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A new composite column technique referred to as Stiffened Deep Mixed (SDM) column has been adopted to support embankment over soft soil to mitigate the post-construction settlement, increase bearing capacity and enhance stability. The SDM column was formed by inserting a precast concrete core pile into the center of a Deep Mixed (DM) column immediately after the construction of DM column. Due to the complicate interaction between concrete core pile, DM column and surrounding soil, the load transfer mechanism between SDM column and surrounding soil has not been well understood yet. This paper presents a series of threeDimensional (3-D) finite-element analyses to investigate the load transfer effect of SDM column-reinforced ground under embankment. First, the numerical method was validated by a comparison with field data in terms of settlements and vertical stress on the head of SDM column. Then, based on the validated simulation method, the 3-D numerical model of the SDM column-supported embankment over soft soil was established, and the influence factors of length of DM column and concrete core pile, cross section area of concrete core pile, column spacing and embankment height on the load transfer effect were investigated, respectively. The results showed that the column spacing and height of embankment fill had significant effects on the load transfer between SDM column and surrounding soil, while the influences of length of DM column and concrete core pile, and cross section area of concrete core pile on the load transfer effect were minor. Finally, four current commonly-used design methods were assessed in the prediction of the efficacy of SDM-reinforced soil under embankment loading. The current commonly-used design methods showed great differences in the load transfer predictions of the SDM column-supported embankment over soft soil due to the existence of outer DM column socket. A modified method was proposed for the use of EBGEO (2011) in the design of SDM column-supported embankment over soft soil.

A stiffened deep mixed (SDM) column can significantly increase the bearing capacity, reduce settlement, and enhance the slope stability of soft clays as compared with a conventional deep mixed (DM) column. This technique involves inserting plain concrete, reinforced concrete or a steel pile into the center of the DM column after the DM column is constructed. In this paper, a series of centrifugal modeling tests were conducted to investigate the performance of an SDM column-supported embankment over soft clay. A model embankment supported only by DM columns was constructed for comparison. Two ideal numerical models of column-reinforced soil under equal stress and equal strain conditions were established to explore the role the column played in accelerating soil consolidation. A parametric study was conducted to investigate the influence factors of the length of the core pile, column spacing, thickness of the underlying soil, modulus and thickness of the cushion, and modulus of the slab on the load transfer of the system, and some recommendations were proposed for its application. The load-transfer mechanism of an SDM column-supported embankment system with a slab was established based on the development of the volumetric strains and the principal stresses in the numerical models.

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