Search

Argillaceous rocks are candidate host and/or cap formations for the geological disposal of nuclear wastes in many countries, including Canada, France and Switzerland. The understanding of the long term mechanical behaviour of such rocks is an essential requirement for the assessment of their performance as a barrier against radionuclide migration. Due to the existence of bedding, argillaceous rocks are inherently anisotropic and the development of stress-strain models for their mechanical behaviour needs to take this anisotropy into account. This paper presents two examples of the practical implementation of stress-strain relationships in finite element models to simulate the excavation damage zones (EDZ) in bedded argillaceous rocks. The first example concerns the EDZ around a micro-tunnel in Opalinus Clay, in Switzerland. The second example relates to the EDZ around the century-old tunnel in Tournemire shale, in France. Both examples show the importance of developing robust stress-strain models that can replicate inherent anisotropy of the rock, and of calibrating and validating the models with a comprehensive set of laboratory experiments. The second example shows the additional influence of dessication and fault zone on the extent and shape of the EDZ. [ABSTRACT FROM AUTHOR]

Design of piles in chalk is considered as an important issue for a number of geotechnical applications in Northern Europe. Few methods exist for predicting the ultimate axial pile capacity in chalk, but little guidance can be found regarding the design of driven piles in this complex material as experience is rather limited. This paper aims to study the short and long-term predictive performance of different pile design methods used in France and the UK where chalk is found widespread in the north-west coast and the south-east coast, respectively. Conventional methods used in France and the UK are compared by considering seven full-scale static load tests performed in Paris Basin and extracted from the LCPC pile database. The ratio of the measured vs calculated pile shaft resistance and base resistance value is analysed and the scatter of each method is studied. The comparison shows large differences between results. Extension of the database is of great importance to improve the predictive reliability. The last part discusses the evolution of the long-term capacity of driven piles in chalk due to ageing effects. Results show an increasing trend after driving, following a hyperbolic evolution curve. [ABSTRACT FROM AUTHOR]

The Meuse/Haute-Marne underground research laboratory was built in the Callovo–Oxfordian (COx) clay formation for the purpose of assessing the feasibility and safety of a deep geological formation to host an industrial radioactive waste repository (Cigéo project) in France. Some observations related to the drifts oriented in the direction of the major horizontal stress remain to be theoretically and numerically understood. In order to contribute to the understanding of the hydromechanical behaviour of the COx claystone, an elasto-viscoplastic model with transient creep was developed, including the inherent elastic and hydraulic anisotropies. Comparison with in situ measurements was made, with encouraging results. [ABSTRACT FROM AUTHOR]

This study presents a series of triaxial tests to highlight the effect of saturation degree ranging from 79.8% to 100% on the behavior of sand subjected to cyclic loading, the development of pore water pressure increment, the volumetric strain at liquefaction state, and the behavior of sand subjected to monotonic loading after liquefaction. The tested sand was Hostun RF sand, fine clear sand that has been widely used in laboratory testing in France. The results show that there is a difference between the behavior of samples having saturation degrees higher and lower than 95%. Besides, the development of pore water pressure increment is affected significantly by the value of cyclic stress ratio (CSR) and saturation degree. The Saturation degree also affects the appearance of criteria of liquefaction as Excess Pore-water Pressure (EPP) and Double Amplitude of axial strain (DA). The analysis of the effect of saturation degree on sample volumetric strain exhibits nonlinear liquefaction criteria for a given maximum value of CSR. The monotonic loading tests after liquefaction showed a small difference between the monotonic compressed behavior of the samples before and after liquefaction. [ABSTRACT FROM AUTHOR]

High-performance concretes reinforced with metal fibres (SFRHPC) have multiple advantages when they are used in the marine environment. These materials provide high strengths at the young age that permit faster formwork stripping, resistance to hydrostatic thrusts due to the tides, structural elements sections' reduction, as well as weight reduction of the structure, and the increase of the abrasion resistance to sand or gravel. The maritime works are exposed to specific seawater aggressions. Seawater contains aggressive salts, which damage the concrete and the steel that it may contain. These salts are mainly chlorides and sulphates. This study investigated the ripening of steel fibre-reinforced high-performance concrete, with 15% substitution of cement by blast furnace slag, in Rance (France's seawater). This experimental study analysed the effect of 6 and 24 months of ripening of the sample, in aggressive water, on the characterisation of the concrete and the microstructure of the cement's matrix and its fibres. Also, in this study, after two years of concrete conservation, we carried out the chemical and mineralogical composition of the seawater. The results showed that there is no significant alteration of concrete kept in seawater and the steel fibres were not altered. In other words, it stayed passivated even after two years of ripening. [ABSTRACT FROM AUTHOR]