What is a retaining wall?
A retaining wall is a structure that retains soil, whereas a dam is a structure that retains water.
There are many ways that a retaining wall can be constructed and designed. The four primary forms of design are:
- Soil Reinforcement
Cantilever Retaining Walls
There are three main types of cantilever retaining walls. They are:
- King Post
- Sheet Pile
- Secant Walls
- Precast concrete L shaped
- Hollow block L Shaped
King Post retaining wall consists of steel UC columns being driven or cast into augured post holes. Concrete panels or timber sleepers are then slid down the channels to fill the gap between the posts.
Sheet Pile retaining walls consist of steel sheet piles being driven in the ground. They are then normally tied back using ground anchors.
Secant Walls are constructed using a continuous line of bored and concrete fill piles. They are used when building large basements.
Precast concrete L-shaped retaining walls are either bolted down or cast in a concrete foundation. The units are made in a precast concrete factory and transported to the site.
Hollow block L Shaped retaining walls are hollow blocks similar to house building blocks. The blocks are laid dry on top of a reinforced raft with started bars. The cavity of the hollow blocks is then filled with concrete. The wall works similarly to the L-shaped precast concrete retaining wall. Hollow block retaining walls are easy to build when access can be an issue.
Gravity retaining Walls
There are four main types of gravity retaining walls. They are:
- Gabion basket
- Concrete block
Gabion basket retaining walls are built using steel baskets normaly 1m x 1m x 2m long and filled with stone. The steel baskets come in various gauges, 3,4,5mm they are galvanised and can be plastic coated. Stainless steel baskets are also available.
Criblock retaining walls are built using timber or concrete frames. The frames are normally, 600, 900, 1200, and 1500 wide. Once the frames are built, they are filled with stone.
Concrete block retaining walls are built using large concrete interlocking blocks. The blocks are normally 600 x 600 x 1800mm or 800 x 800 x 1600mm in size. The size of a concrete block gravity retaining wall is less than a criblock or gabion basket wall due to the mess of concrete being heavier than stone. 2400kg compared to 1600kg
Masonry retaining walls are built using the mass of bricks or concrete blocks. Masonry retaining walls can be built with soil reinforcement allowing the masonry to be constructed using less mass.
Soil Reinforced Retaining Walls
Soil-reinforced retaining walls are formed by excavating and replacing the excavated material in layers. Layers of soil are placed on top of a geogrid.
Geogrid sheets reinforce the soil to stop failure through slippage.
The reinforced soil becomes the retaining structure. Concrete blocks then face up the reinforced earth to give it protection from the elements.
The concrete block wall is connected to the geogrid layers, allowing the walls to be quite slim in form.
Anchor Retaining Walls
An anchored retaining wall can be constructed using any system but includes additional strength using cables or steel bars anchored in the rock or soil behind it. Usually driven into the ground or rock with boring, anchors are then expanded at the end of the cable, either by mechanical means or by pressure grouting.