Marine soft clays are known for their poor engineering properties, which, when subjected to prolonged static and dynamic loading, can lead to excessive settlement of offshore pile foundations and subsequent structural instability, resulting in frequent engineering failures. This study examines the bearing and deformation behavior of jacked piles in these clay deposits under both static and cyclic loading conditions using a custom-designed model testing apparatus. Emphasizing the time-dependent load-carrying capacity and accumulated cyclic settlement of piles, the research uses artificially structured clay to more accurately simulate stratum conditions than traditional severely disturbed natural clays. Model pile testing was carried out to analyze the effects of soil structure and cyclic loading patterns on the long-term response of jacked piles. Key factors investigated include initial soil structure, pile jacking-induced destruction, soil reconsolidation post-installation, disturbed clay's thixotropic effects, and cyclic loading's impact during service. Results show that increasing the cement content within the clays from 0 % to 4 % nearly doubled pile penetration resistance, led to a more significant accumulation of excess pore water pressure (EPWP), and accelerated its dissipation rate. Additionally, the ultimate load-carrying capacity of jacked piles also doubled. Higher cement content slowed pile head settlement rates and reduced stable cumulative settlement values, requiring more cycles to reach instability. Under high-amplitude, low-frequency cyclic loads, hysteresis loops of the model piles became more pronounced and rapid. This study enhances understanding of the long-term cyclic behavior of jacked piles in soft soils, providing valuable insights for designing offshore piles.

A thermodynamic constitutive model for structured and destructured clays is proposed in this paper based on thermodynamic principles on the energy storages and dissipations. The model includes state-dependent relations of hyperelasticity and plasticity without the concept of yielding surface. The proposed nonlinear hyperelasticity is dependent on the sates of soil stress, density, and structure and leads to the limit state surface that varies with the bonding structure from a curved surface for structured clays to a plane surface for destructured clays. The plastic and destructure laws are subjected to the second thermodynamic law and expressed in the elastic-strain space instead of the stress space, which naturally account for the couplings between elasticity and plasticity with the Lode-angle and structure effects. The model is well validated by the predictions of drained/undrained conventional and true triaxial shearing tests for both structured and destructured clays, which well capture the K0 effect, the non-coaxiality between stress and strain, and the structure/destructure effects on the elasticstiffness and strain-softening of clays. For both structured and destructured clays, the critical-state elastic strain is unique under a fixed Lode angle and hence the critical state only relies on the critical-state density and the direction of shearing path.