Cyclic behavior and liquefaction resistance of volcanic soil in simple shear testing

Volcanic grains are porous, light-weight, fragile and have very rough surfaces. They show breakage of asperities and even of the whole grain. These characteristics generally result in a different response under cyclic loading in comparison with hard-grained sands. This paper intends to investigate the cyclic behaviour of a volcaniclastic silty sand with non-plastic fines with respect to liquefaction triggering mechanisms. This is accomplished with undrained cyclic simple shear tests on undisturbed and reconstituted specimens sourced from the foundation soils of an earth dam in Southern Italy. The undrained response of undisturbed specimens, expressed in terms of development of excess pore pressure and shear strain with the number of cycles, is thoroughly consistent with published trends on volcanic soils, and in turn is significantly different from that of hard-grained sands. It is further shown that liquefaction resistance of undisturbed specimens is higher than that of reconstituted ones, thus highlighting the influence of fabric.