The behaviour of loose, anisotropically consolidated Ottawa sand was examined under undrained cyclic loading in the hollow cylinder apparatus. The stress level, the cyclic stress level and the consolidation stress ratio were varied. The instability line of anisotropically consolidated loose Ottawa sand, defined under monotonic loading, is shown to form a boundary in the vicinity of which a sudden increase in the rate of excess pore water pressure and strain accumulation is observed, and the sand strain-softens. However, this unstable response is arrested at phase transformation, and the sand specimens show a stable or temporarily stable effective stress cycle at low and high consolidation stress ratios respectively. Similar behaviour is observed for isotropically consolidated sand, which exhibits initial liquefaction after strain-softening. The terminal excess pore water pressure associated with this final stage is described as a function of consolidation stress ratio, while the development of excess pore water pressure during cyclic loading is uniquely defined for all tests as a function of normalised shear work. The cyclic resistance of the sand decreases with decreasing consolidation stress ratio. Anisotropic consolidation significantly affects the stiffness and damping ratio values of loose Ottawa sand.

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Undrained cyclic loading tests were performed under torsional shear in a hollow cylindrical apparatus on four sands of various densities, initial stress levels, gradings and origins to establish the pattern of excess pore water pressure generation with cycles leading to initial liquefaction. Two equations were derived to predict this pattern. The first is based on the method introduced by Ishibashi et al. (1977) and incorporates density and the effective stress level into the original equation. The second involves a unique relationship between the excess pore water pressure and the shear work imparted to the sand and it was obtained independent of the shear stress amplitude when the dissipated shear work was normalized with respect to density and the effective stress level. The excess pore water pressure required to induce liquefaction was found to necessitate lower normalized shear work from finer sands. These equations can be used to assess the liquefaction potential and/or can be directly related to the amount of seismic energy dissipated in the field.

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