The consolidation behaviour of alluvial soft clay in Gladstone, Central Queensland

Infrastructure, port facilities and road embankments built on existing soft clay sediments impose various geotechnical challenges. A trial embankment has been constructed at the Wiggins Island Coal Export Terminal (WICET), Gladstone, Queensland to investigate the consolidation behaviour of soft, quaternary alluvial sediments. Large settlement associated with prolonged consolidation time is of particular interest. To predict the magnitude and rate of settlement to allow the design to meet often tight construction schedules, consolidation parameters such as compression and recompression indices, pre-consolidation pressure, coefficients of primary and secondary consolidation need to be reliably estimated. In this paper the consolidation properties of soft clay at WICET were evaluated using three approaches, which are: i) laboratory testing (oedometer); ii) field testing (CPTU with pore pressure dissipation); and iii) back analysis of field monitoring results from an instrumented trial embankment. Derivation of the parameters from the above approaches are discussed, with the results compared and assessed. The benefits of back-analysing instrumentation data to improve the construction programme are also discussed.