A team from Krause Landscape Contractors, Inc., installed 2,000 square feet of Canyon Blend Anchor Diamond Pro cut stone for the retaining walls in this Amarillo, Texas backyard, creating room for multiple gathering spaces that include a fire pit, paver patio, and plenty of green grass.

After installation of the leveling pad, base course and drainpipe, the first lift of structural backfill can be installed behind wall blocks stacked at least two feet above grade. The backfill should be placed with a skid-type loader or other equipment, and worked into all voids and cores of the blocks. Blocks with large cores, or large voids between adjacent blocks, should be used to accept the larger aggregates in the backfill mix.

Retaining walls with structural backfill zones are useful in cut wall applications up to 10 feet high, particularly when lot lines, rock outcroppings or other obstructions limit the ability to excavate for geogrid reinforcement. Structural backfill cuts the required excavation depth to 30-40 percent of the wall's height, depending on conditions; geosynthetic reinforcement typically requires an excavation depth of at least 60 percent of a wall's height.

In the mid-1990s, Pioneer Building Products Ltd. developed a retaining wall system supported by a zone of "structural backfill," placed behind and within the wall facing to reinforce the wall blocks. Also known as "no-fines" concrete, structural backfill is a widely available and easily workable mixture of clean stone, cement and water.

When used in combination with blocks of the appropriate shape, structural backfill self-compacts and attaches to the wall block, effectively extending the depth and mass of a wall's facing. Following the installation of the leveling pad, base course, drainpipe installation and stacked blocks two feet above grade, the backfill mix should be poured behind the blocks and worked into the cores and voids of each wall course. Wall blocks with large cores, or blocks with large voids between adjacent units, should be used to more easily accept the larger aggregates of the mix design.

Terraced retaining walls hug the contours of the site, which originally presented a 20-foot sloped grade change, a dangerously steep path, and an unstable railing leading to the lake. Soil with low permeability was added to the planting areas behind the walls, above the backfill zone, to create new planting areas and safe, stable access for the homeowners.

Structural backfill zones are often suitable for "cut" wall applications, where land is carved out of a hillside or roadway and upslope material requires retention. When lot lines, rock outcroppings or other obstructions limit excavation depth for traditional geogrid reinforcement, structural backfill zones can provide support and stability for retaining walls up to 10 feet tall.

This construction method eliminates the need for the construction of a mechanically stabilized earth zone behind the wall facing, reducing the need for heavy machinery and additional manpower. The backfill mixture, upon curing, should have at least 25 percent voids, allowing water to drain behind the wall and serving as the drainage zone required by most building codes. Retaining wall systems with structural backfill, like Pavestone's Anchorplex wall system, can be built with smaller equipment, less labor and better production rates than conventional grid-reinforced walls.