How to Build a Retaining Wall that Runs into the Slope at its Base

Stepping Up the Base

So you’re building a retaining wall with Allan Block and the base of your wall runs into a slope. What do you do? The answer is simple. Step up the base. When building step-ups, begin the base course at the lowest wall elevation. When building step-ups, begin the base course at the lowest wall elevation.

Dig a base trench that is 24 in. (600 mm) wide. The depth of the trench is determined by allowing for 6 in. (150 mm) plus an additional 1 in. (25mm) for each 1 ft. (300 mm) of wall height for the amount or buried block that is needed. The trench also needs to extend into the slope far enough to bury one full block. If a slope is present below the wall, contact a local engineer for assistance.

Compact and level the base trench making a minimum of two passes with a plate compactor. Place the drain pipe at the lowest possible point toward the back of the trench. Place a minimum of 6 in. (150 mm) of wall rock in the base trench and check for level. Compact the base material, making a minimum of two passes with a plate compactor.

Excavate the second step up making sure to accommodate for the base material and buried block. Compact and level the step-up area. Place the base course of blocks on the base material and check for level. Fill the hollow cores and 12 in. (300 mm) behind the block as well as the base area of the next step up with wall rock then backfill with infill or approved on-site soils. Make sure that the blocks and the base of the next step-up are level. Compact the wall rock directly behind the block and the next step-up area a minimum of two passes with a plate compactor. Repeat these steps to the top of the grade. Keep in mind the block at each step-up must be completely buried to maintain the proper base depth and to prevent wall failure due to erosion.

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