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Pipeline Seperation

Pipeline Seperation

Pipeline Seperation

(OP)
We have a 24" steel pipeline going in with 2" max rock backfill. There is a future 24" line proposed 5' away. Would 5' seperation (cl to cl) be enough in order for the future pipe exacavation activities to not disturb the backfill of the first line?

What I am worried about is the trenching for the future pipe impacting the backfill material of the initial installation.

RE: Pipeline Seperation

If the trench is excavated in poor soil, a good practice is to place good embedment to a width of half a pipe
diameter on each side of the pipe. So the planned separation will probably work in most soils.

However, you have not said how deep your pipe will be installed. For deep burial, you will need to consult with a geotechical specialist. It is a good idea to get some soil borings for a project of this scope anyway. Obtaining soil borings may eliminate possible delays in your project schedule due to unforeseen conditions.

Here is a link to a design document for steel pipe.

http://www.steeltank.com/Portals/0/pubs/Welded%20S...

RE: Pipeline Seperation

(OP)
Thanks, it's 4' deep max. DOnt think its a big deal but something to look at

RE: Pipeline Seperation

I would say this is just a bit too close. per bimrs recommendation, you would have 12 inches or less separation between the trench walls. If the material is cohesionless, it likely will cause some settlement

RE: Pipeline Seperation

Another factor to consider is cost impact on future construction. Almost anything can be done somehow, but if the pipes are close enough that a contractor has to modify his methods or take additional care, the cost impacts can be significant. One way you could keep the pipes close and minimize future costs would be to specify the first pipe be backfilled with Controlled Low Strength Material (CLSM, flowable fill) for all or or a portion of the trench depth. It generally costs a bit more than conventional methods of backfill and compaction because of its comparatively higher material cost, but that higher cost is usually considerably offset by savings in reduced equipment and labor costs. Additionally, the total cost of the CLSM option can be further reduced if the required trench width is reduced in the design. Often trench widths are wider than they need to be to allow space for the pipe and cushion, plus enough space for compaction equipment to compact between the pipe and trench wall. Using the CLSM, that width can be reduced so that sometimes it can actually cost less than more traditional methods that require a wider trench. If 6" of cushion material is adequate between the pipe and trench wall, that is plenty of room to place the backfill on the sides of the pipe. The benefit in this case is that when the excavation is performed for the second pipe, the side nearer the first pipe can excavated be through the CLSM, which will be stable and will stand vertically at a depth of four feet. Using this method, 5' apart o.c. is plenty, and will work in almost any soil condition.

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