In order to study the effect of principal stress axes rotation induced by traffic loading on cyclic properties of soft clay in tests

one moving load and one train load are taken as examples to analyze the characteristics of principal stress axes rotation. On the base of loading properties of hollow cylinder apparatus

loading method to simulating the principal stress axes rotation in laboratory tests is given. The vertical dynamics stress can be simplified as sine wave with static deviator stress; and dynamic shear stress can be simplified as a sine wave. The phase difference between the two waves is . In order to simulate the character of principal stress difference changing continuously induced by traffic loading

the amplitudes of vertical stress and shear stress should be different. It is found that the angle of the maximum principal stress is between and or between and when vertical stress without stress reversal is exerted.