[Civil Engineering] PhD ( Dundee u, UK )

Integrated Prediction of 3D Wave-Induced Liquefaction around Breakwater Heads � EPSRC Research Project EP/G006482/1 (2009 � 2012)

INVESTIGATORS:

Professor Dong-Sheng Jeng & Professor Ping Dong

DESCRIPTION:

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. For example, the total length of all breakwaters in Japan is 4,143 km-one fifth of its coastline. In the UK, coastline protection is a major national priority. The construction of new breakwaters and the expansion of existing breakwaters involve major investment. 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.


The phenomenon of wave-seabed-structure interaction (WSSI) has a major bearing on this issue and is central to the design of coastal structures such as breakwaters, pipelines and platforms. Numerous studies of wave-induced seabed response have been conducted since the 1970s, involving the investigations of pore pressure, effective stresses, and displacement. Nearly all of these models have restricted to 1D or 2D cases, which, crucially, represent only part of the problem; little research has attempted to account for real-world, 3D conditions and, as a consequence, the understanding of the dynamics of breakwaters is limited to the individual components of WSSI in isolation, such as the types of wave and the soil characteristics. However, WSSI is a complex, highly-integrated process: to develop new designs and methods of construction and renovation that overcome the problem of seabed liquefaction, analysis and interpretation of WSSI as a whole, unified system in 3D is required. The lack of knowledge of the whole WSSI problem has led to significant uncertainties in breakwater design and management. With respect to seabed stability, most design guidelines compensate for this uncertainty by recommending a conservative approach to design and maintenance for legal and safety reasons; this approach increases costs.

The aim of the project is to understand the mechanisms of WSSI in 3D, and to use this as a basis for developing an accurate predictive model for seabed instability around caisson-type breakwaters enabling the better design, construction and maintenance of breakwaters. The project consists of four pahes:

Phase 1 � 3D wave model. Based on the 2D CORBAS model (Cornell model), we (with Cornell Group) will develop a 3D model for the wave field around breakwater heads. In the model, the seabed will be considered as a porous rather than an impermeable medium.
Phase 2 � 3D geotechnical model. We will develop a poro-elastoplastic model for wave-induced liquefaction, based on the DIANA SWANDYNE-II model (collaborating with Birmingham group). The progressive nature of liquefaction will be included in this model.
Phase 3 � Physical modelling. A series of wave experiments in geo-centrifuges at Dundee group will be undertaken. The centrifugal tests will be compared with wave experiments in wave flume and wave basin in Chinese groups.
Phase 4 � Model integration. We will integrate the models developed in Phases 1 and 2 into a unified model with parameterisations determined from Phase 3.

We are looking for three PhD students to undertake Phases 1-3.

Please read: http://www.personal.dundee.ac.uk/~djeng/project_wssi.htm