Utility horizontal penetration effect on small dam

[soil1999]

I have a small diameter utility pipeline crossing a small dyke/dam (around 2.5 m height). Dam authority is concerned about erosion potential of the dam body due to this horizontal penetration. Do you recommend anything for mitigation/prevention (of any detremintal effect on the dam due to this crossing) other than selected backfill and embedded materials as well as proper compaction. Any guidelines will be greatly appreciated. Thank you.

 

[cvg]

While this is a very low structure, you have not indicated what the potential risk would be. Regardless, any penetration in a dam should be avoided. I would recommend not crossing through the embankment and if you do, make sure it is in the freeboard area. If you must go through, there are technical guidelines for penetrations. A filter diaphram is often recommended.

 

[AussieGeoEng]

1. Avoid.
2. Graded sand filter as cvg suggests.

 

[dgillette]

What AGE said, and also making sure there is good compaction and material selection around the pipe. Best thing is to get the utility pipe bedded in lean concrete, because there is no way in the world you can get good compaction under a round pipe.

I take that back. The best thing is to do all of the above AND arrange it so the penetration is above the normal water surface.

A very large fraction of all dam failures by piping begin at a conduit through the embankment.

Now, backing up a little, is the pipe being laid along the dam lengthwise, or does it go through the dam the short way?

 

[cvg]

bedding a pipe in concrete is a good first step, however, piping failure could still occur if the joints leak or if the pipe breaks or corrodes. Full encasement would be better. Still doesn't prevent "piping" from developing along the concrete / soil interface though. Collars used to be used, but they have been shown to be ineffective, mostly due to poor compaction. Graded sand filter diaphram will capture the flow and convey it safely to the downstream toe of the dam without any of that pesky internal erosion.

 

[fattdad]

concrete cradle for the upstream 2/3rds. Envelop the downstream 1/3 in a gravel filter.

f-d

¡papá gordo ain’t no madre flaca!