Retaining walls of very moderate height may be constructed in L-shaped sections without buttresses, by thickening the walls at the base, and by using sufficient reinforcement to resist the transverse stresses, which, of course, have their maximum value at the base of the wall (Fig. 114). From the standpoint of cubic yards of concrete and pounds of steel, such a wall .is not as economical as the buttressed wall, but the forms are very much more simple and are less expensive. A low wall is always made much thicker than mere theoretical computation would call for, and in such a case the additional thickening for the L design might be little or nothing. For high walls - twenty feet or more - the economy utterly disappears. The mechanics of this form of wall is quite different from the form with buttresses. In the case of a buttressed wall, the vertical plate between the buttresses is merely designed to resist the bursting pressure on a slab which has the buttresses as abutments. When there are no abutments, the pressure on each unit vertical strip of the wall must be computed; and the strength at every section (vertically) must be computed on the basis of a cantilever acted on by horizontal forces. This practically means that the moment increases from zero at the top of the wall to a maximum at the base just above the base-plate. Of course the mechanics of the wall taken as a whole, in its pressure on the subsoil, is identical with that of the other form of retaining wall.

Fig. 113. Section and Plan of Retaining Wall, Showing Reinforcement.

Fig. 113. Section and Plan of Retaining Wall, Showing Reinforcement.