Design for retaining walls

Retaining walls prevent down-slope movement or erosion and provide support for vertical or near-vertical grade changes. Retaining walls are generally made of masonry, stone, brick, concrete, steel or timber. Railroad sleepers used to be an inexpensive retaining wall material. 

Design considerations

Retaining walls need to be designed to ensure stability against overturning, sliding, excessive foundation pressure and water uplift. 

The most important consideration in designing and installing a retaining wall properly is the fact that the retained material is seeking to move forward and down a slope due to gravity. This generates lateral earth pressure behind the wall that relates to the angle of internal friction (phi) and the cohesive strength of the retained material. 

Lateral earth pressure is typically smallest at the top of the wall and increases towards the bottom of the wall. Earth pressures will push the wall forward, or overturn it, if not properly designed. The presence of ground water behind the wall that is not channelled away by a drainage system will also cause an additional horizontal hydrostatic pressure on the wall. 

Types of retaining wall

There are several types of retaining wall, including: 

• gravity 
• sheet piling 
• cantilevered 
• anchored
• soil nailing
• soil strengthened, such as: gabion meshes and mechanical stabilisation. 

Installing a garden retaining wall 

For a general garden retaining wall with a maximum height less than one metre, there are usually several simple designs and material choices available from hardware and building material suppliers. 

Generally, it is good to consult with your local council for design regulations prior to building the wall. Stone can be used for both functional and decorative walls. Bricks are another strong material that will last a lifetime. A timber retaining wall is also strong and cheap to build. 

To find out more, contact HIA’s Building Services team.

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