Engineering optimization and adaptation of vertical breakwaters in deep water

Sea level rise and the expected intensification of extreme sea states are placing increasing pressure on maritime defence structures, especially those originally designed under historical wave-climate assumptions. In this context, vertical caisson breakwaters play a crucial role in harbour protection, particularly in relatively deep waters where rubble mound solutions may become economically inefficient. However, vertical breakwaters are highly reflective structures and may experience severe wave-induced pressures, impulsive loads, and overtopping processes, which can govern both their structural stability and functional performance. This thesis investigates the engineering optimization and adaptation of vertical breakwaters in deep water, with particular focus on the effects of retreated wave walls and post-overtopping flows. A promising adaptation strategy consists of shifting the crown wave wall landward from the seaward edge of the caisson trunk, thereby creating a horizontal or sloping platform on the superstructure. This configuration can alter wave-structure interaction mechanisms without requiring extensive modifications to the main caisson body. Although retreated wave walls have already been adopted in relevant real-world projects, such as the new offshore breakwater of the Port of Genoa and the vertical breakwater of Civitavecchia, reliable design guidance remains limited. The thesis therefore addresses this knowledge gap through an integrated experimental and numerical research programme. The work is structured around four main research questions. First, it examines how the retreat distance of the wave wall affects global and local wave forces, reflection coefficients, and overtopping rates. A large set of small-scale regular-wave physical model tests shows that wall retreat significantly modifies the hydraulic response of the structure. Retreated configurations may reduce loads on the caisson trunk and, in some cases, wave reflection, but they also tend to increase impulsive loads on the wall and wave overtopping. These effects are strongly nonlinear and depend on the combined influence of geometry and wave conditions. Second, the thesis investigates the hydrodynamics of post-overtopping flows acting on retreated wave walls. Large-scale experiments identify three main event types, adapted from green-water classifications: Dam-Break, Plunging-Dam-Break, and Hammer-Fist. The most critical conditions are associated with Plunging-Dam-Break and Hammer-Fist events combined with small retreat distances, where impulsive loads on the wall and trunk may become nearly synchronized. Image-based analysis and force measurements are combined to define synthetic indicators and a parametric map for classifying events and supporting preliminary load estimation. Third, the thesis evaluates the influence of random phase seeding in irregular-wave experiments. Systematic repetitions show that overtopping estimates can be highly sensitive to seed selection, especially when overtopping is controlled by rare events. Conversely, global horizontal forces are generally less sensitive, while vertical downfall loads and local impulsive pressures exhibit larger variability. Finally, the thesis analyses construction-phase vulnerability, when internal caisson cells may remain temporarily exposed to post-overtopping flows. Physical tests and CFD simulations show that internal pressures depend strongly on the filling regime and decrease progressively from the seaward to the landward cells.