An examination of simplified earthquake-induced displacement procedures for earth structures

A critical examination of the procedures commonly used to estimate earthquake-induced sliding displacements of earth structures is essential due to their widespread use and application to new types of systems such as solid-waste landfills. Rigid sliding block analyses are performed, along with decoupled and fully coupled deformable sliding block analyses using a distributed mass model with a mode shape appropriate for an earth structure. Results from using several earthquake ground motions and a sinusoidal input indicate that a decoupled analysis does not always provide a conservative estimate of sliding displacement. Conservative decoupled displacements are calculated for lower values of yield acceleration (i.e., k y /k max < 0.6) when the fundamental period of the sliding mass is less than twice the mean period of the input ground motion. For systems with larger values of k y /k max or large fundamental periods, a decoupled analysis may predict smaller displacements than a fully coupled analysis. However, in these cases, the displacements calculated from both analyses are generally small (i.e., less than a few centimetres). A decoupled analysis generally provides an estimate of the coupled sliding displacement within a factor of three, which is conservative, except for particular cases where caution is warranted. A rigid sliding block analysis can be significantly unconservative, and it should not be used.