We are well into summer and with the new normal we are all experiencing, a lot of us are spending more time at home planning projects in and around the house. I have decided to review some common wall types that are used in residential projects. In this e-newsletter, I will discuss landscape walls. As with most projects, we recommend that you contact a licensed contractor or design professional to assist you with projects of a significant size or complicated nature.
One of the important items to understand with landscape walls is at what height your local building department requires engineering. Most building departments require engineering for wall heights that retain more than three or four feet of soil for any type of site retaining wall.
Common site walls tend to use two methods to hold back soil:
Gravity walls
Cantilevered walls
Gravity walls use concrete or concrete masonry unit (CMU) block that is stacked with soils and geogrid fabric that combine to create a mass of soil that resists overturning. These walls use CMU block with pins between each layer of CMU. Soil is compacted in predetermined layers that coincide with the thicknesses of the CMU layers. The geogrid fabric connects to the pins placed between the CMU block and lays down over the compacted soil. Additional layers of CMU block are placed on pins along with layers of compacted soil. This continues up to the level of the design wall height. The CMU block, geogrid and compacted soil all combine to create a mass that resists overturning and sliding and creates a wall to hold back the soil behind it. The diagram below reflects this process.
Cantilevered walls use CMU block or concrete stem walls with reinforcing as well as reinforced concrete footings to resist the pressures from the soils behind the wall. The reinforced wall and footing combine to resist overturning and sliding. Once the concrete or CMU wall is constructed and complete, soil can be placed behind the wall. The diagram below shows this concept.
This was just a quick overview of some landscape wall types. If you are looking to complete a small project, there are resources available to build landscape walls that do not require engineering. As mentioned above, we recommend contacting a licensed landscape designer and/or contractor to assist with any site wall needs.