279
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
Non-coaxial behaviour of sand in drained rotational shear
Comportement non-coaxial de sable drainé en cisaillement rotationnel
Yang L.-T., Yu H.-S., Wanatowski D., Li X.
Nottingham Centre for Geomechanics, University of Nottingham, Nottingham, United Kingdom
ABSTRACT: This paper presents an experimental investigation into the non-coaxial behaviour of saturated sand in rotational shear. A
series of drained rotational shear tests has been performed on dense Leighton Buzzard sand in a hollow cylinder apparatus. The
degrees of non-coaxiality defined as the deviation between the major principal stress direction and the major principal strain
increment direction were analyzed. The test results demonstrate that the mechanical behaviour of sand under rotational shear is
generally non-coaxial, and the variation of the non-coaxiality degree shows a periodic trend during the tests. It was also observed that
the effective stress ratio has a significant effect on the non-coaxiality of sand. The larger the stress ratio, the lower degree of non-
coaxiality is induced. The results also show that the volumetric strain of sand induced by cyclic rotation of principal stress axes is
mainly contractive. Most of the volumetric change occurs during the first few rotation cycles and its accumulative rate tends to
decrease as the number of cycles increases.
RÉSUMÉ : Cet article détaille une analyse expérimentale du comportement non-coaxial de sable saturé en cisaillement
rotationnel. Une série de tests de cisaillement rotationnel drainé sur un sable Leighton Buzzard dense dans une presse triaxiale à
cylindre creux a été réalisée. Les degrés de non-coaxialité calculés comme l’écart entre la direction de la contrainte principale majeure
et la direction de l’incrément de la déformation principale ont été analysés. Les résultats des tests montrent que le comportement
mécanique du sable sous cisaillement rotationnel est généralement non-coaxial, et que la variation du degré de non-coaxialité présente
une certaine périodicité au cours des tests. Un impact non-négligeable du rapport de contrainte effective sur la non-coaxialité du sable
a également été observé. Plus le rapport de contrainte est grand, plus le degré de non-coaxialité induit est bas. Les résultats montrent
également que la déformation volumique du sable induite par rotation des axes principaux de contrainte est essentiellement
contractante. La plupart du changement volumique se produit au cours des quelques premiers cycles de rotation et son taux
d’accumulation tend à diminuer lorsque le nombre de cycles augmente.
KEYWORDS: non-coaxiality, HCA, drained rotational shear, sand
1 INTRODUCTION.
Non-coaxial behaviour refers to the non-coincidence of
principal stress directions and principal plastic strain rate
directions (Yu 2008). Evidenced by many laboratory
observations, granular materials, like sand, often exhibit non-
coaxial behaviour (Roscoe et al. 1967, Symes et al. 1984,
Arthur et al. 1986, Gutierrez et al. 1991). In many practical
situations, ignoring the effects of soil non-coaxiality may be
unsafe (Yu and Yuan 2006).
Many loading situations such as those induced by
earthquakes, traffic loading and sea waves involve cyclic
rotation of principal stress axes. Extensive experimental studies
on principal stress rotation have been carried out on granular
soils over the past few decades (e.g., Ishihara and Towhata 1983,
Symes et al. 1984, Nakata et al. 1998, Yang et al. 2007, Tong et
al. 2010). Several test results have shown the significant effect
of principal stress rotation on the response of soil specimens.
Plastic deformations as well as non-coaxiality between the
principal directions of stress and strain increment can be
induced due to principal stress axes’ rotation.
Until now, most studies on soils undergoing cyclic rotation
of principal stress axes have mainly focused on the undrained
strength, flow deformation and liquefaction behaviour of soils
during rotational shear. The cyclic behaviour under drained
conditions has not attracted much interest. Very little literature
directly addresses the non-coaxial behaviour of sand under
cyclic rotation of principal stress axes.
This paper presents an experimental investigation into the
non-coaxial behaviour of saturated sand in drained rotational
shear. All the tests were performed in a hollow cylinder
apparatus (HCA) which allows an independent control of the
magnitude of the three principal stresses and the inclination of
the major principal stress axis. The degrees of non-coaxiality
calculated as the deviation between the major principal stress
direction and the principal strain increment direction at different
stress ratios during rotational shear were analyzed.
2 TESTING ARRANGMENT AND PROCEDURES
2.1
Hollow cylinder apparatus
Figure 1. Applied loads and stress components in a hollow cylindrical
specimen.
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