Seismic Characterization and Its Limited Implication for San Pablo Dam

This paper presents the results of the seismic characterization of San Pablo Dam in support of the design of seismic upgrades. The limited implication of characterization is also presented. Previous three seismic evaluations of the hydraulically constructed dam concluded that much of the shell portions of the embankment and the foundation soils were potentially liquefiable; these observations were considered appropriate given the perceived nature of the materials and the process of construction. However, a recent stratigraphic and property characterization conducted on the dam indicated a consistently very clayey, very "lumpy", and over-consolidated nature for almost all the hydraulic shell materials. The foundation soils were also found to be very clayey, but less so, and less over-consolidated. The undrained shear strengths of these materials were derived from the available results of laboratory tests. The recent characterization indicates that the shell materials are unlikely to liquefy while liquefaction of the some portions of foundation soils cannot be discounted. The limited implication of this new characterization is also presented.