Improvement of clay soils in situ using lime piles in the UK

Lime piles, which essentially consist of holes in the ground filled with lime, have been used for two distinct purposes for the treatment of clay soils in situ. The first concerns the treatment of soft soils to improve their bearing capacity and in this case uses relatively large diameter quicklime piles at close spacings. The result is a significant reduction in the water content of the soil, causing densification and concomitant increases in its strength and stiffness. The second application is in the stabilisation of failing slopes, for which both quicklime and lime slurry piles have been used with the intention of causing ion migration and subsequent lime-clay reactions in the surrounding soil. However, although they have been successfully used worldwide, their usage has been relatively limited in relation to other techniques and the applications in which they have been used have been diverse. For this reason the literature on the subject has tended to be inconsistent at best, and in some cases directly contradictory. There is thus an apparent lack of understanding of how lime piles work. This paper aims to produce some clarity by interpreting the literature in the light of recent research. A summary of the stabilisation mechanisms that the current authors believe to operate is presented and the evidence from the literature that supports or contradicts these mechanisms is discussed. The results of this process thus provide a basis of design, albeit using parameters that need further definition for site specific application. For illustration, the design process is discussed in terms of UK application. (C) 1997 Elsevier Science B.V.