Lime stabilisation of clay soils

Abstract

Clay soil can be stabilised by the addition of a small percentage, by weight, of lime, that is, it enhances many of the engineering properties of the soil. This produces an improved construction material and so the technique has been used for many construction purposes, notably in highway, railroad and airport construction to improve subgrades and sub-bases. Generally the amount of lime needed to modify a clay soil varies from 1 to 3 per cent, whilst that required for cementation varies from 2 to 8 per cent. When lime is added to clay soils, calcium ions are combined initially with or adsorbed by clay minerals which leads to an improvement in soil workability, that is, to an increase in the plastic limit of the clay and generally to a decrease in its liquid limit. The optimum lime additive for maximum increase of the plastic limit of the soil is referred to as the lime fixation point Lime added in excess of the fixation point is utilised in the cementation process and gives rise to an increase in soil strength. The increase in strength has been attributed to the formation of poorly ordered reaction products which surround the clay minerals.