Mid-summer, while doing some trail reconnoissance, Rob Hammerlund found that one of the two bridges that are on the north end of the Wilderness Trail was sitting cockeyed on the creek-bank. It turns out that a Spring flood had washed the fill out from under one of the support beams on its west end.
On July 26th I made a quick trip to the site and assessed the problem and potential fix. Apparently, the creek takes a hard turn just under that bridge, and the fill had washed out on the downstream side. These two bridges were put in by the DNR back when the trail was first laid in, which implies that I was not quite sure how they were engineered. Turns out the bridge deck was made of 2″ x 6″ treated boards and the beams were two 6″ x 6″s One deck board had come loose and another was damaged. We weren’t planning on using the Wilderness Trail for the Enduro and we had enough to do to get ready for that, so fixing this bridge got put on the back-burner.
In the days leading up to today’s workday, I used my Solidworks CAD software to design up a “crib” that could hold fill under the ends of the bridge beams regardless of the flow erosion of the creek (theoretically). The design required three 4″ x 6″s to be used to support the bridge beams and some 2″ x 6″s to hold the fill. A couple of short signposts were to be used to anchor the stack of 4″ x 6″s.
I put out a call for volunteers and ended up scoring three club guys and two hangers-on. Rob, Chris Palmer and his two friends Josh Johnson and Jason Naughton, and Bill Lawson filled out the crew. My biggest concern on this project was how to hold the bridge up and out-of-the way while we did the work under its end. It turns out that three guys easily lifted the end of the bridge while two of us placed some ten foot long 2″ x 4″s under the bridge beams and on top of some cut logs to hold the bridge up. Super quick and super simple.
After some head scratching and measuring, we determined that the three 4″ x 6″s stacked up were just the right height (5.5″ x 3 = 16.5″) to support the bridge beams to the height that we were looking for. The design I came up with in my office called for the 4″ x 6″s to be perpendicular to the bridge beams. We decided it made more sense to angle the 4″ x 6″s so that the water would be partially turned by them, instead of having to be turned almost 90 degrees by the creek bank. This should take some pressure off of the dirt bank and maybe keep it from eroding further.
After leveling the first 4″ x 6″ in place under the bridge, we decided to build the “crib” up on the bridge and slip it complete under the bridge and into place. Getting the completely assembled “crib” under the bridge got to be a little tricky, but it sure was easier than trying to build it under the bridge.
With the “crib” in place and under the bridge, there was no way to pound the signpost anchors into place. That was solved by removing the first three deck boards, which opened up the space above the retaining wall to allow use of the post pounder. With that solved, we anchored the wall of 4″ x 6″s and staked the sides of the “crib”. The “crib” was now built and in place.
It became clear pretty quickly that we had not removed enough dirt from under the bridge to fill the “crib”. If you know the site, you probably know that the trail going up the hill from the bridge is kinda steep and is a gradual turn. Over the years the ATVs have worn ruts in the hill, and one rut is much deeper than the other. Did I mention that I had asked each volunteer to bring a shovel? I grabbed my bigger “goddammit” (a mattocks’s ax) and headed up the approach hill and started loosening the dirt on the high-side rut. We formed a “shovel brigade” and started hauling the loose dirt down and into the “crib”. With all of those shovels and all of those guys, it didn’t take very long and the “crib” was filled with nice, gravelly dirt.
With that, we lowered the bridge onto the retaining wall, re-installed the deck boards that we had removed and screwed the bridge to the wall with 10inch timber screws. A little more “shovel brigade” work and the fill at the end of the bridge was packed down and was slightly higher than the bridge deck. Done, done and done. All that was left was to load up the tools and extra lumber onto the ATV, take a few photos, head back to the trucks and, after a little break, go riding.