Culvert Advice -- Plastic vs. Galvanized ?

[Jstpssng]

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

He started this post in 2006 and hasn't posted in over 3 years... hopefully by now he has his road finished. He went with plastic, it would be interesting to see how well it stood up.
If he sized and bedded it properly then chances are that it's still there. We ue mostly plastic now and if they're put in properly they are fine. The biggest problem is teaching grader operators how to keep from putting all of the road surface into the ditch.

 

[Kasamoto]

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?

Most plastic culvert I have seen has a smooth inside and that flows water much better than a corrugated culvert. Also, if you size it so it is a bit small the flow will help keep it cleaned out.

 

[pikewrench]

Piping in the road here require that they be bedded with crusher run (use to be called 33C) gravel which compacts to over 90% when poured into the ditch. The mix dries rock hard, but soften back when wet, but does not migrate when a load is placed on it. Also be aware that the EPA has guidelines when increasing the size of a culvert. Basically the increasing of size can not promote flooding to adjacent land that you don’t own.

 

[larrywalsh]

Seven years ago, I put in a 4 ft steel culvert for a shop driveway across a small creek. Chose 4 ft because that's the same size the county used to go under the state highway a half mile downstream.

Last year, daughter put in same size plastic because that's what the contractor recommended because of potential corrosion. The steel will eventually fail.

Second question:

Definitely go with the larger pipe. Same contractor said minimum he would use anywhere for field drains is 12" and it sounds like you have the potential for a lot of water. The smaller the pipe, the more likely you will have debris clogs, so bigger is better. We even had a small tree get sideways over the 4 ft pipe and cause a clog. We were vigilant and got it out before any overflow damage occured.


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?

Follow experts advice. Gravel below would allow extra drainage in case of clog, but larger pipe means clogs less likely. I'm no expert to advise about weight tolerance, but we have shale packed around the steel pipe and field stone and dirt around the plastic one. Both have supported loaded triple axle concrete trucks with no problem.

Forth Question:

Should I have some kind of grate... A grate WILL collect debris, so will require cleaning. The larger pipe will pass most field debris.

Good luck with your project.

Larry (in East TN)

 

[RalphVa]

Plastic is more friendly to your bush hog blades if you nip the end of it.

Ralph

 

[4570Man]

A double wall plastic is the best. They have the smoothest inside and won’t rust out. Don’t put a grate over it. All they accomplish is clogging up and putting water over the pipe.

 

[Jstpssng]

Seven years ago, I put in a 4 ft steel culvert for a shop driveway across a small creek. Chose 4 ft because that's the same size the county used to go under the state highway a half mile downstream.

Last year, daughter put in same size plastic because that's what the contractor recommended because of potential corrosion. The steel will eventually fail.

Second question:

Definitely go with the larger pipe. Same contractor said minimum he would use anywhere for field drains is 12" and it sounds like you have the potential for a lot of water. The smaller the pipe, the more likely you will have debris clogs, so bigger is better. We even had a small tree get sideways over the 4 ft pipe and cause a clog. We were vigilant and got it out before any overflow damage occured.


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?

Follow experts advice. Gravel below would allow extra drainage in case of clog, but larger pipe means clogs less likely. I'm no expert to advise about weight tolerance, but we have shale packed around the steel pipe and field stone and dirt around the plastic one. Both have supported loaded triple axle concrete trucks with no problem.

Forth Question:

Should I have some kind of grate... A grate WILL collect debris, so will require cleaning. The larger pipe will pass most field debris.

Good luck with your project.

Larry (in East TN)

As I pointed out earlier, this thread was started in 2006 and he already got his driveway in.

Still, you raise valid points for anybody who is putting in a road today.

 

[oosik]

My mile long gravel driveway was constructed in 1982. It has two HD - highway dept - 18" galvanized culverts. The driveway contractor had these as "extras" off some highway project.

Anyhow - they have been in place for some 38+ years and show no signs of rust, corrosion, etc. The driveway contractor refused to use plastic back then. Might have had something to do with - the highway project had already paid for the two chunks of culvert. Whatever........

One can only hope there has been improvements in design/manufacture of plastic culverts since that time.

The other item. I've noticed that on new highway projects - the highway design engineers still specify galvanized steel culverts. If plastic was so great - why not specify that type of culvert? On the overall cost of a new highway or highway modification - the cost difference couldn't be a deal breaker.

 

[RickB]

My mile long gravel driveway was constructed in 1982. It has two HD - highway dept - 18" galvanized culverts. The driveway contractor had these as "extras" off some highway project.

Anyhow - they have been in place for some 38+ years and show no signs of rust, corrosion, etc. The driveway contractor refused to use plastic back then. Might have had something to do with - the highway project had already paid for the two chunks of culvert. Whatever........

One can only hope there has been improvements in design/manufacture of plastic culverts since that time.

The other item. I've noticed that on new highway projects - the highway design engineers still specify galvanized steel culverts. If plastic was so great - why not specify that type of culvert? On the overall cost of a new highway or highway modification - the cost difference couldn't be a deal breaker.

It all depends on the jurisdiction. In NY state all small diameter pipe used under rural roads is double wall plastic, has been for a couple decades or more.

 

[Peter 315]

I just did a job over 500 ft of 12 inch ductile iron pipe for drain , 2 manholes and 4 catch basins...

 

[fried1765]

My mile long gravel driveway was constructed in 1982. It has two HD - highway dept - 18" galvanized culverts. The driveway contractor had these as "extras" off some highway project.

