5. World and European clay deposits
5.1. The character of clay
Clay can have a number of meanings in engineering geology. The term can relate to mineralogy, implying an assemblage of clay minerals; to size, implying an assemblage of clay sized particles (in British engineering terminology < 0.002 mm); or to behaviour, implying a material which contains a sufficiently high clay size/mineral content to influence the material properties.
In traditional litho-stratigraphic nomenclature the term ‘clay’ is used loosely to refer to fine-grained deposits. These may comprise various constituents, including clay minerals, which have been derived from the weathering of the less stable components of the original rock, fine particles of quartz, feldspar and mica, and diagenetic minerals which have developed during the deposition, burial and uplift history of the deposit.
Broadly, the important clay mineral groupings are kaolinite, smectite and illite (Chapter 2) and one or more of these groupings tend to dominate a particular deposit. This is because the character of the clay mineral found in any particular soil depends on factors such as parent material, climate, topography, vegetation, and the length of time over which these factors have operated. In other words particular deposits form or are modified under specific environmental influences. Perhaps the most dominant of these are climate and time.
In tropical regions the relatively rapid chemical weathering associated with high annual temperature and high annual rainfall contributes to the formation of residual clay soils whose mineralogy is controlled by local environmental influences such as the local drainage regime. This mineralogy controls the engineering behaviour. In arid regions clay soils are relatively rare but tend to be saline and dominated by evaporite minerals. These conditions also seem to favour the formation of the clay mineral attapulgite.
Figures & Tables
Concluding the trilogy on geological materials in construction by specially convened Geological Society working parties, this authoritative volume reviews many uses of clays, ranginf from simple fills to manufactured products. Comprehensive and international coverage is achieved by an expert team, including geologists, engineers and architects, who met over six years to produce the book. Packed with information prepared for a wide readership, this unique handbook is also copiously illustrated. The volume is dedicated to the memory of Professor Sir Alec Skempton.
Various definitions of ‘clay’ are explored. Clay mineralogy is described, plust the geological formation of clay deposits and their fundamental materials properties. World and British clay deposits are reviewed. New compositional data are provided for clay informations throughout the British stratigraphic column. Investigate techniques and interpretation are considered, ranging from site exploration to laboratory asessment of composition and engineering performance.
Major civil engineering applications are addressed, including earthworks, earthmoving and specialized roles utilizing clays. Traditional earthen building is included and shown to dominate construction in places. Clay-based construction materials are detailed, including bricks, ceramics and cements. The volume also includes a comprehensive glossary.