Consolidation And Creep Of Soft Estuarine Clay In Newcastle

Soil mixing and other intrusive ground improvement techniques are often go-to solutions for problematic soft soils. However, it is very much worthwhile to undertake detailed project specific studies and use advanced constitutive soil models to demonstrate that expensive ground improvement techniques are not always required. This paper looks at a case study where the Soft Soil Creep model was used in Plaxis to simulate the soft Estuarine Clay found at Kooragang Island, Newcastle and proves that deep soil mixing is not necessary for 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 and understand its consolidation and creep behaviour. Site history and aging of the Estuarine Clay were then 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 past ground movements were able to be correlated with available data including cone penetration tests, shear vanes, inclinometer and extensometer readings. Predictions from the Soft Soil Creep model demonstrate a more sensible representation of current site conditions compared with using basic soil models. This realistic design approach assures confident in optimising the rail embankment design, which brings massive savings on construction costs from eliminating the need for deep soil mixing. The use of an appropriate advanced constitutive soil model, combined with a rigorous study of site specific data, has proven to reduce conservatism in design and increase the substantially benefit of real projects.