Drainage ditch - gravel first or not?

[JJT]

How deep is the pipe going to be? Once you've got 18" of coverage the risk of crushing sewer and drain is significantly reduced, (normal traffic). Look into ADK's N12 pipe - smooth wall inside, corrugated exterior. It has a 10K crush, (3X normal S&D) at 15% premium. It comes in 10' and 20' sections, solid or performated. I've used 1000's of feet of the stuff without ever having a crush problem.

 

[PaulT]

Yes, I could dig the trench a little deeper, then fill with gravel back to that level and lay the pipe. I would prefer to avoid the time of digging and the cost of gravel if laying it directly on the grass will provide the support it needs anyway.

PaulT

 

[PaulT]

The pipe will be about 6-8 inches below the surface. It cannot be any deeper, because it has to direct the water into the culvert that crosses under the driveway. If it were any deeper than that, it would direct water UNDER the culvert, undermining the culvert and eventually washing out the driveway. I get a lot of water volume and force through there during spring and fall storm runoffs.

I think I've decided to use the cheap, smooth bore 4 inch pipe with 1 inch holes on top available from LOWES for about 18 cents per foot in 10 foot sections. First I will lay down landscape fabric directly on the grassy bottom of the swale, then lay down the pipe and wrap the fabric over the top of the pipe. Then I will narrow the swale into a ditch by filling in on the high side of the pipe with hardpan I dug out of another trench. If some of the hardpan slops over, I will pull back on the landscape fabric to keep the pipe fully exposed. Once the hardpan is where I want it, I will flop the fabric back over the pipe and fill the ditch with gravel.

Does this sound like it will work? What problems might I encounter? I already know that having a pipe so close to the surface will cause it top heave during freeze/thaws. Some people have said it shouldn't be a problem for a few years, and then you just re-do the ditch. Of course, if the pipe drains well, there should be no water to freeze in it, and my hardpan doesn't heave that much.

PaulT

 

[Egon]

Paul:
Sounds like you have a plan that will work.

Egon

 

[JJT]

Paul, 6" - 8" of coverage - keep the heavy stuff off or the pipe will get crushed. Is 4" pipe big enough to handle your water volume? Have you thought about going to 6" or 8" culvert pipe? How long of a run? I'm also in upstate NY, (Mohawk valley), how close are you? You don't have to worry about the pipe freezing if you've got a slight pitch, (.25"/ft keeps the water moving). I've got an 800" run of N12 that has been problem free for 10+ yrs.