Development of a constitutive model for a heaving clay from Rosebank
Heaving clays are partially saturated soils composed of a high fraction of the montmorillonite clay mineral. When exposed to free water they undergo volumetric expansion, which often results in differential movements at the surface and damage to building structures founded on the clay. The economic consequences of such damage is severe. Heaving clay causes in excess of R100 million damage in South Africa each year, making it the country's most significant problem soil. The best method of dealing with a heaving clay is through appropriate design. This would be facilitated if methods such as finite element analysis were available to designers. The aim of this research project was to develop a constitutive model for an expansive clay which could be numerically implemented within the finite element method. A review of available literature on expansive clays showed that the heave strain that clay under an applied load will undergo can be expressed in terms of the parameters percent heave and heave pressure. These parameters are influenced by the degree of moisture changes experienced by the soil, and its dry density. Various different methods of establishing the percent heave and heave pressure have been proposed, but the values given by each differ due to the influence of different test stress paths on the results. More detailed examination of the effect of test stress path on the volume of heaving clays was therefore required to resolve the reasons for the differences in the test results, and to give a fuller understanding of the volumetric response of the material for the purposes of developing the constitutive model. Hence a series of laboratory tests was conducted on a clay from Rosebank in the Cape Province to investigate the effect of test stress path on the clay volume.
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