. At-rest soil The soil behind the wall that will theoretically not move. Backfill The material used to fill the space behind the wall. Base course A full course of blocks which... layer of blocks used to build a wall. Crest slope Angle of the soil above the wall usually expressed as a ratio such as 3:1 (3 feet horizontal to 1 foot vertical). Direct...-Anchorage System An installation method that connects earth anchors to retaining wall blocks, that may be used where sufficient space for placement of geosynthetic reinforcement does...