A retaining wall (Dutch: keerwand) is a structure that holds back soil, water or loose material (such as sand, gravel or compost) and so takes up a difference in height. The wall absorbs the horizontal earth pressure and carries it into the foundation, so the ground behind the wall does not slump or wash away.
How it works
Soil against a wall exerts a horizontal pressure that increases with depth. A retaining wall must resist that pressure without tipping, sliding or breaking. The most common form is the L-shaped concrete element:
- The vertical leg holds back the soil.
- The horizontal foot sits under the retained soil, so the weight of that soil keeps the wall from tipping.
- Reinforcement takes up the tensile forces in the concrete.
Other types are the gravity wall (which holds back by its own mass) and sheet piling (for deeper or wet situations).
Application
- Gardens and landscaping — slopes, raised beds, driveways with a height difference.
- Storage bays — retaining walls for sand, gravel or other bulk materials.
- Infrastructure — for roads, underground car parks and water defences.
Points to watch
- Provide drainage behind the wall: trapped water greatly increases the pressure.
- Set the foot on a load-bearing, frost-free foundation.
- The required thickness, reinforcement and foot width depend heavily on the retained height and the subsoil; have higher walls calculated by a structural engineer.
- Precast L-elements are quick to place but need a level, stable base.
Related terms
- Foundation
- Sheet piling
- Water barrier
- Concrete
- Reinforcement
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