steel pipes in soft ground 2

• Mar 29, 2017

• #2

bimr

Civil/Environmental

Feb 25, 2003

9,379

US

Please add some details to your post.

What is the size of the pipe?

"relatively soft ground" is not an engineering term.

What type of "chamber" are you talking about?

Are you talking about restrained piping with flexible joints?

Use of thrust blocks is old fashioned.

 

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• Mar 29, 2017

• Thread starter
• #3

win

Civil/Environmental

Jul 10, 2013

19

MY

Thanks for the reply. Sorry for the misunderstanding. Im more to asking as a general question but maybe i should be more specific. Im looking at larger diameter welded steel pipelines for water suppy e.g above 1000mm. As the valve chambers, blowoff chambers, and anchors are piled while the pipe length is unsupported, im curious as to how do you guys go about designing for differential settlement eapecially if the route is going through peat?
Will Rocker pieces be useful in this? E.g short length of pipe with mechanical couplings on both ends to allow for deflection.

 

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• Mar 30, 2017

1
• #4

LittleInch

Petroleum

Mar 27, 2013

22,940

GB

With difficulty is the answer.

The aim is to avoid differential settlement by providing firm ground under the pipe.

Peat is a nightmare of a material to work with and for large diameter, relatively thin pipes can be catastrophic. The only sure way to deal with it is dig out the peat down to bedrock / firm layer and backfill with something solid to create a subterranean road on which to lay your pipe.

Otherwise as you note, some sort of flexibility is required to avoid the issue. Flexible couplings are also difficult tog et right, especially at that sort of size and can limit the pipe design pressure.

I have seen gently curved hard backfill away from a fixed point like a valve chamber or connection and then rely on the ground level in general to support the pipe, but prevents a hard spot.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

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• Mar 30, 2017

• Thread starter
• #5

win

Civil/Environmental

Jul 10, 2013

19

MY

Good point LittleInch. I understand that another option is to use piled support when the peat layer is too deep and uneconomicla to replace, have there been cases where geotextiles are used as a replacement for piled supports?
Im currently looking for articles and case studies for design and construction of steel mains in poor ground conditions. Any suggestions will be appreciated!

 

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• Mar 31, 2017

1
• #6

BRIS

Civil/Environmental

Mar 12, 2003

525

GB

In Peat i would advise with continuously welded pipe in peat not to build the pipe rigidly into the chamber all the thrusts on the valve will be taken by the welded steel pipe. Simply install the pipe through openings in the chamber and seal the annulus with flexible material to achieve a water seal

Why are the cambers piled - why not let them move with the pipe ?

 

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• Apr 3, 2017

• Thread starter
• #7

win

Civil/Environmental

Jul 10, 2013

19

MY

Letting the chambers move with the pipe might work. How about using geotextiles as a reinforcement to the soil? will that help?

 

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• Apr 3, 2017

• #8

BRIS

Civil/Environmental

Mar 12, 2003

525

GB

If you are in soft deep peat them your pipe will eventually sink - laying the pipe on a raft made of geotextile/geogrid and bedding will spread the load without causing points of differential settlement. We would need to know more about just how soft the material is. I am not a lover of rocker pipes - I think you are better off with continuously welded pipe and minimum interface with any rigid concrete.

 

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• Apr 3, 2017

• Thread starter
• #9

win

Civil/Environmental

Jul 10, 2013

19

MY

Ah i see. As mentioned im more to trying to understand the concept of this. Allowing chambers to settle with the pipe is a good idea. iam very interested on geogrid beddings, any suggestions on where can i read more on this? Perhaps the design guides and examples?

 

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• Apr 3, 2017

• #10

LittleInch

Petroleum

Mar 27, 2013

22,940

GB

The problem is the chamber will still settle at a different rate - probably more - than the pipe.

I have seen underground supports used, but I'm not a fan of those - if the ground under the pipe settles then the pipe ends up holding the ground up which is a lot of weight concentrated in a hard spot.

In general you try and avoid ground like this so there aren't too many examples, especially where you connect buried pipes to hard stuff, but try looking for muskeg pipe construction which is what they seem to call peat in Canada.

digging it out back to solid ground is still the best long term solution

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

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