Characterization of lumpy fill in land reclamation

Abstract

The disposal of large volumes of clay lumps obtained from underground construction activities and seabed dredging is a problem in a highly built-up environment such as Singapore. The use of such clay lumps for reclamation of land is an environment- friendly proposition. Also, the use of these lumps directly as reclamation fill provides a sustainable and cost effective solution to the disposal problem while recycling these materials into one with economic value. A major field study is in progress to evaluate the properties of such fill, as part of the Pulau Tekong Reclamation project, off the eastern shore of Singapore. However the behaviour of such fill is very complicated and is affected by the size, the degree of softening these lumps have been subjected to, the way these lumps have been arranged and the fluid that is filling the voids in between the lumps. A number of series of tests have been conducted to understand better the parametric influence of these various parameters. The lump sizes used range from very small lumps of size of 12.5mm onwards to lumps that are up to 200mm and which require specially design large testing tanks. These results are discussed in this report, with a particular emphasis on understanding what is the key factors affecting the overall behaviour. A lumpy fill is characterised by a dual void systems, referred to as inter-lump voids and intra-lump voids. It is clear that one of the most important parameters is the system overall void ratio, where the lumps themselves are considered like solid, in relation to the inter-lump voids. A new concept void index is introduced for study of the consolidation behaviour of lumpy fill in land reclamation. Lumps with varying sizes but similar system overall void ratio are shown to produce fairly similar behaviour. Another important parameter is the degree of softening. The consolidation behaviour of lumpy fill is strongly influenced by the degree of swelling. Also the pre-consolidation pressures of lump have significant effects on the compressibility behaviour of lumpy fill. Pore water measurement in the inter and intra lumps voids and shear strength measurements under different loading stages are also used to evaluate the closing of inter and intra lumps voids present the lumpy fill system. Olsen (1962) cluster model is also used to study the changes in void ratio and permeability in inter and intra lump voids. Also, the possible stages of consolidation behaviour in lumpy fill were discussed. Finally, confirm the phenomena observed in the laboratory, the few laboratory results were compared with field studies.