What Are the Counterforts in Counterfort Walls Made Of?

Counterfort Walls

• Cantilever walls are among the most common forms of retaining walls, with a stem wall supported by a concrete footing. Footing and foundation structures for basements are cantilever types of walls. These walls are generally considered suitable for heights up to 25 feet. Once heights exceed 25 feet, supports — counterforts — are added to the backfill side of the cantilever wall for additional strength. The counterfort design adds resistance to the forces bearing on the wall, with an economical use of resources.

Counterfort Design

• Counterforts are triangular beams connected vertically to the stem wall and footing or slab, spaced at regular intervals. All three components — footing or slab, stem wall, and counterforts — are constructed with concrete. The counterforts tie the footing and stem wall together, and increase the wall's resistance to shear and bending forces. The weight of the concrete counterforts also contributes to the added strength of the wall. The counterforts act as tensile members on the backfill side, resisting forces pulling at the wall.

Buttress Walls

• When the concrete supports are added to the level side, it becomes a buttress type of retaining wall. Buttress supports act as compression members, resisting forces pressing on the wall. For both counterfort and buttress design, the stem wall is constructed as a continuous slab, and the loads of earth and water pressures should be transferred to the supports. Reinforced steel connects the components, and often the stem wall and footing are poured monolithically — in one pour.

Additional Considerations

• Counterfort walls are used more frequently than buttress walls because the exposed face is free of obstructions, leaving more space for development. The counterforts are generally at center-to-center spacing intervals of about 30 percent to 70 percent of the total wall height. The base of the stem wall is thickened by about 10 percent of the total wall height, and the base slab or footing thickness is constructed according to the same proportions.