Visible signs of cracking, sinking, and leaning are the symptoms of a failing retaining wall, but what is the root cause for these unsightly blemishes and potentially dangerous malfunctions? Every wall has a lifespan and will eventually need to be replaced, but chances are that improper installment or maintenance issues are the cause for an early demise. Identifying the reason for a failing wall in your residential landscape is important to repairing or replacing it.
Can’t Escape Gravity
The purpose of a retaining wall is to hold back large amounts of earth. However, gravity is constantly pulling everything down. A classic battle between an immovable object and an unstoppable force. Who will win? Gravity eventually, but a well-built wall can at least last a lifetime. However, when the proper construction methods are skipped, the wall will lean, bow, and split at the joints. An often forgot about feature of retaining walls is the step-back construction of the wall. The
step-back design counteracts the force of gravity. When done correctly, it should look like the wall is leaning into the slope, not away from it. A good example of this feature is the Hoover Dam.
Some other basic practices skipped during construction include using the correct mortar or adhesive, installing the necessary pins and geogrid for reinforcement, and most importantly using a material that is specifically designed for retaining walls. Some natural stone, prefabricated block, or other landscape materials simply don’t work well as retaining walls.
Water is the Enemy
Similar to most construction, water is the enemy for landscape projects. Water in the form of rainfall is incredibly powerful and can wreak havoc on a poorly built retaining wall. It can erode the wall, wash out the soil around it, and weaken points in the construction. Water will always take the path of least resistance, and when rainfall is not properly designed for, the path of least resistance will be over, under, behind, and even through a built wall. Think of the Grand Canyon and how much stone has eroded over the years to create that amazing landscape. The same effect can happen to retaining walls on a much smaller scale. However, when the amazing landscape is your yard and retaining wall, seeing it wash away is breathtaking for a completely different reason.
The Leaning Tower of Pisa in Italy is the most famous structure built on a weak foundation. The depth below ground was far too shallow and the soils were unstable during its construction. A shallow base and thin footing below a retaining wall can have the exact same effect as the Leaning Tower of Pisa. Soils are constantly shifting, settling, and compacting. In colder climates like Minnesota, the ground will expand and push even more due to the freeze-thaw cycle. As more weight is put on a retaining wall, the soils underneath need to be extremely stable or else the wall will shift and sink too.
Retaining walls can be very expensive to build and repair. When they fail, the urgency to fix them is much higher than other landscape work in the yard. That’s why it is extremely important to inspect for signs of cracking, sinking, and leaning. Erosion and poor construction can all be factors to a prematurely failing wall. We highly recommend that if given the opportunity, to consult an experienced landscape company to build a retaining wall correctly from the start.
Read about the Keys to a Stable Retaining Wall to resolve these symptoms.