An alternative mechanism for the earthquake-induced displacement of the Lower San Fernando Dam

Abstract

The 1971 San Fernando earthquake led to the failure and large displacement of the Lower San Fernando Dam (LSFD) that was constructed by the hydraulic filling method. As such, hydraulic filling has been recognised as producing liquefiable sand deposits, while in situ relative densities as large as 60% have been reported in the LSFD. On the other hand, laboratory element tests on loosest pluviated (through air or water, resembling the soil fabric produced by hydraulic filling) specimens of primarily quartz sands have been dilative, questioning the failure mechanism of the LSFD. In this paper, the LSFD during the 1971 San Fernando earthquake is studied using the results of improved sliding block deformation analyses that incorporate shearing behaviour of two sands with different mineralogies (quartz sand and albite sand with some carbonates) from ring shear tests. The results indicate that sand particle composition and compressibility in the LSFD may have caused its failure and very large deformations even at a dense state (relative density ∼60%).

Keywords:

• sand particle mineralogy
• deformation
• ring shear test
• sliding block analysis
• earthquake
• Lower San Fernando Dam