Failure Mechanism of Helical Anchors in Sand by Centrifuge Modeling and PIV
Publication: International Journal of Geomechanics
Volume 22, Issue 8
Abstract
Helical anchors are receiving more attention these days due to their economic and environmental advantages. However, the behavior of these structures requires further investigation. One of the critical areas requiring further attention is their failure mechanism under monotonic loading conditions. This study presents the results of centrifuge testing of half-models of helical anchors behind a Perspex window, performed to visualize the failure mechanism of screw anchors using particle image velocimetry analysis. The density change that is a result of installation disturbance was simulated by a novel technique. The results showed that embedment depth had a great influence on the failure mechanism of the anchors. The critical embedment depth ratio determined was H/D = 4–5 that separated the shallow and deep behavior of the anchors. Soil was mobilized as a reverse truncated cone in the shallow mode, while a flow-around mechanism was formed in the deep mode. The inclination of the mobilized zone on both sides of the helix was close to the critical state friction angle (29°) in shallow mode. The inclination of the failure surface was related to the dilation angle of the sand in the deep mode. A minimum distance of 3D was recommended to minimize the interaction of adjacent helical plates in a multihelix anchor. In addition, a distance of 4D was suggested to minimize the interaction of adjacent helical anchors in a group.
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Acknowledgments
The second author would like to thank Dr. C.H.C. Tsuha from University of Sao Paulo and Dr. A. Askarinejad from TU Delft for their support and contributions to this research.
Notation
The following symbols are used in this paper:
- C
- cohesion;
- Cc
- coefficient of curvature;
- Cu
- coefficient of uniformity;
- D
- helix diameter;
- Dave
- average helix diameter;
- Dr
- relative density of sand;
- d
- shaft diameter;
- d50
- average grain size;
- emax
- maximum void ratio;
- emin
- minimum void ratio;
- Gs
- specific gravity of solid particles;
- H
- helix embedment depth;
- h
- vertical distance from the soil surface;
- Nq
- dimensionless breakout factor;
- P
- geometrical helix pitch;
- Qu
- ultimate uplift capacity of the anchor;
- U
- vertical displacement of the anchor head;
- W
- effective helical radius;
- x
- horizontal distance from the anchor vertical axis;
- βL
- inclination angle of the failure surface with vertical on the left side of the helix;
- βR
- inclination angle of the failure surface with vertical on the right side of the helix;
- θ
- inclination of the helix with respect to the horizontal plane;
- φp
- peak friction angle;
- φcs
- critical state friction angle; and
- ψ
- peak dilation angle.
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Published In
International Journal of Geomechanics
Volume 22 • Issue 8 • August 2022
Copyright
© 2022 American Society of Civil Engineers.
History
Received: May 18, 2021
Accepted: Feb 8, 2022
Published online: May 26, 2022
Published in print: Aug 1, 2022
Discussion open until: Oct 26, 2022
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