Een probabilistisch model voor de vergelijking van twee golfbrekertypen op basis van economische optimalisatie

Een probabilistisch model voor de vergelijking van twee golfbrekertypen op basis van economische optimalisatie

Laenen, K.C.J.

Vrijling, J.K. (mentor)
De Ridder, H.A.J. (mentor)
Tutuarima, W.H. (mentor)
Voortman, H.G. (mentor)

Civil Engineering and Geosciences

2000-12-01

Breakwaters can be divided into two maintypes: the classic (rubblemound) type breakwater and the vertical (caisson) type breakwater. In general it is assumed that vertical type breakwaters are more economic than classic type breakwaters, due to the quadratic increase of volume of material needed for the classic type breakwater as a function of the waterdepth. In addition to the vertical (composed) type breakwater which has a linear increase. In this study an inquiry has been made to determine the influence of other factors (besides waterdepth) on the economic choice between a classic type breakwater or a vertical type breakwater. To make a fair comparison between the two breakwater types, the influence of the factors on the economic optimal crossection design has been determined. In order to generate economically optimal crossections of both classic and vertical breakwaters an economic optimization model has been made. This model generates, after input of locally dependent hydraulic, geotechnical and economic boundary conditions and material properties, economically optimal crossections for both types of breakwaters. Apart from this the model generates (also for non-economically optimal crossections) total lifetime cost (construction cost and risk), (optimal) chances of failure and material quantities. The model also generates the contribution (in percentage) ofthe different stochastic variables towards the total chance of failure. To determine the risk three scenarios of failure have been taken into account: 1) Transmitted waves behind the breakwater are too high resulting in a disturbance of the transshipment operation (SLS). 2) Transmitted waves behind the breakwater are too high so that entrance to the harbour will be prevented (SLS). 3) Collapsing ofthe breakwater which also leads to a decrease of the protection of the harbour from scenarios 1 and 2 (ULS). In this study the model is applied to an existing case: the Noorderdam breakwater belonging to the project of extension of Maasvlakte 2, near Hook of Holland. It appears that the totallifetome cost of the classic type breakwater is 18% higher than the vertical type breakwater. For both types of breakwaters the total lifetime cost exists of +//-90% construction cost and +/-10% risk. Because of this the economic choice between both types of breakwaters is mainly determined by factors which influence this construction cost. The construction cost for the classic type breakwater is determined for 50% by the cost ofrubblemound in the core. The construction cost for the vertical type breakwater is determined for 75% by the cost ofthe concrete in the caisson. The risk of the classic type breakwater is mainly determined by the occurrence of scenario 1 and for the vertical type breakwater only by the occurrence of scenario 3. The risk for both types of breakwaters is mainly determined by the uncertainty in the hydraulic boundary conditions. For the Noorderdam breakwater a sensitivity analysis has been carried out to determine the influence of certain factors on the optimal choice of breakwater type, which shows that the waterdepth indeed influences greatly the choice of breakwater type. Other factors which greatly influence the economic choice are the unit price ofconcrete and rubblemound. If these are not known with an accuracy of +1-25%, nothing definite can be said about the choice. The scenario 3 damage cost, the percentage ofconcrete ofthe caisson, the length and the planned lifetime of the breakwater can't influence this choice. In this study only 7 factors have been analysed. However, with the designed economic optimization model the sensitivity of more factors can be analysed. Certain factors can be changed at the same time also.

breakwater
optimisation

http://resolver.tudelft.nl/uuid:3f96aed6-c00f-415a-944d-b8a2b33d598d

TU Delft, Civil Engineering and Geosciences, Hydraulic Engineering

Student theses

master thesis

(c) 2000 Laenen, K.C.J.