Root Barriers :
The act of cutting off the roots of trees that are growing near a building and installing a barrier to prevent their reestablishment in the area where they are not desired is called installing a root barrier, a root wall, or root capping. The need for root barriers is related to the fact that expansive clay soil shrinks as it dries out. Any structure that expansive clay soil is supporting will move downward as the soil dries and shrinks. If the soil dries on one side of the structure and not the other, the soil shrinks where it has dried and remains expanded where it has not dried, causing the structure to experience differential settlement. Differential settlement can cause serious damage to a structure. A root barrier is usually installed between concrete foundations or flatwork and adjacent trees within their mature height from the foundation and where there is expansive clay soil to prevent tree roots from consuming moisture from the soil under the area of concern (figure 1). The barriers are installed so that they intersect imaginary radial lines extending from the trunk of the tree to the edges of the foundation. Root barriers can prevent damage to flatwork concrete such as walks and drives or to concrete slab on grade foundations. In some cases it is possible that differential settlement that has occurred because of shrinking soil can be reversed. The soil under a structure will swell or expand as it becomes rehydrated and in doing so will lift the portion of the structure that has experienced differential settlement back to near the level of the structure where differential settlement has not occurred.