Segmental Retaining Walls
Follow along with Randy Brannan as he walks through the process of building a retaining wall.
In our most recent video, Randy Brannan, owner of Roanoke Landscapes, walks us through the process of building a corded Allan block retaining wall.
While projects differ site to site based on preferences of the client or restrictions in your property’s landscape, there are quite a few lessons to be gleaned from this instructional start to finish video. This article seeks to serve as a written overview of the content covered in Randy’s video. For visual clarification and to hear more information from a professional working who has been in this trade for over two decades, we encourage you to watch the video!
On this project, Roanoke Landscapes builds a roughly 9 foot tall retaining wall around the perimeter of a pre-existing in-ground pool. Before we arrived at the property, a wooden retaining wall had begun to give out, raising concerns for the safety of the pool and the pool deck. In order to begin on this project, as Randy explains, he had to acquire a permit through our municipality because the retaining wall would be taller than 3 feet. Additionally, because the wall would also be greater than 6 ft in height, Randy acquired a supplemental design plan from an engineer outside of our company. It’s important to take additional precautions, and extra care when building a wall this tall that needs to support a large weight capacity.
Ensuring Structural Integrity:
When building a retaining wall, the rule of thumb is “the higher the wall, the further you will need to go into the ground.” Because, as Randy explains, there is a factor called Global Stability or the recognition that walls built on a slope have inherent instability. Not to worry! As members of the National Concrete Masonry Association (CMA) we follow strict guidelines and best practices:
From the beginning of a project, we try to steer clients into picking CMA approved products. This project used Chorded Allen Block. Each individual block weighs 85 pounds.
With this wall, as with any wall, we excavated one inch back into the ground for each vertical foot of the wall.
Spend additional time ensuring your first course of blocks (or base block) is level. If not, it’s almost impossible to address and fix as you scale upward.
Address hydrostatic pressure. Where will water escape to so it doesn’t build pressure behind the wall? Roanoke Landscapes places a corrugated pipe with pvc drainage installed at the bottom of the wall to allow for the expulsion of water from behind the wall.
Additionally, we used a product called Geogrid to increase the structural integrity of the wall. The geogrid was placed every 16 inches as we built up, and each sheet ran 6 ft in length. The geogrid works to stabilize the wall with the compacted backfill behind, running both across the backfill and in between the courses of block. Geogrid covers 60% of your wall.
As you build, set each course back one inch from the course below. This leans the wall into the earth, working with gravity and friction to hold the earth behind the wall, effectively wedging the soil in place.
Use suitable backfill, meaning stone (we use #57 Limestone). Backfill can be native soil if it is of sufficient integrity to actually have resistance to it - you can not backfill with only mud or clay, it must be compatible. In this case, we used #57 stone for the first few courses of the wall, then switched to a mixture of excavated dirt from the site and #57 stone.
Each course must be compacted and level. We bring 6 - 8 inch lifts of stone and then compact using a plate compactor for the footings (the plate compactor doesn't work well with anything other than stone). Jumping Jacks get used with both stone and dirt, and are used after the first courses of block are secured into place.
Not a “Do-It-Yourself” Kind of Job
As you might be realizing, building a retaining wall, especially of this size, has hidden variables that must be considered to ensure the structural integrity of your project. A more arduous task than most assume. This is why we believe it’s not a do-it yourself project unless you have the appropriate tools, skills, and permissions from your municipality.
Finishing the Job & How Long to Expect the Project to Last:
When you hire Roanoke Landscapes for a project like this, you can expect a clean job site, professional staff, and communicative project managers. As demonstrated in the video, we reseed and lay hay to disturbed soil upon completion of the project. Our crews are reliable, skilled, and have been doing this for many years. They work efficiently, completing 100 sq ft a day for the majority of the wall, and for baseblock around 50 - 60 sq ft a day.
Cost:
The price you’ll pay to have your project completed varies depending upon several factors. For example:
Size of the project.
Difficulty of the job or landscape. If we’re unable to bring in equipment due to a steep hill or access issues, meaning our crews have to carry the blocks or other materials, it will affect your overall cost.
Having to remove or haul away excavated material increases the price of the project.
Utility issues can affect cost.
If you have further questions, would like to see Randy address an issue in more detail, would like to see him address an entirely new topic, or would like an estimate on a project for your property, reach out!
~RL