Geochemistry in Geotechnical Engineering Problems: Ettringite as Case Study

Abstract

Chemical and environmental changes in soils can affect their geotechnical properties, a fact that is increasingly acknowledged in recent years. Geochemistry offers a wide variety of modelling and experimental tools that can be used to study related problems. An increased number of researchers utilize geochemical modelling and spectroscopy to study changes in soil chemistry in the geotechnical field. This study illustrates the application of this methodology to a significant geotechnical problem, ettringite-induced heave in stabilized clays. Geochemical modelling was used to estimate the ranges of dissolved constituents that are needed to make ettringite, i.e. Ca, Al and SO₄, as well of silica, which is known to influence indirectly ettringite stability. The study illustrates that systematic testing of ion activities in stabilized soils to generate data for modelling is needed, as well as understanding of the relationship of these activities to soil mineralogy, the type of stabilizer and time. Spectroscopy, such as X-ray Diffraction, can aid in this regard by providing an understanding of soil mineralogy, both qualitative and quantitative.