Different Types of Retaining Wall: Retaining walls come in all types, shapes and sizes – from simple gravity walls to bored pile walls for basements and reinforced soil walls using geogrids – to suit a wide range of project needs, and site conditions.
Gravity retaining walls
Gravity retaining walls use the gravitational force of their own weight to resist the lateral earth pressure from the soil behind them, which prevents toppling and sliding. They are the simplest and earliest recorded type of retaining wall, and are usually built of concrete, masonry, brick, blocks or mass cast-in-situ concrete.
Gravity retaining walls are typically designed to be wider at their base, with sloped faces, enabling them to resist the higher lateral earth pressures at depth. As such, this type of retaining wall is easy to build and suitable for retained heights of up to about 3m.
Despite their advantages, gravity retaining walls are not suitable for retained hights above 3m. If built any higher, the retaining structures tend to take up too much space and can end up being too heavy for the ground below, leading to bearing capacity failure. Ultimately, this can result in the wall failing to retain soil.
Cantilever retaining walls
Cantilever walls are built using reinforced concrete, with an L-shaped, or inverted T-shaped, foundation. This kind of retaining wall wall consists of a stem and a base slab (or footing) which sits under the backfill. The vertical stress behind the wall is transferred onto the base, preventing toppling due to lateral earth pressure from the same soil mass, allowing cantilever walls to stand unobstructed.
Additionally, a T-shaped foundation benefits from the weight of soil (and therefore vertical stress) in front of the wall, providing further stability to the retaining structure. Foundations sometimes include a ‘key’ in their base, which sticks into the ground to prevent sliding failure.
A big advantage of cantilever walls compared to other retaining wall types is that they take up little space once built, and are suitable for retained heights of up to 5m. However, construction does require space behind the wall, so these retaining walls are not particularly suited to supporting existing slopes, unless temporary support is provided during construction.
Embedded retaining walls
Embedded retaining walls extend deeper than the excavation to take advantage of passive earth pressure of the ground below to, at least partly, counteract the active earth pressure being exerted on the wall above. Additional support is provided to these retaining structures by internal propping – usually from the base slab, ground slab and any intermediate floor slabs – or by ground anchors installed through the wall.
This type of retaining wall is used to form near-surface underground structures, such as basements, car parks and metro stations. Walls can be huge – those for Westminster Underground Station on the Jubilee Line in London, next to the Houses of Parliament, are 40m deep, for example.
Embedded retaining walls can be built using a number of different methods, depending on ground conditions, how watertight the excavation has to be, constructability (i.e. time, cost and excavation method) and the retained depth required.
For deep excavations, methods include diaphragm walls and panels, as well as bored concrete piles, where piles are either interlocking (secant) or installed next to one another (contiguous). For shallow and temporary excavations, sheet piles and king post walls are commonly used, as shown in the image above.
Different Types of Retaining Wall
- Gravity walls: These walls are the most common type of retaining wall. They are made of solid materials, such as concrete or stone, and rely on their own weight to resist the forces of gravity. Gravity walls are typically the most stable type of retaining wall, but they can also be the most expensive.
- Cantilever walls: These walls are made of thin, sloping panels that are supported by a foundation at the bottom. Cantilever walls are less expensive than gravity walls, but they are also less stable.
- Counterfort walls: These walls are similar to cantilever walls, but they have vertical supports called counterforts that help to resist the forces of gravity. Counterfort walls are more stable than cantilever walls, but they are also more expensive.
- Reinforced earth walls: These walls are made of soil that is held in place by a system of geotextiles and/or geogrids. Reinforced earth walls are relatively inexpensive and can be adapted to a variety of shapes and sizes.
- Sheet pile walls: These walls are made of sheets of steel or concrete that are driven into the ground. Sheet pile walls are typically used to retain water or other fluids.
- Gabion walls: These walls are made of gabions, which are baskets made of wire mesh that are filled with rocks. Gabion walls are relatively inexpensive and easy to install, but they are not as stable as other types of retaining walls.
- Masonry walls: These walls are made of bricks, stones, or concrete blocks. Masonry walls can be either gravity walls or cantilever walls.
The best type of retaining wall for a particular project will depend on the specific needs and requirements of the project. It is important to consult with a qualified engineer to determine the best type of retaining wall for your project.