Select a location where the excavated soil will be roughly equal to the backfill material needed behind the wall.
Continue raking the soil until it’s level. Destroy as many roots as you can to prevent them from regrowing.
Give yourself an additional 18 inches (46 cm) on top of your post height to go in the ground. If your retaining wall is going to be 40 feet (12 m) long, you need 14 posts—40 (length of the wall) divided by 3 (space between each post)—for your wall. If it’s going to be 5 feet (1. 5 m) tall, make sure your posts are 5 feet (1. 5 m) tall with an additional 18 inches (46 cm) on top. In the previous example, if your wall is 5 feet (1. 5 m) tall, you need to stack 10 pieces of 2 by 6 inch (5. 1 cm × 15. 2 cm) boards vertically—5 feet (1. 5 m) divided by 6 inches (15 cm)—to create the height of the wall. Ask the staff to cut you 10 pieces 3 feet (0. 91 m) long for every 2 posts.
Let the shortest piece of your wood hang to prevent jamming.
Use a taut string and stakes or a snapped chalk line to help you create a straight line. If you need to extend your wall with another post to create the final 3 feet (0. 91 m) then do so. Space your posts 16 to 18 inches (41 to 46 cm) apart for load-bearing walls, which are walls that support something aside from their own weight such as a roof.
Call your local utility services number at least 3 to 4 days before digging to ensure it’s legal and won’t damage underground structures, such as power, sewer, water, or gas lines. Consider renting heavy equipment to dig your trench. Saw through large roots with a reciprocating saw or using the tip of your trench shovel. Use a steel bar to loosen rocks.
Use a steel bar to knock rocks loose. Remove large sections of loose soil with a clamshell digger. Saw through large roots by thrusting your shovel down into them or using a reciprocating saw.
Use a hand float the level the surface of the cement with the ground when you’re done.
You can also place 2 by 4 inch (5. 1 cm × 10. 2 cm) boards on either side of the posts to hold them in place.
Read the directions on the package of concrete mix for specific curing instructions, as these can vary between brands.
If your boards are shorter than the length between your posts, cut them so that they sit in the middle of each post. Place 16 penny nails or deck screws between each deck board to space them enough for expansion.
If you need to purchase additional soil, make sure it’s a similar composition as the soil from your trench.
