Irrigation, Drainage, and Landscaping for Expansive Soil

Abstract

Expansive soils are known for their moisture sensitiveness—they will swell when given access to water and shrink when they dry out. For a shallow foundation, this causes heave during the rainy season and settlement during the drought when the clays dry out. This causes cycles of up and down movement of the foundation, causing cracking and fatigue to the structure. Excess irrigation or poor drainage are often blamed as the causes of damage to structures on expansive soils. A more damaging situation could be the lack of irrigation during a drought, causing desiccation of the clays. If trees are located in close proximity to the building, the roots can grow beneath the shallow foundation and then extract moisture during the drought. This will cause the clay to shrink and the structure to settle. The goal in dealing with expansive soils is to try to maintain a constant soil moisture. The elimination of planter areas around the perimeter of the building or surrounding the building with concrete flatwork can help reduce moisture changes.