Anyhow - they have been in place for some 38+ years and show no signs of rust, corrosion, etc. The driveway contractor refused to use plastic back then. Might have had something to do with - the highway project had already paid for the two chunks of culvert. Whatever........

One can only hope there has been improvements in design/manufacture of plastic culverts since that time.

The other item. I've noticed that on new highway projects - the highway design engineers still specify galvanized steel culverts. If plastic was so great - why not specify that type of culvert? On the overall cost of a new highway or highway modification - the cost difference couldn't be a deal breaker.

Plastic pipe IS GREAT!
You are fortunate to live in Eastern Wa., where corrosion is minimal.
Galvanized culvert pipe, frequently lasts less than 20 years, in many areas.
Larger pipe diameters are often best.. to avoid debris clogging.

 

[ovrszd]

It all depends on the jurisdiction. In NY state all small diameter pipe used under rural roads is double wall plastic, has been for a couple decades or more.

90% plastic here. I've installed hundreds. Only had two failures and they were both from fire when burning off CRP land.

I started installing culverts in 1989. Used steel for the first couple years. I'm now replacing the steel culverts I installed. Rust.

 

[sparksbbr]

Which is the preferred type? Plastic
Why? No rust and doesn't stay bent if an accident occurs

Second question:

How do I tell what size to use?
We use an 18", you'll need to judge the volume of water at its worst case. Ours handles the heaviest of rain, without an issue, but if the creek overflows it passes behind 4 other properties before reaching this one and a 6' culvert can not handle the volume

If this an entrance to a driveway that is perpendicular to the road go with two 20' pieces so you'll have a 40' wide entrance and you'll appreciate the extra turning area especially for trailer handling or if a big truck comes in, they can make the turn.

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?

River sand for the bottom up to 1/2 or 2/3 the height and then normal fill. This will help it bed down and tighten, too much dirt can get water logged and gravel can slowly erode. Both of these can allow the culvert to wash out. Sand allows the bottom area around the culvert to drain, keep in mind if you use a 24" culvert try to keep the hole width to only 30".

If you're using the culvert and just placing it in the gully, then filling in to raise the gully to a specific height, there is a bigger challenge and you'll need to use what is best for your area. We're swampy type of soil so clay is our go to in order to raise the ground.

Forth Question:

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

No need to cover unless there will be large pieces of debris that can build up, otherwise it will suck it through and within 15-20 sec at full flow will pop out the other end of a 20' piece.

 

[wtstarters]

Which is the preferred type? Plastic
Why? No rust and doesn't stay bent if an accident occurs

Second question:

How do I tell what size to use?
We use an 18", you'll need to judge the volume of water at its worst case. Ours handles the heaviest of rain, without an issue, but if the creek overflows it passes behind 4 other properties before reaching this one and a 6' culvert can not handle the volume

If this an entrance to a driveway that is perpendicular to the road go with two 20' pieces so you'll have a 40' wide entrance and you'll appreciate the extra turning area especially for trailer handling or if a big truck comes in, they can make the turn.

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?

River sand for the bottom up to 1/2 or 2/3 the height and then normal fill. This will help it bed down and tighten, too much dirt can get water logged and gravel can slowly erode. Both of these can allow the culvert to wash out. Sand allows the bottom area around the culvert to drain, keep in mind if you use a 24" culvert try to keep the hole width to only 30".

If you're using the culvert and just placing it in the gully, then filling in to raise the gully to a specific height, there is a bigger challenge and you'll need to use what is best for your area. We're swampy type of soil so clay is our go to in order to raise the ground.

Forth Question:

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

No need to cover unless there will be large pieces of debris that can build up, otherwise it will suck it through and within 15-20 sec at full flow will pop out the other end of a 20' piece.

If you go with 2 pipes, debris will catch between the 2 pipes, not good, With a single pipe the headwall should extend out at approx a 45degree angle on both sides and start as close to the pipe opening as possible. This will usually help to catch sticks or brush and turn them in to the pipe. A flat or slightly angled headwall will allow stuff to bridge the pipe opening and gradually cause a very restricted flow.

 

[Industrial Toys]

I would go with the largest that the existing terrain will accomodate.

 

[BackRoad]

Life gets easier making culverts longer than 20' if trailers or RVs are planned.

Finishing and grading the ends of the culvert up to driveway level can use up a foot (at least) of culvert on both ends.

Tough to maneuver a trailer into something that restricted.

 

[BackRoad]

.....

 

[PILOON]

Most plastic culvert I have seen has a smooth inside and that flows water much better than a corrugated culvert. Also, if you size it so it is a bit small the flow will help keep it cleaned out.

I second that!
In cold climates adding a slab of HD foam over the top helps a lot come spring thaws. (on top, not under as ground soil heat will rise and help)

Another smart trick is to run , say, 2 inch poly (with access at one end) to introduce heat or steam come spring, just to start a flow as once started flowing water will clean the passage.
No matter how cold running water won't freeze.

 

[Mat4644]

90% plastic here. I've installed hundreds. Only had two failures and they were both from fire when burning off CRP land.

I started installing culverts in 1989. Used steel for the first couple years. I'm now replacing the steel culverts I installed. Rust.

Only failures I've seen were controlled burns that forgot about the plastic culvert.

 

[hawgfan]

Here in Polk County, Arkansas the county replaced a bridge with 4 plastic culverts side by side. This worked well until some genius decided to burn the weeds in the roadside ditch. All four culverts caught on fire and burned to the point that the road had to be closed until a new concrete culvert could be installed. Since then, the road has flooded a couple of times. Maybe we should go back to a bridge at that location.