[AT] OT Low water crossings

[ROBBRUT at aol.com]

Carl, your bridge sounds interesting.  My place has several creeks,  and I 
have used culverts of steel, concrete, and plastic at several places, and  
we also have two fords to drive through.
 
One spot demands a bridge, however,so I wonder if you have a picture or  
something that will help me better understand how yours is built. 
 
And I'd also like to know how big of a vehcle you have driven across  it,
 
Thanks,  Bruce TH\hompson
 
 
In a message dated 2/9/2012 7:28:03 P.M. Eastern Standard Time,  
cgogol at twcny.rr.com writes:

Much of  our property lying lower than the house is prone to flooding from 
a 
major  creek.  I took the same philosophy as your previous owner and where 
we  
have trails we have built "More weather" roads instead of "all weather".  
Constructing private trails using concrete over the pipe would be a bit  
pricy and I have looked for old heavier wall steel pipe that would easily  
take the loads without any compacted material overfill.  This way a  very 
minimum road elevation is required for a driveway without any hump at  the 
pipes.  Keeping the trail lower reduces the resistance to flow  when the 
water raises 4' or so.

For your application only a few  inches of concrete, enough to maintain 
physical integrity over time, would  be required over such pipes.  For 
light 
wall corrugated or plastic  pipes, the use of concrete would still only 
require minimal  coverage.  There may be real engineering recommendations 
available,  but since you are encasing the pipes in concrete you can almost 
treat them  as forms and the thickness over the very top is again not going 
to have to  be all that thick.  6-8" should be enough since the thickness 
of  
concrete is increasing as soon as you move away from the top center of the  
pipe.  The concrete is essentially forming an arch over the  culvert.  If 
you 
wanted, it might be worth placing some short say 24  or even 48" pieces of 
rebar over the top of the culvert that are oriented  perpendicular to the 
culvert's axis.  This would substantially  increase the tensile strength of 
the concrete in that area.

I have  built one bridge that is 18' long crossing a drainage creek that is 
about  6' deep that feeds into the main creek.  A culvert wouldn't work 
well  
here and after much hesitation the span material that was chosen was used  
6" 
X 8" galvanized steel box beams that had seen service as guide rail  along 
major roads.  Three of these are combined together into a plank  by using a 
steel spreader assembly bolted to keep the beams about 3"  apart.  The 
spreaders are placed at the 6' and 12' locations and are  heavy enough to 
spread the load across the three beams.  Two of these  assemblies form the 
bridge.  The total width can be changed by  sliding one of the plank 
assemblies into a wider or narrower  position.  This structure is very 
ridged 
and strong.  The major  design challenge is not to make a bridge carry the 
vehicle load, it comes  from water flowing over the top and uprooted trees 
floating down the  stream in the spring runoff or a storm.  The use of the 
box beams  gives the bridge a profile of only 6" for the water to push 
against.   Trees remain the real problem and cables to upstream anchors 
have 
so far  (5 + years) worked sufficiently.
Carl Gogol
Manlius,  NY

-----Original Message----- 
From: Don Bowen
Sent: Thursday,  February 09, 2012 5:20 PM
To: Antique tractor email discussion group ;  Little houses
Subject: [AT] OT Low water crossings

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%20
drive.jpg

And  a heavier  rain.
http://www.braingarage.com/Dons/Travels/journal/April%2011/images/flooded%20
drive.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/s
ummer.jpg


--  
Don Bowen            KI6DIU
http://www.braingarage.com/Dons/Travels/journal/Journal.html

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