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Étude des effets de site dus aux conditions topographiques et géotechniques par une méthode hybride éléments finis/éléments frontières

Khoa Van Nguyen
Abstract : The purpose of this dissertation is to develop the boundary element method (BEM) and the coupled finite element/boundary element method (FEM/BEM) for elastodynamics a poroelastodynamics, and to study the local site effects and the dynamic soil-structure interaction using these methods. The first part is devoted to theoretical problems. The time-dependant formulations of the BEM and the FEM/BEM enable us to study (semi-)infinite domains. Particularly, the FEM/BEM can also take account of the complex material behaviours. However, these formulations have some numerical difficulties, which may restrict their applicability seismic calculations. These are the numerical stability of the time-marching procedure, the dramatic increase in computing time with the number of time steps and the truncation effect of the half-space. Some techniques, which are intended to improve the performances of these methods, are then presented. An analytical transient fundamental solution is proposed for the application of the BEM to the poroelastodynamics, using two assumptions: the acceleration, relative to the skeleton, of the pore fluid is neglected and the fluid and solid particles are incompressible. This approximate solution in terms of displacements and pore pressures is appropriate for soils under seismic motion. All of these formulations are validated and integrated into the computer code HYBRID. The applications of the BEM and the FEM/BEM in seismic calculations are presented in the second part. The principal characteristics and the physical phenomena of local site effects (i.e. effects of surface topography and alluvial basin geometry on seismic ground motion) are presented. It is theoretically shown that the local site effects may considerably enhance the destruction potential of seismic motion, because they amplify the ground motion, increase the duration of the earthquake and cause differential motions, Parametric studies are carried out and illustrate the important influence on the ground surface motion of several factors the frequency content of the excitation, the impedance ratio sediment/bedrock, the geometry of the relief or the basin (width, depth or height, slope and form), the thickness of sedimentation, the multi-layer effect and the pore water saturation. A study of the dam/foundation interaction shows that it is necessary to consider the effect of the foundation flexibility in seismic calculations of earth dams.
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Submitted on : Monday, May 3, 2010 - 8:00:00 AM
Last modification on : Monday, May 3, 2010 - 8:00:00 AM
Long-term archiving on: : Thursday, September 16, 2010 - 4:36:16 PM

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  • HAL Id : pastel-00001839, version 1

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Khoa Van Nguyen. Étude des effets de site dus aux conditions topographiques et géotechniques par une méthode hybride éléments finis/éléments frontières. Sciences of the Universe [physics]. Ecole des Ponts ParisTech, 2005. English. ⟨pastel-00001839⟩

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