Cyclic Shear Strength of Undisturbed and Remoulded Marine Clays

Undisturbed clay samples were taken from alluvial deposits at seven different urban coastal locations in Japan. At several of the locations samples were taken from different depths in order to sample different sedimentary environments. The samples were then triaxially tested in both undisturbed and remoulded states. A testing programme was devised to separately examine the influence of plasticity index, aging factors and overconsolidation ratio on the undrained cyclic strength of clays. The cyclic data for normally consolidated samples was used to define the cyclic strength of the clays as an intrinsic function of the plasticity index Ip. This was modified to take into account the initial vertical yield stress ratio and degree of aging, and then further modified for the effect of geological OCR. A further series of tests was carried out on samples which were anisotropically consolidated by being subjected to an initial drained shear stress for 24 hours. The cyclic strength of the anisotropically consolidated clays at low initial drained shear stress ratios increased with increasing plasticity. This reversed as the drained shear stress ratio increased. It was possible to define a simple function for the cyclic strength normalised by the isotropic cyclic strength against the initial drained shear stress ratio. This function was shown to be dependent on plasticity index Ip but independent of stress history.