Determine the exact location for the bridge. The banks on either side of the stream or ditch should be firm, with no signs of heavy erosion. Measure the expanse to make sure it is less than 8 feet across.
Use a shovel to dig an earthen shelf out of each bank. The finished shelf should be wide enough and long enough to accommodate one railroad tie laid parallel to the stream or ditch. It should be deep enough to accommodate another railroad tie stacked on top of the first, approximately 12 inches to 14 inches from ground level to shelf bottom.
Drive one piece of rebar into each end of each of the dirt shelves. Leave approximately 10 inches of rebar exposed. When completed, the result should be four rebar posts, two for each dirt shelf.
Use the chainsaw to cut two railroad ties to a length equal to the desired width of the bridge. Use the drill and large bore bit to drill holes through either end of each railroad tie, for accommodating the rebar posts. Fit each railroad tie onto the rebar posts and push down until firmly planted in the dirt shelf. Use the level to check that each railroad tie base is plumb and level.
Select two more railroad ties and drill holes 3 inches deep at either end of each tie. Holes should line up with rebar posts when ties are placed at right angles to support tie. Turn the ties over with the holes facing the ground.
Fit one end of each tie onto a rebar post on ether side of the ditch. Position remaining ties between each end tie to form a solid bridge floor.
Cut both 2-inch by 6-inch boards to a length equal to the width of the bridge, minus 2 inches. Position the boards on the underside of the bridge floor, across all of the railroad ties. Secure with self-tapping bolts at either end and at the center of each board.
Backfill gaps around the dirt shelves with fill dirt or gravel. Tamp the dirt or gravel down to pack it in around the railroad ties.
Things You Will Need
- Measuring tape
- Safety glasses
- Drill with large bore bits
- Railroad ties
- 4 3-foot lengths of 5/8-inch rebar
- Level (at least 4 feet long)
- Fill dirt or gravel
- 2 - 2-inch by 6-inch pressure treated boards
- Circular saw
- 6 jumbo self-tapping bolts
- Railroad ties are heavier than typical lumber of equal size and width. Consider asking a friend, neighbor or family member to assist with moving and positioning the ties. Most railroad ties come in 8-foot lengths, although other lengths are available. The railroad ties for the bridge floor will likely need to be cut to the appropriate length to fit the expanse.