Time-Dependent Bearing Behavior of Uplift Piles in Calcareous Sand

As marine engineering advances, the deformation and load-bearing performance of uplift piles in calcareous sand under sustained loading have become increasingly important to the long-term performance of marine foundations. Static uplift tests and sustained-load model tests were conducted in calcareous sand to examine the effects of pile surface roughness and sand gradation. The time-dependent evolution of pile-head displacement, uplift deformation stiffness, pile axial force, and shaft resistance was investigated, and the displacement–time responses were fitted using the Burgers model. The results showed that pile-head creep displacement under sustained uplift loading developed through two stages: primary creep and steady-state creep. Greater pile surface roughness and well-graded calcareous sand effectively limited long-term displacement. Under the maximum sustained loads, uplift deformation stiffness decreased by 27.4–43.0% over 21 d. At the maximum sustained-load level, pile axial force decreased progressively with increasing embedment depth. The time-dependent redistribution of axial force occurred mainly in the upper and middle portions of the pile and gradually stabilized after 3–7 d, with the redistribution becoming more pronounced as pile surface roughness increased. At the same load level, shaft resistance in the peak zone increased with the duration of sustained loading and gradually stabilized. This increase was more pronounced for piles with rougher surfaces, whereas well-graded calcareous sand facilitated the stable mobilization of shaft resistance. The Burgers model accurately captured the creep behavior of the model piles, with coefficients of determination (R2) exceeding 0.967 in all test cases.