Ion migration associated with lime piles: a review

This paper aims to present a critical review, and in many cases a reinterpretation, of the literature on calcium and hydroxide ion migration from a lime source, a phenomenon commonly termed 'lime migration'. The relevance of this review extends from the classical mix-in-place surface or deep stabilisation techniques to cases in which ion migration is relied upon to treat an intact soil mass, such as in lime slurry pressure injection and lime piles. The phenomena causing migration, and means of their modelling, are presented to provide a context for a discussion of the findings from various laboratory and field experimental studies. The paper concludes that ion migration is not well researched, other than in contaminated ground applications, and is commonly overlooked in ground improvement technique design. Nevertheless, by piecing together the evidence from many studies a clear pattern of the effects of, and influences on, ion migration emerges. It is apparent, for example, that the degree and rate of migration depend strongly on the initial water content (the presence of water in the soil is essential for ion migration) as well as on curing time, soil mineralogy and the presence of gradients other than the chemical gradient. The strong relationship between the chemical and physical influences on ` lime migration' and its effects indicate the requirement of both physical and chemical testing to allow a more integrated approach to research and practical application in this area.