Chemical methods in dewatering clayey slurry for land reclamation (GE27AB/ISP)
Date of Issue2015
School of Civil and Environmental Engineering
Nanyang Technological University
Land reclamation is a process of creating new land from river, lake, or sea by dumping landfill material into it. The first reclamation project in Singapore was carried out at a swampy ground in the area called South Boat Quay in 1822. The country has a plan to carry out more land reclamation project to increase the land area by up to another 10,000 ha in 2030 (Wikipedia, 2015). The reclamation projects in Singapore include expansion of the Changi Airport, Pulai Tekong, Jurong Island, etc. However, due to the limited supply of fill materials, Singapore has to import the landfill material from other country such as Cambodia. This approach will not be sustainable and delay the project. In this circumstance, the other alternative of using the clay material such as marina clay or waste soil from construction site is probably the only choice for land reclamation in Singapore. However, the usage of clay soil for land reclamation faces technical challenges such as very long settlement time as it is in the form of clay slurry. Therefore, in this FYP project reports findings of the technical feasibility of using chemical flocculant for the dewatering of soil slurry. The objective of this study is to investigate the settling behaviour and geotechnical properties of soil slurry and also the effect of chemical flocculant by conducting preliminary test, the settling column tests, and geotechnical properties tests respectively. In preliminary test, the results showed that the addition of Polyacrylamide (PAM) increased the settling rate of untreated clayey slurry. The obvious effect was observed when the PAM increase from 0.5 g/kg dry soil to 4 g/kg dry soil. Cationic PAM+15 type seemed to be the most effective type with optimum dosage of 1 g/kg dry soil. In the settling column tests, the results showed that the settlement rate of treated clayey slurry was faster than that for untreated clayey. The performance varied with the dosage of PAM added. This result is supported by the result from particle size distribution test. Addition of the chemical into clayey slurry increased the soil particle size. However, in terms of the final settlement, the observed soil-water interface height at the end of the experiment was higher in experiment with clayey slurry treated with chemical flocculant. Such increase was possibly due the formation of void. In the geotechnical behaviour, the values of undrained shear strength (Su) were obtained directly from portable vane shear. The results showed that the peak Su value of treated clayey slurry with PAM dosage of 3 g/kg dry soil is 0.9 kpa and 0.8 kpa at the depth of 30 cm and 50 cm respectively from the slurry surface and other batches of zero and lower PAM dosage are zero value. In summary, the results obtained suggested that by using PAM, the settling rate and geotechnical behaviour of marine clay slurry was increased. Further experiments are required to further ensure the suitability and feasibility of marine clay for land reclamation.
Final Year Project (FYP)
Nanyang Technological University