Measurement of shear strength for marine clay

In this study a series of fall cone tests was carried out to investigate the undrained shear strength of soil involved in submarine landslides. Two different remoulded soils, kaolin clay and a natural submarine soft clay collected from the Red Sea (WND), were measured, using three different cones with masses of 80 g, 20 g and 13·6 g. To eliminate the buoyancy effect, all the data have been converted into modified shear strength. The relationship between the modified shear strength and the liquidity index can be described by a unique power law function for a given soil. However, when the liquidity index is above 1·5, the modified shear strength begins to deviate from the original data. The maximum difference is about 20% for kaolin clay and 30% for WND. Hence, the buoyancy effect must be considered when using the fall cone test to measure extremely soft clay. Furthermore, the effects of salt were well captured by the control group experiment, and the result shows that adding 3·5% salt into water increased the shear strength for both clay samples, but WND is more sensitive to changes in salinity.