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Varmuuden kohdentaminen tukiseinien mitoituksessa

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Details

Original languageFinnish
Place of PublicationHelsinki
PublisherLiikennevirasto
Number of pages73
Volume2016
ISBN (Electronic)978-952-317-214-2
Publication statusPublished - 2016
Publication typeD4 Published development or research report or study

Publication series

NameLiikenneviraston tutkimuksia ja selvityksiä
No.7
ISSN (Print)1798-6648

Abstract

In Finland retaining walls are designed by using design approach 2 according to SFS-EN 1997. In design approach 2, partial factors are applied to loads or their effects and to earth resistance. National choices for load combinations and for partial factors have been made based on limited number of comparison calculations. The aim was to
end up having the same safety level as with the total factor of safety approach. Recently, it has been acknowledged, that this has not been achieved.
For loads, the load combinations 6.10a and 6.10b are used. These are given in National Annexes of SFS-EN 1990 (YM (2007) and LVM (2010)). It has been proven that by using these two load combinations the total factor of safety can, in certain cases, be really low. Moreover, it has been proven that currently used partial factors cannot take into account the real uncertainty related to earth pressure calculation. Also the unequal partial factors for permanent and transient loads are complicated to use in numerical analysis.
This study can be divided in to three separate sections. In the first section uncertainties related to determination of characteristic soil parameters and loads are presented. Moreover, the significance of ground investigations is discussed. The uncertainties related to the soil parameters are discussed based on the studies done by Phoon
et al. In the second section design approaches given in EN 1997 are presented together with the national decisions made in Finland, Sweden and Denmark. Furthermore, criticism against the design approaches is discussed based on Simpson (2009), Schuppener (1998) and Schweiger (2013). In the third and the most important part, the calculation examples used in this study, design procedure and calculation results are presented. The aim of calculation examples is to investigate how different design approaches and the uncertainties in soil parameters effects on the design stresses and the total factor of safety, and moreover, to point out possible shortcomings in current design procedure.
Various flaws were found in the current retaining wall design. By using the current load combinations 6.10a and 6.10b, no additional benefit was gained to the design. On the contrary, this just increased the amount of work and complicated numerical calculations. Moreover, the importance of partial factor applied to earth resistance (R,e) was sometimes negligible. Better solution would be to apply the safety straight to the strength parameters, where the real uncertainty is. Based on obtained calculation results, four different options were proposed how the retaining wall design could be done in future. In authors’ opinion, option 3 would lead to the most reliable design.
In addition to these, shortcomings in current design of prestressed anchors were highlighted.

Field of science, Statistics Finland