Experimental behaviour and modelling of an unsaturated compacted soil

This paper reports the experimental study and modelling of the mechanical r esponse of a silty sand used in the core of the Metramo dam, Italy. Specime ns were prepared by compacting the soil at optimum water content conditions using the modified Proctor technique. Tests were performed under suction-c ontrolled conditions by a stress path triaxial cell and an oedometer. The e xperimental program consists of 23 tests carried out in the suction range o f 0-400 kPa. The findings indicate the strong influence of suction on compr essibility, stiffness, and shear strength. The mechanical properties of the soil improve with suction following an exponential law with decreasing gra dient. Furthermore, the soil exhibited collapsible behaviour upon wetting e ven at low stress levels. Interesting results were also achieved in elastop lastic modelling as well. The results led to characterization of soil behav iour with reference to widely accepted modelling criteria for unsaturated s oils, providing noteworthy suggestions about their applicability for granul ar materials with a non-negligible fine component. Finally some remarks are made for the extension under unsaturated conditions of the "Nor sand" mode l for saturated granular soils. The proposed approach yields improved predi ctions of deviator soil response of the tested soil when Cambridge-type fra meworks prove invalid.