Effects of anisotropy on the behaviour of unsaturated compacted clay

  • Rajaradnam Sivakumar

Student thesis: Doctoral ThesisDoctor of Philosophy


During the last two decades, a number of elasto plastic constitutive models have been proposed to model the behaviour of unsaturated soils. Many of the models were developed on the basis of the modified Cam Clay theory for saturated soils. However, the elasto-plastic models for unsaturated soils were validated based on the data obtained from samples prepared one dimensionally compacted into a compaction mould. This process inevitably generates a degree of anisotropy in the samples and additional complexity in the modelling techniques. Therefore, this thesis is aimed at examining the effects of anisotropy on the behaviour of unsaturated compacted clay.

As part of the research, a series of controlled suction and varying suction tests were carried out on unsaturated soil samples that have had an isotropic structure inherited from previous stress history. The samples were prepared using aggregated kaolin prepared at 25% moisture content and subsequently compressed isotropically in a large triaxial cell. The pressure required to compress the samples isotropically in the large triaxial cell was selected in such a way that it would give a specific volume of either 2.2 or 1.98, which is equivalent to the specific volume of the samples obtained from statically compressed kaolin in a one dimensional compaction mould with a vertical pressure of 400 kPa and 800 kPa respectively. The controlled suction tests were conducted in a newly de eloped twin-cell and double-walled stress path apparatus whereas the varying suction tests were conducted in a modified triaxial cell. In addition to this a series of mercur intrusion porosimetry tests, were also performed on isotropically compressed and statically compressed samples to evaluate the effects of pore size distribution on that behaviour of unsaturated soils.
Date of AwardJul 2006
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SupervisorVinayagamoothy Sivakumar (Supervisor) & David Hughes (Supervisor)

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