Expansive soil
shrinks and swells in cycles.
Soil survey maps contain a description of each major soil type in a survey area. Soil that has a high degree of shrinking/swelling potential is referred to as "expansive soil." Expansive soil shrinks when dry and expands when wet. The relative change in volume of soil when it is wet and then dried is an important consideration for construction and landscape. Expansive soil exerts pressure on concrete walls, driveways, house foundations and pipelines. Landscaping near buildings on expansive soil should be a xeriscape type that uses little water. Trees should be planted at least 15 feet from the building. Water drainage is critical to long-term maintenance. Does this Spark an idea?
Texture
Soil with a dense, clay-like texture is expansive. Texture determines the rate at which water moves through saturated soil. Clay soil contains particles less than 0.002 mm in diameter. Particles are minute pieces of mineral with pores in between containing water and air. Clay soil has smaller pore space but more in number and therefore holds more water. Expansive clay soil feels smooth and silky to the touch when wet and powdery-fine when dry. It forms a ribbon when moist and stretched. It forms a cracked hard-pan surface as it dries out.
Structure
Structure of clay soil is dense and closely packed. Soil structure is determined by the overall arrangement of aggregation of particles. Soil aggregates are particles that bind together with minute pieces of living organic matter, including microorganisms. Soil structure is affected by tilling practices, moisture level, freezing and thawing, root growth, earthworms and driving or walking on its surface. In home gardens, clay soil structure can be amended by adding organic matter.
Corrective Measures
Expansive soil on building sites is maintained long-term through proper drainage and appropriate choice of plants. Ground covers reduce moisture fluctuations and minimize soil movement in the shrink-swell cycle. Creeping juniper, hardy yellow iceplant and stonecrop are among the ground covers recommended for expansive soil. Texture and structure of clay soil in the home garden is adjusted by the addition of organic matter such as compost. Compost contains billions of living organisms in each small amount. The natural biological activity of microorganisms improves soil texture and structure.
Tags: clay soil, organic matter, expansive soil, Expansive soil, Expansive soil shrinks, minute pieces, soil shrinks
