Target reliability indices for existing quay walls derived on the basis of the LQI criterion

General frameworks for reliability differentiation have evolved over time and are mainly developed for new buildings. However, recommendations for existing quay walls are lacking. In this study target reliability indices for assessing existing quay walls were derived by economic optimisation and by evaluating the Life Quality Index criterion (LQI). In quay wall design, some dominant stochastic design variables are largely time-independent, such as soil and material properties. The influence of time-independent variables on the development of the probability of failure was taken into consideration in this study, because this affects the present value of future failure costs and the associated target reliability indices. The reliability indices obtained in accordance with the LQI acceptance criterion were a little lower than the target reliability indices derived by economic optimization. The target reliability indices obtained for existing quay walls depend on the consequences of failure and the remaining service life. If failure modes of a quay wall are largely time-invariant and already survived the first period of the service life, the residual probability of failure is lower for an existing quay wall compared to a new quay wall. Hence, this should be considered in the determination of target reliability indices. The method of approach to assess the development of reliability over time can also be used for evaluating target reliability indices of other civil and geotechnical structures.