FLOWSLIDES IN FINITE SLOPES

Flows of of loose saturated granular material can be the post failure evolution of slope sliding. This mechanism refers to the phenomenon of static liquefaction of loose material and is based on the hypothesis that the large deformations experienced during sliding phase induce excess pore pressure in material showing contractive behaviour. The paper reports a study aimed to the prediction of transformation from sliding to flow in a finite slope constituted by loose saturated sand. The study is based on the results of an extensive laboratory investigation on the potential of liquefaction of Toyoura sand, set up by Ishihara et al. (2000). They showed that, for a given minor principal stress, the major effective principal stress at the time of anisotropic consolidation is a parameter controlling dilative or contractive behaviour of the sand under otherwise identical conditions. The initial state of stress of sand slopes, at different void ratio and groundwater level conditions, is predicted by a finite difference model (FLAC) assuming fully drained conditions and linear elastic plastic behaviour of the material. On the basis of the numerical modelling results it is possible to completely define, in any point of the slope, the stress conditions by the two principal stresses and their direction. By relating this state of stress to the residual strength of the sand at the quasi steady state, it possible to localise the zones in the slope showing contractive behaviour and possibly subjected to flow sliding.