Culvert Advice -- Plastic vs. Galvanized ?

[pencil pusher]

hi, I don't normally get involved in these things But.. plastics over galvanized . pros and cons.. plastic needs to be bedded correctly or it will fail. 12" min top fill and sand all about or 3/4 minus at least and it will preform as good as any once bedded in. galvanized is great drop it in the ditch and backfill but if not enough cover it will fail. to be happy with either be sure to compact the backfill. lets not get into tire damage if you can't cross the access properly. galvanized will destroy a tires if it fails and plastic will just collapse Plastic can be bent around a slight curve. we drive loaded tractor trailer combinations over both with success as long as it is bedded right. Never skimp on size. 16" will be min standard all over soon and bedding material needs to be good.

 

[josewalfredo]

I have used plastic, galvanized, and concrete on my 80 acres for decades. All have pros and cons. Concrete is heavy, hard to handle and expensive, but it is the best. Plastic can and will get torn up. Accidentally, sure, but it always does. Metal will rust in acid soils, but there is a cure for that: coat with tar or wrap it. I have metal culvert that has been in the ground with constant flow in highly acidic soil for thirty years. Whatever you use, cover it well so it can take the weight. If it has a significant slope or a lot of pressure on one end, pour cement under it or drive a couple of t-posts on the edge of the downslope end.

 

[ruffdog]

We have alkaline soil here and the County and State install galv pipe. The neighbor excavator also installs galv pipe.

 

[bumperm]

We have a 120 foot 12" galvanized corrugated pipe under our HOA road that has failed 17 years after install. It drains spring water so always has flow. In part, the problem stems from how corrugated pipe is made, formed by rolling a strip of galvanized sheet steel on a mandrel. The edges of the sheet are continuously crimped so they are strong, but not water tight over the long term. Tree roots can find those cracks and then proliferate within the pipe to bung things up. As others have opined, go with a smooth bore plastic.

 

[plumbyII]

Use the biggest pipe you can find. Three reasons, beaver's damming by blockage inside, kids playing in pipe, (my 7 year old sister got stuck in our farmhouse ditch culvert), and gully washers. Most exciting trip with my gramps was barreling down an old railbed cut ravine we used to access his parcel. In a blink, he jammed on the brakes and we skidded to a stop just within inches of a 5 foot deep and 8 foot wide gully cut by storm water right across the roadbed. Here is a photo of a beaver dam in a culvert.

<img src="blob:chrome-untrusted://media-app/c1299409-3dfa-4ba2-bdfa-cf5d9243c83a" alt="beaverdambugacresIMG_20200717_132837 (3) (1) (1).jpg"/>

 

[ruffdog]

Galvanized pipe quality and options can vary. What gauge metal is it...18,16,14,12,10? What coating does it have...a good quality galvanize or a cheaper "coating"? What PH is your soil as it does matter? Here is a great site with hard numbers:

https://westernprecast.com/wp-content/uploads/2018/11/Corrugated-Metal-Pipe-Design.pdf

 

[lgbost]

I need to put in a 20' culvert to extend a road to an RV pad I am building. I need to be able to drive both a 14,000 # motorhome and my 8000 # tractor over the culvert, not at the same time.

I have seen both metal and plastic used, the costs are close in my area.

Which is the preferred type & why?

Second question:

How do I tell what size to use? The county says 12" minimum everywhere, but for the difference in cost I would rather do it right (maybe some overkill) the first time than replace it next year if it is too small.

From the topo map, it looks like the water from 10-20 acres of 15%+ slope drains through this spot. The culvert will have about a 10% slope.

I am sort of leaning to 24" diameter, which only costs twice as much as 12".

The culvert is going into a natural gully and not a ditch. I looks to me like there will be over 3' of fill over the culvert at one end, and over 5' at the other.

Third Question:

Do I need to fill around the culvert with gravel or can I just use the dirt I excavated for the RV pad?

Forth Question:

Should I have some kind of grate to prevent debris from entering the culvert?

