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 pounds annually. Expansive soils are those which experience significant volume changes associated with changes in water content. These volume changes can either be in the form of swell or shrinkage, and are sometimes known as swell–shrink soils. Key aspects that need identification when dealing with expansive soils include soil properties, suction/water conditions, temporal and spatial water content variations that may be generated, for example, by trees, and the geometry/stiffness of foundations and associated structures. Expansive soils can be found both in humid environments where expansive problems occur with soils of high plasticity index, and in arid/semi-arid soils where soils of even moderate expansiveness can cause significant damage. 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 the laboratory, and the associated empirical and analytical tools to evaluate expansive behaviour. Design options for pre- and post-construction are highlighted for both foundations and pavements, together with methods to ameliorate potentially damaging expansive behaviour.