Consolidation properties of recent dredged mud sediment and insights into the consolidation analysis

Ganesalingam, Dhanya (2013) Consolidation properties of recent dredged mud sediment and insights into the consolidation analysis. PhD thesis, James Cook University.

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Abstract

Within the past few decades, increased population and infrastructure development have necessitated planning the development activities on soft soil deposits. In addition to treating the existing soft soils, new land areas are formed in the sea in order to expand the adjacent facilities such as Airports and Ports. Land reclamation projects are increasingly carried out in a sustainable way by reusing the maintenance dredged mud as filling materials. There are number of large scale land reclamation projects, where maintenance dredged mud is utilised to fill the reclamation site, such as Port of Brisbane expansion project, offshore expansion project at Tokyo international Airport and Kansai international airport development project, to name few.

Soft soils show poor load bearing capacity and undergo large settlement under a load application, thus they should be consolidated prior to the commencement of construction activities. The soft layers are preloaded in conjunction with prefabricated vertical drains (PVD) to speed up the consolidation process. In the case of land reclamation works, the dredged mud slurry is first allowed to undergo sedimentation before it is consolidated.

Reliable analysis of time dependent consolidation process and settlement of the soil layer is important to plan ahead the construction activities. Accurate consolidation analysis requires appropriate theories, tools and understanding of the subsoil conditions. Several consolidation theories have been developed to model the consolidation mechanism of soils mathematically, which are solved with boundary conditions relevant to the practical problem to produce mathematical solutions. In the absence of simplistic mathematical solutions, empirical equations and approximations are used to predict the time dependent consolidation and settlement of soil layer. This dissertation focuses on enhancing the consolidation analysis of soft soil layers by the critical review of existing solutions available for the consolidation analysis of single and multi-layers.

The standard mathematical solutions available for the radial consolidation of soil layer were developed considering a uniform initial excess pore water pressure distribution in the soil layer. The potential non-uniform excess pore water pressure distributions that can practically occur were not incorporated in the solutions. Within this dissertation, the effect of different non-uniform pore water pressure distributions on the radial consolidation behaviour of a soil layer, where the pore water flow is radially outwards towards a peripheral drain, is analysed through a mathematical study. Graphical solutions are developed for the average degree of consolidation and pore water pressure and degree of consolidation isochrones are plotted.

To analyse the time dependent consolidation behaviour of multi-layered soil, empirical equations and approximations have been developed to overcome the difficulties associated with the complex mathematical solutions. These approximations do not have any sound theoretical basis and thus have limitation in their application. Another objective of the dissertation is to investigate the applicability of selected approximation in the consolidation analysis of double layer soil considering different properties, thicknesses and drainage conditions. For this, an error analysis is conducted utilising the advanced soft soil creep model in PLAXIS. One-dimensional consolidation of a double layer system is experimentally modelled in the laboratory. The consolidation tests are simulated in PLAXIS to validate the soft soil creep model. Further, expressions are proposed for the equivalent stiffness parameters of a composite double layer system, which was verified using the results obtained from the experiments and PLAXIS modelling.

Sedimentation of soft soil is common in the land reclamations works carried out using dredged mud as filling materials. The initial conditions of the soft soil slurry, such as the water content and salt concentration, influence the settling pattern of particles during the sedimentation. This dissertation presents the extensive laboratory studies conducted to investigate the effect of settling patterns of particles in the final properties of the dredged mud sediment. In the experiments, dredged mud is mixed with sea water and freshwater at different water contents to induce various settling pattern of particles reflecting the sedimentation environment. Series of oedometer tests are conducted for the radial consolidation and vertical consolidation and the compressibility and permeability properties are assessed. From the results the depth variation of the sediment properties and anisotropy between the horizontal and vertical properties are evaluated for the different settling patterns.

Further, the dissertation presents a new estimation method to calculate the horizontal coefficient of consolidation from the radial consolidation tests conducted using a peripheral drain. The proposed method was validated using series of radial consolidation tests, which is described in this dissertation.

Item ID: 29581
Item Type: Thesis (PhD)
Keywords: land reclamation; dredged mud; consolidation process; consolidation analysis; radial consolidation testing
Additional Information:

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

Ganesalingam, Dhanya, Sivakugan, Nagaratnam, and Ameratunga, Jay (2013) Influence of settling behaviour of soil particles on the consolidation properties of dredged clay sediment. Journal of Waterway Port Coastal and Ocean Engineering, 139 (4). pp. 295-303.

Ganesalingam, Dhanya, Sivakugan, Nagaratnam, and Read, Wayne (2013) Inflection point method to estimate c(h) from radial consolidation tests with peripheral drain. Geotechnical Testing Journal, 36 (5). pp. 707-712.

Ganesalingam, Dhanya, Ameratunga, Jay, Scweitzer, Guy, Boyle, Peter, and Sivakugan, Siva (2012) Anisotropy in the permeability and consolidation characteristics of dredged mud. ANZ 2012 Conference Proceedings Ground Engineering in a Changing World: 11th Australia - New Zealand Conference on Geomechanics, 15-18 July 2012, Melbourne, VIC, Australia.

Ganesalingam, Dhanya, Arulrajah, Arul, Ameratunga, Jay, Boyle, Peter J., and Sivakugan, Nagaratnam (2011) Geotechnical Properties of reconstituted dredged mud. Proceedings from the Pan-AM CGS Geotechnical Conference 2011 Pan-Am CGS Geotechnical Conference, 2-6 October 2011, Toronto, Canada.

Ganesalingam, Dhanya, Read, Wayne, and Sivakugan, Siva (2013) Consolidation behaviour of a cylindrical soil layer subjected to nonuniform pore-water pressure distribution. International Journal of Geomechanics, 13 (5). pp. 665-671.

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Date Deposited: 11 Oct 2013 01:34
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040310 Sedimentology @ 33%
09 ENGINEERING > 0905 Civil Engineering > 090501 Civil Geotechnical Engineering @ 33%
09 ENGINEERING > 0905 Civil Engineering > 090502 Construction Engineering @ 34%
SEO Codes: 87 CONSTRUCTION > 8798 Environmentally Sustainable Construction > 879804 Management of Solid Waste from Construction Activities @ 34%
87 CONSTRUCTION > 8703 Construction Materials Performance and Processes > 870304 Stone, Ceramics and Clay Materials @ 33%
87 CONSTRUCTION > 8701 Construction Planning > 870102 Commercial Construction Planning @ 33%
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