The coastal zone is a unique geological, physical and biological area of vital economic, cultural and environmental value. More than two-thirds of the world's population is concentrated in coastal zones, where the coastline is either central or of great importance to trade, transport, tourism, leisure and the harvesting of marine food. Breakwaters are commonly adopted to protect and enhance the utility of coastlines. Worldwide, the combined costs for building new breakwaters and maintaining the existing ones are in the order of tens of billions of pounds a year.Breakwaters are vulnerable to the liquefaction of the seabed foundation, a process that can often lead to significant degradation of the foundation in as little as a few years after construction and sometimes even result in total collapse. The inappropriate design or maintenance of breakwaters can lead to catastrophic coastal disaster. For example, the failure of Sines Breakwater in Portugal caused damage equivalent to almost US$1 billion in reconstruction alone, excluding the huge economic and social impacts on the region. A recent example of coastal tragedy due to failure of breakwaters is that of New Orleans during Hurricane Katrina, putting 80% of the city under as much as 6 m of water and causing deaths and personal and economic chaos. The economic loss from the disaster was more than US$15 billion.In this study, we will firstly extend the existing 2D wave and soil models to 3D, and then integrate them into a single model to provide a better prediction of the wave-induced liquefaction around breakwater heads. A series of physical model experiments will be conducted for the verification of the proposed theoretical models. The proposed research is an essential step towards significantly improved engineering design and remedial action to address foundation-related damage to coastal structures. The underlying conceptual innovation of the project comes from three factors that combine to enable the proper understanding of the WSSI phenomenon: 1) the integration of all three components of wave/seabed interactions around breakwater heads; 2) the treatment of the seabed as a general porous media with large deformation; and 3) the use of 3D rather than 2D modelling. This approach is essential as it is the only way to simulate wave patterns around breakwater heads, model wave energy dissipation in marine sediments (including the critical phenomenon of flow through porous media) and account fully the interactions between waves, seabed and structures. .