Retaining Wall

A retaining wall is a rigid, engineered wall built to support soil laterally so that ground can be held at two different levels on either side of it, allowing a slope steeper than the soil could otherwise hold on its own, a technique commonly used in hillside farming and road construction. The wall works by resisting the lateral pressure of a wedge of soil that would otherwise slide downslope under gravity, and setting the wall further back from the slope reduces the size of that wedge and the pressure it exerts; drainage behind the wall is essential, since trapped water builds up hydrostatic pressure that can undermine the structure, while a drystone wall, built without mortar, typically drains itself. The source consulted for this entry names no single inventor or origin date for the general technique; earlier in the twentieth century, taller retaining walls were commonly built as gravity walls made from large masses of concrete or stone, before lighter reinforced and engineered designs became widespread.