Influence of column position on stability of stiffened deep mixed column-supported embankment over soft clay

When stiffened deep mixed (SDM) columns are used to support embankments over soft soil, the embankment stability becomes one of the major concerns for geotechnical engineers. However, limit studies have been focused on failure of SDM columns under embankment load. This paper conducted a series of scale-reduced model tests to investigate stability of embankment over soft soils with SDM columns, including columns installed under the embankment base, and columns installed only under the embankment crest and the embankment side slope, respectively. A load system consisting of six loading plates was designed to create a uniform surcharge on the embankment crest. An aluminum foil tape was implanted into each core pile in a row to detect the model column failure during surcharge loading, as its electric resistance becomes infinity when the tape was broken due to the rupture of column. With the increase in the surcharge, the failure mode and process of SDM column were analyzed based on the peak stress on the top of column and strain difference along column length and the electric resistance change of aluminum foil tape. The test results showed that the SDM columns under the embankment crest also had effects on enhancing the embankment stability, even though the slip plane may not pass through them. With the increase in surcharge, the SDM columns failed progressively and had possible failure under compression, a combination of compression and bending, and bending depending on locations of the columns under embankment. The progressive failure mechanism was discussed.