina's midlands earlier this year was driven by a cascade of dam failures.Everyone saw the pictures of Columbia, SC but that flooding was mostly due to "normal" causes. The city's drainage system was overwhelmed by rainfall that exceeded historic levels by several orders of magnitude (higher than even a 1,000 year storm) and the Broad river consequently overflowing its banks. However, that wasn't the only place impacted by the storm. South Carolina has an enormous number of small earthen dams, built on private land with the land owner responsible for maintenance.Obviously, these dams were not built to handle such a storm but even if they were, the lack of oversight led to a lack of maintenance, worsening their chances of surviving the initial floods. As upstream dams broke, downstream dams were subjected to massive surges, causing a cascading series of failures, greatly increasing the amount of damage caused by the storm.There are 10,000 to 20,000 unregulated small dams in the state according to the state. They pose an enormous risk as the flooding clearly demonstrated but SC isn't alone in sharing this burden.

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r0m4n0超过 9 年前

I drive past Folsom dam (1952) every day and have watched the incremental maintenance as well as a few large scale projects progress first hand. One of the most amazing things to witness was the construction of the spillway they have been building around the outer perimeter. They essentially are creating a second dam around the main dam to release water from a lower point due to a scare many years ago. Months of sorting dirt and rock at some kind of large facility nearby and a good year of constant trucks moving the dirt down the road. Even the asphalt on the road began to sink from the constant pressure of the heavy loads.A few of the old spillway gate failures over the years are outlined here:<a href="https://en.m.wikipedia.org/wiki/Folsom_Dam" rel="nofollow">https://en.m.wikipedia.org/wiki/Folsom_Dam</a>

nroets超过 9 年前

Currently, the Kariba dam is the one most likely to fail:<a href="http://citizen.co.za/820414/kariba-dam-a-ticking-time-bomb/" rel="nofollow">http://citizen.co.za/820414/kariba-dam-a-ticking-time-bomb/</a>

sizzzzlerz超过 9 年前

How long a dam lasts and how long the reservoir behind it is usable are two different things. A well constructed dam may last 100+ years but if the water flowing into the lake carries heavy sediment loads, the lake will fill up with mud before then if not periodically drained and the muck removed. This is definitely an issue with Three Gorges as well as Lake Powell/Glen Canyon Dam on the Colorado River. In fact, one of the reasons the latter dam was constructed was to act as a catch basin so the downstream Lake Mead behind Hoover dam wouldn't fill so quickly.

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snowwrestler超过 9 年前

Worth a read:<a href="https://en.wikipedia.org/wiki/Risks_to_the_Glen_Canyon_Dam" rel="nofollow">https://en.wikipedia.org/wiki/Risks_to_the_Glen_Canyon_Dam</a>This gives a hint as to why huge dams cannot be drained for maintenance: there is so much water behind them that it would take too long to drain them via the spillways. In fact, the spillways would probably be irreparably damaged by experiencing full flow for that long.

melling超过 9 年前

"Engineers, about 30 percent of the more than 76,000 dams in the United States are older than 50 years--and by 2020, that number will increase to more than 80 percent. That's a lot of old dams, some of which hold back not just water but toxic sediments from early industrial operations."

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peter303超过 9 年前

Some Roman concrete like Pantheon Dome is still good after 1900 years. The Dome was poured in 126 C.E.

jonawesomegreen超过 9 年前

I remember hearing somewhere, perhaps on a tour of the Hoover Dam that the concrete is very good for the time because although the ideal chemical properties of concrete were not well understood at the time, the local aggregates used were relatively pH neutral which has contributed to the dams longevity. I'm trying to find a source for this though and struggling. Has anyone else heard this about the dam?

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