The different types, design and functions of a retaining wall

Here at DSA, we pride ourselves on clear and transparent communications because we know that when our clients understand our recommendations, they feel informed and reassured. Believe it or not, we spend a lot of time explaining retaining walls so thought we’d take the opportunity to share a bit more info on the topic, no holding back!

About retaining walls

Rule number one, never underestimate the importance of a retaining wall. As an essential structural element, retaining walls are used in construction and landscaping to stabilise soil and prevent collapse. In other words, they hold soil in one place, regardless of weather and land levels, come rain, wind or shine. Commonly found in residential and commercial projects, retaining walls not only serve a functional purpose but given the multitude of construction techniques available, they can also enhance the final aesthetic finish of your project.

What are retaining walls?

So, by their very nature, retaining walls must be stable and stiff to hold back the heavy weight of the ground and surcharge above. They are designed to support soil as well as lodgings on the retained surface which means it can be retained at different levels on each side of the retaining wall. Where ground is sloped a retaining wall will go a long way in preventing collapse and creating usable spaces on uneven levels. The engineering of retaining walls means they counteract the forces from the weight of the soil and surcharge, with their reinforcement or anchoring mechanisms. This is why adequate retaining wall construction is crucial for ensuring stability and longevity of your project.

Types of retaining walls

• Gravity retaining walls: As the name suggests, gravity retaining walls rely on their own weight to resist the soil pressure. Typically made from concrete, stone gabion baskets, or brick, these walls are ideal for low-height walls where there’s plenty of space due to the significant footprint, they require to ensure stability. This kind of retaining wall is usually easy to construct with minimal engineering expertise. Gravity retaining walls don’t provide an economical solution when stability is needed for taller, steeper situations – read on.
• Reinforced/hollow block retaining walls: With a reinforced concrete base and stem for extra stability, reinforced retaining walls are great for holding back soil for medium to high retaining applications up to six meters in height. Made from reinforced concrete or concrete hollow blocks, they require careful engineering design for retaining wall stability to prevent sliding and overturing under pressure. This makes reinforced retaining walls popular in commercial, domestic and infrastructure projects where greater stability is required without excessive material use.
• Anchored retaining walls: Anchored walls have piles driven deep into the ground to provide additional reinforcement and strength. These retaining walls are great for heavy soil situations and deep excavations where space is limited such as urban construction sites and areas with steep slopes, allowing for higher retaining wall structures while keeping the material use efficient. With such a complex installation process this option definitely requires specialised design engineering.
• Sheet pile/king posts retaining walls: Made from steel, or timber sleepers, these interlocking sheets are driven into the ground. Most commonly used in waterfront, soft soil conditions, where space is confined. Sheet pile/king post retaining walls offer a temporary or permanent retaining wall solution and sometimes require additional lateral support for deeper installations. You’ll see this type of retaining wall in places like ports, river beds, and excavation sites. Another retaining wall option that requires a structural engineer to ensure long-term stability.
• Reinforced soil retaining walls: Like all things, innovation is constantly finding new ways to design retaining walls and reinforced soil walls are one of them. They integrate geosynthetics or other kinds of reinforcement materials to stabilise the soil through compaction, giving better flexibility, durability and value for money, which is why they are becoming the preferred choice for highways, railways, and embankments. Unlike traditional retaining walls, reinforced soil walls are lightweight and allow for greater design adaptability with the added bonus of being more environmentally friendly compared to the other rigid concrete retaining wall structures.
• Hybrid retaining walls: There’s always the option of combining a few elements from the different types of retaining walls creating a hybrid solution to suit unique site conditions. Such innovative solutions are often found in specialist infrastructure projects such as underground stations and bridges, using latest materials and construction techniques to improve performance, sustainability, and cost-efficiency. Advances in engineering mean there are also new composite retaining wall systems that offer the same great strength and flexibility to suit a range of environmental conditions.

Key design considerations

These are the main things you need to think about when planning your retaining wall:

• Load-bearing capacity: Walls must be able to handle soil pressure and environmental forces such as weather, water, and what the soil is supporting at higher level.
• Drainage: Proper drainage must be in place to prevent pressure buildup which could lead to the retaining wall being overloaded.
• Material: Options include concrete, stone, timber, or geosynthetics, your choice will depend on type of retaining wall, budget, durability and environmental conditions.
• Function and aesthetic: A retaining wall can be an attractive feature of the landscape – or it might just need to do its job and offer structural stability.
• Regulatory compliance: Like all structural components, your retaining wall must meet all applicable building and safety standards.
• Climate and environmental: Some materials are more durable than others making them more suited to extreme weather conditions with minimal maintenance.