ABSTRACT
The paper analyses some experimental results on natural unsaturated pyroclastic specimens carried out by means of direct shear tests both on undisturbed unsaturated and lab saturated samples. The results of suction-controlled tests were interpreted and shear strength envelope recovered. Although an extended Mohr-Coulomb criterion can be expressed in terms of matric suction and net stress, a more satisfactory description of the shear strength of this unsaturated pyroclastic soil was achieved by taking into account both matric suction and saturation degree.
