Retaining walls hold soil back to shape the ground to fit your outdoor designs. The soil within the wall absorbs water from rainfall and groundwater, among other sources. If you don’t drain the water in the soil behind the wall, the wall will break. A drainage system consisting of perforated pipes, filter fabric, and drainage stone drains the water and keeps the wall intact. This type of drainage system is necessary for retaining walls under the following circumstances:
- The wall is four feet high or taller: Walls four feet or taller can cause significant damage if they fail, so it’s best to install drainage behind a retaining wall of this height or taller.
- The soil consists of or contains clay: Clay does not drain well and becomes extremely weak when wet. A drainage system removes water from the clay soil behind your wall to ensure it stays in place.
- The wall is built with concrete or cinder blocks: These materials don’t have any natural joints that allow water to flow through them. A drainage system prevents water from building up and causing the soil to burst through the concrete or cinder block retaining wall.
- The wall is at or near the bottom of a hill: Water naturally flows and drains downhill through soil. If a retaining wall sits at or near the bottom of a hill, that water will pool there. A drainage system removes the water that flows downhill so it doesn’t affect the soil’s or wall’s placement.
- The wall is located near water sources: These sources include groundwater; surface water, such as water from nearby downspouts; and buried water sources, including water mains and irrigation lines. A drainage system can remove water from these sources so the soil behind the wall drains properly.
- The retaining wall is terraced or tiered: Sometimes, retaining walls can create tiered or terraced spaces for plants, steps, or other installations. In these cases, drainage systems keep water from flowing from the higher terrace or tier to the lower one.