ABSTRACT
Geochemical/biogeochemical evolution of natural soils occurs as a normal time-related ageing process, the results of which are manifested in terms of changes in the nature of the soil and its characteristics and properties. This is why soils are often referred to as dynamic living systems. When soils, such as clays, are used as construction or liner/buffer/barrier materials, they are said to undergo maturation and ageing from the day they are emplaced. The same time-related ageing processes apply to clays used as clay buffers and barriers – either as stand-alone systems or as clay buffer/barrier components in engineered multi-barrier systems for containment of high-level radioactive waste (HLW) and hazardous solid waste (HSW)/municipal solid waste (MSW) (see Figures 2.6-2.8 and 2.10-2.12). The term engineered clay buffer/barrier has been used in the literature to mean both a stand-alone barrier and a part of a multi-component barrier (multi-barrier) system. In this book, an engineered clay buffer or barrier is a stand-alone clay buffer or barrier that is designed (engineered) to function as a containment system. When the clay is used as a barrier or liner component in an engineered multi-barrier system (EBS) (as shown in Figures 2.10-2.12) we will refer to this as a clay barrier component. As in the previous chapters, we will use the term clay buffer/barrier to mean both the stand-alone system and the clay barrier component in the EBS. It is implicitly understood that the clay has been engineered to provide the properties deemed desirable as a clay buffer and/or clay barrier for the EBS (see section 2.5.2).
