GEOTECHNICAL PROPERTIES OF SOIL SUSCEPTIBLE TO GULLY EROSION IN KARST AREAS OF SOUTHERN APPALACHIANS

Thick blanket of clay-rich red soil, known as terra rossa is commonly found along fractures, cavities, and between bedding planes of the calcareous, cavernous rocks of southern Appalachians. Soil erosion is a serious and widespread land degradation problem in terra rossa soil. Proper understanding of the soil’s pedology, and geotechnical behavior can lead to (i) better site characterization for safer development, and (ii) restore severely eroded bare soils. The objective of the study was to investigate the physical and geotechnical properties of terra rossa soil on erosion processes. Four one-meter soil cores were collected from various locations within the Knox group rock of southern Appalachians. Total twenty samples were extracted from the cores, and laboratory analyses were performed. The analyses included, soil pedology (moisture content, pH, color, mineral content), and geotechnical property characterization (grain size distribution, atterberg limits, porosity, hydraulic conductivity, and shrink-swell potential). The soil profile above Knox rock exhibits distinct vertical zoning in terms of color, mineralogical and textural characteristics. Quartz, kaolinite, and hematite are the dominant mineral phases in the upper horizon of the soil profile. The underlying horizon, governed by leachate action is dominated by clay minerals like illite, vermiculite and chlorite. In the saprolite zone, weathered relic calcite and dolomite are present. The grain size distribution indicated a similar trend with reduction in sand sized particles with depth. The red soils are non-swelling, low plasticity silt and clay. The soils are well drained in the upper horizon and exhibit reduction in porosity and hydraulic conductivity with depth. The reduced hydraulic conductivity in the lower horizons however reduces the drainage potential. Although the study eliminates the potential for structural damage due to swelling, but the likely changed shear strength parameter can be critical in geotechnical design projects. Additionally precipitation of iron oxide can reduce the drainage characteristics of the soil. This eventually builds up the hydrostatic pressure, and might be detrimental to civil structures, can create soil erosion and landslides in slopes if proper drainage is not installed.