Experimental and analytical investigations on nonlinear dynamic response of caisson-pile foundations under horizontal excitation

As a deep-water foundation, composite caisson-pile foundation (CCPF) is usually subjected to horizontal dynamic loads and moments due to the complicated marine environment. In this study, model tests were performed on three different types of deep-water foundation, including caisson, caisson with four piles and eight piles to investigate their lateral nonlinear dynamic characteristics under various excitation forces. Meanwhile, the effect of scour depth on the dynamic response of the foundations were also studies. The test results indicate that the excitation force and scour depth significantly affect the vibration amplitude and resonant frequency of the foundations with an obvious nonlinear behavior. Compared with the caisson, adding piles beneath the caisson results in a decrease of the vibration amplitude and an increase of resonant frequency, and the configuration of the pile also has an influence. The experimental results are compared with the results obtained by a simplified dynamic Winkler analysis model proposed here. Despite its simplicity, a reasonable agreement between the experimental and the calculated responses was observed. Moreover, scaling laws have been applied in the CCPF model to discuss the dynamic behavior of the prototype foundation.