Geotechnical Investigations and Site Characterization of the Success Dam Seismic Remediation Project

Success Dam is located on the Tule River, near the city of Porterville, California. The dam is a rolled earth-fill embankment approximately 44 meters (145 feet) high and 1036 meters (3,400 feet) long. The embankment is comprised of a central impervious core protected by upstream and downstream outer pervious zones. A majority of the dam is founded on a complex deposit of both Holocene and Pleistocene alluvium. Investigations and studies under the Corps of Engineers Dam Safety Assurance Program (DSAP) demonstrated that remediation is required to prevent dam failure from large earthquake shaking. The Corps of Engineers is designing a seismic remediation of Success Dam that consists of a modified earth-fill embankment centered and aligned generally along the downstream toe of the existing dam. The modified embankment will shift the alignment of Success Dam about 95 meters (310 feet) downstream onto a prepared foundation and will increase the footprint of the dam by 40%. Similar to the DSAP studies that identified the need for remediation, the new foundation area has been investigated in numerous phases to characterize the material properties and distribution for remedial design analyses. High-quality blowcount data ((N₁)₆₀) has been difficult to obtain at Success Dam. Conversely, a large volume of shear wave velocity data (Vs₁) has been collected. Liquefaction assessment has been conducted using both data sets and additional conservatism has been observed in the Vs₁-based procedure compared to the (N₁)₆₀-based procedures as reported in recent years by various researchers. A site-specific relationship between (N₁)₆₀ and Vs₁ is presented that reduces some of the additional conservatism. This paper provides an overview of the investigations, the geotechnical site characterization, and the relationship between field exploratory data sets. Discussions include the in-situ testing methods, the challenges of characterizing potentially liquefiable materials containing significant quantities of large particles, and the development of a site-specific data correlation for liquefaction potential analyses and remediation design.