4. Properties of clay materials, soils and mudrocks

Abstract

The purpose of this chapter is to provide a background to the properties of natural clay materials used in the construction industry and other applications (see Table 4.1). There is a frequent need to evaluate clay materials for civil engineering projects, which has led to a bias in this chapter towards a consideration of their geotechnical properties. The intention is to present this information, and also some data applicable to other applications, in a manner suitable for scientists and engineers with an interest in clay materials. Both fundamental material behaviour and derived parameters are described.This chapter considers the engineering behaviour of rock and soil materials that consist largely of clay mineral grains, together with minor amounts of other minerals. As discussed in Chapter 1, the term clay may mean a material made of clay-sized grains (smaller than 2 µm or 0.002 mm) or of grains consisting of clay minerals (see Chapter 2). Grains smaller than 2 µm may be clay minerals or other materials such as finely ground quartz or rock flour. Clay mineral grains may be larger than 2 µm and they are often bound into silt-sized (0.002-0.06 mm) aggregates. The Chapter concentrates on the properties of the material relevant to the exploitation and uses of excavated or extracted clays and mudrocks, rather than those of soil and rock masses in the ground, which are outside the scope of this report.The behaviour of clays depends on their particle size distribution, mineralogy and moisture content. In