Site amplification effects of a radially multi-layered semi-cylindrical canyon on seismic response of an earth and rockfill dam

Abstract

An analytical treatment of an earth and rockfill dam in a radially inhomogeneous multi-layered semi-cylindrical canyon in a half-space under obliquely incident plane SH waves is presented. In terms of a radial wave function expansion and a transfer matrix approach, a rigorous approach is formulated to consider inhomogeneity of the deformable canyon and associated phenomena of wave redirection, reflection, transmission, scattering and concentration. Upon confirmation of its accuracy with a past exact solution for the degenerated case of a dam in a homogeneous canyon, the multi-layer solution is extended to the case of a dam in a canyon covered by a surficial zone with a power-law shear-wave velocity model as a generalized class of smooth in-situ variations. A comprehensive set of numerical examples are presented to illustrate the sensitivity of the dam response to the inhomogeneity profile of the top canyon zone, the frequency content and the angle of the seismic wave incidence. As illustrated in both frequency and time domains, wave concentration is found to be the main reason for the high amplifications of the displacement within the dam.