Deformation Behaviors and Dynamic Backbone Curve Model of Saturated Soft Clay under Bidirectional Cyclic Loading

Many undrained cyclic triaxial tests considering cyclic confining pressure have been carried out on Ningbo saturated soft clay using a cyclic triaxial system to study the influence of cycle numbers, stress paths, and cyclic stress ratios (CSRs) on the axial strain. The experimental results showed that the development of the accumulated axial strain of saturated soft clay is limited by cyclic confining pressure to some extent under undrained condition. For a given number of cycles, the accumulated axial strain increases as CSR increases at the same slope of loading path, and decreases with the increase of the slope of loading path at the same CSR. As the slope of stress paths decreases, the inclination of the backbone curve of the specimen toward the horizontal axis decreases in the undrained condition. A backbone curve model incorporating the effect of cyclic confining pressure and vibration number is proposed based on the characteristics of the resulting dynamic stress-strain curve. The proposed backbone curve agrees well with experimental data and can be applied under undrained and partially drained conditions.