Effects of Soil Nonlinearity on the Seismic Behavior of Pile Foundations Reinforced with Micropiles
Publication: International Journal of Geomechanics
Volume 24, Issue 10
Abstract
Seismic retrofitting of existing bridges has been in practice for years to meet the stringent seismic requirements set forward by revised design codes. For retrofitting, however, bridge piers are often prioritized while less attention is given to the bridge foundations, which are equally prone to damage under seismic loadings. The current work presents a series of experimental studies in assessing the performance of 2 × 2 pile groups reinforced with micropiles in terms of head-level stiffness and damping under low-to-high levels of static and dynamic loadings, encompassing the influence of loading-induced soil nonlinearity. Practical micropiles inclinations of 0°, 5°, and 10° with respect to the vertical are studied. Experimental results reveal that the head-level stiffnesses of pile groups reinforced with micropiles, contrary to the general expectations, become smaller than the pile group without micropiles at higher levels of applied loading. To elucidate the governing mechanism for such experimentally obtained results, three-dimensional nonlinear finite-element analyses were carried out. Results from the numerical analyses support the experimental results, suggesting that the presence of micropiles may not always increase the head-level stiffness of soil–foundation systems, particularly at higher levels of applied loading where the soil nonlinearity generated at the vicinity of piles and micropiles governs the overall head-level stiffnesses.
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Data Availability Statement
All data, models, and code generated or used during the study appear in the published article.
Acknowledgments
This work was supported by KAKENHI Grant-in-Aid for Scientific Research (C) 22K04280 from the Japan Society for the Promotion of Science, Japan. Any opinions, findings, conclusions, or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the sponsors. The authors would also like to thank Yuji Maruyama and Tosifumi Hikima of Saitama University for their support during the experiments.
Notation
The following symbols are used in this paper:
- Chh
- imaginary part of horizontal impedance functions;
- Cu
- coefficient of uniformity;
- chh
- coefficient of equivalent viscous damping;
- Dmax,60,30,10
- particle size parameters of soil;
- dmp, dp
- diameter of micropiles, piles;
- Es, Emp, Ep
- Young’s modulus of soil, micropiles, piles;
- emax,min
- maximum, minimum void ratio;
- Gs
- specific gravity;
- g
- acceleration due to gravity;
- H
- depth of soil layer;
- i
- imaginary unit ;
- horizontal impedance functions;
- khh
- real part of horizontal impedance functions;
- Lmp, Lp
- length of micropiles, piles;
- u
- applied static displacement;
- Vs
- shear wave velocity of soil;
- γm, γp
- dynamic strain in the model, prototype;
- η
- density scaling ratio of model to prototype;
- λ
- geometric scaling ratio of model to prototype;
- ρs, ρmp, ρp
- density of soil, micropiles, piles;
- ϕ′
- internal frictional angle of soil;
- ω
- cyclic loading frequency; and
- ωm, ωp
- cyclic frequency of model, prototype.
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Published In
International Journal of Geomechanics
Volume 24 • Issue 10 • October 2024
Copyright
© 2024 American Society of Civil Engineers.
History
Received: Aug 29, 2023
Accepted: Mar 28, 2024
Published online: Jul 17, 2024
Published in print: Oct 1, 2024
Discussion open until: Dec 17, 2024
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