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Understanding retaining walls in the landscape

📷Adding in structures to a space to create a focal point is a common practice for professional landscapers, and a very popular item to create is a retaining wall.

Retaining walls can be used to help customers overcome sloped areas in their yard and often add in visual interest to a landscape while serving a functional purpose. Retaining walls can also be used to increase the amount of usable land available in a yard, and they can even provide environmental benefits such as protecting areas from saturation and soil erosion reduction.

If you find yourself in the midst of a retaining wall installation project in the coming months, take a look at a few tips you can keep in mind when creating this eye-catching piece.

Specifics when building

When working with steeper slopes, some techniques you can utilize are the use of interlocking concrete blocks, riprap (loose rock) areas, wood retaining walls, rock retaining walls and terracing. Keep in mind that if you do choose to use wood, it’s a good idea to treat the wood with a preservative to prevent rotting.

If you know the wall will be higher than 3-4 feet, an engineer will be required to assist with the project because of zoning codes and regulations.

The wall should lean into the hill at a minimum of 1 inch for every 12 inches of height in order to maintain a safe load on the wall. This can also help with the drainage when the soil becomes saturated. It’s also possible to redesign the grade of the slope before installing the wall, as this can help direct water away from the wall and could also decrease the amount of slope needed.

To help keep water build-up at bay in poorly draining soils, consider placing drainage tiles behind the wall, but be sure to construct these tiles with a 12-inch-deep layer of backfill that is freely drained, such as gravel.

The cost, height and function of the wall will all depend on what materials your customer chooses for the project, but if the wall is being used strictly as a decorative piece in the yard, almost any kind of material will do the job.

For walls that will be serving the purpose of supporting larger loads, you will need to use long-lasting, durable materials that will be suited for the conditions of the site.

In areas where the wall’s height will be less than 4 feet tall, wood and solid concrete walls are recommended. Keep in mind that wooded walls will deteriorate faster, and concrete walls will have drainage issues that could cause water saturation conditions to occur above the wall.

Keep an eye out for…

When maintaining your customer’s landscape, look for areas in need of a retaining wall.

One area of concentration to focus on is the slopes present in the yard. If you see an area with a slope greater than 3:1, be sure to consult with an engineer. If the slope is over 2:1, it will require structures or specialization techniques.

Ask yourself and your customer how much freezing or frost will both the wall and soil it’s holding come in contact with, and always check the wall’s drainage to see if it’s functioning properly. If it looks like the water will flow heavily on the wall and soil, you may need to add in some drainage.

Take stock of the type of soil in your customer’s yard, as soil with heavy clay content won’t draw water well, but it is less prone to erosion. Sandy soil, on the other hand, will have opposite characteristics.

Check for other structures near the site where a retaining wall might be needed, and if there are existing structures around, consider how they will be affected if or when a retaining wall is installed.

Also remember that if you’re located in an area where earthquakes are prevalent, talk to an earthquake engineer to analyze the wall and make it more earthquake-resistant.

Types of retaining walls

Once you’ve determined that your customer’s yard does need a retaining wall, the time comes to determine which type of wall your customer needs.

Gravity walls will hold the earth by the weight of the wall’s material. They can be formal pavers or even a stack of large rocks, but they can fall easily and should be used for short slopes of 3 feet or less.

Anchored walls are the strongest type and can be combined with other techniques. An anchor is wrapped around the wall, and a base is placed deeper into the hill, which provides the stabilization.

Piling walls use long piles, or poles, that go deep into the soil and above it. Pilings can be made of metal or treated lumber, and they have a good capacity to hold the soil back.

Cantilever walls are similar to piling walls, however, they get added strength from a sort of “arm” that extends back into the hill. This can increase its capacity to stabilize pressure.

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