Elastoplastic modeling cyclic behavior of natural soft clay with principal stress rotation under traffic loading

Subgrade soil subjected to traffic loading imposes significant cyclic principal stress rotation and thus yields complex cyclic behavior. Up to now, the complex cyclic behavior has been validated by experimental studies but is still a challenge in constitutive modeling. For this, an elastoplastic model is proposed to reproduce the cyclic behavior of natural soft clay with principal stress rotation under traffic loading. The effects of small strain stiffness and elastic anisotropy were incorporated into the model to describe cyclic degradation and plastic accumulation behavior. To formulate the plastic mechanism under unloading, the relocatable mapping rules are defined in the deviatoric stress space, which is also applicable to the stress path with principal stress rotation under traffic loading. A revised three-dimensional non-coaxial flow rule which is colinear with a non-coaxial stress rate orthogonal to a reference stress tensor and dependent on the stress ratio is employed to describe the non-coaxiality. The undrained hollow cylindrical torsional shear tests with principal stress rotation under traffic loading and without principal stress rotation for Shanghai natural clay are used to verify the capability of the model. The comparison between simulations and experimental results demonstrates that the cyclic behavior with principal stress rotation under traffic loading can be well captured by the proposed model.