A basement wall holds back soil, which pushes inward towards the basement. A basement wall also typically has a floor at its top, which services to push back in the opposite direction and balance the forces from each side of the building. On the other hand, a structural retaining wall holds back soil, but does not have the benefit of a floor at its top to resist the horizontal pressure of the soil. Consequently, the structural retaining wall needs to be designed and constructed much stronger than your average basement wall so that it is not pushed horizontally by the soil pressure.
The horizontal forces in a structural retaining wall that counterbalance horizontal soil pressure behind it include the friction on the bottom of the footing, the soil in front of the footing toe and reaction of the concrete slab (refer to the sketch).
The horizontal force of friction on the bottom of the footing is greater when the load on top of the footing is greater. This is similar to the friction on the bottom of an iron. An iron is harder to push along the top of the ironing board (i.e., more bottom friction) when the user presses down harder on the top of the iron.
The horizontal force of friction on the bottom of the footing is also greater when the surface area on the bottom of the footing is greater, just as a larger sized iron is harder to push.
The structural retaining wall has a large “heel” so that the weight of soil above it creates high friction on its bottom. The large heel also has a large bottom surface area to maximize the friction. When put together, the structural retaining wall has the large heel to resist horizontal soil pressure from the retained soil. In most cases, your typical basement wall does not need to have a large heel because it has a floor slab to resist the horizontal soil pressure.
We hope you’ve learned a little more about structural retaining walls through this blog and if you need one designed, let Team Engineering become your go-to engineering firm!