Behavior of Large Geotextile Mat Cofferdam with a New Arrangement of Geotextile Reinforcement Stiffness Lying on Soft Sediments
Publication: International Journal of Geomechanics
Volume 20, Issue 8
Abstract
This paper proposes a new arrangement of geotextile reinforcement stiffness for large geotextile mat cofferdams that often suffer from the failure of the bottom layer mat. Cofferdams using this new reinforcement method are poorly understood and require a thorough study to explore their behavior lying on soft sediments which is the prevailing situation for land reclamation projects. This paper investigates the performance of large geotextile mat cofferdams with this new type of reinforcement using a systematic numerical study. The numerical finite element models (FEM) were validated against experimental observations and field test data, where the soil flow mechanism and the cofferdam deformation were investigated. Through discussion of the failure mechanism, limiting stack height, and geotextile tension distribution in a systematic parametric study, it was concluded that the effects of the geotextile stiffness of the base mat of the cofferdam, the strength of soft clay, and the width of cofferdam base were significant, and the negligible parameters include the strength of sand fill and cofferdam slope. Based on the results, it was found that large geotextile mat cofferdams with this new type of reinforcement demonstrate two types of failure mechanisms: so-called local and global failures. An equation is proposed to identify these two different failure mechanisms, which consider the properties of the sand fill, the underlying soft sediment, and the geotextile material. A general guideline is proposed to help design large geotextile mat cofferdams with this new reinforcement, using which both the limiting stack height and the safety factor of cofferdam can be evaluated.
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Acknowledgments
The authors gratefully acknowledge the financial support by the State Key Laboratory of Subtropical Building Science, South China University of Technology (2017KA04) and Science and technology program of Guangzhou (201707020047).
Notation
The following symbols are used in this paper:
- B
- crest width of cofferdam;
- c
- cohesion;
- E
- Young’s modulus;
- Fs
- factor of safety;
- [Fs]
- required factor of safety;
- H
- fill height of cofferdam;
- Hmax
- limiting (maximum) fill height of cofferdam;
- J
- geotextile tensile stiffness of the upper mats;
- Jb
- geotextile tensile stiffness of the base mat;
- k
- slop of cofferdam (= (W − B)/2H = tan β);
- L
- linear meter of geotextile;
- Nc
- bearing capacity factor;
- Sz
- vertical deformation of ground;
- su
- undrained shear strength;
- t
- thickness of mat;
- W
- base width of cofferdam;
- αc
- friction coefficient of contact surface between geotextile and soft clay;
- αg
- friction coefficient of contact surface between geotextile and geotextile;
- αs
- friction coefficient of contact surface between geotextile and sand fill;
- β
- slope angle of cofferdam;
- γs
- unit weight of sand fill;
- effective unit weight of soft clay;
- φ
- internal friction angle of sand fill;
- ψ
- dilatancy angle; and
- υ
- Poisson ratio.
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Information & Authors
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Published In
International Journal of Geomechanics
Volume 20 • Issue 8 • August 2020
Copyright
© 2020 American Society of Civil Engineers.
History
Received: Sep 1, 2019
Accepted: Feb 6, 2020
Published online: May 28, 2020
Published in print: Aug 1, 2020
Discussion open until: Oct 28, 2020
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