Expansive soil is a material that exhibit volume change from change in soil moisture. Since expansive soils have a tendency to change their volume, they cause heavy distress to engineering constructions. 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. Either way, damage can be extensive. Expansive soil will also exert pressure on the vertical face of a foundation, basement or retaining wall resulting in lateral movement. Shrink-swell soils which have expanded due to high ground moisture experience a loss of soil strength or “capacity” and the resulting instability can result in various forms of foundation problems and slope failure.
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). The goal in moisture control is to take actions which will keep the expansive soil at a relatively constant level of moisture content. One system which is being used to treat expansive soil is horizontal and vertical moisture barriers. The purpose of the horizontal barriers is to prevent excessive intake of surface moisture, while vertical barriers used around the perimeter of the structure to cut off the source of water that may enter the soils. This system will maintaining long term uniform moisture conditions beneath the covered area. Vertical barriers should be installed to a depth equal to or greater than the depth of seasonal moisture change.
Another approach is surcharge load which applied on an expansive clay to control soil movement. With swelling pressure of the expansive soil determined, the surcharge load can be calculated.