Lime and cement stabilisation

Weak soils can be improved in strength and workability by the addition of lime and/or cement. Other materials such as pulverised fuel ash (PFA) or ground granulated blast furnace slag can be used, but are not covered in this chapter. However, the principles of application are the same. The use of the process as a temporary measure is generally to provide a sound working surface for construction (although the treated soil has been altered permanently). Lime is usually applied to the soil in the form of quicklime. This has an immediate effect in taking moisture from wet soils and is especially effective in soft, wet, plastic clay. The lime also reduces the plasticity of the clay and so makes it both stronger and more workable. If added in sufficient quantity, it produces a cementing effect with considerable additional increase in strength over time. Cement also reduces the moisture content and plasticity, although less effectively than lime. It does, however, have a greater cementitious effect. It is more suitable for treating lower plasticity or non-plastic soils. The results of adding lime or cement are very soil-specific, so preliminary testing is essential to ensure that the desired effect(s) can be achieved and to find the optimum concentration and type of additive. The effects vary with plasticity and other properties, so that a substantial test programme is needed in variable soils such as glacial till. Blends of lime and cement can be used and other cementitious agents, such as PFA, may be incorporated.