Assessing karst hazards for a nuclear power plant site, southern appalachian mountains, u.s.a

Abstract

Engineering geologic investigations for a nuclear power generating facility sited on carbonate rock in the southern Appalachians employed multiple methods to characterize karst features and assess potential karst hazards to this critical facility. The site is located on Ordovician argillaceous and silty limestone in a low-lying valley where karst features are typically hidden beneath a mantle of residual soil. Karst characterization activities included: (1) an assessment of sinkhole occurrence in the site area based on the interpretation of LiDAR topographic data, (2) site specific geotechnical investigations including corehole drilling, cone penetrometer tests, seismic refraction, microgravity, and geologic field reconnaissance. Mapping of karst depressions shows that depression density varies with stratigraphic unit. Depression density in the site limestone is less than in the adjacent pure Mississippian limestone. The argillaceous and silty nature of the site limestone may inhibit dissolution and the development of large conduits, and may also promote the development of a thick soil mantle covering bedrock irregularities. Detailed geotechnical investigations at the site indicate an irregular top of bedrock with deep depressions, and small cavities clustered within 4Â m of the bedrock surface. Minor cavities were observed to depths of 30Â m. No karst collapse hazards were identified beneath the reactor or other critical facilities. However, analysis shows that karst processes should be addressed in hazard assessments for any additional structures on the site property.