Optimized Design of Foundations on Soft Soil Reinforced by Floating Granular Columns

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.