STABILIZATION OF CLAY SOILS WITH LIME

Clay soil can be stabilized by the addition of a small percentage by weight of lime, the latter enhancing many of the engineering properties of the soil. Clay soils containing montmorillonite respond more rapidly to lime stabilization than do those in which kaolinite is the predominant clay mineral. Lime stabilization produces an improved foundation material and so the technique has been used for 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% whereas that required for cementation varies from 2% to 8%. When lime is added to clay soils, calcium ions are combined initially with or adsorbed to clay minerals. This leads 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 used in the cementation process and gives rise to an increase in soil strength. The initial increase in strength has been attributed to the formation of poorly ordered cementitious products which surround the clay minerals. However, the development of long-term strength appears to be due to the gradual crystallization of structurally ordered new minerals from the initial disordered reaction products. Stabilization of clay soils with lime leads to an increase in their optimum moisture content and is accompanied by a decrease in their maximum dry density. In addition, the permeability of most clay soils is enhanced by the addition of lime, as is their resistance to frost activity.(A)