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 (theta L) or a larger pile-soil relative stiffness (T/L) results in wider and deeper sediment subsidence after 10,000 cycles. As theta L increases from 0 degrees to 80 degrees, 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 theta L increases, klN/kl1 and kuN/ku1 increased more sharply in the initial stage, with a quicker transition from rapid growth to stability. At theta L = 80 degrees, 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.

Under long-term horizontal cyclic loading, the evolution characteristics of the loading and unloading stiffness of piles are an important representation of pile-soil interaction. However, research in this area is limited, particularly regarding the impact of factors like pile-soil relative stiffness. In this study, laboratory tests with a long-term horizontal cyclic loading strategy were conducted to study various factors, including different cyclic amplitude ratios (zeta b), cyclic load ratios (zeta c), and pile-soil relative stiffness (T/L) in sandy soil, on dynamic pile head stiffness. The results show that the normalized cumulative displacement increases with the number of cycles and the ratio of T/L but tends to decrease as zeta c increases. As zeta b increases, the normalized cyclic loading stiffness also rises, while it has little effect on the normalized cyclic unloading stiffness. On the other hand, as zeta c or T/L increases, the cyclic loading stiffness increases while the unloading stiffness decreases. Based on these observations, prediction formulas for normalized cumulative displacement and cyclic loading and unloading stiffness were established and confirmed with test results. The findings of this study provide methodological references for establishing models of pile-soil interaction under cyclic loading and for predicting loading and unloading stiffness under different influencing factors.

In order to study the failure mechanism of a finned pile foundation under horizontal cyclic loads, a physical model test of the pile-soil interaction of finned pile is designed in this paper. Based on the model tests, the pile top displacement, the cyclic stiffness of the pile foundation, and the response of pore water pressure within the soil around the pile were fully studied for the finned pile foundation under horizontal cyclic loads. It is found that the cyclic stiffness attenuation of the finned pile foundation is more severe than that of a regular single pile foundation, but the final stiffness at equilibrium is still greater than that of a regular single pile foundation. The accumulation of horizontal displacement at the pile top and pore water pressure within the soil around the pile mainly occurs in the first 1000 loading cycles, and an increase in fin plate size will reduce the magnitude of pore water pressure and pile top displacement. This study can not only deepen the understanding of the failure mechanism of finned pile foundation under horizontal cyclic loads, but also provide guidance for the design of the finned pile foundation.