Understanding the Different Types of Retaining Walls
Retaining walls remain a crucial facet of construction, whether for building a more elegant home or an engineering marvel. They also make building on sloped land possible. While not indestructible, especially in the face of Mother Nature, they can perform their job well with proper design and construction.
You may have heard of the various types used in construction, from gravity to gabion walls. This article will explain the different types of retaining walls residents can build, how they work, and how to best employ them for your landscaping needs. Let’s take a closer look.
Gravity retaining walls are the most basic, consisting of a single wall with a trapezoidal cross-section. They don’t need any extra anchorages or fixtures, relying on their massive weight and wide base to hold firm against the force exerted by the massed earth.
In designing a gravity wall, height and base width are directly proportional. The ideal dimensions depend on two factors: the fluid pressure of the soil (Q) and the vertical weight of the masonry used (W). Engineers often recommend a Q/W ratio between 0.2 and 0.6 to prevent the wall from overturning or sliding out of place.
The uncomplicated nature of gravity walls makes them a popular and cost-effective choice for landscaping. However, their immense size makes them a poor choice for properties with limited landscaping space. Engineers also don’t advise building them atop soft soil, which is prevalent in Australia’s eastern coastal areas, due to the risk of bearing failure.
As its name suggests, a cantilever retaining wall is a design that harnesses the cantilever effect. It features a far longer base than most retaining wall designs and a reverse slope, meaning the slope faces the earth fill. Extending the base farther into the earth fill reduces the pressure on the wall for less concrete and space.
There are three ways to build a cantilever wall.
- The L-shaped design is the simplest, with the cantilever extending only to the earth fill. Unlike a regular cantilever wall, this one doesn’t have a sloped surface on either side.
- The T-shaped design features a small extension of the base beyond the wall, called a toe or toe slab. The toe helps counteract the downward force exerted on the heel slab.
- Some T-shaped designs have shear keys directly at the base of the wall. This notch helps increase sliding resistance by enacting friction on it.
Because they require less concrete and effort, cantilever walls can be erected higher than gravity walls. However, even with the addition of a shear key, they can still be vulnerable to sliding off place. Additionally, they might not hold firm against clay soil, which exerts a high fluid pressure.
A counterfort retaining wall is similar to its cantilever counterpart but reinforced with transverse slabs called “counterforts” facing the earth fill. The counterfortsconnect the wall and base slabs, which helps further reduce the pressure on the wall.
The counterforts can be built as high as or slightly greater than half of the wall itself. As for the ideal spacing, it depends on the amount of load the wall’s expected to resist, though a good rule of thumb is between 33% and 50% of the wall’s height. Regarding the thickness, another rule of thumb is about 6% of the wall’s height.
Counterfort walls are some of the most resilient designs and can handle immense backfill loads,but they come at the expense of simplicity. Sometimes, you may be advised to settle for buttress walls, which have counterforts on the exposed side of the wall. As far as landscaping goes, these counterforts may appear unsightly.
Sometimes, space limitations can restrict a retaining wall’s design to just the vertical wall—no base slab or sheer key. In these cases, holding the wall steady entails using heavy-duty anchors pulling the wall against the earth fill. The direction of the pull can be fully perpendicular to the wall or at a 15 to 45-degree angle across the earth fill.
With the anchors doing most of the heavy lifting, they can be used on virtually any retaining wall design. Anchored walls are suitable for retaining loose soil and can hold firm amid tremors. That said, anchored walls might give way quickly without adequate drainage, especially when used on loose soil.
This list is by no means exhaustive. Various factors like soil conditions and space will influence the best possible retaining wall design for landscaping. Regardless, understanding how the most common retaining wall options work is sound advice for planning and building one.
Learn more about Pride Fencescapes retaining walls by visiting our website. Don’t hesitate to give us a call if you need a professional’s expertise.