Before getting into why Allan Block retaining walls need to be built correctly, let’s talk about what an Allan Block retaining wall is.
Allan Block (also known as retaining wall block) is a type of concrete brick (block) used to build retaining walls and garden walls. Allan Block can be used to constrain volumes of soil or other earth-based materials to specific areas.
Why Choose Allan Block?
You know what you’re getting with Allan Block in terms of color, size, layout, and patterns. You can see it in a magazine or book, and picture it in your yard. The material in every city will be the same because it’s very consistent.
Allan Blocks come in many colors, sizes and patterns for even the most serious designers! The best part is that most of these patterns work with the jumbo blocks. This mean your first course foundation can be the big ones, and the visible higher rows can be a very decorative creative pattern that turns your retaining wall from a standard one, into a magazine worthy focal point suitable for back dropping any backyard.
Even though Allan Blocks are really heavy they can be handled by hand, which is useful with tight access areas, or small backyards without machine access. Allan Blocks are the most versatile retaining wall material out of all your options.
So, what is the number one reason Allan Block retaining walls fail?
THEY ARE NOT BUILT CORRECTLY.
How can we be sure that retaining walls are not built correctly? Just take a look at any neighbourhood and you will see dozens of walls on the verge of collapsing, or that have already collapsed.
Almost every contractor builds their retaining wall differently. The methods that they use to build their retaining walls are based on speed, ease, cost, and general practices.
Let’s say that the retaining wall that is being built for your outdoor space is made out of Allan Block. Allan Block concrete retaining wall blocks have one method, with specific site variations, that need to be used when building a retaining wall.
If A Retaining Wall Is Not Built Correctly What Happens?
Retaining walls that are not built correctly have varying levels of failure, from minor separation between the blocks, to catastrophic failure where large portions of the wall fall over.
Allan block retaining walls are a mortarless system, that interlock in a dry stacking pattern. They are flexible in nature, and unlike a solid concrete structure will not form cracks.
However poor retaining wall design, installation method, or any other cost saving method will result in failure on some level.
Cost saving methods that are common are contractors not using enough gravel behind the wall, or excavating enough soil before putting down the gravel base.
Gravel is essential for the base to provide a solid level foundation to build upon. It drains water away to eliminate soil erosion, decomposition of the wall material, and to remove the standing water (proper drainage) below the wall system to prevent frost heave in the winter time.
Excavating and removing soil behind your wall, and replacing with gravel will add significant costs to the project, but must be done if you expect it to last for longer than 5-10 years.
Anything outside of Allan Blocks allowable movement for a flexible structure is a failure.
When a homeowner is spending 10s of thousands of dollars there should be a strict standard for quality.
Retaining walls are a big investment when built to best practices. Not only should they do their job of holding back hundreds of thousands of pounds of force ( retained soil), they should be straight, true, and an aesthetically pleasing center piece in your outdoor space and landscaping backdrop.
When having a retaining wall built on your property, making sure that your contractor is trained and following Allan Block guidelines will give you a product that will last decades.