In situ characterization of land reclaimed using big clay lumps

Abstract

Dredging works in the sea and excavations in built-up areas produce large quantities of clay lumps in Singapore. The use of these clay lumps for land reclamation is an attractive proposition for solving the problem of finding dumping grounds for disposal and at the same time creating new land. When these big clay lumps are used for reclamation, however, the land will have large initial interlump voids. These large interlump voids may not close completely, even with surcharge, and may lead to excessive settlement when a structure is constructed on land reclaimed using this material. Two major engineering issues related to the use of clay lumps for reclamation are the size of interlump voids at the end of consolidation and the engineering properties of such ground. The need to know the ultimate state of the ground reclaimed using large clay lumps is critical to its acceptance as a viable fill material. To our knowledge, data on the ultimate state of such reclaimed lands are not available. An extensive site investigation was performed at a test site on the island of Punggol Timor in Singapore, which was reclaimed about 12 years ago using big dredged clay lumps. The thrust of the investigation is to evaluate the present state of the reclaimed land, with special emphasis on identifying the size of current interlump voids. The radioisotope cone penetration test was employed to measure the in situ density of the site. The site investigation also included high-quality soil sampling and laboratory testing to determine the present strength and deformation characteristics of the reclaimed land. The results indicate that the initially large interlump voids have been reduced to the size of intralump voids. However, the layer formed from clay lumps is heterogeneous and exhibits variable engineering properties. Key words: in situ characterization, land reclamation, radioisotope cone penetration tests, wet density, big clay lumps.