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Abstract

An experimental study of static, cyclic and post cyclic undrained behaviour of Fraser river sand in the triaxial test is presented. Static undrained behaviour over a range of deposition densities, from loosest to dense, and a range of confining stress is studied. Compression as well as extension loading paths are included. It is shown that for identical density and stress state the sand is dilative in triaxial compression but contractive in triaxial extension loading. It is shown that at a given confining stress static shear stress can change a dilative sand into a contractive one. Cyclic loading leading to liquefaction is studied at specific targeted densities from loose to dense at a range of confining stress and the liquefaction resistance determined. It is shown that the sand can undergo large deformation even before a state of 100% pore pressure ratio occurs. There is no effect of the level of confining stress on liquefaction resistance of loose sand. The resistance of denser sand, however, decreases with increase in confining stress. During post liquefaction undrained monotonie loading, the sand initially deforms with an essentially zero stiffness which then increases with the level of strain.The effect of maximum shear strain due to cyclic loading, relative density, mode of loading and the level of confining stress prior to cyclic loading on the post liquefaction monotonic undrained response of the sand is investigated. Volumetric strain due to dissipation of excess pore pressure until liquefaction is assessed as a function of maximum shear strain, relative density and confining stress prior to inducing liquefaction. The similarity of post liquefaction behaviour (both stress-strain response and volumetric strain) between sand brought to the liquefied state by cyclic loading and by static load/unload cycle is also investigated.