Arching in geosynthetic reinforced column supported embankments – recent findings from a field case study

As part of the Regional Rail Link project in Melbourne, Australia a field case study has been undertaken by Golder Associates and Monash University that involved the instrumentation of a geosynthetic reinforced column supported embankment (GRCSE). The field case study site is located in inner Melbourne within the Yarra Delta and is underlain by Coode Island Silt, a soft soil well known to the local geotechnical profession. A number of the findings relating to the site characterisation, load transfer platform behaviour, the development of soil arching and global embankment behaviour have been published recently in several journal and conference proceedings. This paper focuses on the arching stress development in GRCSEs and compares arching stress/deformation models. The widely adopted design standards (BS 8006, 2010 and EBGEO, 2010) adopt a “two-step” design approach that de-couples the arching stress/deformation relationship. This is compared with the Ground Reaction Curve method that describes the four phases of arching: initial, maximum, load recovery and terminal phases as a deformation (and time) dependent process. The implications that these arching stress/deformation relationships presents for design is described.