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To evaluate the effects of ambient temperature history on the load-strain-time behaviour, a series of tensile tests were performed on three geogrid types. The applied loading and temperature ( T) schemes included: (i) continuous monotonic loading (ML) at different constant values of T; (ii) sustained (creep) loading (SL) during otherwise ML at different constant values of T and (iii) SL during which T was incrementally increased during otherwise ML. With an increase in T, the rupture tensile strength ( Vmax) and the elastic stiffness decreased while the creep strain increased. For the same ultimate T, the creep strain by scheme (iii) was significantly larger than the one by scheme (ii). The residual rupture tensile strength ( Vres) observed in ML that followed SL was nearly the same as Vmax in continuous ML at the same T, showing that creep is not a degrading phenomenon reducing Vres. A non-linear three-component (NTC) model was modified to incorporate the temperature effects. By modelling the trend that Vmax and stiffness decrease with an increase of T as a negative ageing effect, the modified NTC model successfully simulated all the different trends of load-strain-time behaviour, including creep strains, observed along various load and temperature histories in the experiments. [ABSTRACT FROM AUTHOR]

Evaluation of creep behaviour of polymer geosynthetic reinforcement is important for predicting the long-term performance of geosynthetic-reinforced soil (GRS) structures and determining the creep reduction factor of geosynthetic reinforcement for the design lifetime of a GRS structure. The inherent link between the creep behaviour and the stress relaxation behaviour was confirmed by performing a comprehensive series of sustained loading (SL) tests and stress relaxation (SR) tests and numerical simulations of SL and SR tests on several geogrid types. In the framework of the non-linear three-component (NTC) model, the creep strain in SL is entirely irreversible, while the tensile load decrement in SR is associated with the developed positive irreversible strain with zero total strain rate. Measured systematic relationships between the elapsed times necessary to reach the same irreversible strain rate in SL and SR tests and those between the irreversible strain increments necessary to reach the same irreversible strain rate in SL and SR tests are presented and simulated by the NTC model. It is shown that, based on these relationships, the time history of creep strain can be predicted from given results of SR tests performed for a much shorter period. This method is validated by successful simulations of experimental results. [ABSTRACT FROM AUTHOR]

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]

ABSTRACT: Polymer geosynthetic reinforcement materials exhibit significant elasto-visco-plastic load-strain behaviour that is controlled by, at least, current strain rate. For this reason, it is not possible to accurately evaluate the tensile load history only from a given tensile strain in a physical model test in the laboratory or with a full-scale soil structure in the field. A non-linear three-component model that can realistically simulate rate-dependent load-strain behaviour of polymer geosynthetic reinforcement is described with detailed explanations of the model framework together with the constitutive equations. The algorithms to simulate behaviours in three basic modes, constant strain rate monotonic loading, creep loading and load relaxation, are presented. A working example in Microsoft Excel with a user-defined Microsoft Visual Basic source code is provided in the appendices (which are available as supplementary data on the ICE Virtual Library website) so that readers can readily use the model. [ABSTRACT FROM AUTHOR]

Two tall geosynthetic-reinforced soil (GRS) walls, one 16.7 m high supporting a sloped embankment, and the other 21.1 m high with a level backfill, were constructed to support the taxi way of Mt. Fuji Shizuoka Airport, Shizuoka Prefecture, Japan, which was opened to service in June 2009. As only limited residual deformation during service is allowed and high stability is required, the backfill was a well-graded gravelly soil, which was well compacted at controlled water content and reinforced with geogrid reinforcement. In the respective walls, three representative geogrid layers were fitted with a number of electric-resistance strain gauges to monitor the geogrid tensile strains during and after construction to ensure high stability and sufficient serviceability. After the wall construction had been completed, the geogrid strains were either only increasing at a very low rate, or had stopped increasing, or had started decreasing. A series of in-air tensile loading tests were performed on different geogrid types used for the wall construction to evaluate their elasto-viscoplastic properties. The time histories of tensile force in the geogrid layers were estimated from the measured time histories of the geogrid strains based on a non-linear three-component rheology model using the model parameters determined by the in-air tensile loading tests. After the end of wall construction, the estimated geogrid tensile force was either increasing at a very low rate or was decreasing with time. Even at the locations where it tended to increase with time, the estimated geogrid tensile force never increased greatly by the end of a typical design life (i.e. 50 years) from the value at the end of wall construction. As the estimated maximum geogrid force at the end of the design lifetime is substantially lower than the respective design tensile rupture strengths, it is estimated that creep rupture failure of the geogrid is utterly unlikely. The analysis suggests that these estimates are also relevant when the lifetime is 100 years. The framework to estimate the time histories of reinforcement force from the time histories of measured reinforcement strains used in this study can be applied to other similar cases. [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]