Is there a retaining wall in your future?
The primary purpose of a retaining wall is to resist the lateral pressure of soil where there are steep slopes. These walls may be built with a variety of materials such as stone, brick, concrete block, wood timbers and even metal to name a few.
I appreciate the beauty of a well-crafted stone retaining wall. Unfortunately, a beautiful wall can fail because key components of the retaining wall system have been omitted. Materials that you don’t see in a retaining wall are as important as the aesthetic of the wall itself. Although the visible material that will be the face of the retaining wall is what gives the wall it’s beauty, the gravel base that supports the wall and the porous drainage aggregate (gravel) back-fill and drain tile that convey water away from the retaining wall support the structure. Regardless of the style of retaining wall one prefers, the same engineering principles are inherent in the design and installation of all properly built retaining walls.
Initial client meeting and upon inspection…
I met with a client, regarding a retaining wall that had been installed a couple years earlier and now appeared to be failing. He wanted my professional recommendation on what could be done to correct the problem. The retaining wall was located in the backyard and served to help create a more usable rear lawn that sloped significantly to the shoreline of the neighborhood association lake. The retaining wall turned out to be in fact two separate pre-cast concrete retaining walls that created a terraced planting bed between the lawn area and the shoreline. The entire neighborhood had similar sloping rear yards and chose to address the challenge of the steep slope adjacent to the lake with similar retaining wall systems. The adjacent neighboring retaining walls all looked intact and stable from distant observation. As I approached the lower retaining wall adjacent to the shoreline, however, it was apparent the wall was leaning noticeably forward toward the lake.
Upon further inspection, it became clear that the installing contractor failed to take into consideration the fact that water draining down the slope would collect behind the wall. Although not by design, the wall was acting, in essence, like a dam, holding the water behind the wall – not a typical function for a retaining wall. A second critical mistake was the contractor elected to “cut a corner” and backfill behind the wall entirely with topsoil rather than a porous, free-draining gravel material. This drain stone that was omitted from the wall is an integral material needed for success. The retaining wall is a system and it is only as good as the sum of its parts. By not properly addressing the draining slope and using topsoil for backfill, the contractor sealed the fate of the integrity of the wall.
Mother nature helped the process of failure along
Before the wall failed completely, we recommended the customer contact the installing contractor and ask them to correct the problem (at no cost to the owner). Unfortunately, time was not on my client’s side. Over the next week, there were torrential rains and the wall succumbed to the pressure of the saturated topsoil.
I’ve leaned over a lifetime in the “green Industry”, not to gamble with Mother Nature when it comes to water . . . as she has all the cards, and if you decide to “cut a corner”, I suspect she will show you four aces! Had the retaining wall been installed correctly according to industry standards, with filter fabric, drain stone and drain tile, this wall failure would have never happened. For the installing contractor, the omission of drain stone ended up costing an excessive amount of time and money.
Professionally built, a retaining wall can be a beautiful addition to any home and landscape. However, if installed without a thorough understanding of the engineering principals and components that make up a successful retaining wall system, your investment may also, too soon, become a pile of rubble. A properly built retaining wall will last a lifetime.
Want more information about retaining walls? Check out this blog. So, whether you are considering a retaining wall, a patio or an entire landscape in the near future, keep in mind, it is the things you don’t see that are just as important as what you do see!
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