This is often for the purpose of protecting structures or other plants, but root barriers are also used to preserve soil moisture.
Root barriers were developed to stop trees damaging buildings.
Concrete was historically a common material but since 1992 plastic root barriers have become more common due to their resistance to cracking caused by soil and moisture movement.
[1] They are also moisture-proof, which can be useful to preserve buildings on clay soils by preventing moisture escaping laterally.
In particular, walnut trees secrete the chemical juglone which is toxic to other plants but the use of root barriers can prevent the yield reduction that would normally occur when walnut trees are alley cropped with maize as often occurs in the American Midwest.