A general approach to assess hydro mechanical changes of natural clay barriers due to physicochemical interaction with waste in deep seated waste disposal sites

As engineered structures normally have a functional life up to 100 years, natural barriers have to be incorporated into the design for long-term waste disposal sites. Such natural barriers are formed by thick clay formations. Once a suitable location within the formation has been selected on its geomechanical and hydrogeological properties, it must be guaranteed that these properties do not unfavourably alter when contacted by leachates or radiation produced by the waste itself or oxidation products originating from the containers. In this contribution a general approach is presented to analyse the effect of physico-chemical reactions on the hydro-mechanical properties of clays. This approach is based on the analyses of the occurrence of physico-chemical reactions on three distinct levels: the tetrahedral-octahedral layer (TOT/TO) level, the interlayer level and the clay particle level. Each level is characterised by different physical and chemical processes. These processes related to a specific level, occur on different time scales and provoke different orders of hydro-mechanical changes. (authors)