Fully coupled dynamic analysis of an earth dam

Abstract

The paper studies the seismic behaviour of an existing homogeneous earth dam using a fully coupled finite-element effective stress approach in conjunction with a recently developed multi-surface, elasto-plastic constitutive model for structured soils. The model is calibrated using laboratory test results for the embankment material and the foundation soils. The initial state variables (stress, hardening parameters) are determined by simulating a simplified geological history of the foundation soil, dam construction stages and reservoir impounding, prior to the application of the earthquake shaking at the bedrock level. The paper critically reviews the role of the constitutive model parameters, the hysteretic damping introduced by the model and the additional viscous damping parameters in the accumulation of permanent displacements and in the development and subsequent dissipation of excess pore water pressures due to the seismic loading. The analyses, carried out with reference to a set of earthquake records related to different return periods, show that the overall behaviour of the system in terms of displacements is characterised by a more enhanced deformation pattern of the downstream slope as compared with the upstream one. The large plastic strains accumulation induced throughout the shaking is followed by the development of excess pore water pressures inside the dam and the foundation deposit. Nonetheless, the results are indicative of a satisfactory dynamic performance of the dam, even when subjected to severe seismic loading conditions.