At first glance, retaining walls may not look like they are doing much work. However, they are actually holding back large volumes of heavy soil, fighting erosion to keep it all in place. This soil can get heavy, especially when wet. Imagine lifting up a big bag of soil after a rain, and you’ll get a small sense of the kind of pressures that a retaining wall is under. When you are designing or installing a retaining wall, it is important to know how much weight it can safely hold. If the wall can’t hold the soil behind it, you need a new design.
How Much Weight Can a Retaining Wall Hold?
The exact amount that a wall can hold back depends on its design. However, a well-constructed paver retaining wall that is 4 feet high and 15 feet long could hold back up to 20 tons of weight. That might seem extreme, but it’s important to realize that the average weight of even a single retaining wall block is 53 pounds. Add in friction and adhesives, and together even a small retaining wall built out of them can have a lot of stopping power.
There are many factors that determine how much weight the wall can hold, but one of the most important is the type of retaining wall.
There are four basic types of retaining walls:
- Gravity wall: A gravity wall is the weakest and resists the pressure of the soil behind it only with its own weight. Small gravity walls may be used in gardens and some yards.
- Piling wall: A piling wall extends deep below the wall, using this extra length to better resist the weight of the wall. The downside is that you must dig quite deep to install these walls.
- Cantilever wall: A cantilever wall has a small “arm” extending behind its base. This allows the wall to use the weight of the dirt to better hold itself in place.
- Anchored wall: The strongest wall, anchored walls are held up by cables extending behind them into soil or rock.
For many homes with steep slopes, it may be necessary to use a type of wall that relies on more than just gravity to hold it in place.
How Much Weight Does It Need to Hold?
Are you trying to sort out what your backyard retaining wall needs to hold in order to stay standing? Don’t make the mistake of adding up the weight of all the soil behind the wall. Actually, only a small portion of the soil against the wall will put pressure on it. So long as the soil back a few feet has been undisturbed, it will remain in place even if the wall falls. You only need to worry about the weight in front of this beyond what is called the failure plane.
There are complex ways to calculate the failure plane behind your wall, but this is best left to the professionals. However, you should know that the failure plane looks like a sloping hill. Meaning, the taller the wall, the further the plane is from the wall, and the more soil the wall needs to support. Every foot you add to your wall will require significantly more strength than the last.
What’s the Difference Between a Retaining Wall and a Load Bearing Retaining Wall?
This is actually a common misconception built around some confusing naming conventions.
Retaining walls, by definition, are built to resist horizontal force. That typically means preventing dirt and earth from sliding horizontally, sometimes on an upward slope.
Load bearing walls, by definition, are built to resist vertical force. That means holding up a patio, balcony, or second story.
For a wall to be both a retaining wall and a load bearing wall, it would have to resist forces in both directions. While this isn’t the most common application, it’s absolutely possible.
Therefore, don’t be worried about the ability of a retaining wall to hold back massive amounts of force, even if it’s not called a “load bearing retaining wall.”
Estimate Soil Weight and Wall Strength
Retaining walls should be engineered. We strongly suggest you work with professionals to estimate how strong your wall should and will be.
How to Build the Strongest Retaining Wall
- Compact the base material, but not the soil around it. The soil will natural settle and form a stable trench for your wall.
- Ensure good drainage. Using impervious soil as backfill, landscape fabric instead of plastic tarping, and installing an actual drain near the base means water won’t pool up behind your wall and wreak havoc.
- Installing a reinforcing grid of pin system can provide your wall with superior stability.
- As always, it’s best to rely on the experts.