RETAINING WALL, a wall usually of masonry, erected for the purpose of confining a body of Water in a reservoir, or for resisting the thrust of the ground behind it. Without such a wall the earth would slide, or lie at a considerable angle off the perpendicular. A bank of rock may hold itself, but gravel, sand or loose earth will slide and wash away and requires a retaining wall to confine it. The amount of resistance or strength in the wall depends partly on the material held back and partly on the angle of repose, that is the angle beyond which the sand, gravel, etc., will slide. The pressure against the wall is produced by the material filling the space between the angle of repose and the face of the wall. As a gen eral rule the thickness of retaining walls is made one-third the height of the bank which they are intended to support. In estimating the requisite thickness of the wall, account must be taken of the different ways in which it may be displaced, as by overturning, slipping along its entire base, or the giving way of the upper parts while the base remains. In reservoir
walls of masonry, the thickness should be made practically double that of ordinary earth re taining walls. In the case of loose soil, readily rendered fluid by rains, as at Panama, the greatest engineering difficulties have been, en countered. (See PANAMA CANAL). The great irrigation projects of the West and the Ashokan reservoir in New York presented vast problems in building retaining walls. Consult Cain,