Retaining walls are designed to hold back soil. Building retaining walls to keep hills or other elevated land areas from encroaching on your home and property requires precise planning and an understanding of the forces that work to defeat human efforts.
Retaining walls differ from dams in only one aspect – what they are holding back. For constructing retaining walls, the pressure of the soil against the wall and the effects of frost and freezing are the two key elements to address in planning. Improper design will cause the wall to fail.
The pressure created by the material being held back comes from more than just the dirt – the amount of moisture in the soil must also be considered. Wet soil can weight upwards of one hundred pounds per cubic foot, and retaining walls must be strong enough to handle this load; an appropriate drainage system for your area will help with controlling moisture buildup. In addition to the weight of the soil itself (wet or dry), anything resting on top of the wall or atop the material behind it must also be factored in.
As soil freezes it expands and presses against anything holding it back. Known as frost heaves, this pressure will wreak havoc on improperly constructed retaining walls. The impact of frost and freezing can be mitigated by making sure an adequate drainage system is in place.