A gravity wall is a type of retaining wall. It gets its name because it uses the force of gravity to remain upright. Like other retaining walls, gravity walls are used to separate or terrace different levels of land. They are built against hillsides and designed to resist the lateral force of the earth behind them. Used in landscape design, gravity walls can transform uneven terrain into usable, flat surfaces.
In its simplest form, a gravity wall consists of stacked stones or blocks of concrete. Requiring no additional materials or technology, these walls have been around for thousands of years and can be found all around the world. Historically, gravity walls have been used to separate different levels of earth as well as to keep earth and water separate. A wall built from stacked stones needs to be repaired or rebuilt frequently, because the force of the earth or water behind it will eventually knock it over.
Modern gravity walls are usually built from hollow, interlocking materials, such as cinder blocks, which add frictional resistance to the force of the wall’s weight. Hollow building materials are advantageous because they are easy to transport and light enough to be lifted and maneuvered into position by hand. After the materials are in place, they can be filled with small stones, which give the wall greater weight and resistance; a gravity wall must be built heavy in order to hold back the earth behind it.
Thicker at the base than at the top, a gravity wall is often built slanting back against the earth it is retaining. Aesthetically, this incline, called battering, makes the wall appear strong, and seeing a backward curve is a sign that the wall is functioning properly. Over time, the force of the hillside will cause the wall to bulge outward. A gravity wall that appears to be leaning outward might be unstable and ready to be rebuilt.
Depending on the type of soil that needs to be retained, a gravity wall works best when it is no taller than 3 or 4 feet (1 or 1.3 m) high. Generally, the wall must be constructed to be half as thick at the base as it is tall, which can make building tall gravity walls impractical. Anchoring the wall to the hillside is recommended for gravity walls more than 4 feet (1.3 m) high. This anchoring provides extra stability and increases the life of the wall.