International Symposium on Mitigative Measures against Snow ...

<strong>International</strong> <strong>Symposium</strong> on Mitigative Measures against Snow Avalanches
Egilsstaðir, Iceland, March 11–14, 2008
occurred around the time of maximum snow depth. The onset of melting led to a sharp
decrease in the loading. There were no indications of an increase in the loading due to deformation
or gliding introduced by melting.
4.3 Reliability and performance under overloading
There have been much more damages of the rows of the snow nets than for the steel bridges due
to overloading of a similar magnitude as described above. The continuous rows of the steel bridges
with a varying structure height were better adapted to the terrain and to local variations in
snow depth than the snow nets. Furthermore, the continuous rows of the steel bridges provide
much better lateral stability than the snow nets. Lack of lateral stability appears to be an important
failure mechanism for some of the damages that have been observed in the snow nets. The stiff
steel constructions appear for this reason to be able to survive more overloading than the nets
without damage. Failure of net posts with micropile foundations in loose materials and of snow
nets with narrow post spacing has given valuable experience about proper design of supporting
structures for the heavy loads experienced in Iceland. This experience indicates that the steel
bridges have greater reserve strength to withstand local overloading without damage and that
maintenance costs due to failure will in general be higher for snow nets than for steel bridges.
4.4 Corrosion
Serious corrosion problems have been encountered in all wire ropes of the Geobrugg and EI
nets indicating that corrosion protection of wire ropes traditionally used in Alpine snow nets
are unsuitable for Icelandic conditions. These problems are very serious and hard to solve. It
is recommended that steel bridges are in general hot-dip calvanised for Icelandic conditions.
The experience in the test area indicates that with that type of protection, corrosion is not a
problem for steel bridges.
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Figure 7 Comparison of galvanized and black type of snow bridges in the lowest row of
the J. Martin snow bridges (left). The row with EI snow nets was deformed by the
heavy snow loads, partly due to lack of lateral stability.
4.5 Environmental aspects
Undoubtedly the landscape is less interfered with nets than with snow bridges, especially if
those are not galvanized. In time the galvanization leads to a gentle grey colour, well adapted
Jóhannesson and Hopf 149