Allan Block retaining walls

allan block retaining wall

Allan Block retaining walls

How to build Allan Block retaining walls

Steps and ideas for building an Allan block retaining wall in Nanaimo

What affects your retaining wall design?

Learn what you need to do to before you build a retaining wall.  Having the proper plan will make your landscape or allan block wall project simple.

What is the overall purpose of your wall?

Do you need more usable space, do you have a drainage problem that needs fixing, or maybe you want to add curb appeal.

What are Allan block walls?

A concrete block wall is a wall made up of standard size concrete blocks. The standard Allan Block dimensions are 8 inches, however, depending on the design parameters and standards set by an engineer for the concrete structure, the block sizes may vary.

Planning Your Allan Block wall Project

Careful planning is the key to a successful wall project.

Follow these simple guidelines to ensure the walls you build will stand the test of time.

Use the information here for Landscape Walls to plan, design & build your own landscape project.

Start by determining the overall purpose of your project.

Are you trying to create more usable space, solve a drainage problem or simply add curb appeal?

Do you want planters, stairs or other design features?

Once you have your wish list, you can determine if, where and how you will build it.

Sketch out the position of the walls on a scaled diagram taking the necessary measurements as needed. Make sure to mark their locations and any other design features.

Indicate the position of all structures, trees and landscape features.

This plan is your initial blueprint for the wall.

Check your local building codes. An approved wall design may be needed to get a building permit to build walls above a certain height.

Call the local utility companies before you dig to have them mark the location of the utility lines.

Buried lines are not only dangerous, but may also prevent you from building the wall where you want.

it’s also a good idea to verify the lot lines and inform the neighbors that there will be construction going on.

when planning your project make sure you can access the site with construction equipment and materials

For sites with restricted access plan out where you will stage and store your block, wall rock and other materials. If building on a hill or a slope the placement of your wall will determine how much soil will need to be removed or brought on to the site.

A cut site is where you cut into the hillside to remove the soil from in front of and behind the wall location. You will need to decide ahead of time what will be done with the excess soil

A Fill site is where you will need to fill in behind the entire wall with backfill materials that will be brought in. You will need to plan ahead to have these materials brought onto the site.

Before beginning construction, determine the type of soil you will be building on.

  • Granular and sandy soils are much better to build on as they allow for good drainage.
  • Clay soils will stick together and put pressure on the walls
  • Organic soils will also stick together and hold moisture and should only be used to finish off the top eight inches of the wall

90% of wall failures are caused by poor water management.

Once you’ve determined the water on your site you must manage the water in two ways;

Surface Runoff and In-wall Drainage

Surface runoff from rainfall and concentrated water sources must be directed away from the wall.

This can be done by grading the site and incorporating berms, drainage ditches or swales to prevent the water from being collected above the wall, identify concentrated water sources such as slopes above the wall. driveways that slope toward the wall, roof down spouts, sprinkler and irrigation system and outdoor faucets when designing walls that will be exposed to these concentrated water sources build in swales and berms to route the water away from the wall. Most of the time, you can hide the swales and berms with plants and landscape materials

In-wall drainage is meant for incidental water only and is managed through the use of wall rock and toe drains. Use wall rock in the block cores and 12 inches behind the wall to ensure in-wall drainage.

Toe drains are used to prevent the water from being trapped behind the wall and building up pressure They must be positioned directly behind the wall at the lowest point possible allowing the water to be vented to daylight if you encounter ground water on your site contact of engineering professional for assistance.

How do I design an Allan Block Garden Wall

When designing your project, be sure to consider design elements such as, wall height, setback, slopes, and surcharges.

These elements will help you determine whether to build a gravity or reinforced wall.

Walls that rely on their own weight and setback are called Gravity walls.

Under certain conditions, a gravity wall is not enough and additional reinforcement will be needed

These are called reinforced walls and they use geogrid to provide added stability.

Geogrid provides a simple solution for walls up to 6 feet high.

Used together, blocks and geogrid create a solid structure with more resistance to soil pressure. Always determine if reinforcement is needed on your project.

The amount your wall leans back into the hill is called “setback”.

Allan Blocks come in 6° and 12° setbacks.

12 degree setbacks provide better leverage and require less reinforcement to hold back the pressure behind the wall.

Any weight above a wall is called a surcharge.

Driveways, swimming pools, patios and slopes are common surcharges.

These walls may need additional reinforcement.

For design assistance, contact local engineer.

Slopes can occur above or below a wall.

Slopes above a wall will add more pressure and weight.

Try to maintain a maximum slope of 3:1 above the wall where you have a ratio of 1 up to 3 back.

A slope below the wall may reduce stability and be prone to erosion.

Contact a local engineer for assistance with this type of wall design. Allan Block offers unlimited design possibilities. The flexible Allan Block Collections allow you to design with patterns, flowing curves, straight walls, stairways and much more

The natural feel of an Allan block classic patterned wall adds a beautiful dimension to your landscape. Both the AB Ashlar and AB Europa Collections can be used to create a variety of patterns. Patterns are typically repeated every two or three courses. Plan on taking a little extra time to build patterned walls, particularly when building one for the first time.

Curved and Terraced Allan Block Walls

Curved walls are simple to design and easy to build. The type block or combination of blocks you choose will determine the radius you can create. Terraced walls can be used to create more usable space and build raised gardens

For projects that include terraced walls, the distance between the walls must be greater than two times the height of the lower wall. If the distance between the walls is less than this, or for all other terraced applications contact your local engineer for assistance.

In -wall planters can be used to add color and break up long stretches of wall.

Compaction under the wall sections that curve back into the hill is very important.

Stairs can be easily designed into your project.

The simplest stairs are built using curves, which do not require special skills or cutting of block and can be built in front of or into a wall and they can also be built parallel to a wall.

With imagination and planning, you can design stairs into any wall project.

when installing stair treads

AB Capstones, pavers and poured concrete are good options.

For finishing your wall, consider using  Capstones , crushed landscape rock, mulches or planting materials.

How to build a Allan Block Classic retaining wall

Getting Started

Once your project has been properly planned out and the designs are complete, you are ready to get started. It is always good practice to make sure that the materials you use are correct. Refer to the approved plans to make sure that the blocks are the right allan block colors, styles and setback. Confirm the reinforcement grid is the correct strength, and size and inspect the wall rock and backfill materials to make sure that they meet the specified requirements. Wall rock is used as base material, within the block cores as well as behind the blocks.

Wall rock must be a compactable aggregate ranging in size from a quarter inch to 1 and a half inches in diameter. This balanced mix of sizes allows for good compaction and serves many purposes in a wall project.

When added to the block cores, it increases the structural stability, locking the blocks and grid together to form a “Rock Lock” connection. It also allows for good compaction inside and around the blocks and prevents settlement directly behind the block. There are three basic types of soils that can be found on any site, sandy soils, Clay soils or organic soils

Sandy soils, clay soils, or organic soils. The simplest way to determine the type of soil you have is to pick it up and examine it.

  • Sandy soil, will not stick together. These soils allow for good drainage and are ideal for building walls
  • Clay soil will stick together to form a ball. These soils retain moisture and may add pressure behind your walls.
  • Organic soils will stick together but will not hold once the pressure is released. NEVER use organic soils when building walls.

If more detailed soil information is required, check with a local soil Professional for further testing.

Be sure to have the proper tools on hand before you begin.

Remember, Safety always comes first. Use protective gear and be sure to follow safety guidelines when using power tools.

Additional Reading: Hardscapes, Paving Stones, Rock Walls, Creative landscaping

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