A retaining wall is a barrier that is specially designed and built to hold back other material and withstand pressure over a prolonged period of time. Often retaining walls are found in basements and hold back soil, but they can be built in other places as well.
The single most significant factor in considering a wall’s structural design and construction is understanding the stress factors that the retaining wall must endure over the course of its life. Lateral pressure on the wall is zero at the top and (in evenly packed substrate) increases proportionally to its highest pressure at the lowest depth.
Unless the wall is designed to retain water, it is crucial to have proper drainage behind it, because improperly drained groundwater can cause hydrostatic pressure to build. If the barrier is not correctly designed or installed, over time this increase in pressure can lead to many problems (like cracks, shifting, buckling and moisture penetration) and ultimately retaining wall failure.
Four of the most common designs used for retaining walls include :
Gravity walls rely on their substantial mass to resist lateral pressure from retained soil. They are sometimes designed to lean into the soil, offering improved stability and longevity. For small landscaping purposes, these are often created with mortarless stone or pre-fabricated interlocking concrete units. Gravity walls are often ’drystone’ and do not have mortar or sealant, offering natural drainage as well as some flexibility.
The main feature of a cantilevered wall is that it uses a ’lever’ to stabilize itself by redistributing the same lateral pressure trying to knock it down. The walls are typically an inverted T shape and have a large footing at the base. As pressure increases (which is highest at the bottom), the pressure on the foot keeps the retaining wall upright and stable. These walls require expert design and installation but use much less material than a traditional gravity wall.
Retaining walls fixed with piles extend below the visible portion of the wall so that lateral pressure from both sides keep the wall upright and stable. Piling walls are very versatile in design. If the soil is loose and lateral space is tight, sheet piling can be used to retain substrate. Conversely, if the piling is constructed sufficiently and can resist bending forces, the walls can take a high load.
An anchored retaining wall can be constructed in any of the ways mentioned previously but can also be further strengthened with cables, poles or other stays anchored in the material behind the wall. The anchor is often bored into the substrate and expanded mechanically or by injecting concrete through it, which expands to form a bulb. This method of load-bearing is technically complex but can be extremely strong or employed when a thin wall is needed that would otherwise be structurally insufficient.
Retaining Wall Failure
All structures can be compromised, regardless of how durable they seem. This occurs naturally, but can be accelerated by a number of reasons including improper drainage, erosion, insufficient construction, poor design and poor material quality.
It is obvious when a wall fails because there will be visible damage and debris, but usually there are obvious signs of distress well ahead of time. If it the wall is bending in the middle, cracking, tilting or leaking, it needs to be repaired or replaced. Even excess odor (a signal of moisture intrusion and structural weakness) can be a sign that a structure is in need of maintenance. Replacing a retaining wall is expensive and time consuming, but repairs require only a fraction of the time and expense that it would take to tear it down and construct a new one.
Repairing a Retaining Wall
There are several options for repairing a retaining wall, depending on the specific nature of the problem. Often the best solution is to use a wall anchor such as the Wall Lock™ system. Wall anchors, when installed by a professional, increase retaining wall strength helping to restore it to a functional condition. It’s important to make sure the wall anchor has been pull-tested after deployment to ensure the most stable installation possible.
Load-bearing walls are obviously extremely important and should only be inspected and serviced by trusted professionals.