Questions about in ground downspout drainage pipe

Old 07-31-18, 05:24 AM
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Questions about in ground downspout drainage pipe

We had a guy install drainage pipes 7 years ago to take the water from downspouts around the house and direct it into the woods behind the house.

He used black inside / white outside plastic pipe. I think that's called ADS? the pipe doesn't have any holes along its length.

I remember when the guy was trenching, he said he hit lots of rocks and mentioned how he put them back in.

a) there's a pitch problem along a stretch. I dug up 20 - 30' of the run. Loads of big rocks above / along side and below the run. Those get pushed up over time and can cause the pitch to change, right? ie putting big rocks back in the ground around the pipe - is that a good idea?

b) would you put that pipe back in the ground or use PVC? Looking into the pipe still in the ground, It's not round... a bit of an ellipse now. PVC won't deform. But might break from rocks / shifting ground?

c) if you say put the ADS back in the ground, what do you use to join them? It looks like they used caulk or similar that didn't bond to the joints..

Old 07-31-18, 07:50 AM
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A. I don't know how but it does seem that rocks have a magical ability to rise up out of the ground. I've never seen them rising and causing a pitch problem but I have seen ground settling cause the affect.

B. I always use smooth wall pvc. If the ground is free of larger rocks and for most applications I use schedule 20 drain piping like sold in the garden center. It is thin walled so it can be deformed by heavy loads. If you want more durability I would go up to schedule 40 from the plumbing dept. And in areas like going under a gravel driveway I use shedule 80 PVC (often gray in color) which is really heavy duty but harder to find.
Old 07-31-18, 08:02 AM
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as usual, thanks for the comments! Yeah, some of these rocks are the size of a fist, some (not just 1) as big as 20" wide or so. I've heard of ground heaving / rocks coming up (ie supposedly what the phrase 'growing rocks' came from?). So something that big moving up and it's under the pipe? That pipe is going up with it.... I think I found the (or 1 of ) the high spots... and a big rock is under it.

sched 20?! never heard of that. just 40 and 80. gotta check garden centers.

you can see some of the rocks I pulled out on the right of this picture. and that was in just a small stretch.

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Last edited by PJmax; 02-23-19 at 11:56 AM. Reason: resized picture
Old 07-31-18, 03:35 PM
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The pipe you used is what I've been using for exterior drainage. I've heard you're specifically not supposed to use Sched 40 PVC outside since while it's sturdy, it's also brittle. So if it shifts or expands/contracts too much, it tends to crack. The lighter weight (black inside pipe which I think is HDPE) which you used, is more likely to move and not break. It also slides together and doesn't specifically need to be cemented - but I guess some adhesive never hurt anything.

I would have never put any rock bigger than a baseball back in the trench. You're just asking for trouble.

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