On this retaining wall project that we built in Kitchener, we had this entire backyard to do which includes a pool patio, gas fire feature, privacy screens, and so much more. It was this specific retaining wall in the back that we needed to retain the slope beyond the wall so that we could build a properly sloped patio.
This retaining wall failed meaning that it is leaning over because of the way it was built. When we build retaining walls we make sure that we have a minimum 6 inches followed by an embedment of at least 6 inches. This ensures that that retaining wall is going to remain stable and not kick out at the base. You will also notice that there is no drainage in behind this wall. We prepare a minimum 12 inches beyond the wall for a drainage area. This includes 12 inches of 3/4″ clean stone to allow that water to freely flow through the back of the wall and then a drainage pipe that exits that water out of the wall.
If a drainage area is not properly prepared beyond the wall, water will be held behind the wall and put pressure on that wall from behind pushing it forward especially with our freeze and thaw cycles in the winter. By preparing a freely draining backfill with the pipe to exit that water out of the system we’re making sure that we control that water that could build up pressure behind our wall and push it forward. Soil is a poor draining material it will hold on to water whereas a clean clear aggregate with no fines will allow that water to flow right through it.
We also prepare 6 inches in front of the wall to ensure that we have a solid pad for that wall to sit on. Without 6 inches in front of the wall and 12 inches beyond the wall behind it for our drainage area and our base that wall could move. Preparing a proper retaining wall requires a lot of excavation because of this. This excavation includes 6 inches in front of the wall, the width of the wall block which is usually 10 to 12 inches, plus 12 inches behind the wall for our base material. That equals about 30 inches wide of base for our wall block plus the height of our drainage material depending on how high we are going with that wall.
Additionally we prepare our retaining walls based on manufacturer’s specifications. Typically if our wall is reaching 3 feet in height above grade we are installing it with a uniaxial geogrid. This is placed on top of our wall block and extends into our backfill area with another wall block being placed on top. This will stabilize our drainage material in behind the wall and reduce movements and pressure placed on that wall. With the height of the wall that we are building here we do not need that in this application.
We prepare our base and compact it separating it from our subsoil with a non-woven geotextile. We then screed a bedding layer on top of our three-quarter inch base of HPB or High Performance Bedding. By doing this we speed up the preparation of that initial course of the wall block which is the most time consuming forced to install everything else after this is just placing block on top of block and filling up that drainage area behind the wall as we build the wall up.
Once we get to our appropriate height we then cap our retaining walls typically with a natural stone cap. We like doing this because of the aesthetic appeal of these caps as well as their length that they provide us. The great thing about natural stone is that it is natural stone all the way through so if it chips you’re always just going to see natural stone. Whereas if a concrete product chips, you will see a difference in the surface versus the actual chipped area which will be exposed aggregate. With the caps being the most likely to chip because of sitting on them over time and walking on them we like to use natural stone because of this.
These caps are 4 feet long, 12 inches deep, and 2 inches high. They provide a 1 inch overhang in front of the wall block and 1 inch behind this particular wall block because it is only 10 inches deep. We like to install our caps with an overhang because of the aesthetic appeal and we can install hardscape lighting under this overhang. These wall blocks vary in depths to provide a three-dimensional contemporary appearance to this wall. We also decided to mix black and grey throughout this wall to add to that contemporary appeal.
We also like to install hardscape lighting underneath each cap. In this case we are installing 6 inches hardscape lighting about every 5 feet. This provides safety at night time as well as an aesthetic appeal to the outdoor living space providing light throughout the area.
With our lighting installed we then adhere the wall caps to the top of the wall using a Hardscape adhesive. And this is our final result on this project.
Materials Used:
6″ Hardscape Lighting