Expansive soils

Expansive soils present significant geotechnical and structural engineering challenges the world over, with costs associated with expansive behaviour estimated to run into several billion annually. Expansive soils are soils that experience significant volume change associated with changes in water contents. These volume changes can either in the form of swell or in the form shrinkage and this is why they are sometime known as swell/shrink soils. Key aspects that need identification when dealing with expansive soils include: soil properties, suction/water conditions, water content variations temporal and spatial, e.g. generated by trees, and the geometry/stiffness of foundations and associated structures. Expansive soils can be found in humid environments where expansive problems occur with soils of high Plasticity Index (Ip) or in arid/semi arid soils where soils of even moderate expansiveness can cause significant damage. In the UK damage often occurs as a direct result of interaction with vegetation and associated water content changes. Soils that experience swell/shrink problems in the UK are typically found in the south and east of the country, notably around London, corresponding to the drier parts of the UK. However, moderate swell/shrink potential can be exhibited across many parts of the country. This chapter reviews the nature and extent of expansive soils, highlighting key engineering issues. These include methods to investigate expansive behaviour both in the field and in the laboratory and the associated empirical and analytical tools to evaluate expansive behaviour. Following this design options for pre and post construction are highlighted for both foundations and pavements, together with method to ameliorate potentially damaging expansive behaviour.