Sedimentation and consolidation behaviour of fly ash-based geopolymer stabilised dredged mud

Jaditager, Mohamed (2018) Sedimentation and consolidation behaviour of fly ash-based geopolymer stabilised dredged mud. PhD thesis, James Cook University.

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View at Publisher Website: https://doi.org/10.25903/5d2e5735cca09
 
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Abstract

Ports conduct maintenance and capital dredging campaigns to maintain channel depths, improve navigational safety of vessels, and to cater for larger ships with deeper draughts. Most of the soft dredged material derived from these dredging campaigns is beneficially used as a fill material for land reclamation purposes. Port authorities undertake land reclamation works to address land scarcity and environmental constraints that are associated with dredged material placement alternatives.

Land reclaimed with soft dredged mud has geotechnical challenges of slow self-weight consolidation, high compressibility and low bearing capacity. To overcome these geotechnical challenges and to alleviate risk of structures settlement, dredged material stabilisation techniques such as chemical admixtures, electrokinetic, stone columns, prefabricated vertical drains (PVDs), and surcharging are implemented.

For these existing dredged material stabilisation methods to be applicable, the land reclamation fill material must have settled, consolidated and gained sufficient strength and stiffness to be traversed by ground improvement plant and workforce. By then, the reclaimed (the man-made) ground becomes similar to a naturally formed soft ground that civil and geotechnical engineers have no control on its soft soil formation processes. On dredging and land reclamation with soft dredged mud slurry project site, dredge cutters and drag heads rip and disintegrate marine sediment turning it into high water content dredged mud slurry. Then, the dredged mud slurry is pumped into land reclamation containment ponds to settle and self-weight consolidate to form soft land reclamation fill material.

The dredged mud slurry takes several hours from the moment it is placed into containment ponds to the commencement of the land reclamation fill material formation. This time slot is sufficient for an early geotechnical intervention to stabilise the dredged mud while it is still in its slurry stage, prior to the formation of the soft land reclamation fill material. Stabilising the soft dredged mud slurry provides an opportunity to manipulate its sedimentation behaviour that controls microstructure, consolidation and compressibility characteristics of the resulting land reclamation fill material.

This research study has investigated feasibility of stabilising 400% water content dredged mud slurry that is derived from Port of Townsville, Queensland Australia, using fly ash-based geopolymer binder at 6%, 12% and 18% by weight. The fly ash-based geopolymer binder is chosen for its tolerance to high water content nature of the dredged mud slurry, binding attributes, cost effectiveness, and environmental benefits. The study examined the influence of the fly ash-based geopolymer stabilisation on the sedimentation and consolidation behaviours, mineralogy and microstructure of the fly ash-based geopolymer stabilised dredged mud.

Settling column tests were conducted to investigate the sedimentation behaviour of untreated and fly ash-based geopolymer stabilised dredged mud slurries. Standard one-dimensional consolidation (Oedometer) tests were used to evaluate the compressibility and consolidation characteristics of the untreated and the fly ash-based geopolymer stabilised dredged mud sediments. X-ray diffractometer (XRD) and scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS) techniques were deployed to analyse the mineralogy and microstructure of the untreated and the fly ash-based geopolymer stabilised dredged mud.

The study found it is feasible to stabilise high water content dredged mud slurry with fly ash-based geopolymer binder. Fly ash-based geopolymer gel coating dredged mud particles in the slurry was found to be the main stabilisation mechanism. It is noted the geopolymer gel coating dredged mud particles in the slurry has exacerbated flocculation of the stabilised dredged mud slurry, extended its flocculation duration, reduced settling time and shorten overall sedimentation duration. The SEM with EDS analysis showed the fly ash-based geopolymer stabilisation has altered the microstructure of stabilised dredged mud, changed its particles arrangement and reduced its desiccation shrinkage cracks. Subsequently, the fly ash-based geopolymer stabilisation has improved the compressibility and consolidation properties of the stabilised dredged mud by reducing its coefficient of volume compressibility (mᵥ) and increasing its coefficient of consolidation (cᵥ) and permeability coefficient (k). However, the XRD analysis found no correlation between the fly ash-based geopolymer stabilisation and the mineralogy of the fly ash-based geopolymer stabilised dredged mud.

Item ID: 58933
Item Type: Thesis (PhD)
Keywords: consolidation, dredged material, dredged mud, fly ash, geopolymer, land reclamation, maintenance dredging, marine sediments, sedimentation, stabilization
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Copyright Information: Copyright © 2018 Mohamed Jaditager.
Additional Information:

Publications arising from this thesis are available from the Related URLs field. The publications are:

Jaditager, Mohamed, and Sivakugan, Nagaratnam (2018) Consolidation behavior of fly ash-based geopolymer-stabilized dredged mud. Journal of Waterway Port Coastal and Ocean Engineering, 144 (4). 06018003.

Jaditager, Mohamed, and Sivakugan, Nagaratnam (2017) Influence of fly ash-based geopolymer binder on the sedimentation behaviour of dredged mud. Journal of Waterway, Port, Coastal, and Ocean Engineering, 143 (5). pp. 1-9.

Jaditager, M., Lovisa, J., and Sivakugan, N. (2014) Maintenance dredging at Port of Townsville. International Journal of Environmental, Chemical, Ecological and Geophysical Engineering, 8 (12). pp. 734-737.

Date Deposited: 17 Jul 2019 00:08
FoR Codes: 09 ENGINEERING > 0905 Civil Engineering > 090501 Civil Geotechnical Engineering @ 100%
SEO Codes: 87 CONSTRUCTION > 8702 Construction Design > 870201 Civil Construction Design @ 100%
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