Wave Force on a Partially Immersed Caisson Supported on Piles

This paper describes total wave-induced forces, moments on a pile-supported vertical caisson through an experimental investigation. It is crucial to comprehend the total force acting on the vertical caisson-pile-supported breakwater (VC-PSB) as the integration of measured dynamic pressure on the front face might give only an approximate estimate due to scarce pressure port locations. The experiments were carried out in a wave flume in three water depths (0.79, 0.87, and 0.95 m), and the model was subjected to regular waves with wave periods ranging from 1 to 2.6 s for each of which two wave heights 0.1 and 0.15 m were employed. A larger pile spacing-to-diameter ratio (s/D > 7) was maintained so that the piles had a minor contribution to the dissipation of incident wave energy. A force balance with six-component force sensors was used to measure the forces in all directions, and the moments were estimated knowing the lever arm distance of force sensors. The measured shoreward horizontal forces are compared with those computed from the standard formula for an elevated vertical caisson with a negative air gap. The structure was found to experience more vertical force than horizontal force for the three water depths considered. The vertical forces decrease exponentially with an increase in the relative depth. The horizontal forces decrease with relative submergence as the exposure area of the caisson exposed to waves decreases. The moment variation is primarily identical to the horizontal force variation.