Abstract

During site investigations at Changi EastReclamation Project, boreholes intersected Singapore Marine Clay and provided a large number of undisturbed samples for laboratory testing. The unit ranges up to 40 m thick and comprises two distinct layers with an intervening desiccated zone. Mineralogically, the upper layer consists of kaolinite and smectite with small amounts of mica and chloride. The lower layer consists of quartz, kaolinite and smectite with small amounts of mica, chloride, albite, orthoclase, pyrite and halite. The desiccated zone is an overconsolidated layer of lower marine clay and its mineralogy is similar to that of the lower marine clay. Engineering characterization of the Singapore Marine Clay demonstrated that the upper layer is highly plastic with high moisture contents whereas the lower layer is medium to high plasticity with relatively lower moisture contents. Both the upper and lower marine clays are highly compressible with low permeabilities and the intermediate clay is less compressible. Both upper and lower marine clays are lightly overconsolidated and the intermediate clay is highly overconsolidated due to desiccation. Undrained shear strengths are typically around 5 to 10 kPa at the seabed and increase with depth. The effective frictional angle of the upper marine clay ranges from 22.5° to 27.5° whereas that of the lower layer ranges from 22° to 26°. Friction angles at the critical state are found to be 28° and 32° for compression and extension respectively.

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