Bearing behaviors of large-diameter monopiles in soft clay under horizontal cyclic loading based on centrifugal model tests

The response characteristics of large-diameter monopiles under static and dynamic loads are obviously different from those of traditional small-diameter piles. To study their cyclic responses, the centrifuge tests on the large-diameter monopiles in soft clay under horizontal cyclic loading are carried out. Through a contrast study on the cyclic responses of monopiles under different working conditions, the laws of deformation characteristics, stiffness weakening and excess pore pressure accumulation of large-diameter monopiles are investigated. The test results show that the increase percentage of the bending moment caused by the number of cycles is less than 10% of the first maximum bending moment. With the increasing amplitude of one-way cyclic loads, the whole large-diameter pile-soil system can go through the elastic stage, elastoplastic shakedown stage and ratchet failure stage. The unloading stiffness, lateral cumulative displacement and excess pore pressure of soils around the piles are affected by the cyclic amplitude and number of cycles. Additionally, the unloading stiffness is also positively correlated with the pile diameter. The negative excess pore pressure can significantly accumulate at the pile toe of large-diameter rigid piles, which may offset the effects of soil weakening on the lateral behaviors of a monopile. When the amplitude ratio of the cyclic loads is below 68%, the whole pile-soil system is stable, and the lateral resistance of soils insignificantly weakens. It is recommended that the loading secant stiffness of p-y curve within the wedge soil flow zone should be reduced by 0.8 to consider the cyclic weakening effects.