This work introduces a novel multi-coupled numerical framework for modelling the fracturing of protective structures subjected to natural hazards such as tsunami waves and debris flows [3]. The proposed methodology combines three advanced computational strategies: (i) the Particle Finite Element Method (PFEM) for simulating free-surface fluid flows governed by the three-dimensional Navier–Stokes equations and wave generation dynamics, (ii) the Shallow Water Finite Element Method for efficient large-scale wave propagation modelling [5], and (iii) a robust Finite Element–Discrete Element (FEM–DEM) [1,2,3,4] coupling to accurately capture the nonlinear fracture behaviour of solids. The solid domain is discretised with FEM elements that, upon cracking, transition into discrete particles governed by DEM, allowing the accurate representation of crack propagation, material separation, and contact interactions. The fluid domain, handled via PFEM, is dynamically remeshed to accommodate evolving fluid–structure interfaces induced by structural damage. A partitioned strong coupling strategy ensures accurate fluid–structure interaction, including convergence acceleration through relaxation techniques to model added-mass effects. This integrated approach enables the realistic simulation of complex scenarios involving large-scale impacts on coastal and civil infrastructure, such as breakwaters, retaining walls, and dikes. Several validation examples are presented to demonstrate the robustness and efficiency of the proposed methodology in predicting multi-physics responses during extreme events.