Study on estimation of natural frequencies of pier foundations according to the progress of scouring

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  • IRI Hiroki
    Railway Technical Research Institute, Disaster Prevention Technology Division
  • FUJIWARA Shoma
    Railway Technical Research Institute, Disaster Prevention Technology Division
  • WATANABE Satoshi
    Railway Technical Research Institute, Disaster Prevention Technology Division

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Other Title
  • 洗掘の進行過程に応じた橋脚基礎の固有振動数の推定に関する検討

Abstract

<p>Extreme rainfall events have been increasing in recent years. Scour is becoming more frequent. It is important to continuously measure the natural frequency, which is one of the stability evaluation indexes of pier foundations, during rising water and to evaluate the progression of scour. Therefore, in this paper, large-scale model tests were conducted to investigate the progression of scouring. The relationship between the degree of scour and natural frequencies was analyzed using a method based on microtremors continuously estimating natural frequencies. In the case of simulated side scour, the natural frequencies showed a linear decrease with the progress of scour. On the other hand, in the case of bottom scour, the natural frequency decreased significantly after the bottom excavation rate (the ratio of scour to pier width in the downstream direction) exceeded 20% to 25%, as the pier deformation and tilt increased toward the side where scouring occurred. When the temporary recovery process of the ground was simulated, the natural frequency showed a recovery trend but remained at about 70% of the initial value.</p>

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