Bridge my troubled water!

July 5, 2006 8:45 AM

I have a 50 acre property divided in half by a creek. I need to build a bridge so I can drive my tractor into the back half. What are my options?

Lots more info required, I know, so here goes:

The creek is very seasonal, but drains a large area so is a torrent in spring (the last bridge was washed away). It never dries up completely.

The span from bank to bank needs to be 20 feet or so, although the unsupported span could be less, maybe 16'. A culvert is an option, although it would need to be large to handle the water flow. The banks are about 4' high.

The creek is in Ontario and is subject to Ministry of Fisheries regulations.

The bridge needs to be able to take a Kubota 40HP tractor plus implements such as bush hog, trailer, snowblower etc.

It needs to not be ugly.

So far I have been looking at the following options:

Culvert (cheap, possibly ugly, possibly problematic to put in a big enough one).

Flatbed bridge (possibly ugly, needs crane access which would tear up some of my planting)

Steel beam supported wooden-deck bridge (also needs crane access, possibly expensive).

Wooden bridge (engineering problem is how to make it strong enough, durability issues).

I need to keep the cost below $20,000. By my own calculations, I could build a timber bridge for about $10,000 which would take the tractor weight, but I'm looking for other people's experiences.

Extra points awarded for solutions which are beaver-resistant, since I have several colonies of the bastards.

posted by unSane to Home & Garden (13 answers total)

We have a much smaller but also seasonal culvert. Our drainage expert (quite literally, retired NYS drainage contractor) put a 3' diameter plastic drain pipe in the creek and filled the rest in with dirt to create bridge. Our conditions are probably different... the creek bed is a good 4-5' below grade at that point so the bridge actually flat with the grade.
posted by jdfan at 9:10 AM on July 5, 2006

Best answer: When I was in the Forces here in the UK, we built a similar smaller bridge for a charitable trust. It was two steel i-beams coated in waterproofed paint, with a wooden bridge built on top, making it durable and easy to maintain. We trucked the iBeams in and laid them by hand, though admittedly there was 30 or so of us. This was a volunteer force of young soldiers, male and female, with little or no experience, using hand tools, led by one experienced Army engineer. It's still there, six years later. You should see if there's a group of young people (Scouts, ROTC etc) in your area who might be willing to do something like this in exchange for a cookout afterwards, could be a really fun thing to organise.
posted by Happy Dave at 9:16 AM on July 5, 2006

Forgot to say, we also poured and drilled small concrete piers for the I-beams. No idea how much it cost, sorry!
posted by Happy Dave at 9:17 AM on July 5, 2006

Have you considered finding the local army corps of engineers (or equivalent) and suggesting it as a training exercise? They have to build bridges for tanks, etc quickly, so I'm sure they are looking for ways to train their new recruits....
posted by baggers at 9:20 AM on July 5, 2006

There was a previous bridge question, some of the links in the comments may help. I particularly liked the railcar bridge idea. If the bridge is placed well above the high water mark, you should be able to avoid both washout and Ministry of Fisheries problems.
posted by jellicle at 9:21 AM on July 5, 2006

I don't know how big a 40hp Kubota is but if it is car sized my great uncle used a 40' container to span a 30' gulley on his property. A 20' would do the trick in your case and you could side it with whatever you wanted to meet the not ugly requirements.

You'd still need to pour footings that would require ministry approval because you are messing with a creek. And some kind of heavy equipment would be required to place the container though you may be able to do it with just a pair of A frames and some temporary mid creek bracing.

You could also look at double T concrete floor systems (example specs(PDF)). Again a crane and footings would be required but it would go very quick.
posted by Mitheral at 9:35 AM on July 5, 2006

Here is a 40HP Kubota tractor.

A couple of telephone poles should be long enough and strong enough to support a 20-foot span. Not ugly? Depends on what you build on top of it.
posted by Kirth Gerson at 10:26 AM on July 5, 2006

Response by poster: Actually it's an L4300. Once you add in a full-size loader, the calcium in the tires and a (possibly loaded) implement, it's very heavy and I wouldn't trust a couple of telephone poles.

When driving a tractor over a creek, 'probably' isn't that great...
posted by unSane at 10:48 AM on July 5, 2006

Calcium in the tires? That is an intriguing idea. Whyfore?

Perhaps you can get a truss manufacturer to help. In my area (interior BC) there are innumerable bridge-builders: they service the logging industry. I should think your tractor is not heavier than a loaded logging truck.

Don't put down the telephone poles quite yet: I've noticed a number of old logging road bridges appear to be built from locally-felled trees (ie. basically unfinished telephone poles). Again, they support the weight of a loaded logging truck, multiple times a day. They are, however, built like the bloody Queen Mary: there is inevitably a shedload of wood in them.
posted by five fresh fish at 7:12 PM on July 5, 2006

Railcar brodges will support a logging truck and are definetly the easiest and cheapest of the options you've so that would be my suggestion, but you'll be lucky to come in under $20K with the price of steel the way it is.
posted by fshgrl at 9:01 PM on July 5, 2006

five fresh fish writes "Calcium in the tires? That is an intriguing idea. Whyfore?"

Increases traction without increasing sprung weight. You can use water too but only if temps remain above freezing.
posted by Mitheral at 10:11 PM on July 5, 2006

Best answer: Maybe you can find a decommissioned bridge and rehabilitate it? In BC we're pulling up endless logging road bridges (closing the roads). Buy a case of beer for the area chief and you could probably get one of those...
posted by five fresh fish at 7:57 AM on July 6, 2006

Response by poster: Calcium in the tires also increases stability by lowering the center of mass, makes the tractor less likely to roll over on a gradient (a big killer of tractor drivers round here).
posted by unSane at 8:27 AM on July 6, 2006