Culvert installation

JD Farmer · Nov 29, 2011

Three pictures, one to show what happens when it floods and the other two shows how we have it dug out now and ready to place a 24" double wall plastic culvert in the trench. We will pack it in with limestone and either pour concrete walls on each end or lay up sandstone, bricks, and what ever other rocks I have on hand.
The question is, how much top fill will we need and will it hold up when it floods and goes over the top? Plan to finish off the top surface with #4 limestone.
In the past it has never washed out the road because it was packed limestone with some concrete and other rocks in the top foot of the stream bed.
Previous culvert was only a 6" plastic layed near the top with some concrete over it, always plugged or colapsed.

Billy NY · Nov 29, 2011

I think its a crap shoot to say what would happen to the cover over the culvert pipe. If you undersize it, maybe just undersized for a rare occurrence, like 100 year flood or something, water at the speed it looks like in the photo, could erode a several feet of compacted cover in no time, once it backs up at the culvert abutment.

What would bug me is having undersized the pipe, then applying the labor to build the apron or abutment, just to have it washed out again.

Hydraulics and drainage knowledge applies here. If were me, I'd want to install a much larger pipe and construct concrete abutments, use large stones, rubble or what have you to reinforce beyond that, still no guarantee, or I'd leave it open til I had the funds to do it right, nothing more aggravating than having to repair or rebuild frequently.

I think precast concrete box culverts would be justified here, 24" poly - ethylene, propylene corrugated pipe just seems undersized for the volume of water shown. We just learned what a 500 year event can do around here, there is no stopping it.

PS, like the rustic effect that photo shows with the outbuildings/barns.

old · Nov 29, 2011

I will tell you this since I have BTDT if you figure you need 24 inch ones got with 36 inch ones. Then be sure if you can to fill up on both sides so as to keep the water from eating around the culverts on either side. Or in other words bigger in the case is by far better

Lloyd In South Carolina · Nov 29, 2011

I agree, bigger is better. I would also add, given the flow you have there, I'm not a fan of the plastic pipe. It floats!! I'd go with the concrete version.

L.

JD Farmer · Nov 29, 2011

Give what has been said, I agree bigger is better but in this case I don't have the room for bigger. To be big enough I beleive it would have to be a 4' culvert....so that would mean going to a box style culvert not so high but wider.

Which begs the question.....the next stream over from this one is out behind my other barn and I placed a 24" culvert there back in '95, has never washed it out and most all the fill is dirt with a little creek bottom sand and gravel placed around it along with the stone walls.

The pic is from the same rainfall after it stopped and I got out there and found this mess...

jackinok · Nov 29, 2011

I kind of agree with billy here,its hard to say. MY rule of thumb is if i think a 24" will handle it i put in a minimum of a 36" or more. Theoretically you dont want any running over the road. Theres just no predicting what will happen. If theres some doubt as to what size to get,try getting in touch with you local wcs,or scs people. They should be able to put you in touch with their local engineer who calculates these things. It allways surprises me as to how large they recommend. Just fyi,check around you and see if there is anyone making precast concrete pipe near by. Here at least they will give you the ones that have a slight defect,and thats what i use. they are tough to move around and work with but the make a really good culvert. And another tip,DO NOT pack the tin horn in with rock or gravel,water will run right through it and make it wash more. proper way is to pack it in good with plain clean dirt or clay. Then just add enough rock on ends to slow water hitting the ends of pipe. Loose rock wing dams on ends "should" be five times the width at base than the height. They stay in place by weight.

jackinok · Nov 29, 2011

notice in your second picture,how water is standing on the back side?what you have there is a classic retention pond type deal. If the weight of the water on the back side ever exceeds the weight of the road its gone. In the first picture it appears you have a lot more fall(at least to me) if you put the same deal in there,its very possible it wouldnt stay in my opinion. The force of the water from the fall,combined with the weight of the water backed up,plus the erosion of any running over the top would probably be too much. I agree, i would go bigger there if it were me. Of course your the man on the ground so to speak LOL.

Stephen Newell · Nov 29, 2011

That first picture is way too much water for a single 24" pipe. You would need to lay two pipes to handle that much water. I have one like that in a ravine which has that much water but I have 8' of dirt over the top of it and sometimes the water comes backs up to the road.

Bob Bancroft · Nov 29, 2011

I have several culverts around on owned and rented land. Most have very little cover as I have put in the biggest culvert I could. I have no problem with them even crossing with a heavily loaded truck.

JD Farmer · Nov 29, 2011

Well shoot, you guys are making me wish I'd left the darn thing alone.
The object is NOT to stop the water from going over the top, but instead, when it does...keep everything in place.....so thats why I am trying to keep fill as low as possible while letting the water over the top and holding what I have in place as it does so.

Maybe a concrete slab on top to keep the washing down and also to add weight to help hold it in place??

Somewhere in between 6" culvert and this 24" I had planned, something should work?

S2710 · Nov 29, 2011

I am not a fan of plastic culverts because they will curl up on the ends when exposed to the elements. So if you already have the culvert I would use it but when you get it in the ground pour a head wall and also a pad acrosse the road so when you get a heavy rain the cement on the road will act as a spill way and not wash out your road. JMO

Bob

gitrib · Nov 29, 2011

No one has mentioned a low water bridge. They have been used on county road in our state with great success. Just build a solid road bed tha the water can flow over. They can be used in conection with smail culverts. They use them in some parks.
gitrib

larry from md. · Nov 29, 2011

I agree bigger is better and one large is better than 2 small.The small ones like to plug with debre.The one big disavantage of big ones is they are HEAVY.I can lift a 27incher with my loader (580c casetlb), but a 30 is too much.Looking at those machines they are way too small for big ones.

