Dual Wall HDPE Culvert vs Metal?

[ovrszd]

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...

That doesn't work well. You can't get fill material tight around the lower half of the culvert.

Best is dig it wide enough to lay the culvert in the middle and pack material on both sides.

 

[smiley]

[Quote Originally Posted by /pine View Post
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...

QUOTE=ovrszd;5494451]That doesn't work well. You can't get fill material tight around the lower half of the culvert.

Best is dig it wide enough to lay the culvert in the middle and pack material on both sides.[/QUOTE]


-----------Until you can get a Whacker in there, we found the best tamping tool especially when the trench is tight, is a short 2x4. Tamp toward the center of the pipe from both sides as that punches material into any voids under the pipe. Don't over do it, but it is more likely you'll run out of steam before you could raise the pipe---------
Smiley.

 

[fried1765]

That doesn't work well. You can't get fill material tight around the lower half of the culvert.

Best is dig it wide enough to lay the culvert in the middle and pack material on both sides.

Correct !!!

 

[crashz]

If you make it a tight fit for the pipe, you cant tamp backfill under & completely around the pipe. With voids under the pipe, it will lack support & crush much more easily. Properly compacted backfill all around the pipe is key for strength.

Bingo. Compaction is key. Get all of the soil as tight as you can around the culvert, even if you have the use a shovel handle to pack it in around the corrugations. The better you pack the sub-grade, the longer the culvert and the driveway will last.

 

[/pine]

You must think that a round object like a pipe distorts equally with applied pressure to a single plane...it does not...think of a circle inside of a square...push down from the top and the circle will mostly distort perpendicular to the applied pressure...the voids at the tangent points between the bottom center and the sides will see little if any distortion...i.e, the earth there will see no pressure...

Also, if you are planting a culvert for a municipality or government agency etc...you have to follow ASTM guidelines which depending on the local strata usually requires a plate compactor to a specified density for any undisturbed earth...

 

[/pine]

BTW...
The single most common fault with culvert installations has nothing to do with the pipe itself or the support to prevent distortion...it's voids in the overall fill that eventually fill in from the top leaving depressions at the surface even on paved over installations...

The most common fault of pipes (distorting) is them becoming an oval because the sides of the ditch were not compacted enough to prevent the pipe from distorting...


Also the majority of municipalities and gov. agency contracts call for bedding material (pea gravel) surrounding the pipe...that generally does not require plate compacting....

 

[ovrszd]

Okay.

 

[3Ts]

There is also flowable backfill. It's not concrete, but uses the same ingredients and has a psi strength of between 50 and 300 (compared to concrete's 2500+). It typically has the same density as undisturbed soil and can be excavated in the future. If over 100 psi it will require a machine like a backhoe to break it up. It does not need tamping, but you do have to be sure the pipe doesn't float.

 

[smiley]

That doesn't work well. You can't get fill material tight around the lower half of the culvert.

Best is dig it wide enough to lay the culvert in the middle and pack material on both sides.

Well you may think it won't work well and I'm not a train driver, but I do have 40 plus years of hands on, down in the dirt, road building in about every capacity from ditch digger to superintendent and laying hundreds of miles of pipe, from 4" drainage on up to 8' box culverts, most always under the watchful eye of NYS DOT engineers and inspectors. Although there are some places that require uncompacted bedding, we were required to spread the specified select fill in the trench, grade it to 1/4 " tolerance, tamp it to specs and set the pipe. If jointed pipe like concrete was being set, a slot for the bell would be shoveled out as it was set. Then the select backfill would be uniformly spread in the trench on both sides in apprx 4" lifts and leveled by laborers who were REQUIRED to poke the fill under the pipe and tamp it in at an angle with either a shovel handle or 2x4 etc., to fill slight voids, corrugations and compact the material . Not perfect but better than no compaction. The angled hand tamping was necessary because the side of the vibratory tamper will hit the pipe and leave 6" or more of uncompacted material on all pipe 12"or larger. As the simplified illustration below demonstrates, most of the compaction zone force is directly under the drum/plate/etc. and drops off rapidly to the side ---- A plate tamper, trench roller, etc. would then make the specified number of passes to obtain the correct compaction that is determined by the backfill material, moisture content and other specs. The following lifts are added following the same procedure up to half the diameter of the pipe, then the compactor will work right up to the pipe with no hand tamping necessary.
There are other ways to do it including that mentioned by /pine using more expensive but time saving materials like pea gravel or small crushed stone, because they are basically self compacting and the vibratory tamper just settles it into any voids. We used that method almost exclusively on highway shoulder underdrains, using a trencher that pulled a trailer carrying and laying 250 ft rolls of pipe and could do miles per day. I recall one 4 lane job over 20 miles long we did, where we put in nearly 100 miles that way.
Smiley

 

[ovrszd]

Well you may think it won't work well and I'm not a train driver, but I do have 40 plus years of hands on, down in the dirt, road building in about every capacity from ditch digger to superintendent and laying hundreds of miles of pipe, from 4" drainage on up to 8' box culverts, most always under the watchful eye of NYS DOT engineers and inspectors. Although there are some places that require uncompacted bedding, we were required to spread the specified select fill in the trench, grade it to 1/4 " tolerance, tamp it to specs and set the pipe. If jointed pipe like concrete was being set, a slot for the bell would be shoveled out as it was set. Then the select backfill would be uniformly spread in the trench on both sides in apprx 4" lifts and leveled by laborers who were REQUIRED to poke the fill under the pipe and tamp it in at an angle with either a shovel handle or 2x4 etc., to fill slight voids, corrugations and compact the material . Not perfect but better than no compaction. The angled hand tamping was necessary because the side of the vibratory tamper will hit the pipe and leave 6" or more of uncompacted material on all pipe 12"or larger. As the simplified illustration below demonstrates, most of the compaction zone force is directly under the drum/plate/etc. and drops off rapidly to the side ---- A plate tamper, trench roller, etc. would then make the specified number of passes to obtain the correct compaction that is determined by the backfill material, moisture content and other specs. The following lifts are added following the same procedure up to half the diameter of the pipe, then the compactor will work right up to the pipe with no hand tamping necessary.
There are other ways to do it including that mentioned by /pine using more expensive but time saving materials like pea gravel or small crushed stone, because they are basically self compacting and the vibratory tamper just settles it into any voids. We used that method almost exclusively on highway shoulder underdrains, using a trencher that pulled a trailer carrying and laying 250 ft rolls of pipe and could do miles per day. I recall one 4 lane job over 20 miles long we did, where we put in nearly 100 miles that way.
Smiley

What?