Abstract: Stiffened deep mixed (SDM) column is a new ground improvement method for soft soil foundations, and has been successfully applied in ground improvement projects in roadways and railways recently. However, due to inadequate understanding of the instability mechanism of the embankment supported by SDM column, there is no mature theory to guide the design. In this paper, strain-softening model, which can reflect the post-failure behavior of column materials, was used to model the scale-down 1g model test of stability of SDM column-supported embankment. The sequence and modes of SDM column failure were investigated through examining the developments of plastic zone and force changes in SDM columns in the failure process. The results showed that the columns did not fail simultaneously in the process of embankment failure. The columns near the center of embankment failed by compression at first, followed by the sequence bending failures of the columns under embankment slope from the toe to the shoulder. The slip surface did not completely pass through the failure positons of the columns due to the existence of columns. Accordingly, the failure mechanism of SDM column-supported embankment was interpreted. The semi-rigid column method based on residual strength in the currently-used code yielded close factor of safety to the model test, but its feasibility still needs a further study.

Key words: stiffened deep mixed column, embankment, strain-softening, progressive failure, numerical simulation