Analysis of the effect of spatially varying earthquake ground motion (SVEGM) on the response of a typical medium-sized earth dam indicates that SVEGM can have a significant effect on the stresses generated in stiff material near the base of the dam. However, the sensitivity of the stress response to different coherency functions at the base can be dramatic. The variation of coherency at low frequencies is found to be critical. Empirical coherency functions proposed by several investigators (Harichandran, Hao, Novak, Luco and Wong, etc.) yield significantly higher stresses near the base when SVEGM is included, but the coherency function proposed by Abrahamson does not. Seismic wave propagation does not significantly affect the dam response.
The dam was modeled with 3-D finite elements and linear random vibration analysis was used. The response due to SVEGM is compared with those due to various simplified excitations. In addition, a preliminary reliability analysis using the Mohr-Coulomb strength criterion is performed. Statistical moments of the maximum shear stress, which is non-linearly related to the Cartesian stresses, are computed using Monte Carol simulation as well as an approximate first order second moment method. Techniques to simplify the excitation for use with simplified mechanical models of the dam are presented.