Optimized Design of Foundations on Soft Soil Reinforced by Floating Granular Columns
Publication: International Journal of Geomechanics
Volume 24, Issue 5
Abstract
This paper studies the design of foundations built on thick compressible soft soil layers that are reinforced by floating columns. Based on a recent methodology, the suggested design combines the bearing capacity and settlement verifications to provide an optimized improvement area ratio (IAR). Then, an optimized length for the floating columns is obtained by introducing the admissible long-term settlement of the unreinforced compressible sublayers and assuming that the total short-term settlement vanishes at the end of project construction. This paper focuses on the variation in the consolidation settlement of the unreinforced compressible sublayer versus the length of the floating columns. The discussion of this design methodology highlights the feasibility of a potential reinforcement solution when producing a cost-effective design, which assures an optimized IAR within the reinforced upper layer and an optimized length for the floating columns. Using typical case history data, a parametric study showed that reinforcement with end-bearing columns is not required to control the admissible long-term settlement. Instead, the suggested design method enables the determination of the optimized length of the floating columns, which satisfies the admissible residual settlement and consolidation time. The comparison between the proposed results and numerical predictions by Plaxis 2D shows good agreement, which confirms the feasibility of an optimized length for floating columns and avoids the systematic adoption of end-bearing reinforcement in columns.
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Notation
The following symbols are used in this paper:
- B
- rigid raft width;
- c
- cohesion;
- Cc
- compression index;
- cv
- coefficient of vertical consolidation;
- Dc
- diameter of column;
- De
- diameter of influence area;
- E
- Young’s modulus;
- e0
- initial void ratio;
- H
- thickness of the soft deposit layers;
- Hc
- length of column;
- Hu
- thickness of the unreinforced sublayer;
- Nc
- number of columns;
- q
- uniform vertical load;
- rc
- radius of column;
- re
- radius of influence area;
- s
- consolidation settlement;
- Sc
- axis-to-axis spacing between columns;
- tc
- time of consolidation;
- Tv
- time factor;
- Uv
- degree of consolidation;
- z
- layer depth;
- α−β
- coefficient, depth ratio;
- γ
- unit weight;
- δLT
- long-term settlement;
- δres
- residual settlement;
- δST
- short-term settlement;
- δtot,adm
- allowable short-term settlement;
- η
- improvement area ratio;
- Δσ′
- excess of vertical stress;
- ηopt
- optimized improvement area ratio;
- effective overburden stress;
- ν
- Poisson’s ratio; and
- φ
- drained friction angle.
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Published In
International Journal of Geomechanics
Volume 24 • Issue 5 • May 2024
Copyright
© 2024 American Society of Civil Engineers.
History
Received: May 29, 2023
Accepted: Nov 21, 2023
Published online: Mar 12, 2024
Published in print: May 1, 2024
Discussion open until: Aug 12, 2024
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