Anisotropy in the permeability and consolidation characteristics of dredged mud

Dredging and land reclamation is a billion dollar industry that is spread around the coastal regions of Australia. Maintenance dredging is carried out regularly in many major Australian ports and in several cases the dredged mud is pumped ashore into containment paddocks at high water contents. When the dredged mud settles, there can be segregation with possible anisotropy. The sedimentation of the dredged mud is followed by self-weight consolidation which can take a long time. To accelerate the consolidation process, prefabricated vertical drains and surcharge are often used. To analyse the consolidation process of the dredged mud with vertical drains it is necessary to have a proper understanding of the anisotropic characteristics of the dredged mud. The objective of this paper is to summarise the results of laboratory consolidation studies carried out on reconstituted dredged mud specimens that were sedimented from slurry at high water contents in the order of 270%. The horizontal and vertical coefficients of consolidation were determined on separate oedometer tests with appropriate drainage boundaries. At every pressure increment, vertical permeability and volume compressibility were estimated to evaluate the variation of consolidation properties with depth. Strong anisotropy in horizontal and vertical directions was observed and the variations of consolidation properties and compressibility with depth were assessed.