25th January, 2021

Common Retaining Wall Failures

In hilly areas, retaining walls are common sights because of how useful they are. These structures help to prevent earth from eroding off a slope and also allow for people to transform curved land into several levels of flat ground. Through retaining walls, property owners can prevent unwanted changes to their landscape and better utilize their areas. Retaining walls may also act as guards for nearby roads that run near hills, preventing rocks and soil from sliding down into passing traffic. However, working against gravity to support high ground is not easy. Without thorough consideration in design, retaining walls can shift and even collapse over time. Common retaining wall failures appear very similar with the walls bulging, cracking, and otherwise falling down. Therefore, we’ll discuss the main causes behind them as a means of categorization.

Unforeseen Weight

Sometimes the actual weight that a retaining wall must hold up is greater than its design allows for. This problem may arise because the property owner places extra objects or structures on the land that weren’t originally there. A retaining wall designer would not be able to anticipate such changes and the wall may not be strong enough as a result. It’s also possible that the property owner may not have spoken to the designer about certain details that could affect the wall.

For example, if they want to keep vehicles near it, this would add to the weight that the wall must sustain. When a retaining wall is put up against more than it can handle, it can give way to the earth that it is holding. Fortunately, experts can reinforce a wall when this kind of failure occurs by affixing it with tieback anchors. Pouring additional concrete to bolster the wall’s base either by increasing its width or elongating it is another option, too.

Weak Foundation

A common retaining wall failure may also develop because of an unstable foundation. This issue has to do with the earth that the retaining wall stands on more so than flaws that exist within its own components. If the ground is loose, any heavy weight that stands on top of it is liable to cause it to compress. When this happens, the ground and the structure on it will move. For a retaining wall, this leads to instability and unequal weight distribution that can then make it break apart or fall over. Designers must study the soil and remain aware of seasonal weather and the presence of water within it. Certain soil varieties can be too soft to provide a solid foundation for a retaining wall, while others may expand and contract because of water movements, freezing, and thawing. Factors like these can place limitations on how high and heavy one can successfully build a retaining wall in a particular area.

Inadequate Drainage

Inadequate drainage is chief among the causes of retaining wall problems. At times when precipitation falls and seeps into the earth or builds up behind a retaining wall, a powerful pressure develops. The water pushes against the wall with greater force than the soil does alone and seeks to find a way downward. A system of drainage is necessary to allow water avenues of escape before it can damage the retaining wall. However, some walls do not remove water as much as they should. You may observe some surface water pooling in the ground right next to the top of the retaining wall when it has nowhere to go. We can further subdivide insufficient drainage failures into two groups: saturated backfills failures and nonfunctional weep holes failures. Note that the two can appear together in one retaining wall.

Saturated Backfill

Backfill is the higher ground that the retaining wall holds up. Saturation occurs when it soaks up water and becomes heavier as a result. When it comes to proper drainage of a retaining wall, it takes more than underground pipes and holes to direct water away. Designers must also consider the types of materials that they place in the ground behind the wall. Anything that contains clay is unsuitable for soil near the retaining wall because it will absorb and hold water, hindering drainage. At the same time, clay expands, which only serves to further intensify pressure on the wall. Builders should grade the ground with gravel. This allows water to easily trickle through the channels that lead it away from the retaining wall.

Poorly Designed Weep Holes

Weep holes are the openings on the faces of retaining walls in which water can exit. They may get clogged with plants and other matter without the right surrounding materials. If this happens, they can no longer perform their roles and water pressure can increase to the point where the wall fails. Once again, gravel is necessary as a separator between the weep hole pipes and the more compact soil where plants grow. The pipes that lead to the weep holes themselves should have small perforations or some type of fabric netting that water can easily permeate.

Lack of Reinforcement

Large retaining walls that lack reinforcement are more likely to fall apart as they constantly contend with their loads. In the context of retaining walls, reinforcement comes in the form of anchoring structures. Anchors are usually metal rods with one end extending out of a wall to hold it in place and the other end buried in the ground behind the wall. To work efficaciously, anchors need to sit in precise positions along the wall. Should there be too few with too much space between each, unreinforced sections of the wall can bulge out and break. Anchors may also not exist deep enough into the ground to provide ample support to a retaining wall.

Armed with the knowledge regarding these causes of failure, you can create retaining walls that will remain strong. If you’re thinking about what building materials will make a retaining wall more reliable, contact Tangent and inquire about our structural lumber made from HDPE. Our plastic wood is both strong and resistant to outdoor forces, making it ideal for retaining walls.