Field-measured Poisson's ratio of geotextile-encased granular column

The performance of a geosynthetic-encased column (GEC) supporting an embankment is often analysed by measurement of the total deformations under the embankment, the hoop tensile force in the geosynthetic encasement and the vertical stresses shared between the GEC and the surrounding soft soil. Several analytical solutions are available in the literature for calculation of the stresses and deformations of a GEC under an embankment. Generally, the existing formulations use a constant value of Poisson's ratio for the granular column material in their computation. This study describes the variation of Poisson's ratio of the composite material GEC with computations based on the real-time measurement of the radial and vertical deformations of a GEC. Accordingly, specific equipment was developed to allow the determination of changes in the GEC diameter. The vertical deformation was also recorded using a settlement sensor placed on the top of the GEC. The results showed a significant variation of the field Poisson's ratio due to the increase in vertical stress caused by the embankment construction and also due to the gain in the confining stress of the surrounding soft clay due to its higher degree of consolidation.