Eddie - I'm kind of far along into using the RR ties. I got four of the five utility poles across the span today and they're resting on the RR tie sills. However, all of the poles are longer than the 18' span - I didn't measure but I think they're in the neighborhood of 25 feet. So I could conceivably put another type of sill under the poles where they overhang the RR ties. This would also get my sills further back from the bank, which would be a good thing. Of course this would also increase my span.
Radioman - the erosion in that bend is made worse by a storm drain that deposits into the creek at that bend. You can't see it in the pics, but it is downstream of the bridge. Putting supports for the bridge further back on the bank is a good idea - I'm thinking about it. The A truss bridge design you describe sounds interesting but I don't quite follow you. The A frame is above the bridge with a center pole? I can't picture it.
Here are some pics from today's work.
I got the poles to the bridge site with a chain and the FEL hooks. I lifted one end of each pole a few inches off the ground and drug them backwards up my driveway, onto my front trail and down to the bridge site - slow and steady. I then unhooked the FEL chain and pushed the poles from the opposite end to get them close to the sill. Getting the first pole across was tricky. Once it was resting on the RR tie sill the sill wanted to roll when I tried pushing the pole across. I thought with the weight of one pole pushing down on the sill it might be worth trying to push a second pole over. That worked.
I thought I might push the second pole all the way across the creek without the back end of the pole tipping up, but no such luck. I got it to within a foot of the opposite bank and then it popped up. I pushed the back end down with the FEL and managed to get the bucket angle so that I could both hold the end of the pole down and push it the final distance across the creek. With the second pole across I went back to the first pole and used the same method. Got the first one across as well with no sill movement.
Once I had two poles across I used chains and come alongs to squeeze them together so that the third and fourth poles could be pushed across by riding on top of the two paired poles. Hopefully the pictures make this clearer.
With four poles across I went to get the fifth pole. I knew it would be a challenge. It is huge. 14" in diameter and probably 25+ feet. I wrestled with it out in front of the house for about a half hour before I decided it wasn't worth it. Just didn't feel safe - got up on three wheels a time or two. Felt like the pole was steering the tractor more than I was. So before I took out any mailboxes or neighbors' cars I decide to put the pole back where I found it. Maybe I'll cut it up into smaller pieces and use it for something else.
After not getting the big pole across and looking at the condition of some of the ones I did get across I'm thinking about trying to buy two more poles, which would give me a total of six. Maybe marrying two sets of three together and spacing them to match the tractor tire spacing. Three poles tied together is going to end up being 2.5 to 3 feet wide. Not sure if I mentioned it before but I'm thinking the bridge will be 8 feet wide.
