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
The snow depth in a part of the test area became very high during several winters and the
structures have become partly overfilled and heavily loaded. In addition to the measurement
results, several lessons have been learned from the performance of the structures under these
conditions. A part of the snow bridges from J. Martin was damaged in a storm that lifted the
footplates of the structures shortly after their installation in the fall of 1996. This was repaired
by drilling anchors through the groundplates of all the posts that are mounted on groundplates.
Several micropile post foundations in loose material failed in the Geobrugg net row
during the first winter. This was repaired in the fall of 1997 by replacing the micropiles of
these posts with groundplates. A part of the EI net row with a short spacing between net posts
has failed, indicating a design failure in this net type. The wire rope in the top loop of one
upper anchors in the Geobrugg net row broke in 2006 indicating that an improvement in the
tube shield of these anchors is desirable. Serious corrosion problems have been encountered
in all wire ropes of the Geobrugg and EI nets indicating that corrosion protection of traditional
Alpine snow nets are unsuitable for Icelandic conditions. These failures have been taken into
account in requirements that are made to supporting structures in Iceland which have been
formulated based on the results of the experiment in Siglufjörður (Jóhannesson and Margreth,
1999; Jóhannesson, 2003).
Figure 1 Location map of the supporting structures in Grindagil in Siglufjörður showing
the installed instruments (left) and a photograph of the uppermost row of steel
bridges (right).
3. LOAD MEASUREMENTS
Tension in three upper anchors of the snow nets, and compressive forces and moment loads in
one net post have been measured with continuously recording instruments. Maximum
Jóhannesson and Hopf 145