How to Build a Retaining Wall

Overview:

Retaining walls have been around for thousands of years and are basically used to hold back the earth. Retaining walls hold back the earth in areas where there are steep inclines. In ancient cultures retaining walls were widely used to make terrace gardens in mountainous terrain so agricultural crops could be grown.

Retaining walls are still used today in modern construction along driveways, landscaping lawns and backyards. In the old days they were made of stacked stones but in modern construction they are made primarily from landscape bricks (blocks), timber, and concrete. A timber retaining wall or a landscape timber retaining wall is the least effective as the timber rots after approximately ten years. Stone and brick retaining walls will last for decades if they are constructed correctly and a masonry retaining wall will last for a century.  

The challenge of how to build a retaining wall is to build them so they will withstand the side load of the earth behind them without tumbling down.  In a cold climate you must consider the effects of frost in the soil that will cause the earth to expand causing the wall to fail. The soil that you are trying to hold back is being pulled towards the center of the earth by the forces of gravity in addition to the force of the down slope, lateral load component. The retaining must be strong enough to offset the pushing force of the soil behind it from frost and the down slope component. The higher the wall the greater the stress is from the earth behind it. It is best to limit the height of the wall to three to four feet to avoid wall failure.    

The retaining wall base must be set solid soil. Dig a trench about two feet deep along the track of the wall. If you intend to build a poured concrete wall in a cold climate region the base of the wall should be below the frost line, about three to four feet from the surface. A poured concrete wall should be at least ten inches thick with reinforcing bars placed in the wall. For landscape terrace walls, build of landscape blocks that are less than three feet tall, the footing under the wall does not have to be as deep but it should be comprised of solid soil such as compacted gravel.

See: Building a Stonewall