Dual Wall HDPE Culvert vs Metal?

[CTSNicholas]

Meant for title to be Dual Wall HDPE Minimum depth vs Metal

I found an old thread here discussing pros and cons of metal vs plastic culvert pipes. I'm running into an issue where I need a 15" culvert pipe, 20' long. I already got a dual wall HDPE plastic one for the use, but according to the documents it says it needs 18" of fill to withstand the H-25 rating, which, in my terms is basically a concrete truck. If I did my math right....

I simply can't afford to build up the driveway that much to have 18" of fill dirt above the pipe. It says a minimum of 12" fill if I'm going to pave the point above this culvert, but I definitely won't be doing that any time soon especially during house construction with all the grading to be done.

I was hoping I could hear some comments from y'all and see if any of you have less than 18" or even less than 12" of fill above these dual wall corrugated culvert pipes, and what the most weight was driven over them; i.e. how much axle weight. I will have at least 5, if now 10 concrete trucks driving over this culvert during construction phase. I want to get the dirt base in, then order some mudrock or crushed concrete as a driveway base and live my life, but I don't want to order the rock if I need to be temporary mounding 18" of dirt above this culvert for the heavy trucks.

I thought as a compromise I would use a steel culvert instead, but that means spending another $500 and not using this plastic one, and apparently the steel ones require 12" of fill above them, so that would only gain me 6". I know I have seen old steel ones exposed and driven on, but that is a moot point as I have a plastic one now and want to try using it with the minimum amount of fill above it to prevent having such a tall driveway. The driveway will already be at least a foot higher than any yard.

 

[RNeumann]

Use the HDPE and be done with it. If it’s installed correctly and you aren’t in beach sand I’m sure it will be fine. The rating (I’m guessing without seeing spec sheet) is for roads and highways- not a driveway that will see 5-10 trucks. Plus HDPE is the gold standard for underground- near indefinite life.

 

[4570Man]

I have an 18” plastic culvert in my backyard that’s only got a few inches over it and I’ve driven my backhoe and loaded 1 ton dump truck over it.

 

[CTSNicholas]

I have an 18” plastic culvert in my backyard that’s only got a few inches over it and I’ve driven my backhoe and loaded 1 ton dump truck over it.

That's somewhat reassuring to hear. I'm sure a full concrete truck will be much more than a 1 ton dump truck but still impressive nonetheless. Can I ask, did you just use clay for backfill? That's what I'll be using since it's not very economical to bring in crushed concrete like the professional road crews do. It will be clay, packed as much as possible maybe even with a cat track or bucket.

 

[LouNY]

My culverts originally where the older single wall hdpe ones.
I have replaced two of them with the double wall ones the only reason for the replacement was to increase the length and because one of them had plugged up with silt and trying to clean the single wall was getting to be an exercise in frustration. The other single wall had gotten exposed on the top zero cover and started to collapse, I expect that it was the triaxle sand truck that started it's collapse as it never had the recommended cover and the cover had migrated off from weather and snow plowing. The areas with 3 inches of fill where still in good shape with minimal deformation after 20 years with gravel delivery and sand delivery trucks and fuel oil truck travel every year.
If the fill around the culvert gets well compacted around the culvert before a heavy load goes across it 3-5 inches of cover will work unless it is very coarse fill.
The best backfill would be a sandy clay that compacts like a rock the backfill will actually support the culvert and help prevent distortion.

Just saw your newer post,
compacting while backfilling in 2-3 inch lays will work the best.
A track machine does not do a good good of compacting, the purpose for tracks is flotation, tires compact better.

 

[/pine]

The more compacted (undisturbed is best) the earth is along the sides of the pipe and the tighter the pipe fits against the sides determines how much the pipe can deflect from weight pushing down on the top...

i.e., dig the ditch just wide enough to get the pipe in...

 

[CTSNicholas]

My culverts originally where the older single wall hdpe ones.
I have replaced two of them with the double wall ones the only reason for the replacement was to increase the length and because one of them had plugged up with silt and trying to clean the single wall was getting to be an exercise in frustration. The other single wall had gotten exposed on the top zero cover and started to collapse, I expect that it was the triaxle sand truck that started it's collapse as it never had the recommended cover and the cover had migrated off from weather and snow plowing. The areas with 3 inches of fill where still in good shape with minimal deformation after 20 years with gravel delivery and sand delivery trucks and fuel oil truck travel every year.
If the fill around the culvert gets well compacted around the culvert before a heavy load goes across it 3-5 inches of cover will work unless it is very coarse fill.
The best backfill would be a sandy clay that compacts like a rock the backfill will actually support the culvert and help prevent distortion.

Just saw your newer post,
compacting while backfilling in 2-3 inch lays will work the best.
A track machine does not do a good good of compacting, the purpose for tracks is flotation, tires compact better.

That's very impressive. Reading these comments makes me feel a lot better about not doing 18" I'll try for as much fill as possible but I'd like to be able to only have to have 6, 8, maybe 10 inches of dirt above the culvert. Maybe 8" of fill and then 2" of mudrock/crushed concrete when all said and done. I'll keep that in mind and forgo using the caterpillar ran parallel to the pipe for compaction. I can try and use the bucket bottom to pack.

 

[RickB]

Use the HDPE and be done with it. If it’s installed correctly and you aren’t in beach sand I’m sure it will be fine. The rating (I’m guessing without seeing spec sheet) is for roads and highways- not a driveway that will see 5-10 trucks. Plus HDPE is the gold standard for underground- near indefinite life.

Unless you are in an area prone to grass /brush fires.

 

[Industrial Toys]

You could add some geotextile as well.

 

[sdquick]

Put in HDPE. It will be good with your plans for normal driveway traffic. If you are worried about heavy traffic for a short time or one time drive then you could build up over the culvert with a "bump" to distribute some of the load and then after.