Seismic Stability Evaluation of Indian Valley Dam

Indian Valley Dam is a 207-foot high zoned earthfill embankment located on North Fork Cache Creek about 6 miles north of Clear Lake, Lake County, California. The reservoir capacity at normal maximum water surface is 300,000 acre-feet. The construction of the dam and appurtenant facilities was completed in 1974. A small hydro-power generation plant was added in 1983.
Recent seismic sources studies in the project area indicated that local faults such as the Bartlett Springs fault (Chalk Mountain segment) are potentially active and producing peak ground acceleration of about 0.56g at the dam site for Maximum Credible Earthquake. The original seismic criteria of 0.10g was used for the design of the dam. The dam is on the high hazard classification.
The seismic stability analysis of the dam and appurtenant structures were performed pursuant to Federal Energy Regulatory Commission's (FERC) Part 12 requirements. This paper focuses on the seismic stability of the embankment. The analysis of the dam was performed using simplified procedures as well as non-linear dynamic finite element modeling. Yield accelerations calculated for various sections of the dam varied between 0.5 and 2.5 feet. A non-linear finite element analysis was subsequently conducted to refine further the estimated embankment deformations and indentify the magnitude and distribution of the deformations during and after the shaking within the entire embankment geometry.
The objective of the finite element analysis was to provide further insight on time history of the earthquake-induced deformations within the dam. The caluculated permanent displacements within the embankment mass were about 2 feet vertical deformation at the crest and about 2 and 0.8 feet of lateral displacement at the upstream and downstream toes respectively. The calculated vertical deformations compare well with observed earthquake-induced deformations of similiar types of embankment dams.