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An Alternative Analysis of Vibration Tests on Two Pile Group Foundations

by Alex Sy, Klohn Leonoff Ltd, Richmond, Canada,



Document Type: Proceeding Paper

Part of: Piles Under Dynamic Loads

Abstract:

Published quick-release horizontal vibration tests on two pile group foundations supporting large transformer banks are analyzed in this paper using the dynamic impedance approach embodied in the computer program DYNA3. The larger foundation contained 8 vertical and 8 batter piles, while the smaller foundation contained 6 vertical piles. Both pile caps were fully embedded and the piles consisted of concrete-filled steel pipes embedded in 12.2 m of loose sandy soils overlying glacial till. The results of the analysis are compared to the published measured data. The computed fundamental frequencies are in excellent agreement with the measured natural frequencies, if the measured free-field shear wave velocities are corrected to account for the effect of pile installation in closely-spaced pile groups. The analysis also showed that dynamic pile-soil-pile interaction has a significant effect on pile group stiffness, whereas the pile cap-soil interaction has a more significant effect on foundation damping. The computed damping ratios are found to be much larger than those observed. The results indicate that foundation damping is a more difficult parameter to predict in practice than stiffness.

Subject Headings: Pile foundations | Soil-pile interaction | Vibration | Pile tests | Pile groups | Damping | Structural dynamics

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