Failure mechanism of geosynthetic-encased stone columns in soft soils under embankment

The reaction of geosynthetic-encased stone columns (GECs) in soft soils under embankment loading was modeled with an indoor physical model test and numerical models using three dimensional and two dimensional finite element methods. The experimental and three dimensional numerical modeling results showed that the failure of the GECs is caused by the bending of the columns rather than shear. Three dimensional finite element analysis showed that the distribution of unbalanced lateral loading acting on the columns is symmetric about a ‘hinge point’ above the plastic hinge, rather than triangle or uniform distribution. An equivalent shear resistance model of the GECs is proposed based on the distribution of the unbalanced lateral loadings on the wall. The stability of the embankment was analyzed in two dimensional finite element method by transforming the columns into equivalent soil walls using equivalent bending resistance and equivalent shear resistance methods. It was found that results from equivalent bending resistance method is closer to the estimations from the three dimensional analysis, which agrees with the bending failure mechanism of the GECs. It is suggested that one more row of such columns may be required to provide higher lateral resistance in the soils in front of the toe to improve the stability of the embankment.