Investigation on the Behavior of Stiffened Caisson Installation in Uniform Clay from Large Deformation Modeling
Publication: International Journal of Geomechanics
Volume 20, Issue 9
Abstract
Suction caissons, widely applied in offshore engineering, suffer from significant uncertainties about the flow mechanism of the surrounding soil during installation, especially for caissons with ring stiffeners. Large deformation finite element (LDFE) analyses are carried out to investigate the behavior of stiffened caisson by visualizing the soil flow mechanism during the caisson penetration. The LDFE method was first validated against centrifuge test data and good agreement was obtained. A systematic and detailed parametric study was then conducted by considering a large variety of parameters, including stiffened caisson geometry, interface friction coefficient, and soil shear strength. The results show that the ratio of caisson diameter to stiffener width and the normalized soil strength has a significant influence on the soil flow mechanisms. The definitions of critical rotational soil flow depth (Hr) and the limiting cavity depth (Hc) were employed to quantitatively describe the behavior of the observed soil flow mechanisms. An equation was developed to describe the maximum height of the inside soil heave. Prediction of the total penetration resistance was described with a simplified flow mechanism around stiffened caisson based on the observed LDFE results.
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Acknowledgments
This research was supported by the National Natural Science Foundation of China (51879183, 51890913), the State Key Laboratory of Subtropical Building Science, South China University of Technology (2017KA04), Science and Technology Program of Guangzhou (201707020047).
Notation
The following symbols are used in this paper:
- Ab
- area of the base of bottom stiffener (close to tip);
- Abase
- area of cross-area of the skirt;
- Ai
- area of the inner wall of skirt below ground surface;
- Aib
- area of the inner wall of skirt below bottom stiffener;
- Aig
- intact area between the trapped soil between embedded stiffeners gaps and the adjacent soil;
- Ais
- intact area between the stiffeners vertical face and adjacent face;
- Ao
- area of outer wall of skirt below ground surface;
- At
- area of the tip of skirt;
- b
- stiffener width;
- D
- caisson’s outer diameter;
- d
- penetration depth with caisson tip as reference point;
- db
- penetration depth with bottom stiffener as reference point;
- d2
- penetration depth with second stiffener as reference point;
- E
- Young’s modulus;
- F
- total resistance of installation of caisson;
- Fi
- inner frictional force of skirt;
- Fib
- inner frictional force of skirt below bottom stiffener;
- Fig
- inner frictional force along sliding surfaces above bottom stiffeners;
- Fis
- inner friction between stiffeners vertical face and soil;
- Fo
- frictional force of the outer wall of skirt;
- Ft
- tip resistance of skirt;
- Ftb
- tip resistance of skirt tip and bottom stiffener;
- Hc
- limiting cavity depth;
- Hr
- limiting depth for inner soil to rotate around bottom stiffener;
- h
- stiffener height;
- hin-max
- maximum inside soil heave height;
- L
- caisson length;
- Ncb
- vertical bearing capacity factor of the base of bottom stiffener;
- Nct
- vertical bearing capacity factor of the tip of skirt;
- ng
- stiffeners number when penetration depth larger than Hc;
- s
- spacing of stiffeners (edge to edge);
- su
- undrained shear strength of clay;
- t
- skirt thickness;
- w
- distance from skirt tip to the base of bottom stiffener;
- α
- roughness between structure and soil;
- γ′
- effective unit weight of clay;
- v
- Poisson’s ratio of clay;
- Ф
- friction angle of clay; and
- Ψ
- dilation angle of clay.
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Published In
International Journal of Geomechanics
Volume 20 • Issue 9 • September 2020
Copyright
© 2020 American Society of Civil Engineers.
History
Received: May 9, 2019
Accepted: Mar 24, 2020
Published online: Jun 18, 2020
Published in print: Sep 1, 2020
Discussion open until: Nov 18, 2020
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