Nonlinear Dynamic Analyses of Austrian Dam in the 1989 Loma Prieta Earthquake

Two-dimensional nonlinear dynamic analyses (NDAs) of Austrian Dam in the 1989 Mw=6.9 Loma Prieta earthquake are presented using the finite-difference program FLAC with the user-defined constitutive model PM4Silt and following engineering procedures common in practice. This relatively homogeneous, 55-m high embankment dam is comprised primarily of low-plasticity clayey sands and clayey gravels. The dam experienced estimated peak ground accelerations of 0.4–0.6g during the earthquake and developed extensive cracking with crest settlements up to 859 mm. The engineering properties of the compacted embankment materials are estimated based on the available isotropically consolidated undrained triaxial compression and resonant column test data. NDAs were performed using two alternative calibrations for the PM4Silt model and four different input motions. Sensitivity of the computed deformations to various modeling parameters and assumptions was examined. The computed responses are shown to be in reasonable agreement with the observed crest settlements, embankment deformation patterns, and excess pore pressures. Limitations in the material characterizations and analysis procedures and their possible effects on the analysis results are discussed. The results of this study provide support for the use of these analysis methods and engineering procedures in seismic evaluations of compacted earthfill embankments.