Retainer walls are another term for concrete columns. While they may look simple, they are also quite complicated, requiring many steps to be taken before they are ever installed. First, a foundation is required to provide an adequate base for the piers. The width of the piers will depend on the depth of the excavated area. Retainer walls can be installed using either in-place or floating piers. In-place piers are anchored into the ground below and pre-drilled for the wall installation. Float piers are not drilled in the ground but simply stand on the surface. Concrete piers are cemented into the ground above the excavation to provide a strong, stable structure that is secure from erosion and moisture. The thickness of the material necessary to support the piers will depend on the depth of the excavated area. Before the concrete columns can be poured, the column must be excavated to the proper depth. It is necessary to have the column drain well so it does not dry out...