Retaining walls, Trench Drains, and Septic Tanks Retaining Walls Dig a trench 25mm deeper than chosen material width where Biobarrier® is to be installed. Prune and remove the roots of existing trees. Place Biobarrier in the trench at finished grade level, securing with pins. Backfill the trench, compact the dirt to ensure there are no … Continue reading Retaining walls, Trench Drains, and Septic Tanks