Construction and uses of retaining walls

Retaining walls are used on construction sites to prevent soil erosion. They are designed to hold back the earth, so water can flow through it and away from the building. The soil is used as a dam while the water builds up behind it, acting as a natural breakwater. Different strengths and weaknesses in the soils make up a retaining wall, which means they cannot always withstand all forces applied to them.

The design of retaining walls depends on the type of soil they’re being built on and their intended use. 

Earth retaining walls and rock retaining walls are the other types of walls. Both types of retaining walls are designed with the same basic principles in mind. They need to resist lateral pressure (the force exerted forward), thrust (the sideways force caused by the movement of soil), and uplift (the upward force exerted by gravity).

 

Types of retaining wall

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There are three types of retaining walls: vertical, sloped, and curved. These are all designed differently to suit their purpose. But they all act the same way- to hold back soil that would otherwise erode from buildings or objects.

 

Use of retaining wall

Retaining walls serve as versatile structures that not only enhance the visual appeal of landscapes but also provide essential structural support. These walls find a range of applications, offering both functional and aesthetic benefits. Here are some common uses of retaining walls:

Creating terraced garden beds

Retaining walls are often employed to transform uneven or sloped landscapes into multi-level terraced garden beds. These walls allow for better soil retention and prevent erosion, creating flat and usable spaces for planting a variety of vegetation. Terraced garden beds not only add depth and texture to the landscape but also provide an opportunity for creative gardening and landscaping.

Supporting a raised patio or deck

When designing outdoor living spaces like patios or decks on sloped terrain, retaining walls play a crucial role in providing stability. By holding back the soil and creating level surfaces, retaining walls offer a solid foundation for constructing raised patios or decks. This not only maximises usable space but also ensures the safety and longevity of the outdoor structure.

Preventing erosion along a steep slope

One of the primary functions of retaining walls is to prevent erosion along steep slopes. These walls effectively hold back the soil, preventing it from being washed away by rainwater or runoff. By stabilising the soil and controlling erosion, retaining walls contribute to the overall health and integrity of the landscape.

Building a decorative boundary around a property

Retaining walls can serve as decorative elements that define the boundaries of a property while adding an aesthetic touch. These walls can be designed using various materials, textures and colours to complement the overall architectural style of the property. A well-designed retaining wall can enhance the curb appeal of a property and create a polished look.

 

Retaining wall: Construction

• Retaining walls are usually constructed on grade, with the top surface sloping slightly toward the base of the wall. 
• The top layer of the stone should be at least 10% wider than the base layer so that it will remain in place when enough pressure is applied to support the weight. 
• In some cases, there may be no need for an entire foundation but rather a few feet of soil placed directly on grade. This type of wall is called a “base” wall because it has no superstructure above it.
• In other cases, there may be several layers of stone with one or more concrete or masonry layers above them. 
• Then there will be several types of retaining walls used on construction projects depending on how much weight each type must bear.

 

How do retaining walls function?

Retaining walls are engineered to hold back soil or fill material at a steeper angle than the material’s natural angle of repose—the maximum angle it can naturally maintain without collapsing. To achieve this, they must withstand the horizontal, or lateral, pressure exerted by the retained material. The lateral pressure from the earth depends on the vertical stress imposed by the material behind the wall, which is determined by the height of the backfill and its density. Consequently, the greatest lateral pressure occurs at the base of the wall because deeper backfill increases the vertical stress.

 

Which lateral pressure theory should you use?

• The lateral pressure theory is used when evaluating retaining walls’ stability because it considers both vertical and lateral forces acting upon them. 

 

• Using two equations, it predicts how much weight will be exerted upon a wall by engineering calculations based on factors such as material quality, density, and strength, both compressive and flexural. 

 

• Lateral pressure theory should always be used when designing any retaining wall because it provides information about how much material is needed and where it should go to support it properly.

