Culvert Advice -- Plastic vs. Galvanized ?

[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.