Paper Presented at 2005 USSD Conference A Case History -Dewatering the Saluda Dam

Abstract

ABSTRACT The Saluda Dam Remediation included the construction of a Roller Compacted Concrete Berm (1.3 million cubic yards) and a Rock fill Berm (3.5 million cubic yards) along the downstream toe of an existing earthen dam in order to withstand a future seismic event similar to the Charleston earthquake of 1886. An excavation to non-liquefiable soils or bedrock was required prior to Berm construction. To accomplish this construction, the installation and operation of an extensive groundwater dewatering system was required to protect from slope instability due to unstable and wet dam soils, to lower pore pressure, and to control groundwater elevation and seepage within the excavations. Failure to control water during and after dewatering could result in flooding of the excavation, unstable or unworkable sub-grade, uplift of construction features, safety issues, delays in the project, loss of fines from the dam, or a host of unstable conditions such as boils, springs, blowouts, seeps, or piping effects. Catastrophic conditions with this unique dam could have arisen due to the fact that Columbia, South Carolina was just eight-miles downstream of the Dam and over 120,000 lives would have been at stake had a Dam breach occurred. Obviously, this dewatering challenge was incredibly exceptional in that an entire dam was to be dewatered, not just an individual excavation. Dewatering efforts were centered on construction efforts and construction schedules, which didn't always agree. In addition, construction of the dewatering system needed to keep up with the fast-paced construction schedule. Pumps were sometimes turned off and on to test the effects of pumping on the soils or bedrock at certain locations. Dewatering became critical if a deep well malfunctioned above an excavation location. Furthermore, if there was a location where the pore pressures were too high to begin or continue excavation, deep wells or eductor lines had to be drilled on a very short notice to avoid costly delay charges from the General Contractor. Additional complications arose with the reluctance of Dam contractors to assume the responsibility for the dewatering and related safety impacts on dam stability. Perhaps the biggest challenge occurred when the plans changed from an excavation start in the center cells to a simultaneous start of excavation of both the northern and southern cells. This Paper will present a case history of the design and implementation of the dewatering system required to facilitate the remediation of the Saluda Dam. The paper will discuss initial design, field modifications, contractual difficulties, and related topics