Another Bridge Post

Alan L. · Mar 23, 2004

I have a creek about 12 feet wide and pretty deep. The banks overflow once or twice a year. I want to do a bridge about 6 feet wide, something the kawasaki mule can cross, but mostly a walking bridge.

My plan had been to sink 2 large posts on each side, about 2 feet back from the bank, and build a frame to run I-beam or some other heavy timber across. The problem is, I'm afraid that when the water gets up, the water will want to wash out the dirt between the cemented posts and the creekbed itself.

When the water gets up, it doesn't seem to flow real fast, because its a very wide area that it gets into.

Anybody have any ideas?

Joe1 · Mar 23, 2004

Any way to build up a berm on each side far enough back to get some solid ground for a concrete footing and use an old steelframe wood deck railroad flatcar without the trucks for the bridge? It will be about 8' wide and if a 40' flatcar would give you plenty of solid ground on each side. If the berm and footing can be raised high enough, washout shouldn't be a problem. The "bridge" could probably handle 20 - 40 tons. The flatcars themselve can be bought for less than the cost of moving it.

This site unseen "solution" of course is from a non-engineer 1,200 miles away. But seriously, I have seen a few railroad flatcar bridges, and I was never afraid to drive on them. The stakepockets on the sides would even provide an attachment point for a guardrail of sorts. Even Ted Kennedy wouldn't be afraid to cross that (an historical, not political comment).

Joe

JJT · Mar 23, 2004

How deep is pretty deep?

I put 4 12" culvert pipes in and built a road over my creek. Spring thaw overruns the culverts but the road bed is clay and stones and it doesn't wash out.

txdon · Mar 23, 2004

I have built a bridge similar to the one you need. I used a 4' culvert, 12 loads (5X10 trailer) of rock, and dirt. I double stacked the rock on each side and filled with dirt. I put an overflow area so when the water gets close to flowing over the bridge it flows around it, about 20 feet from the bridge. It has held up good. see attachment

alco141 · Mar 23, 2004

i am not an engineer but would think that 2 feet would not be far enough back from the bank, the high water may wash out your pilings on either side.

i think you could go either of two ways, either drive some pilings deep and back away from the bridge, or make the bridge so you could skid it away from the stream in the spring. that is what some folks here do, each spring they just pull the bridge over the creek, and after the flood season.

BB_TX · Mar 24, 2004

Alan - I have been working on the same problem, except I need to span closer to 20' over a creek that is 8'-10' deep. My thinking is that I will move back at least 3' from the edge for a concrete footing. Then dig about 6" to 1' below grade, set a form to extend about 1' above grade, and about 2' thick, extending the width of the bridge. Then dig 2 12" holes as deep as my PHD will dig just inside each end of the form. I would either round off the ends or build the form to a point upstream and downstream to smooth the water flow. That would take 1 to 1 1/2 yards concrete per footing depending on the bridge width.
Don't know if you are interested, but last weekend I was on 121 east of Melissa when I passed Collin County Steel & Pipe. They had a prefabbed bridge setting out by their front gate. Made with Ibeams, welded square tube hand rails, and diamond plate decking. It had 4 sheets of DP decking end to end, so I guess that makes it 4' x 32'?? Looked like a pretty well built bridge that could be dropped in place. Did not take the time to stop and talk. I don't know if they make those to order or what they might cost?

dmccarty · Mar 24, 2004

You might also want to consider adding rip rap around the base
of the pier/structure. That should help prevent/minimize any
scouring of the structure that would take place with a fast moving
high water event.

Later,
Dan McCarty

BB_TX · Mar 24, 2004

Good point, Dan. Like Alan, by creek is normally a trickle. But 2 or 3 times a year during a heavy storm, it turns in to a flash flood.

Egon · Mar 24, 2004

I just may be reiterating old posts but has consideration been given to consult with a competent engineer.

Site conditions and maximum flows and pretty deep are all vague items to one not familiar with the site in question. What works for me may not work in your conditions.

And due to proffesional etiqite the proffesions may not help due to the unknown factor.

Egon

Alan L. · Mar 24, 2004

Egon, consulting an engineer just make way too much sense. Actually, I'm hoping to spend maybe $1000 on the bridge, and the engineer would eat up most of that I'm sure.