To maintain navigable waterways, each year extremely large volumes of material are dredged. Materials removed from harbours and rivers by dredging operations, consists of solids from the bottom of the waterway along with large amounts of water. Due to the high water content of dredged material, the sites which dispose the materials are generally not suitable for construction, owing to the high degree of potential consolidation under fairly low loads. However, given the growing scientific knowledge and public awareness of using dredged material as a valuable resource, beneficial use of dredged material has become a viable option for many projects. Thus, it is becoming more important to understand and properly estimate the relationships of consolidation, diffusivity and desiccation of fine-grained dredged materials.
In the present study, industrial clay mixtures that exhibit similar properties to dredged sediments found on the coast of Australia were investigated to determine correlations with diffusivity and Atterberg limits. These clays are 100% Bentonite, 100% Kaolin, 60% Bentonite-40% Kaolin mixture, and 80% Bentonite-20% Kaolin mixture. This thesis investigated specimens of higher liquid limit than the data presently available in both the United States and Australia to further analyse desiccation of dredged materials.
A simplistic graphical linear solution is currently available for modelling desiccation of fine-grain spoils. However, the linear solution is supported only by soil mixtures with liquid limit lower than 100%. This thesis study provided three additional data with liquid limit values up to 375%. The correlation, however, remains relatively poor. Based on the additional data obtained, the relationship between liquid limit and diffusivity was found to be better explained by a non-linear curve. Investigation into specimens with high liquid limits is required to further support this analysis.
Analysis of the relationship between liquid limit, diffusivity and effective stress were also examined, based on data from dredged materials found in Australia and the present study. A three-dimensional surface fit was able to be graphed, based on linear regression principles. The data showed that the surface is twisted due to specimens with high liquid limits. However, the magnitude of the twist is relatively small, and there is currently insufficient data collected with high liquid limit to statistically prove an inconsistency with the theory.
Further analyses were conducted using data of dredged materials from previous experiments obtained from the United States, and found no correlation with the supporting theory to those dredged materials found in Australia.
It is the recommendation of this report that further research and validation is required to improve the analytical solutions of the model of desiccation of soils. There currently exist insufficient data with high liquid limit clay, between 200 to 400%, to determine whether a significant relationship exists between, liquid limit, diffusivity and effective stress. Continuous research into this field of study is strongly recommended.