Keywords: pore pressure, consolidation, marine sediment, soil plasticity.

Design of marine structures considering their stability is a rather complicated problem. One of important factors which has to be taken into consideration in the design procedure is the wave-induced seabed instability in the vicinity of the structures. It has been well documented that ocean waves propagating over the ocean surface exert dynamic pressure fluctuations on the sea floor. These fluctuations further generate an excess pore pressure within the soil skeleton, which have been recognized as a dominant factor in analyzing the seabed instability. Recently, some marine structures (for example, the Sine Breakwater in Portugal) have been reported to be damaged by seabed instability at their toes [1]. Furthermore, it has been observed that a deep scour hole exists near the tip of a marine structure [1]. Without proper maintenance at these sites, failure of structures may be expected.

In general, the wave phenomenon in the vicinity of a marine structure contains two types of wave system, occurring in front of and at the head of the structure. Most previous investigations for the wave-seabed-structure interaction have been limited to either two-dimensional cases or a three-dimensional case in front of a breakwater. Only a few attempts have been made for the case around breakwater heads [2,3]. Among these, Jeng [2] derived an analytical solution for the wave-induced oscillatory soil response around the head of a breakwater. He considered the seabed as an infinite medium in his analytical model. However, a mistake was found in one of the governing equations used in his model [3]. Later, Li and Jeng [3] proposed a three-dimensional model for the residual pore pressure around breakwater heads. Furthermore, a detailed investigation for the combined oscillatory and residual pore pressure in a porous seabed in the vicinity of breakwater heads is reported in [3].

All the aforementioned investigations have been limited to poro-elastic model. It has been well known that poro-elastic models are only valid for small deformation. For large deformation, especially for the case of seabed instability, soil behaviour requires a more sophisticate model such as a plastic model. To the authors' best knowledge, there is no such plastic model for three-dimensional wave-induced seabed response around breakwater heads available in the literature. In this study, we will develop a three-dimensional poro-plastic model for the wave-induced soil response around breakwater heads. Based on numerical examples, we concluded that relative difference between elastic and plastic models are significant affected by wave periods and water depths. The wave height significantly affects the development of residual pore pressure versus time. Furthermore, plastic soil behaviour plays an important role in a seabed of low permeability.

1

R. Silvester, J.R.C. Hsu, "Sines revisited", Journal of Waterways, Port, Coastal and Ocean Engineering, ASCE, 115(3), 327-344, 1989. doi:10.1061/(ASCE)0733-950X(1989)115:3(327)

2

D.-S. Jeng, "Wave-induced liquefaction potential at the tip of a breakwater", Applied Ocean Research, 18(5), 229-241, 1996. doi:10.1016/S0141-1187(96)00033-8

3

J. Li, D.-S. Jeng, "Response of a porous seabed around breakwater heads", Ocean Engineering, 35(8-9), 864-886, 2008. doi:10.1016/j.oceaneng.2008.01.021

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £95 +P&P)