Yielding and critical state behaviour of a compacted alluvial silt

The mechanical behaviour of a compacted alluvial silt has been investigated by means of triaxial tests on saturated and unsaturated samples. The soil was used for the construction of the impervious core of the Locone Earth Dam, in the South of Italy. Aim of the experimental work is to determine a complete set of mechanical parameters to be used in calculations of deformation of the earth dam at the end construction and at the first and controlled filling. An extensive triaxial testing program has been developed, focusing on the yield behaviour and the critical state of the compacted soil in both saturated and unsaturated states. Different stress paths have been followed in order to detect the yield condition. This condition has been identified by means of the strain energy criterion. The yield surface is near-elliptical and inclined in the stress space, and shows a relevant dependence on suction. The uniqueness of the critical state has been observed for saturated and unsaturated samples if the hydro-mechanical coupling of the stress strain behaviour is taken into account.