What Is A Concrete Cantilever Retaining Wall?
What Is A Concrete Cantilever Retaining Wall?
Cantilever walls are reinforced concrete and have an L-shaped or inverted T-shaped base. The vertical tension behind the wall is transmitted to the foundation, preventing it from collapsing as a result of lateral earth pressure from the same soil mass.
A T-shaped foundation also benefits from the weight of the earth (and hence vertical tension) in front of the wall, giving additional stability. To prevent slide collapse, foundations may have a ‘key’ in their base that sticks into the ground.
Cantilever walls have a significant advantage over other retaining walls in that they take up minimal space once completed and are appropriate for retained heights of up to 5 m.
However, the building requires room behind the wall, so they are not well adapted to sustaining existing slopes unless temporary support is given during development.
When A Shear Key Is Provided In A Reinforced Concrete Retaining Wall?
Reinforced concrete retaining walls are popular for building walls due to their strength and durability. However, retaining walls are not immune to failure due to sliding.
One common failure mode for retaining walls is due to shear failure. Shear failure is caused when the wall loses its strength due to the combined weight of the soil and the concrete. This can be avoided by installing shear keys at the wall base.
Shear keys are small metal bars installed at the base of a retaining wall. The purpose of shear keys is to increase the extra passive resistance developed by the height of shear keys. This extra resistance helps to prevent the wall from failing due to shear failure.
Shear keys are typically installed in pairs. This means that the shear keys are positioned one above the other.
This purpose is to create a height differential between the shear keys. This differential creates extra resistance to the force applied to the wall due to shear.
Shear keys are an important part of retaining wall design. By installing shear keys at the wall base, we can help to prevent the wall from failing due to shear failure.
How Do You Build A Concrete Retaining Wall On A Slope?
Here is how you can build a concrete retaining wall on a slope;
Excavate
Drive pegs at opposite ends of the site and attach a length of twine if you’ve planned a straight wall.
The string should be aligned with the planned wall’s front or parallel to where you want the wall’s front to be.
Establish A Level Base
The foundation material and the first layer of blocks must be level to build a structurally strong wall.
Drive two stakes into the ground with their heads where the bottom of the first row of blocks will sit to provide a level base.
Rest a straight piece of 2×4 timber over the tops of the stakes to level them. Place a 4-foot level on the board and confirm the stake placement.
Firm Up The Base
A hand tamper will be enough for most walls, but gas-powered tampers may be rented for larger constructions.
As a final option, a 4×4 might be deployed. Compact the first few inches of foundation material, then add a few more.
Repeat until the stakes’ tops are visible through the foundation material.
Level The Ground
Level the top of the foundation material using a straight 2×4 to ensure it is flat. This is critical; if they aren’t level, you’ll be battling against the base and first course of bricks throughout the construction process.
Lay The Foundation Blocks
Begin putting blocks at one end, one at a time. Check the level from front to rear using a torpedo level. Tap the blocks together with a rubber mallet until they are level.
Put sand or base material under a block if it has to be raised.
On the first course, level every block. It is responsible for most of the labor, receiving all of the pressure from the wall and establishing how to level the wall.
When you’re finished with this layer, pack native dirt around the fronts of the blocks to keep them in place while you add the next one.
Keep Stacking Blocks
Begin with a half block on the second course. The wall will be more structurally sound with staggered joints.
Editor’s Note: To cut, use a brick chisel to score a line around the block, then tap until the block separates. Rent a masonry saw from a tool rental store if you need to make a lot of cuts or carve unique capstones.
Backfilling
Backfill with crushed gravel and tamp it after each level is placed. This allows for better drainage and prevents tree and plant roots from harming your wall.
Aside from the gravel backfill, drainage that extends beyond the wall is critical to the wall’s strength.
Install a length of perforated drainpipe towards the gravel’s bottom to divert water from behind the wall. Backfill gravel should be at least 8-12 inches thick.
