A series of undrained cyclic shear tests was performed on loose samples of Shirasu to assess the influence of grain size distribution on the liquefaction susceptibility. The relative density of samples was 50%. Testing was carried out on various combinations of the gravels, the sands and the fines. The tests were carried out over a range of confining stresses. Three different kinds of cyclic strength characteristics were defined in this study. First, for sandy Shirasu without gravel the cyclic strength increases with increasing confining pressure. Second, the cyclic shear strength of sandy soil with gravel is independent of initial confining pressure. Third, for gravely Shirasu the cyclic shear strength decreases significantly with increasing confining pressure.
