A cantilever wall is the most common structure used to hold back soil or other earth material. This soil, called backfill, is retained in positions that it would not normally be in, and would collapse under the influence of gravity without the retaining wall or if the structure failed. A cantilever wall is constructed from reinforced concrete and is built with a stem and base slab that is thinner than in other types of retaining walls. The base is comprised of a heel, which lies underneath the soil, and a toe that sits on the outer part of the wall base.
Cantilever construction is most effective when walls are less than 25 feet (about 7.6 meters) in height. A cantilever wall consists of cantilever footings, structural steel, tie beams, and concrete. Main steel is placed on the side that experiences the most tension, while nominal steel is placed in the opposite side and helps control structural shrinking when concrete is poured. The wall can be designed with a larger heel so that the base of the wall supports a greater amount of soil, which effectively becomes part of the wall’s mass. A retaining wall can be built with a larger toe if this design consideration is determined to be the most effective.
The outer surface of a cantilever wall can be covered with any material for decorative or durability purposes. There is no outer material that contributes to overall structural strength. It is the design considerations prior to this step that determine how strong the wall is, and professional consultation is almost always necessary in building strong retaining walls. Adding an outer covering may make it possible to blend the wall into its natural surroundings so it does not impose on the aesthetic quality of parks or nearby structures.
In designing a cantilever wall, engineers must take into account the pressures that can act to push the wall and those that prevent it from moving. The resistance of the wall to ground motion must be accounted for in earthquake-prone areas, where retaining walls often respond by tilting or rotating. Soil structure has an influence on the type of motion most likely to occur, and pre-construction engineering studies can determine the most resistant structural configuration. Soil type, ground water, construction material quality, and proper calculations of ground characteristics and wall reinforcement have significant impacts on how a cantilever wall performs in the real world.