Wave-Current Loads on a Super-Large-Diameter Pile in Deep Water: An Experimental Study

Featured Application With the continuous development of marine engineering, super-large-diameter piles have been designed and constructed in deep water with complex and severe waves and currents. It is an important challenge in engineering design to determine wave and current loads of the super-large-diameter pile reasonably and accurately. However, the hydrodynamic coefficient given in the current design specifications are determined based on the model tests of small-diameter piles, which will no longer be applicable to the calculation of wave and current loads of super-large-diameter pile. In this article, taking one of the 6.3-m super-large-diameter piles of the main pier foundation of the Xihoumen Rail-cum-Road Bridge as the research object, we focused on the wave and current load characteristics and development laws of the super-large-diameter pile, and proposed the hydrodynamic coefficients of the super-large-diameter pile suitable for deep water, strong wave and current conditions. It can provide important reference for the engineering design of super-large-diameter pile for the foundation projects of cross-sea bridges, offshore platforms and offshore wind turbines in the future. Recently, the diameters and construction water depths of the pile foundations of planned and newly built sea-crossing bridges have been increasing greatly. Hydrodynamic loads are the key control factors in the design of super-large-diameter piles. However, most of the previous studies focused on the inline force on the pile with a small diameter, and there were few cases to consider the impact of the transverse force on the hydrodynamic load of the pile under wave-current actions. In this study, to understand the hydrodynamic loads on such deep-water super-large-diameter piles, the prototype was one of the 6.3-m piles used in the Xihoumen Rail-cum-Road Bridge, and 1:60-scale model tests were carried out in an experimental tank, with the actions of regular waves and waves combined with currents used as loads. The influence of the current velocity and static wave height on the inline and transverse forces on the pile was measured and analyzed. The experimental results indicate that with increasing current velocity, the fluctuation characteristics of the wave-current-induced inline and transverse forces change significantly, and their peak values increase obviously compared to those induced by only waves. In particular, the peak transverse force increases tens of times and can become equivalent to the inline force. The modified Morison formula and Kutta-Joukowski formula are used to derive the correlations between the drag coefficient C-D, inertia coefficient C-M, lift coefficient C-L, and redefined Keulegan-Carpenter number KC*. Under wave-current action, the transverse force contributes quite significantly to the hydrodynamic load on a super-large-diameter pile, making it easier to trigger extreme structural loads. The results presented herein are an important reference for the engineering designs of such super-large-diameter piles.