Modelling Behaviour of Soft Estuarine Clay in Newcastle using Soft Soil Creep Model

Soil behaviour is complex, non-linear and very much dependent on its stress state conditions. Advanced constitutive soil models have become more commonly used in an attempt to come closer to simulating realistic soil behaviour. This paper looks at the use of Plaxis Soft Soil Creep model to develop an appropriate representation of the soft Estuarine Clay soil behaviour found at Kooragang Island, Newcastle for the optimisation of a rail embankment design. A review of field/laboratory tests and back analysis of field monitoring data from a trial embankment were undertaken to derive design parameters of the Estuarine Clay. Site history and ageing of the Estuarine Clay were modelled using Soft Soil Creep model in Plaxis, which allows calibration of the stress state conditions at present time with field conditions. The calculated soil strength profile and ground movements in the past were able to be correlated with available data including CPTs, shear vanes, inclinometer and extensometers. Predictions from the Soft Soil Creep model demonstrate a more sensible representation of current site conditions compared to using basic soil models. This realistic design approach assures confident in optimising the rail embankment design, which brings massive potential savings on construction costs. The use of an appropriate advanced constitutive soil model, combined with a rigorous study of site specific data, has proven to reduce conservatism and substantially benefit real projects.