Seismic Stability Modification Requirements for Pineview Damby Peter Shaffner, U.S. Bureau of Reclamation, Boise, United States,
David Mayer, U.S. Bureau of Reclamation, Boise, United States,
Mark Barraclough, U.S. Bureau of Reclamation, Boise, United States,
Document Type: Proceeding Paper
Part of: Geotechnical Practice in Dam Rehabilitation
Pineview Dam is located 8 km upstream from Ogden, Utah, and about 8 km from the Wasatch Fault Zone. Preconstruction information and construction records available at the outset of the dam safety evaluations showed that loose Bonneville Lake deposits comprised a portion of the foundation and that artesian pressures existed in the foundation. To evaluate seismic stability, drilling, and crosshole shear wave velocity testing were performed. Initial evaluations of these data indicated a serious seismic stability problem requiring emergency action, including water storage restrictions which would seriously impact local water users. In order to facilitate analysis and design of a modification before inflows to the reservoir increased in about 4 to 6 months, a rigorous exploration program, engineering geology assessment, and geotechnical evaluation of the complex foundation stratigraphy were completed to more accurately establish the requirements of any dam safety modifications. This work led to: (1) development of useful procedures for characterizing liquefaction potential in a lenticular sandy gravel/gravelly sand complex, (2) a remarkably explicit characterization of deposits formed from the combination of three depositional/erosional environments, (3) useful correlations between crosshole shear wave velocities and standard penetration testing, (4) development of a very efficient interactive exploration and analysis process, and finally, (5) selection of remedial treatment measures that could be rapidly designed and constructed.
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