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...