The Ballina bypass is part of the upgrade of the Pacific Highway currently being undertaken between Newcastle and the Queensland border. The bypass consists of a 12km length of road, much of which is over soft alluvial clays that will require the construction of embankments up to a height of 5m. The thickness of the soft alluvial clay deposits along the road alignment varies between 7m and 25m. Soft alluvial clays commonly exhibit large secondary settlements. This paper presents the results of a series of incremental oedometer tests that were conducted to investigate the secondary compression of the clay. In particular, the influence that the change from a lightly over consolidated state to a normally consolidated state has on the secondary compression is investigated. The results show Ca is low before the preconsolidation pressure is reached, peaks at a value of approximately 0.055 at a vertical effective stress of about twice the preconsolidation pressure and then decreases. Secondary compression was observed to obscure primary consolidation for low load increment ratios.
The Ballina bypass is part of the upgrade of the Pacific Highway, between Newcastle and Queensland. The new road is to be built over low land areas consisting of deep deposits of very soft alluvial clay. The average height of embankments will be 3m but in places embankments as high as 5m will be required at the approaches to bridges and overpasses. The thickness of soft alluvial clay deposits along the road alignment varies between 7m and 25m. The thickness of the clay layer, combined with the high secondary compression commonly exhibited by soft alluvial clays, may produce a significant secondary settlement component of the total settlement. In particular the magnitude of secondary compression is observed before, during and after the preconsolidation pressure is reached.
