Assessment and analysis of Queensland clay behaviour

Rankine, Briony Rachelle (2007) Assessment and analysis of Queensland clay behaviour. PhD thesis, James Cook University.

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Abstract

Within the past few decades, increased population and infrastructure development has necessitated the reclamation and development of previously undesirable sites for civil engineering works. In Australia, significant development has taken place along the Eastern coastal belt. This region is lined with saturated clays of significant depths (15 m to 20 m) which are typically characterized by high compressibility, low bearing capacity, and high lateral displacement upon loading.

The most common and economically viable technique for soil improvement of these foundations is the use prefabricated vertical drains (PVD) in conjunction with preloading. This method accelerates the consolidation process by shortening the drainage path of the soil in the radial direction, and has been used in a number of large projects including the Muar Plains Trial Embankments, Changi East Reclamation Project and the 2nd International Bangkok Airport. Nevertheless, there are very limited case studies of soft clay projects in Australia.

General theory of soil behaviour is well established based on the broad classifications of granular and cohesive soils. . However, due to the innumerable environmental and physical processes a soil may be exposed to during its formation, there is natural variance in soil properties. Thus, a holistic approach is advocated for geotechnical calculations at any site. The design methods should be used together with field observations, as well as data obtained from in situ and laboratory testing.

When examining the deformation behaviour of clays, engineers are interested not only in the consolidation and compressibility characteristics of a soil, but also the index properties of it. The index properties of a soil describe certain critical stages in soil behaviour, and also the consistency of a soil. Within this dissertation, the index properties of soils from a number of different sites around Queensland have been tested within the laboratory, and analysed statistically. Beta distributions have been Further to this characterization, the inherent variation introduced solely as a result of the manual nature of testing these properties, has been examined and quantified. Covariance between index properties has been examined, and equations specific to Queensland soils produced to describe it.

Laboratory testing and examination of the consolidation and compressibility characteristics specific to Queensland clays have also been undertaken, and are correlated to the measured index properties.

Commonly, settlement calculations for a given embankment loading are considered in three stages - immediate settlement, consolidation settlement and secondary compression. Generally, the consolidation phase contributes the most significant portion of settlement in clays. Calculations for this phase undertaken by using the assumptions of average coefficient of volume compressibility, m[v], and also instantaneous loading. However, both assumptions are incorrect, and can lead to gross miscalculation of the settlement magnitude. A new method of analytically determining the settlement of a foundation taking into account the stress dependence of m[v], and also the loading sequence of an embankment has been formulated and is described herein.

Furthermore, the dependence of the coefficient of volume compressibility (m[v]) on the overconsolidation ratio, and consistency of a soil has been examined and an empirical correlation developed to describe it.

The coefficient of secondary compression (C[α]) was also examined in the same manner. While no definitive trend was established to describe the influence of consistency on this parameter, it was found that smaller C[α] values should be expected for increased overconsolidation ratios.

This dissertation also presents the case study of an embankment constructed in South East Queensland. This case study has been numerically modelled using the finite difference package FLAC. This embankment was comprised of three different sections. The first two embankment sections were installed with vertical drains at spacings of 1 m and 2 m respectively and the third, was the control case, and was left free of ground improvement.

Lastly, lateral displacements which develop in soft clay foundations during and after the construction are a major source of concern for engineers due to their detrimental effect on the behaviour of adjacent structures and amenities. A method of predicting the short term lateral displacements induced through embankment loading has been developed. The dependence of these displacements on soil properties, embankment geometry and also distance from the embankment toe are also examined.

Item ID: 24950
Item Type: Thesis (PhD)
Keywords: Australia; Australian East Coast; civil engineering; clay soils; compression; consolidation; design; index properties; settlement; soft clays; soil behaviour; soil behaviour; soil consolidation; soil mechanics; soil properties; South East Queensland
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Rankine, B.R., Sivakugan, N., and Messer, T.R. (2004) Anisotropy of consolidation parameters in artifically sedimented clays. Proceedings of the 9th Australia New Zealand Conference on Geomechanics. To the eNZ of the Earth , 8-11 February 2004, Auckland, New Zealand , pp. 717-723.

Rankine, B., Sivakugan, N., and Wijeyakulasuriya, V. (2005) Observed and predicted behaviour of clay foundation response under the Sunshine Motorway trial embankment. Proceedings of the 16th International Conference on Soil Mechanics and Geotechnical Engineering. 16th International Conference on Soil Mechanics and Geotechnical Engineering , 12 - 16 September 2005, Osaka, Japan , pp. 951-954.

Date Deposited: 12 Feb 2013 05:20
FoR Codes: 09 ENGINEERING > 0905 Civil Engineering > 090502 Construction Engineering @ 100%
SEO Codes: 87 CONSTRUCTION > 8799 Other Construction > 879999 Construction not elsewhere classified @ 100%
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