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spacial variability of seismic ground motions : arch dams

Abstract : Spatial variability of seismic ground motions (SVGM) denotes the differences between two time histories of the ground motion recorded at different locations, generally at the ground surface. The modeling of SVGM and the understanding of its influence on the dam's response are necessary so as design codes start to incorporate its effects in their provisions. This study presents a measure and a profound investigation of SVGM at the dam-foundation rock interface of an arch dam. In-situ measurements are used to quantify SVGM and numerical simulations to deeper understand the particular physical phenomena that contribute to SVGM at the interface, i.e. local canyon topography and rock-structure interaction. The in-situ data comes from a seismological experimental campaign that has taken place on and around Saint Guérin arch dam over the period of six months. The campaign was held in the framework of the present thesis. The subset of events consists of low to moderate magnitude local and regional earthquakes. Thus, analysis is allowed in the linear range. Firstly, dynamic analysis of the arch dam is conducted; the frequencies of vibration, the damping coefficient and the crest amplification are estimated based on ambient noise and seismic records. Then, SVGM is quantified by means of phase and amplitude variability using coherency estimates and standard deviation of difference of Fourier amplitudes respectively. High variability is observed both in phase and amplitude at the dam-foundation rock interface. Once the estimators of variability are obtained from the data, parametric models are fitted to them. Focus is given on two observations : 1) the ground motions in the free field appear to be slightly less variable with respect to the motions at the dam-foundation rock interface and 2) at the dam-foundation rock interface, there is higher variability around the frequencies of vibration of the dam. These observations suggest that the presence of the structure along with the canyon topography increase SVGM. This increase though seems to be small given that the observations are satisfactory fitted by parametric models based on data coming from flat seismic arrays. Numerical simulations in the SPECFEM3D code, based on the spectral element method are used to deeper investigate the in-situ observations by decoupling the various causes of SVGM and evaluating the impact of each one. A parametric study using a simplified canyon topography attempts to identify the effect of local canyon topography on SVGM while a geometrically accurate model of the Saint Guérin arch dam and its canyon topography gives us a better insight on the dam-foundation rock interaction impact on SVGM. Although both features are found to increase SVGM, their impact remains secondary. The findings of the present research are expected to contribute in enhancing our understanding of SVGM at the dam-foundation rock interface and proposing variability models used in arch dams' design.
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Submitted on : Friday, January 19, 2018 - 10:58:16 AM
Last modification on : Friday, March 25, 2022 - 9:44:03 AM

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KOUFOUDI_2017_diffusion.pdf
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  • HAL Id : tel-01688196, version 1

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UGA | CNRS | 3S-R | STAR | RESIF

Citation

Eleni Koufoudi. spacial variability of seismic ground motions : arch dams. Mechanics of materials [physics.class-ph]. Université Grenoble Alpes, 2017. English. ⟨NNT : 2017GREAI036⟩. ⟨tel-01688196⟩

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