Reliability analysis of quay walls using metamodelling

Abstract

Reliability analysis is a rational method for dealing with uncertainties. It is increasingly used for the design and assessment of (civil) structures. Reliability analysis, possibly in combination with performance data, allows for instance to update (extend) the lifetime of existing quay wall structures. This gives economic advantages when assessing quay walls, figuring there are thousands of kilometres of quay walls worldwide. Soil-structure analysis (e.g. analysis of quay walls) is however complex and in general requires finite element (FE) models. Conventional reliability methods are mostly incapable of dealing with FE models because they have long (infeasible) calculation times e.g. Monte Carlo, or they cannot deal with the typical noisy and incomplete FE model output e.g. FORM. One way of dealing with these challenges is by using a metamodelling approach, i.e. build up and make use of a response surface on a limited number of model evaluations. One specific application which uses metamodelling is ERRAGA, which is an abbreviation for Efficient and Robust Reliability Analysis for Geotechnical Applications. This thesis investigates the potential of ERRAGA/metamodelling for reliability analysis of quay walls in engineering practice.\medskip

In this thesis ERRAGA is tested on two realistic case studies located in the port of Rotterdam. The first case is called the ‘Sleepbootkade’, a quay constructed from a combi wall with anchors. The second case study is called the HHTP-quay, a combi wall with relieving platform and MV-piles. In the first case focus is placed on getting to understand the details and workings of the ERRAGA method. In the second case focus has been put on the creation of the reliability model and the practical applicability of ERRAGA using the experiences of the first case. Two critical limit states are tested within the case studies: wall failure in bending and geotechnical failure. Especially the limit state geotechnical failure is challenging as relevant output parameters are known to be noisy and/or incomplete.\medskip

The main finding of this thesis is that reliability analysis of quay walls using ERRAGA in combination with a numerical model shows good potential. ERRAGA can generate reliable and accurate results within only hundreds of realizations, hereby overcoming the main drawbacks of existing reliability methods. Main drawback of the ERRAGA method seems to be its inherent complexity and ‘black box’ nature. For the user to employ the full potential of the method some more in depth knowledge and especially the user-defined settings are required. Based on the gained experiences in this thesis some first recommendations are presented for the use and application of ERRAGA in projects.