Study on unified evaluation for in-situ dynamic strength of clays during earthquake

For the purpose of this research programme，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 many different depths in order to sample different sedimentary environments.The samples were then testes in both undisturbed and remoulded states.A testing programme was devised to separately examine the influence of plasticity index，aging factors，rate effect and overconsolidation ratio on the undrained cyclic stength of the clays.The cyclic data for the normally consolidated samples was used empirically to define the cyclic strength of the clays as an intrinsic function of the plasticity index I y D2p文件D2.This was then modified taking into account the vertical yield stress ratioσI D2 vy文件D2‘/σI D2 vo文件D2’，degree of aging and geological OCR.The cyclic strength of anisotropically consolidated clays at low initial drained shear stress ratios increased with decreasing 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 R I D2 ISO I2 against the initial drained shear stress ratio.This function was shown to be dependent on plasticity index I个D 2p个D 2 but stress history.

For the purpose of this research programme, 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 many different depths in order to sample different sedimentary environments. The samples were then testes in both undisturbed and remoulded states. A testing programme was devised to separately examine the influence of plasticity index, aging factors, rate effect and overconsolidation ratio on the undrained cyclic stength of the clays. The cyclic data for the normally consolidated samples was used empirically to define the cyclic strength of the clays as an intrinsic function of the plasticity index IィイD2pィエD2. This was then modified taking into account the vertical yield stress ratio σィイD2vyィエD2'/σィイD2voィエD2', degree of aging and geological OCR. The cyclic strength of anisotropically consolidated clays at low initial drained shear stress ratios increased with decreasing 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 RィイD2ISOィエD2 against the initial drained shear stress ratio. This function was shown to be dependent on plasticity index IィイD2pィエD2 but stress history.