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This paper presents details of a study that deals with determination of engineering properties, identification of phases of major hydration products, and microstructural characteristics of a zinc-contaminated (referred to as Zn-contaminated in this paper) kaolin clay when it is stabilized by a cement additive. Investigations were carried out with respect to the effect of the level of zinc (Zn) concentration on the overall soil properties including Atterberg limits, water content, pH, stress–strain characteristics, unconfined compressive strength, and secant modulus. In addition, X-ray diffraction, scanning electron microscopy, and mercury intrusion porosimetry studies were conducted to understand the mechanisms controlling the changes in engineering properties of the stabilized kaolin clay. The study reveals that the level of Zn concentration has a considerable influence on the engineering properties, phases of hydration products formed, and microstructural characteristics of the stabilized kaolin clay. These changes are attributed to the retardant effect of Zn on the hydration and pozzolanic reactions, which in turn alters the phases of hydration products and cementation structure – bonding of the soils. Theoretical simulation of the pore-size distribution curves demonstrates that the cement-stabilized kaolin exhibits bimodal type when the Zn concentration is less than 2%, whereas it displays unimodal type when the Zn concentration is 2%. With an increase in the Zn concentration, the characteristics of the interaggregate pores in terms of volume and mean diameter change considerably, whereas those of intra-aggregate pores remain nearly unchanged.

Vacuum preloading of clay deposits is becoming an increasingly popular ground improvement technique. Although many studies have been reported in literature, the mechanism of vacuum preloading is still not properly understood. Soil under vacuum preloading is expected to undergo an inward lateral deformation, therefore the influence of lateral deformation on volumetric strain requires further analysis. This paper addresses this aspect through laboratory studies on reconstituted samples of kaolinite. The Rowe cell apparatus was modified to measure lateral deformation under various states of stress because lateral and vertical deformation of soil depends on its state of stress and associated lateral pressure. A method for predicting the volumetric and lateral strains under vacuum consolidation is proposed and then applied to two case studies in China.

Engineers in geotechnical practice work on increasingly complex problems with increasingly powerful numerical tools. Effective solutions to design problems need good information about the site and parameters (or functions) that describe how the soil will behave under the proposed loadings. These loadings can include heating, drying or wetting, time effects, and chemical changes as well as the more common structural loads. This paper outlines issues that need to be considered when laboratory tests are used to produce soil properties for use in numerical analyses. The focus is on soft to moderately stiff saturated clays. Similar considerations for in situ tests, stiff clays, and sands are not considered.Key words: clay, testing, characterization, properties, constitutive modeling.

The Cam-Clay model for isothermal mechanical behaviour of clays has been extended to take account of the effects of temperature on stress–strain behaviour. The assumptions used in constructing the new model are based on published results and on new data presented in the paper. The model allows prediction of how heating and cooling affect volume changes, pore-water pressures, and strengths for both normally consolidated and overconsolidated saturated clays. It permits modelling of observed reductions in the overconsolidation ratio with increasing temperature. The model provides accessible qualitative explanations for temperature effects that were previously difficult to understand. It will also allow easy implementation for quantitative modelling in triaxial stress fields. Results predicted by the model are compared with data collected by the authors at temperatures up to 100°C. The model does not account for changes that occur in clay minerals at higher temperatures, for example, in bentonites at temperatures higher than about 150°C.Key words: clay, triaxial, temperature, modelling, elastic–plastic, Cam-Clay.