Geological-Seismological Evaluation of Earthquake Hazards at St. Stephen Powerhouse, Cooper River Rediversion Project, South Carolina, and Newmark-Sliding-Block Type Deformation Analysis of Embankments

Abstract

Abstract : An evaluation of the geological seismological hazard was conducted at the St. Stephen Powerhouse Project, which is part of the cooper River Rediversion Project in South Carolina. The project is located about 60 km North of Charleston, SC, and consists of a reinforced concrete powerhouse structure founded on rock, flanked by rolled fill earth embankments, founded partially on rock and partially on alluvium. For the purposes of this study, the alluvium is assumed to be competent, not susceptible to liquefaction. The Maximum Credible Earthquake (MCE) is estimated to correspond to a magnitude 7.5 event, 55 km from the site, resulting in peak ground accelerations at the site of 0.32 and 0.35 g. The Operating Basis Earthquake (OBE) is estimated to correspond to about a magnitude 5 event, resulting in a peak ground acceleration of 0.04 to 0.05 g at the site. The Newmark sliding block analyses indicate deformations in the maximum section under the MCE will be negligible, less than 1 cm. However, deformation under retaining walls and embankments founded on natural ground may be on the order of 15 to 35 cm.