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EFFETS DE SITE DU BARRAGE EN ENROCHEMENT DENIS-PERRON (SM-3), QUÉBEC
Session: Earthquakes and Geohazards I / Séismes et géoaléas I
Daniel Verret, Hydro-Québec Production (Canada)
Denis LeBoeuf, Université Laval (Canada)
Éric Péloquin, Hydro-Québec Production (Canada)
Spectral analysis of strong-motion and ambient noise were carried out at the Denis-Perron (SM-3) dam to evaluate possible site effects and the actual frequency of resonance (FN). This dam is a rockfill embankment dam standing 171 meters high, built in a narrow valley with its abutments resting on a gneissic rock foundation. Strong-motion stations were installed on the dam's crest and on the left bedrock abutment. The spectral response is estimated from a series of three small earthquakes that occurred in 1999 and 2002. The FN was estimated by calculating standard spectral ratios using the bedrock station as the reference site. For all earthquakes, the spectral amplification curves show a clear peak between 2.0 and 2.2 Hz, in the transverse direction, and between 1.55 and 1.8 Hz, in the longitudinal direction. Amplification ratios range between 5.0 and 18.5 in the transverse directions and between 2.8 and 19.5 in the longitudinal direction. When the site response is evaluated from ambient noise recordings and using the H/V technique of interpretation, the FN is about 2.1 Hz in the transverse direction and 1.8 in the longitudinal direction. A strong amplification of the vertical motion component was also observed at both station sites.
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