New parallel water pipeline 4

[JohnWeal]

We have a DN800 water pipeline installed adjacent to a road. There is a requirement to put an additional DN1200 water pipeline running parallel to the DN800 pipeline.

What is the minimum distance to allow between the pipelines or from the existing trench?

We have to do the usual surveys etc but for now as an approximate hydraulic calculation will run as close as possible to the existing pipeline subject to further studies including constructability.

Regards
John

 

[DSB123]

Have a look at the pipeline code for distances between lines.

 

[bimr]

For parallel large diameter pipelines, concern should be given to pipe-trench interaction and trench requirements.

When buried pipes are installed in parallel, principles of analysis for single pipes still apply, however soil cover must be greater than minimum. In other word, the design of parallel buried pipes requires an additional analysis for heavy surface loads (given that a common trench is used). In fact for buried parallel pipes soil slip between the pipes becomes the bottleneck for the distance calculation. Talking about 1 m or more separation then the concern becomes faded but it all depends on your pipelines diameters and soil density.

If the pipelines are in separate trenches, then embedment stability becomes a concern when a trench is excavated parallel to an existing buried flexible pipe. You should address what would happen to a buried flexible pipe when some or all the side support is removed in a parallel excavation. Ans also the existing trench stability itself is an issue to concern. At less than minimum side cover, X, side support is lost and the soil on the pipe must be supported by the pipe. If ring stiffness is inadequate, the pipe collapses.

For a detailed discussion, please refer to "Buried Pipe Design" by A. P. Moser, Steven Folkman chapter 3.

Also, see page 34 of the Welded Steel Pipe:

https://www.steeltank.com/LinkClick.aspx?fileticket=jbA_GxbWtEg=&tabid=108&mid=502

The minimum distance will depend on the burial depth. The equation on page 34 shows 6 feet of separation for a pipe buried 2 feet and 8.5 feet for a pipe buried 5 feet.

 

[LittleInch]

Bimr makes some very good points.

AFAIK, there are no specific distance in any coeds for parallel pipe separation, or if there are any it is on the basis of laying both at the same time.

Installing a new one next to an existing one all comes down to impact of construction on the existing pipe. 1200mm is a pretty big pipeline and the trench will need to be in the order of 2.5 m deep??

Work out what sort of trench you're going to excavate and allow sufficient soil depth to cover the other pipe and prevent side slip or movement of the existing pipeline.

If your intention is to completely uncover the existing pipe ( will be costly and time consuming) and then lay the new one as if you were laying both at the same time then I would go for min 1 m edge to edge, purely on the grounds of future maintenance access.

Otherwise I would go for a 5m centre to centre min separation for pipes this big.

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

 

[JohnWeal]

Many thanks for taking the time to give a nicely detailed response.
Regards
John

 

[LittleInch]

Note this is aimed at cross country / open ground routes.

In more congested locations then you could, in theory at least, use trench boxes / side supports / sheet piles and excavate a slit trench to support the trench sides.

Then you could get down to maybe 400-500 mm edge to edge, but it's very expensive to do it that way.

Always helps if the nearby pipe is owned by the same company....

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

 

[rconner]

You don't mention the service of the little smaller line (some locales/AHJ's also have regulationss with regard to separation distance between piopes of different services). There have also been past threads on sucxh subjects - search "separation distance" etc. on all threads.

 

[bimr]

The buried pipe calculation is similar to the one presented in the welded pipe handbook. See attached.

 

[BigInch]

Buried pipe calculation distance is only one, perhaps quite minor, factor that needs to be considered. Ease of construction, construction traffic loads and safe distance requirements to prevent damage to the existing pipeline is likely to outweigh minimum distances determined from soil parameters.

 

[robyengIT]

see also :

ASCE MOP 125

AWWA C604-11

 

[robyengIT]

and may be it can help this too :

http://wwww.concrete-pipe.org

Design Data 5 (DD5)- multiple pipe installation