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With the trench dug and leveled- you're ready to install the foundation row of timbers.
Starting at one end of the trench, place a 6x6 on the ground. Make adjustments to keep the timbers level and straight (images 1 and 2). Use a small sledgehammer to shift things into place and check plumb with a level.
When the bottom row of timbers are in place, use a power drill and a spade bit to drill two pilot holes down through the top of the timber – about 4 feet apart (image 3). The bit should be the size of the rebar.
To pin the timber in place, use an 18-inch piece of rebar driven into the soil with a 2-pound sledgehammer (image 4).
Continue with the next piece. Install a straight, continuous row of foundation timbers in this manner. Make sure the row is level across the entire length of the wall.
Offset the joints as you install the second row. Pre-drill holes for the spikes about every 8 inches. Secure this second row to the foundation row with 60d spikes, using the pre-drilled holes.
Build the next row, remembering to stagger the timbers. Again, attach each row to the row below it using 60d spikes (image 1).
Use a hand saw to cut off any excess in order to make the ends of the wall even (image 2). Repeat the process, building subsequent rows and offsetting the timbers so that the ends of every row are in alignment (image 3).
Most retaining walls require drainage and are built with a perforated pipe set behind the wall in a gravel base. Because the grade of this yard has a slight slope that will promote water runoff, we can skip this step on this project, but we will add gravel for drainage and back fill with dirt.
Once you have all the timbers in place (and backfilled), add a top cap.
We're using 2x12 planks cut at 45 degree angles and fitted together in a point. Center the 2x12 cap on the top timber, allowing a 3-inch overhang on both sides. If you need more than one plank to cover the length of the wall, cut them on a 22-degree angle to fit them together.
Attach the top plank using 3-inch wood screws driven every 12 inches.
Then, remove the ends of the boards, leaving a 3-inch overhang.
To finish the project, we round the corners with a simple 45-degree cut (image 4).
With your retaining wall now complete, you can paint or stain it to your taste. Now you can take advantage of the newly leveled area of your yard.