Although most people are unaware of their existence or purpose, retaining walls are the supports that allow us to explore the full potential of our garden. Chances are, you pass at least one every day without realising exactly what it is. So, just what are retaining walls, and how are they used to transform mundane gardens into stylish havens of serenity?
What Is a Retaining Wall?
A retaining wall is a structure that holds soil in place laterally, keeping it in position at a sloped angle. They come in a variety of materials such as concrete block, poured concrete, timber and steel. There are 4 main types of retaining walls- gravity walls, piling walls, anchored walls and cantilever walls. Each one has its own merits and benefits.
Gravity walls are the most basic retaining wall. They bear the load of the soil with their weight and generally require a trench to be dug or a concrete footer to anchor them. With their basic nature, gravity walls do not have the strength to withstand heavier loads and so should only be used for short slopes.
Piling walls are comprised of a thin sheet of steel, wood or vinyl that is implanted into the soil. For adequate support, at least one-third of the pile should be driven under the ground. They have good load-bearing capacity and can be reinforced with anchoring supports for added strength.
Anchored walls are the strongest of all retaining walls. The wall structure can be built from a variety of materials before being wrapped with the anchor, which is then driven deep into the ground to stabilize the wall.
Cantilever walls are also known as reinforced retaining walls. They have an added slab foundation that extends from the wall at a 90-degree angle, creating an L shape. This foundation is buried in the soil, which weighs the wall down so that it won’t tip or lean forward.
How Do Retaining Walls Work?
Retaining walls work on basic engineering principles. Before starting construction, the builder calculates what the required load-bearing capacity is and builds the wall to strength accordingly.
Factors to consider when calculating the load-bearing capacity include the lateral earth pressure from the soil, axial forces, the size of the slope bearing on the wall, impact loads and possible wind forces.
Other elements that impact the functionality of the wall are the type of soil in the area, what kind of drainage is in place, and how much frost the wall will be subjected to. People living in earthquake zones may need to get extra guidance to ensure the stability of their wall.
With such a range of variables, it may be wise to consult an engineer if you are building the wall yourself, though the general rule of thumb is that this isn’t strictly necessary if the wall is lower than 3 feet tall.
What Are Retaining Walls Used For?
Retaining walls serve both as a practical and aesthetic feature. For gardens with slopes or varying levels of elevation, they are used to hold the earth back, allowing the owner to create an area of even ground that is more usable than sloped terrain. They also allow the gardener to safely create flower beds on steep inclines without the chance of soil collapsing on them.
In an aesthetic sense, they add visual appeal and interest to any garden. The variety of materials available enable the user to create anything from a rustic, cosy feel to something more structured and formal.
In areas with sliding hills, retaining walls are used to prevent soil erosion, which can compromise the foundations of buildings. This is often achieved by a technique called ‘terracing’. Terracing offers protection and helps to create pedestrian access in the form of steps. This is a popular option in gardens as it creates fantastic definition, and the spaces between the walls can be used as planters while the walls themselves can be used as a seating feature.
Along with these benefits, retaining walls can be used to manage water runoff. This is done by designing the wall so that sections of it are strategically placed to redirect the flow of runoff through the area. This needs to be carefully planned to ensure that the new flow direction doesn’t cause problems elsewhere.
Retaining Wall Issues
An incorrectly built retaining wall can lead to catastrophic failure. This is commonly seen where the structure is tilting, cracking or crumbling. These problems usually stem from the load capacity being miscalculated or the supports being positioned wrongly. They can also occur where there is insufficient drainage, as flooding around the wall weakens it.
How Much Do They Cost to Build?
The average cost of building a retaining wall depends on the size and nature of the project. Self-building allows you to set your budget by sourcing and choosing materials to suit, though you may also need to pay an engineer to consult with you regarding load-bearing capacity.
If you are hiring a builder, you will have the added cost of labour. The average hourly rate of retaining wall builders is $55 per hour, meaning the more complicated your wall design is, the more costly it will be to build.
The potential cost for the whole project depends on what part of the country you live in. In South Australia, you can expect to pay $380 per square metre. On the other hand, in Western Australia where labour is a lot cheaper, prices start at $70 per square metre.
Retaining Walls Melbourne
Here at Taylor Fencing, we are masters of creating exceptional retaining walls that are built to spec to suit your requirements. Our highly trained staff will consult with you every step of the way, ensuring that the finished product is something that we can both be proud of. Call us on 03 9738 1153 to discuss your project or contact us here for a no-obligation consultation and quote.