The Seismic Coefficient in Earth Dam Design

The limitations of methods of earthquake-resistant design of embankments based on pseudo-static analysis and incorporating a static seismic force designated by a seismic coefficient are discussed. It is suggested that both from considerations of soil behavior under cyclic loading conditions, and for purposes of assessing embankment deformations due to earthquakes, the development of a method of predicting dynamic seismic forces and their variations with time would provide a more reasonable approach for design purposes. A method of accomplishing this objective is suggested, and representation of the results by an equivalent simplified seismic force series is proposed. For embankments that can be considered to have a uniform shear modulus, charts are presented for determination of the equivalent seismic force series. It is pointed out that limitations in available dynamic response analyses require that some judgment be exercised in selecting design parameters. However, the results presented in the paper provide a useful basis for guiding this judgment. Furthermore, the results show that in designating seismic coefficients for design purposes, it is important to distinguish between embankments of different heights and material characteristics as well as different positions of the potential slide mass within the embankment.