A Conceptual Model for Structured Clay Under Long-Term Traffic Loads

Natural soft soils beneath transportation infrastructures sustain typical structured properties and are characterized by high sensitivity and poor engineering performance, which pose great challenges for the efficient operation of high-speed trains. Under traffic loading, soft subsoils present shakedown response and accumulate no negligible deformation. While few constitutive models are available both for the long-term behavior description of soft soils under cyclic loading and structure degradation of soil. Herein, a conceptual constitutive model within bounding surface theory framework was established to depict the dynamic behavior of soft clay under high-cycle, low-amplitude loading. The bounding surface could expand due to the hardening effect caused by contractive plastic deformation, and it could simultaneously shrink due to the weakening effect caused by both soil destructuration and excess pore water pressure. To further validate the proposed model, relevant triaxial tests were referenced. The consistent plastic deviatoric strain and excess pore water pressure from tests and the prediction confirmed the effectiveness of the proposed model. Following a comprehensive analysis of the varying internal variables during cyclic loading and a thorough investigation into the damage effects related to plastic strains, the model was considered capable of reasonably describing the structure destruction of soft soil to long-term cyclic load.