Modelling the behaviour of the Ballina test embankment

As part of the Australian Research Council Centre of Excellence for Geotechnical Science and Engineering (CGSE) research program, an instrumented embankment was constructed on soft ground with and without the use of prefabricated vertical drains at Ballina in northern New South Wales (NSW, Australia). To better understand the behaviour and to help build a more robust geotechnical model for the Ballina site, a comprehensive characterisation study was carried out on the subsurface soil. This paper presents the results of a back analysis on the test embankment with wick drains at Ballina, in which the soft clay layers have been modelled using Modified Cam Clay. A 2D plane strain finite element model in ABAQUS was used to predict instrumentation recordings for a 3 year period. The results of the back analysis suggest that the Modified Cam Clay model is able to predict the behaviour of the embankment but care is needed in parameter selection to account for anisotropy, destructuration and most significantly, time dependent behaviour. The complex evolution of soil properties during wick drain installation and consolidation also created difficulties in confidently describing individual soil parameters.