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Long-Term Cyclic Loading Tests for Offshore Pile Foundations Based on Hydraulic Gradient Modeling

Long-term dynamic response of pile foundations for offshore engineering has attracted more and more attention. The deflection accumulation and the natural frequency offset of the soil-pile system are two vital issues for the safety of offshore projects. However, the research on this topic is deficient because of the lack of effective test approaches. In this study, a new device was developed to investigate the long-term lateral cyclic response of a soil-pile system based on hydraulic gradient modeling. The downward seepage force was employed to create a supergravity field of high g-level. A long-term laterally cyclic loading unit was developed to simulate the cyclic loads under high g-level condition. This device was validated by comparing the results of a short-term centrifuge model test. The device was successfully applied into long-term cyclic loading tests of pile foundation. The test results showed that long-term cyclic loading induces the densification of the sand, the accumulative deflection of the piles, and the natural frequency variations of the soil-pile system. The limitations of 1 g-level model test in characterizing the long-term dynamic response of soil-pile system were clarified by comparing the results from 1 g-level and 100 g-level long-term tests.