Recent Developments in Evaluation of Earthquake-Induced Permanent Displacement of Earth Slopes

Recent advances in evaluation of earthquake-induced permanent displacement of earth systems are addressed herein. Currently, seismic design of geotechnical structures emphasize on the quantification of system performance with the prescribed levels of permanent displacements. Accordingly, evaluation of earthquake-induced permanent displacement in geotechnical structures such as earth embankments and slopes is a topic of consideration for the geotechnical engineers. Different studies are available for estimating earthquake-induced permanent deformation of earth slopes and embankments. In general, these studies can be divided into three categories: analytical and semi-analytical, empirical and semiempirical, and numerical studies. Analytical and semi-analytical studies are simplified dynamic methods based on Newmarkian rigid block analogy. Based on this analogy, the rigid block displaces once the exciting acceleration exceeds the critical (or yield) acceleration. The original Newmarkian analogy assumes the sliding mass as the rigid block directly subjected to the input acceleration. The decoupled analysis is based on a rigid block but dynamic response of the system is calculated to obtain the equivalent acceleration as the input motion for the sliding block analysis. The decoupled analysis does not consider dynamic response of the slipped mass, while this response affects the overall behavior of the system. In a fully coupled analysis, dynamic response of the sliding mass and the permanent displacement are modeled together so that the effect of sliding displacement on the ground motions is taken into account. Through the empirical approaches, researchers developed correlations to predict seismicallyinduced displacement of slopes using databases of field case histories. These studies make clear that traditional rigid block analysis does not yield acceptable results for the seismic performance of large engineered earth structures. Besides, they provided detailed treatments of specific combinations of site and shaking conditions that are and are not adequately modeled by rigid-block analysis. Furthermore, other semi-empirical correlations have been presented based on the results of the analytical and semianalytical approaches. The third category aims to incorporate advanced constitutive models and numerical procedures such as finite difference, finite element, discrete element, and hybrid methods. This category soon began to be applied to slopes, particularly earth dams, and it provided a valuable tool for modeling the static and dynamic deformation of soil systems. However, advanced constitutive models, which are capable for simulation of soil behavior under dynamic loading, commonly require many parameters such as a high density of high-quality data and sophisticated soil-constitutive models. This problem may prevent prevalent usage of the advanced numerical approaches for estimation of earth slope displacement. For this reason, use of simplified method is preferable for evaluation of seismic permanent displacement. In this paper, major studies and recent developments on the methods of seismic slope displacement are explained based on the aforementioned categories. Moreover, advantages and disadvantages of the recent approaches are explained.