Excavation for a retaining wall is the process of removing soil to make way for the gravel and retaining wall blocks.
I cannot stress how important the excavation & soil disposal step is in building your Allan Block retaining wall.
The retaining wall blocks by themselves are not what retains the soil. Instead, the combination of the blocks and gravel behind them work together to hold back a tremendous amount of weight year after year for decades.
The gravel behind the retaining wall does 2 things. First, it provides drainage to the surrounding soil, so its lighter to retain. Secondly, wall rock compacts better than soil, and has a higher friction angle. Both of these things add up to reduced pressure on the blocks. The vast majority of retaining wall failures are due to inadequate amounts of drainage behind the retaining wall.
The reason I’m explaining why you need gravel behind your retaining wall at the excavation step of your project, is because the excavation step is when we dig and make enough room for the structural components of your retaining wall (block and gravel).
For a gravity retaining wall (under 4’ in height and no weight surcharges to the wall), we need 6” of gravel in front of the wall, 12” for the block, and a minimum of 12” of gravel behind the wall. Because Allan Block lean back into the soil they retain we need more excavation the taller the wall is. At the bottom the block and gravel combine to 30”, and at the top of a 4’ high wall we need 36”.
When soil is excavated it expands by 1.4X. If we take a 100’ long retaining wall we need to remove and dispose of 68.56 cubic yards or about 6 full size dump trucks.
Aside from the work to excavate this soil, this soil needs to be brought to the road and loaded into awaiting dump trucks.
Once the soil is removed almost all the soil (aside from the room the blocks take up) has to be replaced with gravel.
Roughly 6 dump trucks of soil would be removed, and 5 dump trucks of gravel, 10 pallets of block and caps would have to be brought in.
Contractors who do not specialize in building retaining walls simply do not own the most efficient equipment to move this much soil out, and bring the blocks and gravel in.
Add to the mix that most retaining walls are in a backyard, or on properties with elevation changes ;doing this work by hand is not an option.
Because we are a retaining wall installation company, we own every piece of equipment we want to build the very best retaining wall. Our narrow excavator is 39”, our two track dumpers that carry soil, gravel and blocks are 31” wide, and our compact track loader sits on the road loading dump trucks.
Doing this work with equipment is fun, efficient, and ensures you get the very best built Allan Block retaining wall.
The biggest mistake you can make is having an Allan Block retaining wall built by a contractor who doesn’t excavate and remove enough soil for the blocks and gravel. This is the most problematic step, and the one contractor’s cheat to lower the cost of your project.
Here at Back 40 Landscaping we not only know how to build great retaining walls; we have the integrity to ensure that no part of the construction process is cheated. You deserve that.