Landscape Elevation

Retaining walls are useful structures that form a transition between areas of different elevation. Retaining walls allow steep, unusable slopes to be avoided. A retaining wall will make use of the vertical forces from the wall itself and any soil above the wall’s footing to resist the lateral forces from the soil being retained. This balance can be upset when additional lateral forces act on the wall. When water accumulates behind a retaining wall, the lateral forces acting on the wall increase. The more water that has collected behind a retaining wall, the greater the hydrostatic pressure on the wall will be. If the overturning moment (caused by the total lateral forces) exceeds the resisting moment (caused by the total vertical forces), the wall will fail.   There are several ways to prevent water from building up behind a retaining wall. Weep holes should be drilled through the wall. Weep holes allow water to escape from behind the wall. These holes should be regularly spaced in the horizontal direction. Retaining walls with a height greater than a few feet should also have weep holes that are regularly spaced in the vertical direction, forming a grid pattern. Another method for relieving hydrostatic pressure is to install a drainage pipe behind the wall. This should be a perforated pipe, to allow water to enter it through the length of the wall. The pipe can be located just above the footing, or can be located at a higher elevation. Taller walls may require ...