Investigation of Shrinkage and Swelling Behaviour of Expansive/Non-Expansive Clay Mixtures

Abstract

This paper presents an investigation of physical and engineering properties of expansive clays prepared by reconstituting Na-montmorillonite bentonite mixed with natural non-swelling Bangkok clay. The Bangkok clay contents were varied to 0, 20, 40, 60, 80 and 100% by weight. This investigation aims at highlighting the influence of the non-swelling clay content on physical and mechanical properties of the mixture by paying particular attention to its effect on shrinkage and swelling potential. The basic physical properties were determined, along with the unconfined compression, oedometer, compaction and CBR characteristics. The linear shrinkage bar tests and swelling tests were also performed to observe the areal shrinkage and vertical swelling strains. In addition, a microstructure investigation was conducted through X-Ray diffractometer (XRD) and scanning electron microscope (SEM) observations. By increasing the Bangkok clay content in the mixture clays, the compressive strength and CBR values were markedly increased, while the plasticity and the swelling and shrinkage strains were reduced significantly. Correlations were established between the index properties and other properties such as the maximum dry density (MDD), the optimum moisture content (OMC), the CBR, the compression index (C_c), and the swelling index (C_s). These correlations were tested against data from some previous studies on other soil types including natural expansive clays and found to be applicable satisfactorily in most cases. It was also found that a relatively large increase of non-swelling clay content is necessary to obtain markedly larger strength, while the plasticity is greatly reduced by a minor increase. The above findings will be useful in designing earth works where locally occurring expansive clays are desired to be used with minimum improvements.