Viscosity, yield stress, remolded strength, and liquidity index relationships for sensitive clays

The rheological behavior of some sensitive clays has shown that there are positive relationships between plastic viscosity, yield stress, remolded shear strength, and liquidity index. Based on the various correlations, remolded strength values can be predicted for soils with a liquidity index as high as 6. For a liquidity index varying from 2 to 5, the remolded undrained shear strength and plastic viscosity vary from about 90 to 5 Pa and from 200 to 7 mPa∙s respectively. It has been observed that most sensitive clays behave either as a Bingham or a Casson fluid, the latter behavior being related to less sensitive clays of higher pore-water salinities. Increasing the salt content from 0.5 to 30 g/L modified the rheological behavior of a single test soil from that of a Bingham to that of a Casson type of fluid. Such modification in the pore-water salinity illustrates how soils can have similar plastic viscosity and similar remolded strength but different yield stresses. The range of viscosity measured for sensitive clays is very different from that of values obtained from back analysis of subaerial or submarine slides where viscous flow can be expected.