Base Installation Mark location of retaining wall Excavate wall location Compact the base trench Install drain pipe, wall rock and level Base Preparation To start your layout, place stakes to represent the location of the front of the retaining wall. Using a string line or paint, mark out the entire length. A garden hose is an excellent tool to use when laying out curved walls. Excavate the area by removing all surface vegetation and organic materials from the area. These cannot be used as backfill material. If reinforcement is needed excavate behind the wall to accommodate the design length of the geogrid. Refer to your approved plans for exact length. Starting at the lowest point, dig a base trench the length of the wall. More information on retaining walls where the base trench steps up a slope. Retaining Wall Base Trench Dig a base trench 600 mm wide the length of the wall.** The depth of the trench will be 150 mm plus an additional 25 mm for each 300 mm of wall height for the amount or buried block that is needed.** Compact the base trench making a minimum of two passes with a walk behind plate compactor. Foundation soils at the bottom of the base trench must be firm and solid. If the soils are made up of heavy clay or wet soils, or the areas have been previously excavated, remove this material and replace with a granular material, compacting in 200mm lifts or less. **For walls under 1.2 m dig the base trench 460 mm wide and 100 mm deep plus additional to account for the amount of buried block needed. Base Material Video: How to prepare the base A drain pipe is required for any reinforced wall or any wall over 1.2 m tall. Place the drain pipe at the lowest possible point toward the back of the trench and vent to daylight every 15 m. More information on drainage and water management. Place a minimum of 150 mm of wall rock in the base trench and rake smooth. Compact the wall rock making a minimum of two passes with a plate compactor. Check the entire length for level, and adjust as needed.