Failure of Tapo Canyon Tailings Dam

Abstract

The failure of the Tapo Canyon tailings dam was one of the most striking failures of an earth structure to result from the January 17, 1994 Northridge, California earthquake. The failure involved a 60-m-wide breach of a tailings dam with a maximum height of 24 m, and 60 and 90 m downstream displacements of two sections of the dam. The failure resulted from liquefaction of the impounded tailings and possibly of the embankment materials. A significant volume of liquefied tailings passed through the breach in flows which extended hundreds of meters downstream within a natural drainage channel. The tailings dam failure, which occurred in a largely undeveloped area, caused no deaths or injuries, but did result in considerable economic losses for the owners of the tailings dam and a downstream water-treatment facility affected by the tailings flow slide. In this paper the writers will outline the construction history and geologic conditions at the site, and describe the strong influence of these factors on the characteristics of the embankment failure.