Roots cause both direct and indirect damage to infrastructure.
Direct damage is related to the forces exerted by expanding roots
and typically affects only light infrastructure such as roads,
curbs, and sidewalks. Indirect damage is associated with soil
movement resulting from changes in moisture content precipitated
by roots. In cases of indirect damage, concrete cutoff walls
prevent root growth in undesired areas. A typical application of
cutoff walls is to exclude roots from soils near the foundations of
buildings. This is necessary because root moisture absorption
causes soil shrinking and differential settling, which causes significant
structural damage to foundations and walls. Cutoff walls
are especially prevalent in areas characterized by plastic clays
such as London, U.K. They are installed by digging deep
trenches between trees and the desired protection area. These
trenches, often many meters deep, are filled with concrete slurry,
thus creating a subterranean wall. In extreme cases, cutoff walls
are secured to the bedrock