Saturday, December 22, 2007

Building Homes & Roads on Western North Carolina's Unstable Soils Can Cause Landslides

Roads built of micaceous soil material are subject to landslides.
Acid leachate stains of metasedimentary rock.

According to Michael Sherrill

"Crystalline rocks, such as mica schist and mica gneiss, are high in mica content. This rock tends to produce soils and saprolite high in mica content. Soils and underlying saprolite erode easily and are difficult to compact when used as earthen foundation material. Soils such as Fannin and Chandler have a high mica content and are poor as engineering materials. Micaceous rock tends to weather deeply. Most micaceous saprolite commonly extends tens of feet below the soil surface."

"The relationship of soils to metasedimentary rock formations in western North Carolina is difficult to interpret. Metasedimentary rocks generally are composed of thin beds that dip at some angle from the horizontal. When slopes parallel the bedding dip, soils are very susceptible to landslides. Some thin beds contain sulfur compounds and produce a yellowish leachate during road building. This leachate is very acid. When this leachate enters nearby streams, fish kills and other aquatic damage commonly occur. The map unit descriptions in modern soil surveys discuss this soil/geologic problem and discuss possible solutions." For more information about Western North Carolina landslides and unstable soils please visit 1979-1999: Two Decades of Progress in Western North Carolina Soil Surveys
Michael Sherrill, Soil Scientist, Natural Resources Conservation Service

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