Expansive soil is a material that exhibits volume change from change in soil moisture. Foundation soils which are expansive will “heave” and can cause lifting of a building or other structure during periods of high moisture. Conversely during periods of falling soil moisture, expansive soil will “collapse” and can result in building settlement.

One approach which can be effective in mitigation of swelling and shrinkage of expansive soil involves application of measures to protect the soil mass from excessive wetting or drying (moisture control). One system which is being used to treat expansive soil is horizontal and vertical moisture barriers. This system will maintain long term uniform moisture conditions beneath the covered area.