Stabilisation and treatment of clay soils with lime. Part 1 - basic principles: Bell, F G Ground EngngV21, N1, Jan 1988, P10–15

Abstract

Clay soil can be stabilised by the addition of a small percentage, by weight, of lime. This produces an improved construction material. 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. Montmorillonitic clay soils respond more rapidly to lime treatment than do those in which kaolinite is the dominant clay mineral. 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 initial increase in strength has been attributed to the formation of poorly ordered reaction products which surround the clay materials. However, the development of long-term strength appears to be due to the gradual crystallisation of structurally-ordered new minerals from the initial disordered reaction products. The principle uses of the additions of lime to clay soils is for, firstly, stabilisation of subbases and subgrades in pavement construction and, secondly, to dry out wet soils. Lime treatment also has been used to stabilise embankments and canal linings, and to improve foundation soils. In the latter instance soil is stabilised beneath strip or raft foundations, or lime piles or columns are formed. (TRRL)