Effect of stress direction on the cyclic resistance of sand

In total, 55 undrained cyclic torsional shear tests were conducted at a constant mean confining stress, σ_0m, constant intermediate principal stress ratios, b = (σ₂− σ₃)/(σ₁− σ₃), and principal stress directions, α. The cyclic resistance of loose, isotropically consolidated specimens exhibited a dip in strength, with the lowest values for α being 45°, an angle at which α was oriented such that the potential shear band directions dovetailed with the plane having the weakest strength (i.e. horizontal plane). For a given α, the cyclic resistance decreased to the lowest values for b = 0·5, at which the value of the principal stresses was different in the three major directions. For dense specimens, the direction of the major principal stress had no significant influence on the cyclic resistance. For loose, anisotropically consolidated specimens, higher cyclic resistances were observed at the point of approaching the direction of the major principal stress during the consolidation and loading stages.