Expansive soils can cause serious problems. According to the Arizona Geological Survey, expansive soils in the state cause millions of dollars in damage annually to roads, swimming pools, driveways, walls and foundations. The soil expansion coefficient, which helps determine the expansion ability of a soil type, aids builders in creating structures resistant to damage from soil expansion. You may need to know soil expansion coefficients for DIY building projects; this information can commonly be provided by your local building codes. Does this Spark an idea?
Definition
An expansion coefficient is a numerical constant used to describe the degree by which a material expands. Expansion coefficients appear most commonly in relation to thermal expansion -- the expansion of materials as temperature increases. A soil expansion coefficient describes the rate at which soil expands as it absorbs water. The expansion coefficient of a material appears as a decimal that represents its expansion rate in a specified unit, such as inches or millimeters. Determining actual expansion entails multiplying the coefficient by a variable - in the case of soil expansion, the amount of water absorbed.
Expansive Soils
Expansive soils contain clay minerals capable of absorbing water. As these minerals absorb water, they expand, causing the soil to expand. Common clay minerals in expansive soils include smectite, bentonite, beidellite, vermiculite and chlorite. The pressure of expanding soil can easily damage manmade structures in the soil. When expansive soils dry up and begin contracting, they crack and fissure; cracked, dry soil can expand extensively in the presence of moisture. According to Geology.com, these soils can enlarge their surface area by as much as 10 percent.
Soil-Expansion Coefficients for Homeowners
In most cases, you don't need to know expansion coefficients for the soil around your home. Engineers, architects, builders, soil scientists and geologists are the only people who really need this information. Ostensibly, you need a basic understanding of your soil expansion coefficient if you undertake a DIY construction project on your land. For instance, if you build a shed in expansive soil, you need to build that shed with your expansion coefficient in mind to help avoid damage to your shed. You local building code should provide guidelines for building in expansive soils in your area. By following building codes, you can avoid the complex math and science associated with soil-expansion coefficients.
Determining Soil Expansion Coefficient
You cannot use generalized information about soil types to determine expansion coefficient because all soils, even those of similar types, exhibit slightly different compositional elements. For instance, two clay mineral soils containing smectite and bentonite may exhibit different expansion coefficients based on the percentages of each mineral present in the soil and the total volume of that soil in an area. The United States Soil Conservation Service uses the COLE test to determine the expansiveness of soil. This entails the use of plastic resin, suction devices, numerous soil samples and complex formulae.
Tags: soil expansion, expansion coefficient, expansion coefficients, expansive soils, soil expansion coefficient, building codes, clay minerals
