Model tests of prefabricated horizontal drains with vacuum preloading on clay slurry for land reclamation
Goh, Joel Han
Date of Issue2016-05-24
School of Civil and Environmental Engineering
Land reclamation is a process of creating new land, usually from coastal areas, rivers or lakes by filling it with suitable soil materials. Pioneer reclamation projects in Singapore were carried out at a swampy ground in the area called South Boat Quay in the early 1800s. Singapore has plans to carry out more land reclamation projects to increase the land area by another 10,000 ha beyond 2030. The reclamation projects in Singapore include expansion of the Changi Airport, Pulau Tekong, Jurong Island, etc. Due to the limited supply of fill materials, Singapore has to import the landfill material from other countries such as Cambodia. However, this approach will not be sustainable in the long run due to the increasing cost of landfill materials. Hence in this report, we look into the use of marine clay and clayey soils as an alternative material to the granular soils that are typically used. The usage of clayey soil has its own set of challenges with the fine grained soils presenting a much longer settlement and consolidation time, which could result in potential delay in projects and eventually sustained economic losses. Therefore, in this project we also look into the use of vacuum to accelerate the settlement and consolidation process. This FYP project reports the findings of the technical feasibility of using the chemical flocculant hydrated lime on the consolidation, and vacuum pressure on the settlement and dewatering of clayey soil. The objective of this study is to investigate the settling behaviour and geotechnical properties of soil slurry(both marine clay and kaolin) under the effect of the chemical flocculant hydrated lime(Ca(OH)2) by conducting preliminary trials in 1L cylinders. In the first preliminary trials using kaolin slurry, the results showed that the addition of hydrated lime(Ca(OH)2) holds no bearing over the rate of settlement, and in fact, samples with lower lime content exhibited faster settlement rates. Samples with 0% lime content were able to achieve 50-100% more settlement as compared to samples with 2%, 4% and 8%. Results also showed that samples with higher water contents are able to achieve higher settlement rates. In the next preliminary trial using marine clay, no settlement was observed at all. The disparity in results from both trials is mainly due to the difference in permeability between kaolin and marine clay, with the latter having a significantly lower permeability and hence the lower settlements achieved. Finally in the settlement tank test, horizontal drains were sewn onto a geotextile fabric and placed at the middle of the clay slurry in a 1m by 1m by 1.5m tank. A pump was attached to the horizontal drains to pump out the water, and the effectiveness of this method on the settlement rate of the kaolin slurry was determined. Results indicate that the rate of settlement when using both the pump and horizontal drain can be up to 12 times as fast as if the clayey slurry were to self-consolidate. However, a few problems were encountered with the method of data collection and as a result of unexpected reactions of the settling clay, certain measurements(porewater and settlement) could be slightly affected. Recommendations and appropriate improvisations to the experiment will be discussed in the following sections.
Final Year Project (FYP)
Nanyang Technological University