How High Can I Put Dirt on a Brick Wall?

Gravity

• The problem with building a brick retaining wall is that the force of gravity working on the dirt that it is holding back can sometimes be too great for the wall to withstand. A cubic foot of wet soil can weigh as much as 100 pounds. If you multiply that number times the number of cubic feet your retaining wall is holding back, you will easily see that the amount of weight can quickly cause a wall to collapse. The gravitational forces working on the dirt are pulling it downward and outward at the same time. If dirt will be used to cover the top of the wall, this puts additional pressure on the wall to retain itself, let alone the dirt.

Measurements

• No exact system of measurement can be used to determine how much soil pressure your brick wall can withstand. Soil conditions in different geographic areas can affect the relative weight of the soil throughout the course of a year. One way to get a feel for how much soil your wall can retain is to simply drive around your area and assess the height of other retaining walls that have been in place and survived for a considerable period, as suggested by Tim Carter at Ask the Builder.

Limits

• As a rule of thumb, Tim Carter says to keep your brick retaining wall at 3 feet or less in height to be able to withstand the force of the dirt. The important thing to remember when building a retaining wall is that it becomes less stable the higher you build it. This also holds true if you are building the wall first and bringing in the dirt later. Try not to pile up your dirt higher than 3 feet, even if your wall is significantly higher.

Considerations

• It is possible to offset some of the force of the dirt in the way that you construct your wall. In general, friction between the bricks is likely to provide a decent bulwark against collapse. However, using mortar will solidify the wall, as will building it at a slight backward slope toward the dirt. This will help offset some of the push against the wall.