Earthquake Induced Excess Pore Water Pressures in the Upper San Fernando Dam During the 1971 San Fernando Earthquake

The excess pore water pressure developed in the Upper San Fernando Dam during the 1971 San Fernando Earthquake has been evaluated in several studies. Almost all of these studies indicate large excess pore pressure ratios developed only in the upstream and downstream shells which are not consistent with the limited deformation of the dam and the piezometer responses during the earthquake. In this paper, the construction and field observations of the behavior of the Upper San Fernando Dam are reviewed and a simple approach involving Newmark’s (1965) and Makdisi-Seed’s (1978) permanent deformation and limit equilibrium slope stability analyses are used to estimate the excess pore water pressures developed in the core and downstream shell areas during the earthquake for comparison with field measurements. The major differences of this analysis with previous studies lies in the assumptions regarding the selection of the failure plane, liquefiable zones, and mobilized shear strengths. The results explain the field piezometric observations and the limited displacement of the dam