How to build Allan Block retaining walls in Nanaimo
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Building Allan Block retaining walls
Steps and ideas for retaining walls with Allan block in Nanaimo, BC
What affects your retaining wall design?
Learn what you need to do to before you build a retaining wall in Nanaimo. Having the proper plan will make your landscape or retaining project simple.
What is the overall purpose of your retaining wall?
Do you need more usable space, do you have a drainage problem that needs fixing, or maybe you want to add curb appeal to your Nanaimo home.
What are Allan block walls?
A concrete block retaining project is 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 sizes may vary. Check with your local Nanaimo supplier for upto date information.
Planning Your Allan Block retaining wall project
Careful planning is the key to a successful retaining project.
Follow these simple guidelines to ensure the walls you build will stand the test of time.
Use the information here for retaining walls to plan, landscape 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?
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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 installation on a scaled diagram taking the necessary measurements as needed. Make sure to mark their locations and any other design features. Also look at retaining wall costs, factoring blocks, end blocks, corners and caps, drainage, base, backfill and steps. Also check to see if you need to do any cutting and how that will be done.
Indicate the position of all wall structures, trees and landscape features.
This plan is your initial blueprint for the retaining wall.
Check your local Nanaimo building codes. An approved design may be needed to get a building permit to build walls above a certain height.
Call the local Nanaimo 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 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. You may need to contact the City of Nanaimo to confirm this information before starting your project.
when planning your retaining wall 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 materials. If building on a hill or a slope the placement of your retaining project 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 project 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 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 finished project
- 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 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 Drainage
Surface runoff from rainfall and concentrated water sources must be directed away from your project.
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. Driveways that slope toward the wall, roof down spouts, sprinkler and irrigation system and outdoor faucets when designing, that will be exposed to these concentrated water sources build in swales and berms to route the water away. 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 rock and toe drains. Use rock in the cores and 12 inches behind to ensure good drainage.
Toe drains are used to prevent the water from being trapped behind and building up pressure They must be positioned directly behind 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.
Some great choices for retaining wall products:
Abbotsford Stack Wall
Cypress Stone
Mini Beltis
Mutual’s Stack Stone
Metropolitan
Artforms
Ashlar Tandem
Melville Tandem
Versa-lok
Weston Stone
Zenwall
How do I design a retaining wall
When designing your project, be sure to consider design elements such as, heights, 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’ and they use geogrid to provide added stability.
Geogrid provides a simple solution for any retaining 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 of lean 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 is called a surcharge.
Driveways, swimming pools, patios and slopes are common surcharges.
These may need additional reinforcement.
For design assistance, contact local Nanaimo engineer.
Slopes can occur above or below a wall.
Slopes above will add more pressure and weight.
Try to maintain a maximum slope of 3:1 above, where you have a ratio of 1 up to 3 back.
A slope below, may reduce stability and be prone to erosion.
Contact a local nanaimo engineer for assistance with this type of concept. Allan Block offers unlimited possibilities. The flexible Allan Block Collections from your local Nanaimo supplier will allow you to design with patterns, flowing curves, straight lines, stairways and much more
The natural feel of an Allan block classic concept 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 finished result, 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 or combination of blocks you choose will determine the radius you can create. Terracing 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 is less than this, or for all other terraced applications contact your local engineer from Nanaimo for assistance.
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 and can be built in front of or into the concept and they can also be built parallel.
With imagination and planning, you can design stairs into any project.
When installing stair treads, AB Capstones, pavers and poured concrete are good options.
For finishing, consider using Capstones , crushed landscape rock, mulches or planting materials.
How to build a Allan Block 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 you have the right allan block colors, styles and setback. Confirm the reinforcement grid is the correct strength, and size and inspect the rock and backfill materials to make sure that they meet the specified requirements. Rock is used as base material, within the cores as well as behind the blocks.
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 project.
When added to the 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. 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.
- Clay soil will stick together to form a ball. These soils retain moisture and may add pressure behind.
- Organic soils will stick together but will not hold once the pressure is released. NEVER use organic soils when retaining.
If more detailed soil information is required, check with a local Nanaimo top 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.
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