Factors affecting the containment properties of natural clays

Abstract

AbstractNatural clays are often relied upon to provide containment for the safe disposal of wastes, either as an in situ material or as an engineered fill material. It is generally assumed that these materials will permanently exhibit a low permeability, and that they are isotropic and homogeneous. However, anisotropies and discontinuities are often present in clays, or may be induced by deformation which can occur during or after construction of waste disposal sites. Anisotropic fabrics may also be developed or enhanced within clays as they are compacted and consolidated. Many landfill sites are dynamic environments where deformation will occur both within the waste and in the material surrounding the waste. When clays deform, for example due to slope instability or differential settlement, the deformation will generally be accommodated by the development of discrete microscopic shear zones which have the potential to significantly change the containment ability of clays. This paper presents the results of a study to investigate the variation in the permeability of clays as a result of their deformation. Natural examples, theoretical studies and experimental data are combined to demonstrate that fluids will preferentially flow along shear zones or induced fabrics. The data are used to demonstrate that, in a dynamic environment such as a waste disposal site, the permeability of clays can increase substantially in materials which become heavily deformed.