| Summary: | With the aim to achieve a better understanding of the time-dependent behaviour of clays, particularly stiff natural clays, a critical review of literature and a program of laboratory testing have been carried out as part of this research work. With emphasis on examining the effects of viscosity and ageing, a series of advanced triaxial and oedometer tests were conducted, which have added significant data to the existing database of results and addressed important "grey areas" highlighted from the literature review. The performed experimental studies included a) An examination of the influence of ageing and global axial strain rate on the vertical elastic shear stiffness of kaolin and reconstituted London Clay in one-dimensional and isotropic compression test combined with bender element testing. b) Characterisation of the influence of strain rate and strain acceleration on the monotonic stress-strain behaviour of reconstituted London Clay from a complex series of triaxial compression and extension tests. c) An examination of the influence of structure, both natural and artificial, on the strain rate dependent behaviour of London Clay and artificially cemented kaolin in triaxial compression tests, in addition to an investigation of the influence of ageing (in this case curing of the cement) on the monotonic behaviour of cement-mixed kaolin. Based on the literature review and findings from the performed experimental studies a framework for the conceptual time-dependent behaviour of natural clays was formulated with the underlying intention to characterise parameters that could eventually be used in a model for natural clays. Finally, on the basis of proposed conceptual behaviour a preliminary numerical study was carried out examining the implementation of general viscous behaviour into the advanced BRICK model of soil behaviour. KEYWORDS: clays fabric/structure of soils laboratory tests time dependence.
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