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External Loads on a Buried Pipeline

External Loads on a Buried Pipeline

External Loads on a Buried Pipeline

(OP)
Hi All,
I'm trying to figure out a methodology for determining external live and dead loads on a soon to be abandoned 34" pipeline. The concern is that over time as it deteroriates, it will collapse. This pipeline is at various depths and 1102/Spangler's methods are ultra conservative. 1102 says it will never fail and Spangler says that it fails in 2' of cover. These methods are used for designing a pipeline and not for an abandoned line. Any thoughts? Thanks.

RE: External Loads on a Buried Pipeline

Spangler was developed for culvert design, however it does not include cyclic stress.

My practice has been to use 1102, but with no internal pressure.

Learn from the mistakes of others. You don't have time to make them all yourself.

RE: External Loads on a Buried Pipeline

For a 34" line I believe you only have two serious options - Dig it up and remove it or fill it in. You can fill it in with foamed concrete, grout, anything inert that has some compressive strength. I've seen 300 - 500m sections filled like this.

As you say eventually it will collapse - your problem is you don't know if that is 5 years, 10 years or 20.

what the eco warriors normally don't like is getting holes and water transmission from one part to another then coming out as horrible brown water.

This is not normally an engineering thing, but a legal / regulatory / environmental issue. Depends on your location, regulations, land agreements, current environmental "duty of care", abandonment details etc.

You could always keep the CP on or add lots of sacrificial anodes and turn off the CP system and then hope it doesn't collapse before it becomes someone else problem.... winky smile

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: External Loads on a Buried Pipeline

You need to remember that "abandoned" is normally a dirty word to bean counters and management as this implies all sorts of issues as I noted above, so I was a little surprised you used it. De-commissioned, mothballed, removed from service are all weasel words, but don't have the legal issues about abandonment. The company can't shirk its responsibilities in this - it had good use out of the line for decades properly - now it needs to put it to rest in a proper manner.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: External Loads on a Buried Pipeline

so, assuming this thing was designed to handle the loading originally, it will not fail until it has deteriorated significantly. I have seen numerous buried sewer pipes, installed under paved arterial roads, nearly totally disintegrated at the soffit (commonly called eggshell), and with no apparent effect on the pavement above. Unless the pipe is quite shallow, live loads have little effect and the soil over the top of the pipe arches exerting relatively low loads on the pipe. So it will likely remain for many years. So the analysis needs to determine what the rate of corrosion is, what the existing condition of the pipe is, what is the likelihood that it will fail catastrophically and can you tolerate it when it happens. Or grout with low density expanding foam and be done with it.

RE: External Loads on a Buried Pipeline

(OP)
Thanks everyone for the ideas--just for clarification, it's outside the US so abandoned is their term. They want options of where they can use foam vs grout vs low-density concrete to maintain the live and dead loads at crossings. I'm not a CE so I'm struggling with trying to figure out what media to fill the pipeline when it's at different depths at crossings. There's hundreds of crossing so an optimization strategy is what I'm trying to determine.

RE: External Loads on a Buried Pipeline

Fill it with this stuff and be done with it.
Even at a lowest 300 psi strength it's 10 X as strong as the original soil ever was.
If the pipe rots, nobody will ever know.

http://www.google.com/url?sa=t&rct=j&q=&am...

Learn from the mistakes of others. You don't have time to make them all yourself.

RE: External Loads on a Buried Pipeline

either foam or cement grout can easily meet the structural requirements (compressive strength / deformation). it just comes down to cost and long term stability of whatever product you decide to use.

RE: External Loads on a Buried Pipeline

If your key concern is crossings and they are pretty straight, have you thought about lining them with a fairly close fitting PE tube or concrete sections then just sealing it up. You never know when a duct under the road will turn out to be useful and could be cheaper than pouring all that grout / concrete in. Just a thought before you block it up for eternity.

You still need to seal up your other sections, when the foamed stuff BI has is ideal and generally recognised as fit for purpose in sealing pipes.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: External Loads on a Buried Pipeline

(OP)
Thank you everyone--this has helped!

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