Financial risks assessment of the breakwater construction phase

Abstract

During construction of breakwaters, adverse weather conditions can result in damage, in the form of reshaping and loss of material to the open work fronts of the structure. Based on literature research, analysis of work methods, analysis of damage to older breakwater projects and interviews, it was deduced that during construction, the open work fronts of the submerged core section, emerged core section and underlayer section are in particular prone to the following damage mechanisms: - Reshaping of the submerged core due to head-on and oblique wave attack - Reshaping of the emerged core due to head-on and oblique wave attack - Reshaping of the underlayer due to head-on and oblique wave attack. - Mixing of rock material of different sections. - Overwash of dislocated material. When a damage event occurs, construction is delayed as repair works are needed. This delay increases the probability of encountering unfavourable conditions in the remaining construction time. Such positive feedback complicates any quantitative risk assessment. The main objective of this thesis was to investigate the feasibility of a computational model with which risks related to the construction phase of rubble mound breakwaters in sea-state conditions can be assessed. By simulating the construction process in time with a fully probabilistic process-based model, the financial risk due to storm-induced damage during construction can be assessed. Due to the stochastic behaviour of the parameters used in the building process simulation, the simulation outcome itself is characterized by a stochastic behaviour. To calculate the financial risk, the simulation is run multiple times like a Monte Carlo simulation. Quantitative damage calculations in the model were performed using methods reported in the relevant literature. However, currently available literature did not cover all damage mechanisms or the full extent of it. For these damage mechanisms, some newly developed methods were introduced. The damage profiles predicted by these methods turned out to be in excellent agreement with data from an older breakwater project. This older breakwater project was used as a reference case to test the model and analyses its performance. Furthermore, a sensitivity analysis on the breakwater parameters showed that the nominal diameter of the core and underlayer material and the start date of construction works have the strongest sensitivity on the financial risk.