Pond outlet culvert-HW & anti-seep collar question
Pond outlet culvert-HW & anti-seep collar question
(OP)
I want to use a 12" pipe to outlet a detention pond. It is only 30' length going thru the embankment. The profile will slope up 4:1 to provide 2' of cover over 10' of the pipe, then slope back down 4:1. I planned on using a HW at the inlet and outlet end. When is anti-seep collar needed?





RE: Pond outlet culvert-HW & anti-seep collar question
I don't know where you are working - in some states you need a minimum of a 24" pipe (3' area) to outlet a pond.
Again - check the state or local regs.
RE: Pond outlet culvert-HW & anti-seep collar question
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RE: Pond outlet culvert-HW & anti-seep collar question
Any body in their right mind will ask, "heck, the water will just pour through that gravel, eh fatt-dad"? Well, I guess. What happens actually is whatever water does make it along the upper 2/3rds will issue in to the gravel bedding but the confining stress will be too great to exceed the critical gradient (i.e., and therefore begin piping failure). I'd look at this before I was bullyed by a local jurisdiction into using seepage collars.
f-d
RE: Pond outlet culvert-HW & anti-seep collar question
Collars are not allowed around here for outlet pipes through dam embankments. A filter diaphram is required, regardless whether any of the pipe is placed in a cradle. Make sure that your granular filter material is filter matched to the structural fill. this might require sand instead of gravel or a two layer granular filter.
RE: Pond outlet culvert-HW & anti-seep collar question
I have also seen the pipe encased in concrete for the upper portion of the run instead of just placing concrete up to the spring line.
Remember that the concrete cannot be bank poured. It is important to COMPACT the soil backfill/fill up against the concrete to reduce the seepage.
With all of that said, if I'm reading the original post correctly, there is less than 10 feet of head on the pipe and the side slopes are 4(H):1(V). With that low of seepage head and the length of the seepage path, it is unlikely to matter how the pipe is installed unless the soils are very errodable.
RE: Pond outlet culvert-HW & anti-seep collar question
I would agree other than to say, I worked on a job with very similar conditions and during a storm (i.e., water just pouring across the outlet structure and high gradients throughout), there was a catistrophic failure along the pipe. I wish I could post a photo, but the upshot of the whole thing related to unsuitable compaction along below the spring line of the pipe. At least a concrete cradle to the springline confirms the presence of something in that little area you can't see and allows for a proper surface to place the compacted soil trench backfill.
f-d
RE: Pond outlet culvert-HW & anti-seep collar question