How to Add Drainage Pipes Behind a Wall

A retaining wall is used to prevent a hillside from eroding by stabilizing the base of the hill. When building a retaining wall, it's important to install a drainage system to carry water away from the wall. Otherwise, water can accumulate at the base of the wall, where it can wash away the soil and destabilize the wall. If your retaining wall doesn't have a drainage system, you can retrofit a system into its base.

Shovel or mini-excavator
Gravel
Rake
Drain tile
Hacksaw
Coupling fittings
Landscaping fabric
Drainage aggregate

Instructions

- 1
  Dig a trench along the uphill side of the wall that is 8 inches wide and goes about 6 inches below the base of the wall. If the wall is too large for you to dig the trench by hand, rent a mini-excavator to dig the trench.
- 2
  Pour 2 inches of gravel into the trench behind the wall. Smooth the surface with a rake, and slope it slightly in the direction in which you want the water to drain.
- 3
  Cut drain tile to fit along the base of the wall, connecting different sections with coupling fittings. Drain tile is perforated plastic pipe that allows water to flow through.
- 4
  Wrap the drain tile in landscaping fabric and lay it on the gravel inside the trench. The landscaping fabric prevents dirt from entering the drain tile and clogging it. The drain tile functions by allowing the water to drain into it, where it is carried away from the wall, protecting the base of the wall from erosion.
- 5
  Pour drainage aggregate into the trench over the drain tile until it's about 3 inches below the top of the wall.
- 6
  Backfill the gap over the drainage aggregate with dirt, and smooth the surface.

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