Retaining Walls FAQ

Retaining Walls - FAQ

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What is a retaining wall?

Typically, a retaining wall is a wall that retaining soil or compacted earth. Often also referred to as retention walls, retainers, CRB Walls, and garden walls. The weight of the soil exerts a lot of pressure on the wall, so the wall needs to be designed to withstand these earth pressures. This makes the design of the retaining wall infinitely more important than the design of a regular boundary wall which is a simple barrier or fence between two properties. So if you are looking for a wall to create a level surface, more useable space or to create terraces, then a retaining wall is what you are looking for.

What are cantilever retaining walls?

Cantilever retaining walls are the more traditional types which rely on a combination of a heavy base which provided leverage about which it resists being pushed over by the soil. These usually have very heavy concrete bases and reinforcing steel connecting the base to the main wall. Drainage and waterproofing are very important to reduce the pressure on the wall and to keep it dry on the exposed side. This type of retaining wall is suitable for high walls at steep or even vertical angles. They are often the most expensive type of retaining wall since they rely on the mass concrete and steel reinforcing to resist the earth pressure. The exposed wall can be clad with face brick, stone or even tiles to transform it into a beautiful feature.

What are dry stack retaining walls?

Dry stack retaining walls are often referred to as segmental block retaining walls, garden walls (because they are usually planted to soften the concrete face), and CRB (concrete retaining block) walls. They are the spoon shaped wall blocks that are so often seen on the sides of roads where ever there is a steep embankment to retain.

What are gravity retaining walls?

Gravity retaining walls are seen in all forms from Mass Concrete, Brick and Mortar, Stone or Concrete Block Retaining walls.

They can be installed vertically, but are more cost effective with some kind of back slope to them. These are very cost effective for low walls, but as the wall becomes higher, the amount of material needed at the base increases. For walls higher than 3m it is usually more cost effective to use an alternative design method such as cantilever or geofabric reinforced Retaining Walls.

What are the typical costs of retaining walls?

Unlike free standing walls, a retaining wall is very much an engineered structure just bridge or a tunnel would be. The design, and as a result, the cost are influenced by many on site parameters such as the soil conditions, the drainage of surface stormwater and subsurface water, the loading above the wall, the angle of the wall can recline, the finished face of the wall (i.e concrete block, stone, or brickwork) and most importantly, the height of the wall. Having said that, one should expect a low retaining wall to cost from R450/m2 including installation to R2200/m2 for very high verticle walls.