A Pipeline, An Earthquake, No Problem

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."

Comments

Greatest engineering marvel?

[Ianoo]

The article is very interesting, but I'd hardly call an earthquake resistant stinky oil pipe America's greatest engineering marvel...

Anyone remember Apollo? Or the space shuttle? Or do these count as technology? I'm sure plenty of "engineers" worked on the space shuttle and plenty of "scientists" worked on fault-resistant oil pipelines.

Doubling design tolerances

[henrygb]

This makes the case nicely for taking the number you think of first, and then doubling it. In this case the requirement was for 20 feet of landslip, and in the event there was 18 feet of slip - above average but below the maximum.

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.

Permafrost More Fearsome

[4of12]

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

[mahonri5]

On the note of permafrost, the pipeline (when it is above ground anyways) has heat pipes attached to it, that, for lack of a better word, suck the heat out of the ground, keeping the permafrost nice a frozen. Check out Alyeska Pipeline's page on pipeline facts for details.

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 with a lot. And you can't quite tell from most pictures, but the thing is huge. Most sections that are above ground are designed to let animals pass right under without noticing it.

Of course the big benift of the pipeline has to be the money involved. It brought a whole bunch of people up to Alaska to work on the pipeline and still (if I remember correctly) oil is the number one source of income. Most of my friends growing up either worked for the state, or the oil companies. (or contracted for both) Makes for a very interesting time when oil prices drop and the oil companies start letting people go. Not the funnest times around.

But that's my rant, I've been out of the state for the better part of four years anyhow.

Which average, exactly?

[peacefinder]

The best guess of Alyeska's seismic experts was that in a magnitude 8 earthquake -- the largest expected -- the ground could shift up to 30 feet, but the average would be 10 feet, along the fault. Alyeska engineers designed for a number in middle.

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 length of the fault is 10 feet. And at this point here, where the pipeline is, we expect it to move no more than 20 feet."

On the other hand, maybe they just got lucky. :) either way, it's a nice piece of engineering, to come through without even a dent in the actual pipe.