Stem wall design

To design a stem wall, you must first consider the footing design. This is because the stem wall rests on the footing, and it cannot be placed too high or too low. The stem wall should also be deep enough to support its weight and any additional weight that may be placed on it by vandals or other intruders.

For example, say you want to build a retaining wall that’s tall enough to reach from your house to the end of your driveway. In this case, you’d want a sturdy footing made of thick concrete. That could support the weight of both your house and driveway. You’d also need space above this ground level so that you could install a platform for planting flowers or other landscaping purposes.

If you only plan on placing one plant on top of your new retaining wall, you might consider putting it at ground level instead of building a platform above it. But keep in mind that plants grow better under good lighting.

Designing the footing

The footing is the first construction member of the building and is responsible for safely transmitting the weight of the upper building to the ground. A footing is part of the foundation construction process. It is typically composed of concrete reinforced by rebar, which is poured into a trench excavated earlier. 

Providing support for a foundation and preventing it from settling is the purpose of footings. It is especially important to have good footings in soils that are difficult to work with.

There are many ways to design a retaining wall. The most common way is to use concrete or stone for the stem and footing. You can use concrete blocks or wood. The type of material will depend on your budget and the materials available in your area.

If the soil on either side of the wall is loose enough, you can use a retaining wall with no footing. This kind of design would be best used if there was no need for stability or if already existing trees could provide extra support for the walls. If there is no soil on either side, it is possible to make a retaining wall with only one course of blocks placed on top of each other.

Another option is to use multiple layers of blocks stacked up against each other like bricks in an archway pattern so that they make up one continuous wall reaching from top to bottom without any gaps between them. 

 

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Housing.com POV

Retaining walls are vital structures in construction, designed to withstand various forces and serve multiple purposes. Their construction and design depend on factors such as soil type, intended use, and the lateral and vertical pressures they must withstand. Retaining walls prevent soil erosion, provide structural support, and enhance the aesthetic appeal of landscapes. They are used in creating terraced gardens, supporting raised patios, preventing erosion and defining property boundaries. The construction of retaining walls involves careful consideration of footing design and material selection. Lateral pressure theory guides the design process to ensure stability and effectiveness. Overall, retaining walls are versatile and essential components of both functional and visually appealing landscapes. 

 

FAQs

What are retaining walls used for?

Retaining walls are primarily used to hold back soil or other materials, preventing erosion and creating level surfaces on sloped terrain. They are also employed for structural support, landscaping purposes, and defining property boundaries.

How do I choose the right type of retaining wall for my project?

The choice of retaining wall depends on factors such as soil type, site conditions, intended use, and aesthetic preferences. Consultation with a professional engineer or landscaper can help determine the most suitable option for your specific requirements.

Are retaining walls difficult to maintain?

Retaining walls generally require minimal maintenance, but periodic inspections are recommended to ensure structural integrity. Regular checks for signs of erosion, cracking, or displacement, especially after heavy rainfall or seismic activity, can help identify and address any issues promptly.

Can retaining walls be installed on any type of terrain?

Retaining walls can be installed on various terrains, including sloped, uneven, or hilly landscapes. However, site assessment is crucial to determine factors such as soil stability, drainage, and load-bearing capacity, which may influence the design and installation process.

Do I need a permit to build a retaining wall?

The requirement for permits varies depending on local regulations and the specific characteristics of the project, such as wall height and location. It's advisable to check with your local planning or building authority to ascertain whether a permit is needed before commencing construction.

How does a building's footing work?

Footings are the parts of foundations that transfer loads to the soil.

How does retaining design work?

Supporting walls are used to retain soil laterally at different levels on both sides by supporting it laterally.

How steep is the slope of the retaining wall?

High-volume roads, high-cut slopes, and terraces should be considered for cement masonry, RCC walls, and gabion walls. The latter is also suitable for steep slope angles between 30° to 60°, where higher walls are required.

When building a retaining wall, how thick should it be?

Two brick skins should be tied together or bonded to a minimum thickness of 215mm.

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