ESTIMATION OF PHYSICAL PROPERTIES OF OKURA DAM DURING EARTHQUAKES APPLYING THE CERS METHODS AND CONSIDERATION OF FACTORS CAUSING FLUCTUATIONS

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  • CERS法による大倉ダムの地震時物性値の推定と変動要因の考察

Abstract

<p> The CERS methods have been proposed as one of the methods to realize health monitoring of structures and ground. Here, the CERS methods are applied to measure the physical properties of a concrete dam. The target of this study was the Okura Dam, located in the Tohoku region of Japan, which is the only double arch dam in Japan constructed in 1961. In this dam, seismic observations have been conducted at the crest of the thrust block placed between the two arches and at the inspection gallery.</p><p> On March 11, 2011, 50 years after its completion, this dam was attacked by the 2011 Tohoku earthquake (Mw9.0), but no damage was reported. In this paper, the wave propagation velocities between observation points at the crest of the thrust block and in the inspection gallery are directly measured by the CERS methods from published strong motion records, and changes in physical properties are discussed.</p><p> As a result, it was confirmed that the stiffness of the thrust block dropped to about 60% of that before the earthquake during the Mw9.0 strong motion, and recovered to about 70% by the end of the recording. Also, it can show the influence of the reservoir level on the variation and damping of the physical properties. The CERS methods applied in this study can directly measure the variation of wave propagation velocity and damping factor in real time from the observed waveforms, and can be useful to determine the seismic health of dams and other structures.</p>

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