What are the different types of retaining wall?
by Andrew Lees, on January 21, 2021
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.
In our last blog we looked at the basics of retaining walls, and established that they are vertical, or near-vertical structures designed specifically to retain soil, and create level areas for maximising development space and reducing sloping on sites.
In our in-depth introduction to retaining walls, we also took a look at what purposes retaining structures achieve, how they work and how they are designedand constructed. This time around, we’re going to give a detailed overview of the main types of retaining walls available and give an insight to how they work, as well as their advantages and disadvantages.
The four main types of retaining wall are:
- Gravity retaining walls
- Cantilever retaining walls
- Embedded retaining walls
- Reinforced soil retaining walls
Use the links above to jump to the retaining wall types you’re most interested in learning about.
Ground Coffee Ask Andrew Episode 2: Andrew Lees explores the different types of retaining wall available to engineers.
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.Source: AsmithNJIT at English Wikipedia
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.
Example of an embedded retaining wall
Source: Störfix at English Wikipedia
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.
Visit our article on types of piling in construction for a more in-depth look at how different types of piles can be used to support retaining walls and other structures.
Reinforced soil, or mechanically stabilised earth, retaining walls
Reinforced soil retaining walls, sometimes referred to as mechanically stabilised earth walls, are constructed using layers of geogrid to reinforce the soil into a stabilised mass. This increases the bearing capacity of the retaining structure, along with its resistance to differential settlement.
These types of retaining walls have been discussed in more detail in our "what is a reinforced soil wall?" blog, and if you’d like to learn more about settlement types, try reading our geotechnical settlement blog.
Tensar's wall and slope systems
TensarTech reinforced soil wall and slope systems include precast concrete, dry-laid modular block systems (with the option of adding architectural, masonry or brick finishes); precast concrete panels; gabion and crib walls; and robust units suitable for aggressive marine environments. Our reinforced soil slope solutions can create vegetated slopes with angles of up to 70˚.
If you have an upcoming project and require the support of Tensar's design team, please submit your project details onto this form. Tensar’s design team can produce a free of charge “Application Suggestion” to illustrate what Tensar can achieve and how much value can be added to your project.
Want to learn more about retaining walls?
Learn more in our introduction to retaining walls guide.