Distance between pipes

[SMIAH]

We have a project where we have to place 2 pipes parallel on a water distribution network.
The pipe will be made of PVC DR-18 with diameters of 8'' and 6''.

What would be the different considerations as to determine the distance between these two pipes?
I was thinking of specifying at least 12'' exterior to exterior for compaction.
If there is a leak in the future, it might be close...

Is there any standard ?

 

[jgailla]

I haven't seen a standard for this situation, but I try to keep the pipe 3 feet apart minimum so that future excavation is easier.

 

[dicksewerrat]

The pipes only have to be far enough apart for the most incompetent repair person, now or in the future. 3 feet should be enough for PVC.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[bimr]

Buried Pipe by Moser has a discussion of this. The factors include the burial depth, wheel loading, pipe material, pipe diameter, and soil properties.

For trench stability, at least 2 feet between pipe spring lines should generally be maintained should excavation be necessary to repair one of the pipes.

If trench stability is not a requirement, the pipes may be installed closer together. Depending on the soil properties and loadings, higher levels of compaction of the soil column between the pipes may be necessary.

 

[chocobo1198]

Considerations...
Some people already noted:
1. Compaction - make sure a jumping jack or equivalent gets in there. Min. 2 feet I'd say wall to wall.
2. Repair/maintenance - need to be a able to strap a saddle around the leaky spot or replace some piping. 3 feet wall to wall should be comfortable as others have said.

Other considerations:
1. Do you have air valve assemblies or in-line meters? If you need to put a barrel around one pipe, you may end up putting a barrel around both pipes... consider manhole size and space required for operations and maintenance.
2. Do the two parallel pipes ever cross over to each other or tee off elsewhere as branches? What are the valving requirements? Leave enough space for reducers, valves, and other fittings as required.
3. House connections... you're probably trying to save money by common trenching... but if there are a lot of house connections, you may end up digging a lot more laterally to have these connections installed. If you split up the trenches and have them installed close to property line on either side, you reduce risk of damaging the neighboring water main during a break. My District flags mains on the same street, never mind common trenching, due to seismic purposes. This comment might not apply for your scenario.
4. Don't use sand for backfill

 

[SMIAH]

Thanks for the answers.
The reason behind this concept is mainly to reduce the amount of dead end on 2 separate pressure network (see concept attached - sorry for Paint ).
3' might be too much here. We're dealing with rock and we wanted to use the existing trench as much as possible.
I don't think stability will be an issue here. We're dealing with 8' depth and we'll be using compacted material above.

1. Do you have air valve assemblies or in-line meters? If you need to put a barrel around one pipe, you may end up putting a barrel around both pipes... consider manhole size and space required for operations and maintenance.
2. Do the two parallel pipes ever cross over to each other or tee off elsewhere as branches? What are the valving requirements? Leave enough space for reducers, valves, and other fittings as required.
3. House connections... you're probably trying to save money by common trenching... but if there are a lot of house connections, you may end up digging a lot more laterally to have these connections installed. If you split up the trenches and have them installed close to property line on either side, you reduce risk of damaging the neighboring water main during a break. My District flags mains on the same street, never mind common trenching, due to seismic purposes. This comment might not apply for your scenario.
4. Don't use sand for backfill

1. We keep 2' between existant manhole (ext. to ext.).
2. No crossing. Valves will fit with 2'
3. Each side of the road (housing) will be on a different pipe (different pressure network)
4. We will be using 0-3/4'' or sand

So 2' would be enough.