Backfill
Soil placed in front of and behind base course units. Also soil placed behind drainage aggregate. All backfill should be well compacted. Loose backfill will add pressure on walls, collect water, cause settlement and will not anchor soil reinforcement materials properly. Backfill that is behind a wall containing soil reinforcement is often referred to as reinforced soil.

Base Course
The base course is the first layer of SmartSlope units placed on the leveling pad. Extra care should be taken to ensure that all base course units are level front to back, side to side, and with adjacent units. Unevenness in the base course becomes magnified throughout succeeding courses.

Compaction
Applying mechanical force to soils so they are no longer compressible. It is important to compact foundation and backfill soils to prevent future wall movement. Compaction is often accomplished using a hand tamper or a vibratory-plate compactor (available at most rental stores).

Course
A horizontal layer of retaining wall units.

Drain Pipe
Typically, a four-inch perforated pipe placed behind the wall at the base of the drainage aggregate. The drain pipe helps to direct large amounts of water from behind the wall to areas where it can accumulate safely away from the wall.

Drainage Aggregate
Clear, free-draining, angular gravel placed directly behind retaining wall units to expedite drainage. Drainage aggregate should not contain fine particles that could impede water flow.

Embedment
SmartSlope Living Retaining Walls should have at least one full course of modules embedded below grade. Embedment may be increased for special conditions such as slope at wall base, soft foundation soils, and shoreline applications.

Grade
The ground level, or ground elevation.

Gravity Wall
A retaining wall without soil reinforcement where unit weight alone provides resistance to earth pressures. Gravity walls are generally less than ten feet in height and do not support steep slopes or other large loads above the walls.

Impervious Fill
Backfill placed above and below the drainage aggregate. Impervious fill helps to prevent large amounts of water from running down behind the wall or getting to the leveling pad. Generally, compacted fine grained soil is used as impervious fill.

Leveling Pad
The base on which a wall is constructed. Leveling pads consist of well-compacted crushed stone, gravel, or coarse sand. The most commonly used material for leveling pads is that which is used locally as road base aggregate.

Load
Weight or pressure placed on a retaining wall — usually from the back or top. Nearby slopes, driveways, buildings, and tiered walls all represent potential loads on retaining walls. Designs for retaining walls that support loads should be reviewed by a qualified, licensed professional engineer.

Setback
The distance that each course is aligned behind the preceding (lower) course. Each course is set back 2 7/8 inch from the front of the course beneath it. This arrangement causes walls to cant back into retained soil. Canted walls are structurally more stable than vertical walls because gravitational forces "pull" walls into retained soil.

Soil-Reinforced Wall
A retaining wall that incorporates horizontal layers of soil reinforcement material behind the wall. Soil reinforcement combines with soil to create structures that are strong and massive enough to support large loads. Soil-reinforced walls generally require a design by a qualified, licensed professional engineer (P.E.).

Soil Reinforcement
High-strength, polymer geosynthetic material, such as fabric or geogrid, that is buried in horizontal layers behind soil-reinforced retaining walls.

Tiered Walls
Two or more stacked walls with each upper wall set back from the underlying wall. Tiered walls can be attractive alternatives to single tall walls and can provide areas for plantings. To prevent an upper wall from placing a load on a lower wall, the upper wall must be built behind the lower wall a distance of at least twice the height of the lower wall. Tiered wall designs should be reviewed by a qualified, licensed professional engineer.