Pre-Assessing the Feseability of a Design a Performance Function for Scour Protection Systems in Offshore Foundations

Tiago João Fazeres Ferradosa, Francisco de Almeida Taveira Pinto

Thursday 2 july 2015

8:45 - 9:00h at Amazon (level 1)

Themes: (T) Water engineering, (ST) River and coastal engineering

Parallel session: 10B. Engineering - River

The scour phenomena present a considerable risk to the stability and operability of an offshore or coastal structure (De Vos L. et al., 2011). Several authors have been developing research, of great importance, regarding the prediction of scour (e.g. Melville B. & Coleman S. E., 2000, Sumer S. & Fredsøe J., 2002, Whitehouse R. et al., 2011) and also concerning the theme of scour protection (e.g. Nielsen A. et al., 2013, Matutano C. et al., 2013). The design of offshore foundations and the analysis performed to the scour problems is still often based on empirical or semi-empiric approaches (De Groot et al., 2006). The nature of these techniques does not account for the variability of major variables, as the bed-shear stress, velocity or the turbulence levels, among others. In order to reduce the uncertainty, in the design of offshore foundations, new approaches can be considered, namely the ones based on risk and reliability analysis, which are already applied in other types of hydraulic structures, for example, Li C. et al. (2012), and Cheng J. & Li Q. (2009). Applying these probabilistic approaches implies the definition of a solid performance function which aims to describe the desired limit state of a designed structure. Once the performance function is obtained, it can then be used for the calculation of the failure probability. This allows the project criteria to be defined taking into consideration the variability of scour phenomenon, instead of only using the analysis performed purely based on the factor-of-safety which do not account for such uncertainties (Faber M., 2009). The present study aims to pre-assess a possible performance function and its feasibility, in order to be used in the design of scour protection systems for offshore foundations, such as offshore windfarms. A case laboratory study is presented, where the performance function is mainly based on the scour depths around a mono-pile foundation. Keywords: Scour, Performance Function (g-function), Monte-Carlo Method, Probability of Failure and Scour Protection.