Wave-induced Hydrodynamics and Scour at Complex Piers on Sloped Beach

Pier scour under wave in near-shore area leads to vulnerability to safety of the pier and superstructure. Most pier scour induced by current or wave has focused on solid piers. Comparatively, much less attention has been paid to the scour at complex structures. One type of the complex geometrically piers consists of a pier, pile cap, and pile group, is commonly built as foundations for marine or coastal structures, such as bridges, etc. This work focused on wave-induced hydrodynamics and scour at the complex pier located vertically on a sloped beach. With respect to effects of the water shallowing when wave approaching and propagating to the sloped beach, an unsteady RANS-VOF model coupling with a morphological model and sediment transport models was used to simulate the wave propagation and eventually the scour around the complex piers. The model was validated approvingly using an experimental case conducted by Tonkin (2003). The simulations were set with solitary wave of H/h = 0.2 ~ 0.4, non-cohesive bed material of d₅₀ = 0.35mm, the pile cap of 0 ~ 0.5h height exposed to the water from the bed, where H is the wave height, h is the water depth, d₅₀ is the median diameter of the bed material. The results of the wave dynamic characteristics, scour depth distribution around the complex pier, and the scour mechanics related with local turbulence vortex were obtained and discussed. The comparison of scour depth with that of a single solid pier was conducted, and then found that the scour depth increase with the pile cap height exposed to the water, and the KC number of wave. The deepest scour is located at the side of the piles where bed shear stress and vortex induced by the wave is more intense.