POTENTIAL FOR SPECIAL-PURPOSE UNDERGROUND FACILITIES IN GRANITES OF THE SOUTHEASTERN U.S.

Granite plutons and similar rock masses in the southeastern U.S. (SE US) are a geological resource potentially suitable for development of special-purpose underground facilities. Underground facilities in bedrock are recognized world-wide as usually superior to above-ground facilities if there is a compelling need to 1) protect against severe weather, earthquakes, electromagnetic pulses, or attacks by terrorists or enemy nations; 2) minimize costs for utilities, maintenance, and insurance; 3) create a low vibration, constant temperature, and constant humidity work environment; and 4) reduce environmental impact at the earth’s surface. Life-cycle costs for large underground facilities can be significantly lower than for equivalent above-ground facilities, although capital cost is commonly higher. Excavation cost—a major capital cost component in underground facility construction—can be reduced by using sites with good-to-excellent geotechnical and geohydrological properties, modern underground excavation technologies, and tunnel entry instead of shaft entry for access to the underground. Dimension stone quarries in the SE US granites are evidence of the presence of rock masses potentially suitable for construction of large-span caverns and room-and-pillar facilities without the need for extensive and expensive ground support. Especially attractive is the potential for using tunnel entry to develop underground facilities within the interiors of large, dome-like, topographically elevated granite rock masses. Possible underground facilities in SE US granites include refrigerated natural gas storage, underground data centers, specialized manufacturing plants, refrigerated/frozen food storage warehouses, and exceedingly hardened civil and military depots for equipment and supplies needed for emergency response and recovery. Underground facility development at any site will depend on site-specific geological and geohydrological conditions, as well as on overall economic feasibility, public acceptance, and other considerations. However, if viable, development of special purpose underground facilities in SE US granitic rock masses could provide considerable benefits in local, state, and regional economic development, physical security, and natural hazard protection.