RANKINE'S THEORY AND THE COULOMB'S WEDGE THEORY ARE COMMONLY USED FOR THE DESIGN OF THE RETAINING WALLS.

Design of Retaining Walls:-- A vertical wall backed with earthy materials is subjected to a thrust which tends to overturn it as well as cause it to slide. In the design of a Retaining wall the thrust on the back of the wall due to earth pressure is calculated and the wall made of such a cross section (thickness) the weight of which will resist the movement due to the thrust and the resultant force on the base lies with in the middle third to ensure that there is no tension at the base. In cohesive soils the resultant should fall at or near the middle of the base, because in such soils unequal settlement of the toe may start a vicious circle. It is also necessary to check that the stress at the toe does not exceed the allowable bearing capacity of the soil and that the wall does not fail by sliding bodily forward on the base. The pressure at the back of the wall is greater the heavier the material and the less the angle of the repose. Two theories are commonly used for the design of the Retaining walls:(1) Rankine's theory and (11) Coulomb's Wedge theory. The Rankine and the Coulomb solutions give the same result for a vertical wall and a horizontal backfill if no wall friction is allowed for. Rankine's theory assumes the earth a homogeneous incompressible granular mass with no cohesion and is thus more appropriate for cohesion less soils, eg, sand, gravel, broken stone. It makes no allowance for adhesion, or for friction between the earth and the back of the wall.