Integrated prediction of wave-induced liquefaction for stable breakwater heads
- Dr. Dong Jeng
- Professor John Small (University of Sydney, Australia)
- Professor Phillip Liu (Cornell University, USA)
Breakwaters are a major feature of the world's coastlines, and are vital to the economies and lifestyles of many coastal regions for the protection of coastal waters that they provide. The construction of new breakwaters and the expansion of existing breakwaters involve major investment. Breakwaters have always been vulnerable to the liquefaction of the foundation seabed, which leads to the degradation of their structure and function in as little as a few years, and often results in their total collapse (e.g., Sumer & Fredsøe 2002). Breakwater renovation does not fix the underlying problem, and is expensive and disruptive.
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 vertical breakwaters, pipelines and platforms. Numerous studies of wave-induced seabed response have been conducted since the 1970s, involving pore pressure, effective stresses, and displacement. Most of these models have involved 1D or 2D cases, which represent only part of the problem; little research has attempted to account for real-world, 3D conditions. Thus, the understanding of the dynamics of breakwaters is based on the investigation of 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 requires the analysis and interpretation of WSSI as a whole, unified system in 3D.
Our aim is to achieve a deep understanding of the mechanisms of WSSI in 3D, and to use this as a foundation for developing a significantly more accurate predictive method for seabed instability around caisson-type breakwaters. Specifically, we will: (1) develop 3D numerical models for the interactions of ocean waves, seabeds and breakwaters; (2) determine the fundamental mechanisms of wave-induced liquefaction, which lead to seabed instability around breakwaters, and to conduct numerical studies to quantify the effects of the key parameters-wave and soil characteristics and the configurations of structures; (3) conduct wave tank experiments to verify our theoretical models; and we will develop strategies for practical engineers to protect the foundations of marine structures.
Our science for accurately predicting damage to breakwaters will enable the significantly better design, construction and management of breakwaters. Sydney and Cornell Universities have formed a multidisciplinary team to achieve the aim, through a groundbreaking program of the numerical and physical modelling of WSSI around breakwater heads. The strength of the Sydney group is the numerical modelling of WSSI systems, and geomechanics; Cornell will contribute its strengths in wave modelling and its expertise in and facilities for the physical experiments. The collaboration will provide Sydney with access to unique experimental capacity, and will enable Cornell to bring its theoretical modelling significantly from 2D to 3D, with significantly wider application and power.
This project is supported by Australian Research Council Discovery Grant (2008-2010).