Graphical and digital slope stability analyses for Giles County, Virginia

Slope stability maps are useful in seismic hazard evaluation, land use and emergency planning, and geomorphological studies. Such maps were generated for Giles County, Virginia (approximately 1000 square km) by the synthesis of data sets for topographic slope, surficial deposits, geologic structure, and seismic slope response. Both graphical and digital techniques were used to generate a topographic slope map. Relevant limiting slope angles according to seismic shaking and land movement studies are <15, 15-35, and >35 degrees. These slope categories were integrated with geologic factors (presence/absence of colluvium; dip direction of bedrock) to develop a set of 12 slope stability categories tailored to the Appalachian Valley and Ridge geologic/topographic province.

The techniques developed are directly applicable anywhere in the Appalachian Valley and Ridge province and can be adapted to other similar physiographic provinces. Both the slope map and the regional slope stability map can be produced graphically or digitally. The graphical method is inexpensive and fast when used to examine the detailed slope stability of a small area (7.5 minute quadrangle or less about 150 square km). The computer method but is more cost-efficient than the graphical method when studying the slope stability of larger areas.

The location and type of slope movement triggered by seismic shaking, torrential rainfall, rapid snowmelt, or human activities can be estimated with the use of a regional slope stability map. Integration of the slope stability map with additional factors (such as joint pattern, seismic intensity attenuation pattern, or the local water table) results in a more detailed map for specific site studies.