Comparative study on bearing mechanism of pile in marine calcareous sand and terrigenous siliceous sand subjected to failure-inducing cyclic loading

The underlying mechanisms governing load transfer and bearing capacity of pile in marine calcareous sand under failure-inducing cyclic loading controlled by extreme stress and displacement remain poorly understood. A series centrifuge experiments were conducted on single piles subjected to monotonic compression, monotonic uplift, and failure-inducing cyclic vertical loading in dry calcareous sand, with comparative tests performed in siliceous sand. Complementary numerical simulations were conducted using the discrete element method (DEM) to analyze the particle breakage at the pile-soil interface. The ultimate uplift bearing capacity of the pile decreases after cyclic loading, with the reduction being more pronounced in calcareous sand than in siliceous sand. Conversely, the ultimate compressive bearing capacity increases by approximately 2.5 times in calcareous sand, whereas only a modest increase of 6% is observed in siliceous sand. The evolution trends of load sharing ratios in calcareous and siliceous sands are completely opposite. In calcareous sand, significant variation of ratio occurs during the initial cycles, while in siliceous sand, changes predominantly emerge during the later stages. Since the significant particle breakage in calcareous sand, the capacity gap between the two soil types narrows under cyclic loading.