JD Farmer · Nov 29, 2011

That's what I am trying to say there gitrib, around here we call them a WVA car wash!

I plan to use concrete head walls, at least 8" wide and 8 to 12 feet long on top and depending on what we hit digging the trenches how deep they will be.

We have had over 1.5" of rain since we dug the trench on Sunday morning, with more expected tonight. So far its making about enough water to fill an 18" pipe.

That first picture was of around a 3" or more downpour in about 2 hours. In '98 we had the 100 year flood.....10" of rain over night.

jackinok · Nov 29, 2011

i was going to suggest a low water bridge also,just make sure if you go that route to slope the edges enough you dont bend something on your implements going across. cant tell though,may be in the way of entrance to barn?

jackinok · Nov 29, 2011

that may work,BUT (all ways a pessimist isnt there) if you dont concrete the whole upstream side,down below grade,water will simply wash under your slab and take it away. Been there done that.also if concrete cracks water will wash out dirt below it and it will collapse. Been there done that also! If it were mine and i wanted water to flow over it, i would seriously consider a low water crossing. Thats what they are designed for. just slope sides of ditch and lay a slab about 6" thick.looks like your pretty deep though. a slab with sides sloping enough may be so long as to be cost prohibitive.

showcrop · Nov 29, 2011

I agree that your 24 inches looks half as big as you need. I will urge you to remember that when roads wash out they wash on the DOWN STREAM side. The gravel gets washed out from under the pavement and then the pavement collapses. You will need a continuous rip rap slope from the travel surface all the way down to the stream bottom to keep your road from washing out.

jrh009 · Nov 29, 2011

(quoted from post at 20:49:01 11/29/11)
I agree that your 24 inches looks half as big as you need. I will urge you to remember that when roads wash out they wash on the DOWN STREAM side. The gravel gets washed out from under the pavement and then the pavement collapses. You will need a continuous rip rap slope from the travel surface all the way down to the stream bottom to keep your road from washing out.

To determine the proper size you have to analyze the total net drainage area and then apply a 50 yr storm event . This gives you capacity. Then you select dia and slope of the pipe to determine flow rate. Also a consderation is the pipe material for resistance. Slope is a major factor!

Cover over the pipe is only a structural issue to prevent pipe crushing so it is related to wheel load. If you do not have a structural pipe you need a minimum of the pipe dia over the top of the pipe. The pipe needs to be bedded in granulars to the spring line of the pipe as a min. and compacted to 100%.

If you do not have the hydraulics worked out then I would install the culvert such that I could create a spillway in the roadway surface of armor stone on one side of the culvert. In the event of higher design load the water simply by passes over the spillway and does not erode the material around the culvert.

Hope this makes some sense to you, it is not an eyeball calc. Topo maps are a great aid for seeing the total drainage area

VicS · Nov 29, 2011

I have been a road Commissioner. What everybody says is right, but in the real world we just have to do the best we can and with the tools we have at hand and the cash available. A 24 in plastic pipe will surely do. It won't matter if the water goes over it a few times a year. Just fix the ends like you did on your earlier one. Water has a harder time moving big rocks. I used a lot of plastic culverts the double walled ones that are slick inside. Don't need to worry about crushing them if you back fill evenly and with dirt or CA 6, small rock with lime. They don't turn up on the end. Their only enemy is FIRE. Vic

paul · Nov 29, 2011

It's good to have a foot of fill over the pipe to keep it from crushing. Little more is better if you can, but a foot is good. Be sure the ground is rounded - properly bedded - to the culvert, so the culvert doesn't have any gaps or deformaties that will make it egg shaped or eventually collapse or eventually wash out from voids.

As to washing, looks like you have some serious water rates & slope there, will take good rip rap and bigger gravel/rock to keep it from washing out. As mentioned, they tend to wash away from the downstream side, so pay attention to that side of it.

--->Paul

kyhayman · Nov 29, 2011

I've got a similar spot, flow looks pretty close. I put in a 36 inch with 2 feet of top fill and 6 inches of crushed stone on top. Did great until a 20 year rainfall event sent the whole mess a quarter mile down stream. Now I've got the 36 with a 24 beside it, aligned top to top so the 24 only kicks in at high flow. The whole thing is capped with a 10 foot wide 22 foot long 8 inch concrete slab. Slab is 3500 psi, fiber reinforces with 4 inch pipe 6 inches apart with welded bracing to hold it in place for rebar. At each corner I dug 36 by 36 inch bell holes and let the concrete fill them too as anchors. Bridge has a v in the center and slopes toward down stream to allow for overflows. Water has been over it 3 times in 10 years.

kyhayman · Nov 29, 2011

I've got a similar spot, flow looks pretty close. I put in a 36 inch with 2 feet of top fill and 6 inches of crushed stone on top. Did great until a 20 year rainfall event sent the whole mess a quarter mile down stream. Now I've got the 36 with a 24 beside it, aligned top to top so the 24 only kicks in at high flow. The whole thing is capped with a 10 foot wide 22 foot long 8 inch concrete slab. Slab is 3500 psi, fiber reinforces with 4 inch pipe 6 inches apart with welded bracing to hold it in place for rebar. At each corner I dug 36 by 36 inch bell holes and let the concrete fill them too as anchors. Bridge has a v in the center and slopes toward down stream to allow for overflows. Water has been over it 3 times in 10 years.

JOHNNYfromMI · Nov 30, 2011

You have a 24 inch culvert, use it.
Compact the dirt as you backfill in small layers.
Ends turning up? Never saw that happen, unless it was from a grass/brush fire.

Culvert installation

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