Application of soft material for reclamation fill

Abstract

Singapore is a city state with limited land space, hence to cope with the growing demands of land use, land reclamation has to be carried out. However, there is severe shortage of granular fill materials (sand) as reclamation fill. On the other hand, a large amount of soft cohesive soil (marine clay) is generated through infrastructure development and maintenance dredging works. The disposal of these excavated spoil and dredged materials becomes a problem in the land-scarce Singapore. These two problems can be overcome if an innovative method can be developed to use these abundant soft materials to replace the acute shortage of granular fill material for land reclamation works. However soft clay is not extensively used in reclamation works due to limited knowledge about its behaviour during the filling and settling process.

The objective of this project is to investigate the suitability of using marine clay as fill material for land reclamation. This report details the study of the behaviour of a clayey fill material during settling. A total of 13 lab scale settling column experiments with varying parameters (e.g. height, filling sequence, existing medium and presence of chemicals) were carried out to analyse the optimum conditions for the settlement of marine clay. The results showed that when filling is carried out in stages, the final interface is lower. In addition, the presence of the coagulant, aluminium chloride, also results in a lower final interface level. This study suggests a possibility of enhancing the settling velocity of clayey fill materials by adjusting the fill operations. However, further studies need to be done to fully understand the settling properties of marine clay to consider the effects of other parameters which were not considered in this study e.g. pH, temperature, varying coagulant concentration, etc. Also the duration of the tests were only carried out for a maximum of 40 days due to time constrain, hence it is recommended that observations should be done over a longer period.