A Pipeline, An Earthquake, No Problem 21
polarfleece writes "November 3 is the first anniversary of the Denali Fault Earthquake that rocked Interior Alaska. America's greatest engineering marvel, the Trans-Alaska Pipeline just happens to cross the Denali Fault and, as described in Dan Joling's AP story "Alyeska engineers anticipated the effects of a bruising quake" the line came through just fine."
Re:Greatest engineering marvel? (Score:1)
If all you did was watch the Discovery channel, you'd think all engineers had a bad problem forseeing natural disasters.
Re:Greatest engineering marvel? (Score:2)
Re:Greatest engineering marvel? (Score:2)
Doubling design tolerances (Score:3, Interesting)
But as the article says: Though there was minimal damage, the earthquake may have one potentially expensive effect: the pipeline is now out of compliance with original design criteria that require it to be able to survive 20 feet of horizontal motion.
Perhaps next time they will specify 20 feet as the safety requirement, but build to allow 40 feet, so that they do not have to rebuild after every landslip.
Re:Doubling design tolerances (Score:4, Insightful)
Depends. How often do they have to [partially] rebuild as a part of basic maintance vs how often earthquakes occure.
Earthquakes in most cases happen a bunch at a time [several months], and then nothing for a long time [years], while pressure builds up.
The pipelines needs maintance. Each pipe can be replaced, and they inspect it regularly to make sure all the pipes are holding up. When a pipe fails inspection (which if done right means it is still fine, but failure is expected after a time, they have to repair/replace.
So if the total movement from an earthquake cycle is less than 20 feet, and they will have to replace that section anywhere between cycles, there is no hurry to do it now, and no need to redesign for more margin because they won't go through a second cycle before normal maintance already fixes the problem.
OTOH, seeing 18 feet of movement when you planed for 20 seems too close for comfort. My gut feeling is they should redesign for at least 30 feet of movement when they repair that section, just for margin of safety. However I'm not a geologists, nor a pipeline engineer, so I don't know what is a reasonable margin.
Re:Doubling design tolerances (Score:3, Insightful)
Re: Doubling design tolerances (Score:3, Insightful)
> I can't see doubling the average as good engineering practice, especially if doubling the average doesn't get you outside the expected maximum range of movement. I think they were allowed to use unconservative numbers, and they got away with it (for which I'm glad).
Yeah, if that's what they actually did then you have to wonder about their engineering qualifications. If the design case could result in 30', they should have allowed for 30'. No ifs, buts, maybes, or averages.
Consider, for example, a s
Re: Doubling design tolerances (Score:1)
I assume you live in Lake Woebegone, where ALL of the kids are above average.
Re:Doubling design tolerances (Score:1)
Which average, exactly? (Score:3, Interesting)
It sounds odd and insufficient to design for twice the "average" movement. However, the definition of "average" is notoriously loose in journalistic writing.
Perhaps they meant: "In places, the fault could move 30 feet, but the average movement over the entire le
Re:Doubling design tolerances (Score:3, Insightful)
The whole skill here is balancing cost vs. risk. If it costs 10X to design for 40' of movement vs 20' of movement, then it's obviously not practical in the least. It's a much better choice to design for 20', and invest part of the massive savings in a "rainy day" insurance policy that covers the slim chance of a larger-than-expected earthquake. Financially this comes out way ahead of your fanciful "double everythi
Permafrost More Fearsome (Score:3, Interesting)
IMO, that's not the greatest engineering feat associated with the pipeline.
I'd reserve that honor for the resilience of the pipeline to a much slower amplitude shaking.
Namely, frost heaves from permafrost, ground that is normally frozen year-round. Scrape off a little ground cover to build a house, a road, or plant a utility pole and suddenly there's a difference freeze/thaw cycle that will do real Bad Things.
You have to either keep all frozen all the time, or largely unfrozen and fairly dry soil.
There's a reason that roads have 6 ft of gravel on them for insulation to protect the underlying permafrost.
Permafrost, Money, Pointless Ranting (Score:2, Interesting)
On another note, while the pipeline might not be the engineering marvel some would expect, consider it's roughly 800 miles long, above ground, below ground, below ground and refigerated, and built back in the 70's. This thing puts up
Re:Permafrost, Money, Pointless Ranting (Score:1)
Something like 80% oil
5% tourism
5% other
The state gets so much income from big oil that there is no state tax, and the residents are even given a yearly check "for being residents".
Trust me, alaskans are big oil people. They have reaped many benefits from big oil.
Heak, without oil, nobody really wants alaska. (does russia ring a bell?)
-Grump
At risk of reinforcing a stereotype (Score:1)
I work in the oil business (refining) and I am thinking of safety every day. Reviews are done throughout the design process that question what are the consequences if X happens. And if the consequences are unacceptable, we have to design them out or we can't go any further. It is very humbling t
Remarkable (Score:2)