Coupling effects of P-waves and S-waves based on cyclic triaxial tests with cyclic confining pressure

In the earthquakes with high intensities, the effects of P-waves on the soil layers cannot be ignored. The coupling effects of S-waves and P-waves are simulated by the specific stress paths in the cyclic triaxial tests with cyclic confining pressure. The influences of the phase differences and ratios between cyclic shear stress and cyclic normal stress on the behavior of cyclic strain are studied. It is found that the specific stress paths which are composed of both cyclic shear stresses and cyclic normal stresses are appropriate to simulate the coupling effects of S-waves and P-waves. The phase difference strongly influences the cyclic strength of saturated clays, i.e., when the phase angle is 180°, the cyclic strength is the lowest, and when the phase angle is 0°, the cyclic strength is the highest. With the increasing ratios, the development speeds of cyclic strain are becoming more different from the results of conventional cyclic triaxial tests. These findings indicate that the effects of P-waves are significant, and in some cases the conventional cyclic triaxial tests may overestimate the cyclic strength of saturated clays, which is adverse for aseismatic design.