Effects of pile groups and wave dynamics on the hydrodynamic load of offshore pile caps

Pile group-cap structures are vital in offshore platforms, with pile caps experiencing complex hydrodynamic loads influenced by pile groups and wave conditions. These loads significantly impact the structural stability and hydrodynamic performance of the cap. This study investigates the effects of pile groups, pile spacing, and hydrodynamic conditions on pressure distributions and horizontal forces. Experiments were conducted in a 7.5 m × 1.5 m rectangular wave flume using a pile group-cap structure consisting of a square pile cap and four cylindrical piles. The experiments analyze vertical and lateral pressure distributions and horizontal resultant forces under varying wave board speeds, water depths and structural configurations. Results show that smaller pile spacing increases vertical pressure by up to 19.8% at mid-cap heights on the wave-facing side, while larger spacing raises wave-back pressures by 12.5%, particularly in deeper water. Lateral pressure distribution varies with pile spacing, with closer spacing concentrating pressure at inner positions and wider spacing amplifying outer pressures. Horizontal forces differ significantly, with pile groups amplifying wave-facing forces by 48.24% and reducing wave-back forces by 46.34% compared to a solo cap. These findings underscore the need for optimized pile spacing and reinforcement to enhance load distribution and resilience offshore.