Retaining Wall Backfill Guide: Best Materials + How They Work

Retaining walls are used to hold the soil in its place and prevent the side of a slope or hill from collapsing. At the same time, they can make the area they’re protecting more attractive since they can be quite beautiful structures. 

This guide will help you find answers to questions that revolve around retaining wall backfill materials, and their benefits. 

We want you to get the best value for your money when building your own retaining wall, so read on!

Gravel

Gravel is a type of base material used as a backfill, and it is the best backfill material that you can use. We recommend using gravel with at least 12 inches to backfill a retaining wall. For the rest of the space behind the wall, you can use compacted native soil. 

For a retaining wall backfill, it is recommended to use clean, coarse gravel that is 3/4 inch to 1 inch in diameter. This type of gravel allows for proper drainage and prevents soil erosion behind the retaining wall. The gravel should be placed in layers and compacted properly to ensure the stability of the retaining wall.

Pros:

• Drainage: Allows water to drain through it, reducing lateral pressure building up behind the retaining wall.
• Cost-effective: Relatively inexpensive compared to other materials such as concrete or crushed stone.
• Easy to install: Easy to spread and level.

Cons:

• Erosion: Gravel can be subject to erosion over time, which can undermine the stability of the wall.
• Maintenance: Need to be replenished or leveled periodically to ensure the wall remains stable.
• Appearance: May not have the same aesthetic appeal as other materials, such as crushed stone or mulch.

Retained Soil

This material consists primarily of sand or gravel that’s been compacted down to create a solid base for the wall itself. It can be placed directly into the area where you’ll be building your wall, or it can be used as an additional layer in conjunction with other materials like concrete blocks or stone.

Pros:

• Cost-effective: Can save on costs associated with importing backfill materials.
• Environmentally friendly: Using retained soil as a backfill can reduce the environmental impact of a project, as it eliminates the need to transport and process materials from elsewhere.

Cons:

• Stability: May not be as stable as imported materials, and may require additional compaction or stabilization methods to backfill a retaining wall.
• Quality: It may contain organic matter, clay, or other materials that can compromise the stability and integrity of the retaining wall.
• Drainage: Retained soil may not have the same drainage properties as other materials such as gravel and may lead to hydrostatic pressure and failure.

Concrete

Concrete can also be used as an effective backfill for most retaining walls, especially if you plan on using it as part of a larger structure (like a patio). You’ll want to make sure that the concrete has been cured adequately before putting it into place though—otherwise it might crack or break apart over time!

Pros:

• Stability: Can provide a strong foundation for the retaining wall
• Durability: Durable and long-lasting material that can withstand weather and temperature changes
• Low maintenance: Requires minimal maintenance once installed
• Aesthetics: Can be poured in any shape and color, providing a polished and uniform look to the retaining wall

Cons:

• Cost: More expensive than other materials such as gravel or drainage stone
• Heavy: Can be difficult to transport and install due to weight
• Not suitable for all soil conditions: Not the best option for soils that are high in clay or organic material 

[Related: The Cost Of Trenching And Backfilling In Arizona]

FAQs About Backfill Material for Retaining Walls:

What is the best material to use for backfill?

Gravel is a common choice for backfill material in retaining wall construction because it allows proper drainage and can help prevent the buildup of water pressure behind the wall. It also provides a stable base for the wall and helps to distribute the weight of the soil and other materials being retained.

What do you backfill a small retaining wall with?

Generally, it is best to use a granular material such as gravel or crushed stone for backfill. These materials allow for proper drainage and help prevent water pressure buildup behind the wall. It is also important to use the appropriate size and type of material for the specific application.

Another option is to use a drainage pipe behind the wall and then fill it with gravel or crushed stone. This will help to direct water away from the wall and prevent hydrostatic pressure from building up behind it.

Get Professional Help for Your Retaining Walls Today!

If you’re still unsure about what material should be used to backfill a retaining wall, Specialty Grading can help you out! We are the leading expert in grading, earthworks, and construction industries in Prescott Valley, Arizona. 

Contact us today at (928) 899-8313.