Curly,

I am a small farmerthat grew up on a farm in NC and a civil engineer. I have two Kubota tractors and a bobcat. I would not use galvanized pipe. It will eventually rust out. With that many acres flowing into it, and depending on your local rainfall, I'd suggest at least a 24 inch pipe. I'd consider a concrete pipe. Usually if there is a concrete pipe manufacturer near you you can go get seconds/culls at a reduced cost directly at the factory. If you put a flared transition on each end you'll greatly help the flow. A 24 inch pipe with flared ends will carry as much as a 30 inch without flares. It makes the flow laminar rather than turbulent. If you have front end forks or a backhoe on your tractor you can place the concrete pipe with no problem. The loads you quoted are not an issue for plastic or concrete at the depths you have . Once you have a foot or more of cover that usually isn't a problem. Use dirt to backfill, not sand or rock. You don't want water to be able to flow outside the pipe. Get the joints as tight as possible so leaks won't wash out the pipe.

Larry

 

[RickB]

The only concern with a properly sized and installed double wall plastic pipe would be a raging brush or grass fire. If you are in an area susceptible to fires I would use concrete. Galvanized steel would be my last choice.

 

[tthopskin@yahoo.ca]

I need to put in a 20' culvert to extend a road to an RV pad I am building. I need to be able to drive both a 14,000 # motorhome and my 8000 # tractor over the culvert, not at the same time.

I have seen both metal and plastic used, the costs are close in my area.

Which is the preferred type & why?

Second question:

How do I tell what size to use? The county says 12" minimum everywhere, but for the difference in cost I would rather do it right (maybe some overkill) the first time than replace it next year if it is too small.

From the topo map, it looks like the water from 10-20 acres of 15%+ slope drains through this spot. The culvert will have about a 10% slope.

I am sort of leaning to 24" diameter, which only costs twice as much as 12".

The culvert is going into a natural gully and not a ditch. I looks to me like there will be over 3' of fill over the culvert at one end, and over 5' at the other.

Third Question:

Do I need to fill around the culvert with gravel or can I just use the dirt I excavated for the RV pad?

Forth Question:

Should I have some kind of grate to prevent debris from entering the culvert?

plastic or steel . if its in water the plastic will lift just like a banana . steel in water yes it will rust but years and years down the rd . but it should never lift . plastic junk . 30 years working with culverts . and plastic there junk

 

[iamrich]

I also agree with most of the comments. I have a very similar property to yours. I have 28 acres with my driveway having sections of 17% slope and 1500 feet long. the property is heavily wooded so a lot of leaves and debris gets washed down in the fall. I had installed about 6 plastic culvert pipes that are about 18" and some are covered by anywhere from 1 foot to three feet of soil and stone mix. I have had no problems after about 15 years of driving a 32,000 pound mobile home with a super large excavator, bulldozers, cement trucks and fully loaded dump trucks filled with rocks over the culverts.
A couple of words of advice. Make sure you use double wall plastic. This is the type that has the smooth inside and has the ridges on the outside. You can use 16 or 18" culvert for some of your areas that would have less debris and use the 24" where you think the leaves and branches might accumulate.
I have one culvert that is placed where my road ditch meets with an old logging road and has a 16" culvert. I wished and may change it someday to a 24". Once or twice a year I need to take the excavator and make sure I clean out the debris from the entrance since a clump of leaves will start to back up the entire works and the water will flow over and down the driveway. Once I take a bucket or two of leaves out of the opening, it's like unplugging a toilet. The rest of the leaves and debris flush out quickly. In no way should you use a grate or anything that will block the flow at the entrance to your pipe, that would be the equivalent of putting in a smaller pipe.
If for any reason you find that any of the pipes and locations are being overwhelmed with a heavy storm, you can always add another one or two pipes uphill to provide more drainage.
My biggest problem is that my grade is so great that water builds up speed going down the steepest part of the driveway and doesn't roll off to the side where my driveway make a 90 degree bend. I wished that the road contractors had listened to me more by putting a crown on the middle of the road to divert the water more to the sides. My road gets ruts from the water washing away the top material and I may have to pave it in these spots. Good luck with your project.