A series of ring shear tests was conducted to investigate the development of particle breakage with shear strain for a carbonate sand. It was found that at very large displacements the soil reached a stable grading, but that the final grading was dependent on both the applied normal stress and the initial grading. The particle breakage caused a volumetric compression, which again ceased only when the stable grading had been attained, emphasising that critical states as observed at much smaller strains in triaxial tests are not rigorously defined. Despite the severe degradation of the soil particles the mobilised angle of shearing resistance was found not to change significantly.Nous avons mené une série d'essais de cisaillement annulaire afin d'enquêter sur le développement des cassures de particules avec une déformation de cisaillement pour un sable carbonate. Nous avons trouvé qu'avec de très importants déplacements, le sol parvenait à une granulométrie stable mais que la granulométrie finale dépendait de la contrainte normale appliquée et de la granulométrie initiale. La cassure des particules provoque une compression volumétrique qui, encore une fois, ne cesse que lorsque la stabilité granulométrique est atteinte, soulignant le fait que les états critiques tels que ceux qui sont observés avec des déformations bien plus petites dans les essais triaxiaux ne sont pas rigoureusement définis. Nous avons trouvé que malgré la dégradation sévère des particules de sol, l'angle mobilisé de résistance au cisaillement ne changeait pas de manière significative.

In this paper results from laboratory tests on London Clay and artificially cemented kaolin are presented and used to develop a preliminary framework for the timedependent behaviour of soils, applicable to stiff clays and other soils. In the same way that the natural structure of clays has been shown to influence their monotonic behaviour, it is shown that it can also alter their response to changes in strain rate. The relative influence of the two main components of post-sedimentation structure-overconsolidation and diagenesis-on the time-dependent behaviour of London Clay was investigated in triaxial compression tests. The study was carried out in two steps, comparing first the behaviours of normally and overconsolidated reconstituted samples of London Clay subjected to stepwise changes in strain rate, and then the behaviours of overconsolidated reconstituted and undisturbed London Clay samples. The test results show that overconsolidation does not seem to affect the response of reconstituted London Clay to strain rate changes, which is consistent with published data on other stiff clays. However, intact and reconstituted overconsolidated samples show different behaviours, highlighting that it is the elements of structure resulting from diagenesis that influence the time-dependent behaviour of London Clay. Effects of cementing on strain rate sensitivity were investigated in triaxial compression of artificially cemented kaolin. The results obtained were different from the results for London Clay, suggesting that the difference in strain rate effects in the intact and reconstituted London Clay cannot be simply associated with cementing. A preliminary framework is proposed, where the timedependent behaviour of soil depends on its particulate or continuum nature.