Expansive clay

Expansive clay is a clay soil that is prone to large volume changes (swelling and shrinking) that are directly related to changes in water content.[1] Soils with a high content of expansive minerals can form deep cracks in drier seasons or years; such soils are called vertisols. Soils with smectite clay minerals, including montmorillonite and bentonite, have the most dramatic shrink-swell capacity.

This article is about natural soils that swell. For lightweight aggregate product, see Expanded clay aggregate.

The mineral make-up of this type of soil is responsible for the moisture retaining capabilities. All clays consist of mineral sheets packaged into layers, and can be classified as either 1:1 or 2:1. These ratios refer to the proportion of tetrahedral sheets to octahedral sheets. Octahedral sheets are sandwiched between two tetrahedral sheets in 2:1 clays, while 1:1 clays have sheets in matched pairs. Expansive clays have an expanding crystal lattice in a 2:1 ratio; however, there are 2:1 non-expansive clays.[2]

Mitigation of the effects of expansive clay on structures built in areas with expansive clays is a major challenge in geotechnical engineering. Some areas mitigate foundation cracking by watering around the foundation with a soaker hose during dry conditions. This process can be automated by a timer, or using a soil moisture sensor controller. Even though irrigation is expensive, the cost is small compared to repairing a cracked foundation. Admixtures can be added to expansive clays to reduce the shrink-swell properties, as well.[3]

One laboratory test to measure the expansion potential of soil is ASTM D 4829.

See also

References
  1. Hobart king, "Expansive Soil and Expansive Clay: The hidden force behind basement and foundation problems". Geology.com. Accessed March 19, 2015.
  2. Science.gov clay related articles
  3. Biswas, Rajdip, and Nemani Kriscna. “Effect of fly ash on strength and swelling aspect of an expansive soil.“ Department of Civil Engineering National Institute of Technology. Visited on November 19th, 2015.
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