New Formulation for Estimating the Moment Capacity of Rocking Shallow Foundations Resting on Partially Saturated Soil
Publication: Journal of Bridge Engineering
Volume 26, Issue 11
Abstract
The ability of shallow bridge foundations to dissipate earthquake energy via rocking has gained significant attention by bridge engineers owing to recent efforts to quantify the performance of rocking footings. This paper presents a new formulation for estimating the moment capacity of rocking bridge foundations resting on all types of soils under varying saturation and surface flux boundary conditions. The proposed formulation uses the moment capacity equation originally employed for saturated soils, classical effective shear strength parameters, and a representation of the soil–water retention curve (SWRC) to accommodate partially saturated conditions that may commonly exist below the shallow foundations of bridge substructures. A closed-form equation is incorporated in this formulation for the matric suction and effective saturation profiles to directly implement surface flux boundary conditions when analyzing the moment capacity of rocking foundations supported on partially saturated soils. The formulation implements a new method to predict the air entry suction for partially saturated soils, representing a key step towards improving the accuracy of moment capacity. A parametric study is performed to investigate the sensitivity of the moment capacity to primary design variables and various surface flux boundary conditions. The analyses demonstrate that flow conditions have a negligible and strong influence on the moment capacity of coarse- and fine-grained soils, respectively. Predictions from the proposed formulation were compared against two sets of experimental data obtained from large-scale shaking table (on sand) and snap-back (on plastic silt) tests and indicated good agreement with experiments.
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Acknowledgments
This research was supported by SPR 830 funded by the Oregon Department of Transportation (ODOT) and coordinated by Dr. Matthew Mabey, P.E.; this support is gratefully acknowledged. The contents of this paper reflect the opinion of the authors and do not necessarily reflect the views of the sponsor. The second author thanks Professor Emeritus Bruce Kutter for helpful discussions on the topic of rocking foundations.
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Published In
Journal of Bridge Engineering
Volume 26 • Issue 11 • November 2021
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© 2021 American Society of Civil Engineers.
History
Received: Oct 14, 2020
Accepted: Jul 20, 2021
Published online: Sep 14, 2021
Published in print: Nov 1, 2021
Discussion open until: Feb 14, 2022
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