Soils and soft rock that tend to swell or shrink due to changes in moisture content are commonly known as expansive soils. Changes in soil volume present a hazard primarily to structures built on top of expansive soils. Most engineering problems caused by volume changes in swelling clays result from human activities that modify the local environment. They commonly involve swelling clays beneath areas covered by buildings and slabs or layers of concrete and asphalt, such as those used in construction of highways, canal linings, walkways, and airport runways.
Houses and one-story commercial buildings are more apt to be damaged by the expansion of swelling clays than are multi-story buildings, which usually are heavy enough to counter swelling pressures. However, if constructed on wet clay, multi-story buildings may be damaged by shrinkage of the clay if moisture levels are substantially reduced, such as by evapotranspiration or by evaporation from beneath heated buildings.
The most obvious manifestations of damage to buildings are sticking doors, uneven floors and cracked foundations, floors, walls, ceilings, and windows. If damage is severe, the cost of repair may exceed the value of the building.
Probably the greatest amount of small building damage has impacted those constructed when clays were dry, such as during a drought, followed by soaking rains that prompt swelling of clays. Other reported cases of damage involve volume increases due to moisture from broken or leaking water and sewer lines, watering of lawns and shrubbery, and modifications of the surface that produce ponding.
Many of the buildings, critical facilities, infrastructure and lifelines, and hazardous materials facilities in the City of Plano are exposed to the expansive soil risk. However, increased awareness of risk and improved building practices over the past several decades have helped to mitigate this risk.
The following are some tips that you can consider to help mitigate the risk of your home being damaged by expansive soils:
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Remove large trees and bushes that grow within ten feet of the house. Large plants tend to dry out the soil unless a drip irrigation system is installed.
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Use drip irrigation systems to water vegetation. Drip irrigation minimizes the amount of water used and maintains a more even soil moisture content.
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Ensure that downspouts and roof gutters do not deposit water close to the foundation. If possible, redirect roof water into closed pipes that empty onto the street or other suitable location.
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Slope the soil or concrete away from the foundation. Such construction aids runoff and helps prevent water from puddling or seeping into the ground.
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