Flow failure-Some data on onset condition

Landslides of flow failure type mostly occur in very fine sands or nonplastic silty soils that are deposited in very loose state. It has been shown that the residual strength of these soils depends significantly on the soil fabric, but it is very difficult or even impossible to take undisturbed specimens from these soils. This is why in situ tests are very important if combined with the undestanding of the state boundary between dilatative and contractive behaviour. To contribute to this understanding, a series of laboratory data is shown in terms of brittleness index versus initial stat ratio obtained on various sands and non-plastic silts and using three distinctive methods of specimen preparation. For the tested materials, contractive behaviour can be expected if the consolidation pressure (under conditions of isotropic consolidation) is at least 2 times larger than the mean effective stress at the quasy steady state line.