[AT] OT Low water crossings

[charlie hill]

Don,  I can't really help you other than to say that if you use a culvert 
made for road crossings the manufacturer should be able to tell you how
much cover it requires for a given load.  Dirt is cheaper than concrete. 
Depending on the circumstance I'd be looking at building a "head wall" or
"wing wall"  of the ends of the culvert.  That could be wood timbers, 
concrete, stacked bags of concrete mix, sand bags, rip rap or a number of 
things.
Then with the culvert set in place I'd want an appropriate amount of 
compacted fill on top as Cecil suggested.  You can cut down on the amount of
fill required (the depth of the fill) by using geotextile fabric (see this 
site http://geotextile.com/downloads/PropexLL507.pdf for an example).
If there is a road contractor near you he might have a small amount on the 
end of a roll, a remnant,  you can get to do your job.  When all  that
is done you can pave the road surface with 4 to 6" of concrete depending on 
how well your subsurface is compacted and gross weight of vehicles
you expect to come down your road.

Someone spoke about the strength of concrete.  That is true.  You can get 
concrete with compressive strength generally from 2500 psi to 5000 psi.
However,  the concrete that is used on highways and runways is typically 
classified by flexural strength rather than compressive strength.  The
difference is that the "flex" concrete has a high amount of "entrained air" 
(air bubbles in it) to allow the concrete to flex under the load.  That 
concrete
is typically classified by terms like 450 Flex or 550 flex.  With all that 
said I don't think that is anything you need to concern yourself with.  For
what you are doing I'd probably use something like 4000 psi concrete with 
fiber added and I'd have them mix it dry and add plasticizer to make it flow
easier with a lower water content.

That's about the best my memory will allow.  If your local concrete yard 
only handles driveways and house footings they might not even know about 
"flex"
concrete anyway.  Oh, as for the added fiber, you can get that now as 
fiberglass fiber or a sort of plastic fiber.  I've never used the new 
plastic fiber but I hear it
works well.  The fiberglass fiber is tough stuff and helps reduce cracking. 
It also cuts down on or eliminates the amount of reinforcing wire mesh or 
rebar you need to use in the
concrete.

Hope that helps some.

Charlie




On Thu, Feb 9, 2012 at 5:20 PM, Don Bowen <don.bowen at earthlink.net> wrote:
> My driveway crosses two little creeks.  They are usually dry except
> during storms when they can be as much as four feet deep.  After a storm
> it may take days for them to come down.  The first crossing is gravel
> and the previous owner had build a concrete and rock dam on the
> downstream side to control washouts.  The result kept the water over a
> foot deep for days after a small rain.  I cut a slot in the dam and now
> it drains down to about 6 inches in a day.
>
> The second crossing is a concrete low water bridge with two culverts.
> usually within a few hours of a rain the water is under the concrete
> flowing though the culverts.  The problem here is that the culverts plug
> with gravel in heavy rains.  The reason is that who ever built the
> crossing has the outlet end of the culverts higher than the inlet by
> several inches.
>
> I plan to take out the culverts and replace them with a single larger
> culvert properly installed.  What I need to know is how thick the
> concrete must be above a given size of pipe.  I am assuming that the
> larger the culvert diameter the thicker the slab over it must me.
>
> As for the gravel crossing I want to build a concrete crossing.  I need
> to know what I need to do and references.  I have a good idea what is
> needed but I would like comments from those with experience.
>
> You can see in this picture the right culvert is plugged.  The water at
> the inlet is almost at the top of the culvert.
> http://www.braingarage.com/Dons/Travels/journal/May%2011/images/flowing.jpg
>
> This is what it looks like after a heavy rain.
> http://www.braingarage.com/Dons/Travels/journal/April%2011/images/flooded%20drive.jpg
>
> And a heavier rain.
> http://www.braingarage.com/Dons/Travels/journal/April%2011/images/flooded%20drive.jpg
>
> The gravel crossing after a rain before I opened up the dam a
> little\http://www.braingarage.com/Dons/Travels/journal/January%2011/images/summer.jpg
>
>
> --
> Don Bowen           KI6DIU
> http://www.braingarage.com/Dons/Travels/journal/Journal.html
>
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