Nonlinear Coupled Seismic Sliding Analysis of Earth Structures

Earthquake-induced sliding displacements of earth structures are generally evaluated using simplified sliding block analyses that do not accurately model the seismic response of the sliding mass nor the seismic forces along the slide plane. The decoupled approximation introduced to capture each of these effects separately is generally believed to be conservative. However, recent studies using linear viscoelastic sliding mass models have revealed instances where the decoupled approximation is unconservative. In this paper, a coupled analytical model that captures simultaneously the fully nonlinear response of the sliding mass (necessary for intense motions) and the nonlinear stick-slip sliding response along the slide plane is presented. The proposed sliding model is validated against shaking table experiments of deformable soil columns sliding down an inclined plane. The effect of sliding on the response of earth structures is evaluated, and comparisons are made between sliding displacements calculated using coupled and decoupled analytical procedures with linear and nonlinear material properties. Nonlinearity resulting from stick-slip episodes is often the dominant source of nonlinearity in this problem. The decoupled approximation was unconservative primarily for intense ground motions for systems with low values of ky, larger values of ky/kmax, and high period ratios (Ts/Tm). Results indicate that a decoupled analysis is adequate for earth structures that are not expected to experience intense, near-fault motions. However, for projects undergoing intense, near-fault ground motions, a fully nonlinear, coupled stick-slip analysis is recommended.