A New Method for Predicting Pile Accumulated Deformation and Stiffness of Evolution Under Long-Term Inclined Cyclic Loading

Piles in marine environments are subjected to various loads of differing magnitudes and directions, and their long-term stability has attracted much attention. Most research focuses on lateral cyclic loading; there are few full-scale tests that consider the effects of cyclic loading at different inclined angles. A long-term inclined cyclic loading strategy was used to carry out laboratory tests to study different inclined angles on the pile. The results show that a smaller inclined angle (θL) or a larger pile–soil relative stiffness (T/L) results in wider and deeper sediment subsidence after 10,000 cycles. As θL increases from 0° to 80°, the peak displacement at the pile head during the first load decreases, while the accumulated displacement initially decreases and then increases. For slender piles, the normalized inclined cyclic loading stiffness (klN/kl1) and unloading stiffness (kuN/ku1) first decrease and then increase. For semi-rigid piles, both klN/kl1 and kuN/ku1 gradually decrease. On the other hand, as θL increases, klN/kl1 and kuN/ku1 increased more sharply in the initial stage, with a quicker transition from rapid growth to stability. At θL = 80°, peak values are reached early during the initial loading phase. Based on this, prediction formulas for inclined cyclic cumulative displacement, loading stiffness, and unloading stiffness were established and verified.

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