DEEP SOIL MIXING FOR SEISMIC REMEDIATION OF THE CLEMSON UPPER AND LOWER DIVERSION DAMS

The Clemson Upper and Lower Diversion Dams are similar, random earthfill dams constructed in 1960-1961 to protect lands and facilities at Clemson University. Because of a loose silty sand / sandy silt alluvial foundation layer, the dams were susceptible to downstream liquefaction slope failures during or following the design earthquake (amax = 0.2g). The remedial design to prevent seismic instability consisted of deep-soil mixing along the downstream berm of each dam. The soil-mix elements were designed to form transverse shear walls oriented perpendicular to the dam axis which would carry the seismic loads in lieu of the weak soil layer and a longitudinal wall oriented parallel to the dam axis at the upstream end of the transverse walls which would assist in resisting the movement of soils between the transverse walls. Design of the soil-mix remediation addressed the feasibility of soil-mix, slope stability, dynamic behavior of the dam, anchorage of the soil mix walls, alternate failure surfaces, continuity of drainage, and quality assurance. Construction demonstrated that the use of soil mix shear walls to provide reinforcing of the loose soil against seismic deformations and liquefaction shear slides can be feasible and cost effective. Construction also provided lessons for future soil mix projects.