Building a Forest Bridge-Groundwork & Footing

Our stream crossing to date was wide enough to get my tractor and truck across. However, our finished bridge will be 14' wide and this necessitated removal of some trees and widening of the road. It also left me with one big-ass root to remove from a 7 trunk swamp maple which was right next to the stream inlet. Even with my backhoe, it took me 4 days of surgical digging and root cutting with a hand axe to get that bugger out. I also needed to reconstruct the stream inlet with large rocks and regrade the road bank. We had a bit of a drought going and I was lucky to be able to work while there was very little flow.

Prior to placing the first two blocks on the far side of the stream, I used my back hoe to excavate a trench to set the cement blocks in.






I placed a 4" slotted drain pipe the length of the trench (sloped downhill) which will drain to daylight on the down stream side.









Around the drain pipe and under the blocks is 3/4" crushed stone. This is all wrapped in water permeable filter fabric.










On top of the fabric is a thin layer of gravel which was raked and packed to level. It may be overkill but this drainage layer under the blocks will avoid any chance of frost heaving (which at 3500 lbs each probably won't happen but I'd rather be safe than sorry). This also allowed me to provide a level surface to set the blocks on. A logging truck with a grapple was used to pick up the blocks at the cement plant and to set them in place once we got back to our bridge site. Due to the reach of the arm on the logging truck, I am unable to do both sides of the stream at the same time. So, I'll have to get the truck to come back to set the second two blocks when I am ready with my second hole. Final tweaking of block position was done with my backhoe.


Once the first two cement blocks were in position, the down hill (stream) side was bermed with rock. Large rocks were carefully placed against the blocks and packed as tightly as possible, wedging them into and against the soil left from excavation. These were topped with smaller rock. This area will be covered by bridgework and will be much less accessible after the beams go on so now was the time to do this.


The uphill side of the blocks was backfilled first with one-man rocks (an old expression meaning those that can be managed by "one man") again packed tightly, then a layer of crushed stone which filled the voids between the large rock nicely, then gravel spread in thin layers and hand tamped till level with the top of the blocks.

The area around the first two blocks will not be tractor-accessible once the second hole has been dug so now was the best time to do this "finish" work. I was lucky enough to have a pile of rocks close by left by the farmer who originally cleared this area years ago. In Maine, we have no shortage of stone...

The second set of blocks was set and finished like the first. I ordered a load of small 1-2" round stone and used this to re-finish the stream bed which I had gently smoothed with my backhoe prior to digging the second trench. We're having a bit of a dry spell and the stream has been dry for two weeks now so I was able to work this area easily. With the blocks now set, I can place the 5 steel beam on them to create the framework for our bridge.