It is an engineered structure constructed to resist lateral forces imposed by soil movement and water pressure. Retaining walls are commonly used in combination with fill slopes to reduce the extent of a slope to allow a road to be widened and to create additional space around buildings. The three types of retaining walls are gravity, cantilever and anchored. The common terminologies used in retaining wall are shown in Figure 25.


The most important consideration in proper design and installation of retaining walls is to recognize and counteract the fact that the retained material is attempting to move forward and downslope due to gravity. This creates lateral earth pressure behind the wall which depends on the angle of internal friction and the cohesive strength of the retained material, as well as the direction and magnitude of movement the retaining structure undergoes.


Lateral earth pressures are zero at the top of the wall and in homogenous ground increase proportionally to a maximum value at the lowest depth. Earth pressure can push the wall forward or overturn it if not properly considered. Also, any groundwater behind the wall that is not dissipated by a drainage system causes hydrostatic pressure on the wall. Unless the wall is designed to retain water, It is important to have proper drainage behind the wall in order to limit the pressure to the wall's design value. Drainage materials will reduce or eliminate the hydrostatic pressure and improve the stability of the material behind the wall.


Figure 25: Typical View of Retaining Wall