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In order to investigate creep failure behaviour of gravelly soils in the field, a series of triaxial compression tests was conducted on large-scale natural gravelly soil samples. The samples were retrieved by means of a new method using thick, water-soluble, polymer solutions from two tunnel excavation sites in Japan. Creep failure behaviour was evaluated by performing drained sustained loading at prescribed stress states during otherwise monotonic loading at a constant loading rate. Rate-dependent behaviour was also evaluated by stepwise changing vertical strain rate many times during otherwise monotonic loading at a constant strain rate. The observed viscous properties including creep failure behaviour were simulated by a non-linear three-component model taking into account the effects of particle characteristics on the viscous property parameters. The viscous property parameters evaluated for this simulation were compared with those of reconstituted granular materials obtained by previous studies. Shear moduli during the creep failure process, which were measured by the dynamic method, were also analysed. [ABSTRACT FROM AUTHOR]

The authors were set the challenge of thinking about the next 60 years, not only of Géotechnique but of geotechnical engineering in general. They have attempted to do this by talking to colleagues, by dreaming a little, but mainly by trying to extrapolate the trends they see in society and in present-day geotechnical activity. Although the principal emphasis of Géotechnique tends to be research, this is driven by the requirements of design and construction. Hence, in looking to the future, even the future of research, likely trends in geotechnical construction activities are considered first, particularly noting the emerging importance of energy conservation and carbon dioxide reduction. This leads to discussion of the characterisation of material behaviour and investigation of the ground, and the development of design processes. The future of dissemination of geotechnical information is also discussed. [ABSTRACT FROM AUTHOR]

A comprehensive series of triaxial tests were performed on granular materials to study the stress-dependence characteristics of small-strain stiffness (i.e. the quasi-elastic Young's modulus). The tests were performed on large prismatic specimens measuring both axial and lateral strains locally. The small-strain stiffness at a given stress state was measured from the stress-strain response obtained by applying very small-amplitude cyclic normal stresses, in which the single-amplitude major principal strain was less than 0.002%. The stress state of a given specimen was varied along various stress paths comprising both 'small shear' and 'large shear' stresses in both triaxial compression (TC) and triaxial extension (TE) stress space while applying very small stress cycles. At small shear levels (defined as the principal stress ratio within the range between 0.5 and 2.0), small-strain stiffness defined for a given direction was a function of the principal stress in that direction. The unique relationship did not hold at larger shear stress levels when the major- to-minor principal stress ratio was approaching around 3 to 4. In the latter case, both quasi-elastic Young's moduli, defined for both major and minor principal strains, during TC and TE experienced a decrease due to damage to the initial fabric that was triggered by a high rate of plastic straining as well as creep deformation. [ABSTRACT FROM AUTHOR]