Size/depth of small culvert for gravel road? Thickness/type of gravel?

[JimS]

Putting in a gravel road to a detached garage/shop and need to drain about 3000 sq ft that has a small swale currently. Don't have much depth although the slope is at least 2% I think. I did some quick calculations based on this table:

https://www.ncforestservice.gov/publications/WQ0107/xAppx%209%20-%20Talbots%20Culvert%20Table.pdf

Using C = 0.8 (soil here is a fair amount of clay so somewhat heavy, no cover, moderate slope) and used 2 acres as a base, then scaled to 0.075 acre which gave 4.3 sq in.

This seems really small and I know I will have more friction on a small pipe so thinking several 4 in sch 40 pipes because of low height. Maybe 2 or 3 - 4".

I am only going to be able to do a couple inches of cover. Is this going to support heavy traffic? I don't expect much heavy traffic but wanted to get the gravel road in before construction of the garage O it would be quite a mess in the spring. Perhaps I can get the concrete done before things get soggy in the spring and just skip the culvert and gravel until later? Location is St. Louis, MO area. Or do I need to look at steel pipe with thick wall (not culvert pipe)?

Also looking for recommendations for gravel road construction. I may change the road location in a few years so wanted to do a reasonable job but not quite as much as if it was permanent location. Mostly will be lighter vehicles. Maybe an occasional modest RV or delivery truck.

I realize these are pretty open ended questions but short of doing an engineering study trying to determine what is reasonable.

 

[RNeumann]

SDR35/3034 in 4” can take a beating. I’d skip SCH40 unless it’s HDPE which you probably won’t find and typically not classed with “SCH”

You will want to encase them in a nice firm fill- not sand or clay. Space them out so they aren’t relying on each other for structural support- maybe 1’ apart.

 

[RickB]

Small diameter pipe plugs easily and for my $$$ are more trouble than they are worth. I would use a swale, paved or stone, if I could not install a 12 inch pipe.

 

[s219]

Since I have installed a bunch of culverts, I have become familiar with the practices in this area. Small pipes are not recommended because they can plug easily. So the smallest pipes I normally see in use are 8". If using proper culvert pipe, the smallest you can buy around here is 12".

For cover, 12" is the minimum to support construction traffic. And that assumes a properly bedded pipe. You want to build up that "arch" of compacted material around the pipe to carry the load. The pipe itself only forms/supports the arch shape and doesn't support vertical load.

I am sure there are shortcuts you can use for temporary crossings, or ones where you don't care about the pipe plugging up or handling heavy traffic. But if you are concerned with either, then I'd say 8-12" pipe and 12+ inches of cover are minimum specs.

 

[JimS]

RNeumann, what would you consider firm fill? I am thinking at least several inches of gravel below and around the pipes and up to the road surface. 3/4- or CA6. Apparently they are pretty much the same as far as I can tell. I am thinking 10 - 12" is about the most I can get from road surface to bottom of pipe so that would be one 6" with about 4" cover or two or three 4" with about 6" cover.

 

[ovrszd]

I'm with Rick and S219 in regards to culvert size.

My Son's place is oak tree covered. He plugs a 10" culvert.

You'll plug a 4" pipe with grass clippings.

You have no "head pressure" to force the material thru the pipe.

As shallow as you are, I'd look for steel pipe, 1/8" wall or thicker. Only drawback to steel is when mowing around it...