Abstract: Cyclic loadings such as traffic loads, wave loads and earthquake can cause principal stress rotation, which has a significant impact on the long-term settlement and stability of soft ground. In order to study the long-term dynamic characteristics of saturated soft clay under the traffic load, a series of hollow cylinder shearing experiments is performed on the soft soil by adopting three types of principal stress paths including heart-shaped line rotation, circular rotation and directional shear in deviatoric stress space. The undrained cumulative plastic deformation, pore pressure, critical dynamic stress ratio and dynamic strength characteristics are compared among specimens under different experimental conditions. The results show that (1) the critical stress ratio increases, in order, from circular rotation, heart-shaped line rotation and unequal amplitude in tension, to triaxial compression. Accordingly, the cumulative plastic deformation and pore pressure limit decrease in turn for the stable cumulative stage of axial strain. (2) When the vibration times is greater than certain values, the axial cumulative strains of the stable-type specimens have good linear relationships with the logarithm of time under different principal stress rotation paths. Based on this, the cumulative axial plastic deformation equation is developed. (3) Along with the cumulative axial plastic deformation, the pore pressure growth in the soil under different dynamical loadings also shows three kinds of development trend. A three-stage and two-phase mode is found in the pore pressure-time curve and the strain-time curve under the principal stress axis rotation path. (4) When the other conditions are the same, the strength of soil under heart-shaped rotation is higher than that under the circular rotation, and lower than that under the unequal amplitude in tension and compression of triaxial path.

Key words: principal stress axis rotation, stress path, remolded soft clay, accumulated deformation, critical stress ratio