Backfill materials around pipline in slope with high seepage

[soil1999]

Excavation has been made in big slope with fine grained materials with high groundwater table (seepage)to fix the largte diameter watermain line. Go thing that the slope is highly vegetated and not exposed to mechanical load.
Any recommendation on backfill materials around and above the line. I guess native materials (even if they are highly compressible) would be the best.. since using sand will get eroded and other foreign materials may negatively change the seepage regime in the slope.
Thanks

 

[rconner]

Over the years have seen many designers call out periodic transverse anchorage for pipelines on steep slopes (assuming pipe material and anchorage is adequately strong to take the effects, perhaps this could help to stabilize the pipeline and slope?)

 

[waterpipe]

I'm not a civil engineer, but i think when you suspect that there is a seepage (so the trench could be filled by water) then a concrete encasement would be needed.
You can also consider slope breakers (berms perpendicular to the slope) inside the trench and over the finished ground to reduce the runoff velocity and to divert water off the pipeline route and ROW.

Would be nice to hear back of your solution anyhow.

 

[Ron]

For ease of placement, I would consider No. 57 stone for bedding up to about 2/3 of pipe depth, then sand, then native material. Some top-side settlement will occur as sand infiltrates the No.57 stone, but not a big deal....just add a little fill on the cover.

 

[oldestguy]

As to Ron's recommendation, that may be OK, but if this trench is on some slope where water collected by the open stone runs within that stone in the trench, erosion of the natural soil below that trench can occur. If sufficient erosion takes place, the support of the pipe may be affected. It is troublesome for sewers with segmented pipes, but maybe the water line will bridge those conditions? Something to think about.

 

[cvg]

waterpipe had the right idea regarding trench erosion, it can be done by trench plugs constructed of CLSM or clay to periodically block any flow from running through the granular, open graded bedding material under the pipe and causing erosion. Alternatively, instead of #57, consider a well graded crushed rock such as 3/4 inch road base which will have a much lower permeability than #57. Typically, granular bedding only needs to go to the springline, backfill above the springline will have little effect on the pipe since there is no mechanical loading.

 

[mudman54]

is the pipeline going up and down the slope, or transverse along the slope?