Effects of density on cyclic behaviour of anisotropically consolidated Ottawa sand under undrained torsional loading

The undrained response of Ottawa sand to cyclic torsional loading in a hollow cylinder apparatus is assessed at various densities. The cyclic resistance of Ottawa sand is strongly affected by anisotropic consolidation. It is less than half of the cyclic strength of isotropically consolidated material at the loose state; this trend reverses at the dense state. Cyclic strength resistance increases with density irrespective of consolidation path. Anisotropically consolidated specimens develop at all densities a terminal excess pore-water pressure which is less than 40% of the initial effective stress, and fail due to strain rather than pore-water pressure accumulation, contrary to isotropically consolidated specimens reaching pore pressure ratios higher than 70%. The development of excess pore-water pressure is uniquely related to the shear work imparted to the specimen; at the same excess pore-water pressure ratio shear work increases with density, whereas it is not affected by the applied cyclic shear stress amplitude. The phase transformation line is not affected by the consolidation path and appears to be the same under monotonic and cyclic loading conditions.