Evaluation of Structural Alternatives for Seismic Risk Mitigation at Deer Creek Dam

Deer Creek Dam is a zoned earthen embankment on the Provo River in central Utah. The site is potentially subject to very severe earthquake loading, and some foundation materials have been identified as being likely to be liquefied by strong shaking. This could lead to instability or large dynamic deformations of the downstream slope, and possibly a breach of the dam. Several structural concepts were evaluated by the U.S. Bureau of Reclamation to determine the best method to stabilize the embankment. The selected modification concept was a rolled earthfill key under the downstream toe of the embankment, with a berm over it to weight the key and buttress the slope. This concept was selected in the fall of 2002, and in July 2003, a contract was awarded to modify the dam. This paper presents background information on the dam and its foundation, and describes the process of determining that modification is required and designing the modification. The latter includes potential earthquake loadings, in situ and laboratory testing to evaluate the foundation, and analyses of liquefaction potential and the stability of the unmodified embankment. The various concepts for modification are described, along with the rationale for selecting the preferred concept