The mechanics of an Italian silt: an example of ‘transitional’ behaviour

Abstract

By controlling the particle size distribution of an Italian silt, the influence of grading on its behaviour was investigated. As the clay content was reduced, the behaviour changed from a typical clay mode to a transitional form between that of clays and sands that had previously been seen only for gap-graded soils, emphasising that this type of behaviour is possibly much more extensive than previously thought. The work has highlighted several features of transitional behaviour, and in particular that unique normal compression and critical state lines do not exist, that Rendulic's principle does not apply, and that drained and undrained tests do not reach unique ultimate states.En contrôlant la répartition des dimensions de particules dans un limon italien, nous avons étudié l'influence de la granulométrie sur son comportement. À mesure que la teneur en argile baissait, le comportement changeait, passant d'un mode argileux type à une forme transitionnelle entre celle d'argiles et celle de sables -forme vue auparavant uniquement dans les sols gradés à espaces -, ce qui montre que ce type de comportement est peut-être bien plus étendu que préalablement estimé. Ce travail a fait apparaître plusieurs caractéristiques de comportement transitionnel et en particulier le fait que la compression normale unique et les lignes d'état critique n'existent pas, que le principe de Rendulic ne s'applique pas et que les essais drainés et non drainés n'atteignent pas des états ultimes uniques.

Behaviour of MH silts with varying plasticity indices

“…The deviator stresses of the MRV silts with different O CR values were normalised by the effective consolidation pressures, after which the results indicated that the MRV silts had a unique clay-like behaviour. The method identified by Boulanger and Idriss (2006) for distinguishing between sand-like and clay-like behaviours has worked well on both low-plasticity (ML) silts presented by Nocilla et al (2006) and Wang and Luna (2012). Nonetheless, Wang and Luna (2012) likewise reported that the work of Boulanger and Idriss (2006) did not capture the effect of O CR on silt behaviour.…”

“…In a research study, Nocilla et al (2006) recommended identifying a new framework to describe the behaviour of silts in the transitional form. Such a framework has yet to be identified or developed due to the behaviour of silt being perhaps more complex than those of sand and clay.…”

“…Much research has been reported on low-plasticity silt (ML), with a liquid limit (L L ) lower than 50% -namely, by Wang and Luna (2012), Boulanger and Idriss (2006), Nocilla et al (2006) and Hyde et al (2006). They dealt with the characterisation and/or mechanical properties of ML.…”

“…In this research, MH silts with L L that ranges from 52 to 64% were tested, and the results are reported. Nocilla et al (2006) investigated the behaviour of Italian silt with a plasticity index (P I ) of 12% and found that as the clay contents reduce, the behaviour of silt changes from a clay-like behaviour to a transitional form demonstrating behaviours between those of clays and clean sands. For this situation, the silt in the transitional form demonstrates neither a unique NCL behaviour nor any unique CSL behaviour.…”

Compressibility of a Fat Clay mixed with aggregates

“…Nocilla [2] reported that as the clay content was reduced, the behaviour changed from a typical clay mode to a transitional form between that of clays and sands. Shiptona and Coop [3] explored the effects of mixing soils of different grain sizes, covering a wide range of grindings from clayey-silts to well-graded sands and gap-graded soils, they reported that, for such soils, it would be difficult to identify the effects of structure on the mechanics since there is no unique behaviour of the soil when reconstituted, oedometer tests performed indicated that relatively small changes to the nature or quantity of the constituent particles of a soil can change the behaviour quite dramatically.…”