How to Get a Level Retaining Wall Base on a Slope

Start at the slope's lowest point. Dig a 24-inch wide trench. Make the trench deep enough to hold 6 inches of gravel plus a full landscape block. Dig the trench far enough into the slope that at least one landscape block will be completely buried.

Tamp down the trench with a hand tamper. Lay a 4-inch perforated drain pipe in the trench. Extend the pipe 3 to 4 inches past the trench with the remainder of the pipe extending up the slope. Pour crushed gravel into the trench and spread it out into a 6-inch layer with a metal rake. Tamp the gravel down with a hand tamper.

Dig a second trench directly behind the first trench. Dig this trench deep enough to line up with the first trench's gravel layer and long enough to bury at least one full block. Tamp down the second trench's soil with a hand tamper. Allow the 4-inch perforated pipe to sink into the second trench.

Lay retaining wall blocks on top of the gravel in the first trench. Line up the blocks' front edges along the trench's front edge. Set a level on the blocks. Adjust the gravel underneath the blocks so they sit flat in the trench.

Pour crushed gravel into the second trench and behind the retaining blocks in the first trench. Level out the gravel with the retaining blocks' surface. Tamp down the crushed gravel in the second trench with a hand tamper.

Follow Step 3 to dig a third trench directly behind the second trench. Tamp down the third trench's soil with a hand tamper. Repeat Steps 4 and 5 to install retaining wall blocks in the second trench and crushed gravel in the third trench.

Continue to follow the step-up pattern until you reach the top of the slope. Lay retaining wall blocks on top of the block base layer to build up the retaining wall. Backfill behind the wall with soil.