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Reliability of Quary Walls Using Finite Element Analysis

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During the last years the Finite Element Method (FEM) is increasingly applied in the design of quay walls. Especially in case of quay walls with relieving floors and bulk-storage as surcharge load, sub-grade reaction models are limited in their accuracy of modelling the situation. The Finite Element Method often is the only option to more detailed design calculations of quay walls. In the recent years the introduction of Eurocode and the increasing use of Finite Element analysis for design calculations has triggered the update of the CUR Quay walls handbook CUR 211. 

The latter second edition has recently been published. In advance of this second edition it was decided to look into more detail into the combination of FEM analysis in combination with the Eurocode which lead to the study that is described in this article. In order to infer a more fundamental base for the design method with FEM, two quay walls were examined to check the applicability of the existing FEM design method of the Dutch Handbook Sheet Pile structures (CUR 166) on quay walls with relieving floor. Furthermore, it was checked whether the current partial safety factors needed to be adapted. 

This research is done by performing probabilistic FEM calculations. The First Order Reliability Method is incorporated in the software Prob2B (Courage & Steenbergen, 2007) to perform the calculations. It appeared that using the design method of CUR 166 for quay walls with relieving floor leads to an
underestimation of the reliability of the structure. Therefore it is advised to adapt the design method. Furthermore, differences in partial safety factors are proposed to reach the required reliability index.

Introduction
During the last two years, CUR committee 183 has worked on the upgrade of the
Dutch Quay Walls handbook (CUR 211), which was published in November 2013. Two of the main elements that are considered in this new edition are the addition of FEM analysis as a method for design, comparable to the description in the Dutch Handbook Sheet Pile Structures (CUR 166), and the calibration of partial safety factors design with FEM. With respect to the actuality of this update it must be remembered that with the new 2nd Maasvlakte and other changes in the  Rotterdam harbour area, several quay walls are under construction.

One of the arguments for the further introduction of FEM analysis for quay wall design is that for the larger quay walls, relieve platforms are often used under heavy loaded conditions. In that situation one must consider that the piles under the relieve platform may bear a part of the horizontal load that is normally taken by the retaining wall. Furthermore, if the load itself is bulk-storage there are limitations to the accuracy of modelling surcharge load with sub-grade reaction models that are normally applied for soil retaining wall design; horizontal components of bulk storage may be difficult to model;


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