Abstract: A set of tests with the hollow cylinder apparatus are conducted to simulate the oblique incident seismic waves. Tests are performed with two cyclic stress components involving the horizontal shear stress (torsional shear stress) and the vertical shear stress (stress difference between vertical normal stress and horizontal normal stress) to show an elliptical shape in the orthogonal coordinates of stress difference and shear stress. Then the dynamic characteristics of saturated Fujian standard loose sand, consolidated under isotropic undrained condition and applied with cyclic oblique elliptic stress path, cyclic circular shear, cyclic torsional shear and cyclic triaxial path, are studied. The experiment results show that the development of elastic pore pressure can be classified as “sharp dropping type” and “sharp rising type”. The cumulative rates of excess pore water pressure under cyclic circular shear and under cyclic torsional shear are the fastest and the slowest respectively. The normalizing pore pressure is independent of inclination angle of the obliquity of elliptic path, but depends on the ellipticity of cyclic stress path and stress amplitude CSR. Experimental results also indicate that undrained dynamic strength of Fujian sand is closely related to cyclic stress path. The cyclic torsional shearing path and cyclic triaxial path have the highest dynamic strength. The strengths under standard inclined elliptical loading path and under cyclic circular path are lower and the lowest respectively. Approximate circular path can be generated with seismic wave in a particular incident angle. If seismic wave is regarded as vertical incident S wave, the soil liquefaction strength would be overestimated.

Key words: oblique ellipse stress path, strength, cumulative pore pressure, cyclic pore pressure