Construction dewatering at Saluda Dam: Design, testing, and implementation

The proposed Remediation of Saluda Darn, located approximately ten miles to the west of Columbia South Carolina and owned and operated by South Carolina Electric & Gas Company (SCE&G), consists of a 5,500-foot-long Rock Fill Berm and a 2,200-foot-long Roller Compacted Concrete (RCC) Berm. This combination RCC and Rockfill Berm will be constructed along the downstream toe of the existing 200-foot-high earth embankment dam. Should the existing Dam fail during a seismic event, the combination Rockfill and RCC Berm will serve as a backup dam to prevent an uncontrolled release of Lake Murray. Extensive foundation excavations into the residual soil or to bedrock at the toe of the existing Dam are required to facilitate the construction of the RCC and Rockfill Berm. To maintain an adequate factor of safety against slope instability for the existing Dam during construction, the existing phreatic surface within the Dam needs to be lowered substantially by dewatering. Based on the hydrogeologic conditions at the site, Paul C. Rizzo Associates (RIZZO) determined that the dewatering system should consist primarily of deep wells and eductors. Numerous components of this system that have been installed are currently operating to lower the phreatic surface within the Dam and downstream foundation excavation. Engineering analyses consisting of analytical models and finite element analyses were utilized to estimate the approximate spacing and flow rate required for the deep wells and eductors. Early indications are that the dewatering system will be successful in dewatering the existing Dam so that the construction can proceed without delay.