Seismic Analysis of Earthdams Using a Lagrangian Particle Method.

Abstract eng:
Seismic safety of earth or rockfill dams and embankments is strongly conditioned by permanent displacements caused by earthquakes. For a severe earthquake, the permanent displacement pattern results from the combination of displacements generated by volumetric and shear plastic strains distributed within the structure, and those caused by sliding of a soil mass along a failure surface. Numerical procedures commonly used in practice do not consider the strain localization phenomena at failure surfaces and the associated mesh dependence of the solution. Typically, nonlinear finite element or finite difference codes yield an estimate of distributed deformations and dynamic response, without accounting for the plastic strain localization problem. In addition, some of the numerical approaches used in practice do not consider the configuration change caused by large displacements. The material point method or MPM is a lagrangian “particle-mesh” numerical method. It has been previously used in modeling dynamic problems with large displacements and strain localization. With MPM, a body is discretized into a collection of lagrangian particles, which carry all the data needed to define the body’s state. Interaction between particles takes place in a background fixed mesh, similar to those used in the finite element method. The MPM is applied in this paper to model the dynamic response of a concrete faced gravel dam with increasing base movements. A comparison of the MPM displacement results with a simplified Newmark sliding block analysis is presented. The examples show that the MPM is a useful tool to assess the seismic safety of earth and rockfill structures.

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