Culvert Advice -- Plastic vs. Galvanized ?

[Egon]

Cover over the culvert depends on the gauge of the culvert material and diameter. Suppliers should have charts for this. After a certain depth of cover the soil will bridge and support the loads.

Both the inlet and outlet ends should have some riprap on the side slopes and bottom to prevent washing. This is important on the outlet to prevent undercut.

Ideally the culvert should be placed on a compacted base and covered with light compacted lifts. A well graded crushed granular material can be used if available. Keep rocks away from the culvert.

The drainage area sounds considerable for the culvert size but that is affected by soil type and rainfall amounts. You will have seen how much water runs down the gully.

Egon /forums/images/graemlins/grin.gif

 

[kossetx]

Guys, Since you all know so much about culverts, I have a question. I have some 12" schedule 40 pvc pipe. Would 2 runs of this equal, lets say, an 18" single pipe. I know I can calculate area, I'm just asking would it in reality work as well. One thing nice about it is it is smooth inside. I hate to just throw it away.

 

[EddieWalker]

Sizeing pipe and the amount of flow it can handle is a pretty involved formula to get it right. For most people, the general rule of thumb it that for every half inch of diameter, you increas volume by 2 1/2 times.

The 18 inch will handle more water than the two twelve inch ones. Do you need that much capacity?? Will the two 12 do the job?? Hard to say without knowing how much flow you have or the size of your drainage.

The other problem with pipe is that outsides are smooth. It's impossible to stop water from travleing down the sides of the pipe with dirt alone. No matter how tight you compact it, water will still work it's way down the side.

Lake builders use special sleeves to stop this in dams. Concrete also works.

Again, it depends on how much water we're talking about here. Since you considered an 18 inch culvert, I'm assuming there's allot of water your dealing with.

Since the pipes are free, you could always pour concrete at the ends and be money ahead.

If it was me, I'd try the 12 inch pipe and see how it works. But I'm cheap that way and free sure beets out allot of the other negatives.

Eddie

 

[CurlyDave]

The link in PineRidge's post has a table which shows what size is needed.

In my case, I think the table indicates I need something in the 24-30" range.

I am going to go with 24" since I think I overestimated the acreage drained. Also, the only place this goes is to a motor home pad, where I will have septic, water, and power. If it fails, not moving the motor home until I repair it is not a big issue. Plus, the culvert is going to have a significant downslope 10% or so, which should increase its capacity.

If the culvert was on my main driveway, I would get a bigger size.

 

[LBrown59]

<font color="blue">
24 inches might not be enough.

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Maybe the ravine or ditch is to big rather than the culvert to small.
~~~~~~~~~ </font>
Case in point the road ditch along the front of my property is any where from 24'' to 60'' wide and 24'' to 60'' deep.
Last fall I installed 120 feet of 15'' DW Smother Bore plastic culvert in it. In 40 years of living here that ditch has never carried enough water to make the 12'' 40' long culvert under my driveway in that ditch flow at any where near its 12'' capacity even in the heaviest torrential prolonged downpours.

After this installation I've concluded: Base the size of culvert on the volume of water needing carried not the dimensions of the ditch.

 

[LBrown59]

</font><font color="blue" class="small">( I'd be a little concerned whether the plastic culvert could handle the stress.
)</font>

It's not the strength of the culvert that prevents collapse it's the equalized pressure of the earth around it.

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[Buckcreek]

i have a branch that runs through my property It dries up in the summer and runs pretty good through wet weather. i put some 24'' galvanized drain pipes in to get some room to turn around and park , I wonder how long these are expected to last. I need to install some more but where these will be i need them to last forever LOL and i need to be able to drive over them . What would ever one here use , maybe concrete culvert pipe.

 

[LBrown59]

<font color="blue"> He said that he "didn't like to see" 12" diameter pipe that long. He was worried about blockage and said 18" would have been better. </font>

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Wonder what he'd say about my 160 feet of 15''?

 

[Highbeam]

Supposedly, the galvanized CMP pipes will last 30-50 years but we have all seen rusty ones. The coatings vary and have a large effect on life. The corrosivity and wetness of the ground makes a big difference too. Check out some of the websites from the manufacturers and they should give some guidance on expected life.

 

[KentT]

I thought these pictures might add some value to this topic. I just had guys put in an 18" plastic culvert for the driveway on my lot last week. Since there's no permanent running water, and just runoff from a relatively small area, I think 18" is actually larger than needed but I wanted that size as a minimum for easy cleanout, if needed.

Here's a series of pics that show it being installed:

Clearing the trees

Preparing a bed for the culvert

More bed preparation

Getting dirt off the stumps as he piles the brush

32 Feet of culvert lying in the bed, waiting on the fill dirt

Spreading the fill and packing it in

Smoothing the edge of the fill

He packed the edges (the banks) with the bucket, patting it down

Closeup of packing the banks using the bucket

One of the 12 tandem loads of moist, sticky clay that we covered it with

He built up the fill in layers about 6" deep, packing each layer by running over it

Final grade, after 2 tandem loads of topsoil added, and backbladed sith the dozer to sow grass seed in

Grass seed sown on banks, mulched with old hay, and waiting on first loads of base stone

Other end of circular driveway in same state -- waiting for base of 1/5-2" stone

We were lucky enough to find a guy in the neighborhood who was cutting the grade off behind his house -- giving away this nice red, sticky clay that we used to fill around the culvert. It packed so well just by repeately running the excavator over it that the loaded dump truck would barely make tracks in it... We spread the very thin layer of topsoil to cover the ugly clay, with most of it spilling down the banks on each side, just so there would we a good seedbed for sowing fescue to prevent erosion. Now, if my resident flock of wild turkeys don't eat all the grass seed, I should be in pretty good shape! /forums/images/graemlins/shocked.gif