EFFECTS OF VISCOUS PROPERTIES ON THE SHEAR YIELDING CHARACTERISTICS OF SAND

HASBULLAH NAWIR , FUMIO TATSUOKA and REIKO KUWANO 

ABSTRACT: Effects of viscous properties on the yielding characteristics of sand under general stress conditions were evaluated by performing unconventional drained triaxial compression tests on saturated dense Toyoura sand. Shear yield stresses evaluated by applying unload/reload cycles of deviator stress at a fixed confining pressure were noticeably affected by a strain rate change between primary loading and reloading as well as creep deformation at the maximum deviator stress before unloading due to the viscous properties of sand. It is shown that the double yielding concept, describing the yielding of soil in terms of shear and volumetric yielding mechanisms, is relevant to sand. The shear yield loci on the q-p' stress plane were obtained by decreasing and then increasing the deviator stress respectively at different confining pressures. The shape of shear yield loci was also affected by the viscous properties. With an increase in the effective mean principal stress, p' along a given inviscid shear yield locus, the deviator stress, q, increases while the stress ratio, q/p', slightly decreases. It is demonstrated that it is necessary to incorporate the effects of viscous properties when developing a realistic constitutive model for sand. An interaction between shear and compression yielding mechanisms is discussed based on experimental results. 

Key words: constitutive modelling, deformation, sand, triaxial compression, viscous properties, yield locus, yield stress (IGS: D6/D7)