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 structure is light weight and easy to transport and install under difficult topographical
circumstances. With firm rock at the surface the foundation work is limited to bolts grouted into
boreholes. Under such conditions the cost per metre is approximately one fifth of a conventional
supporting structure or snow net of comparable height. The transparent design of the
structure makes them virtually invisible in both summer and winter. This is particularly suitable
in tourist and recreational areas. The growth of plants is not restricted by shadows cast by
conventional supporting structures (Figs. 1−2).
Figure 2 a) Light retention mesh. b) Strut (tread bar) coupled to rock anchor and post.
Mesh with ground clearance clipped to wire going through the adjusting eye bolts.
2. DESIGN
The maximum snow height recorded in the area has only once been above 2 metres in 30
years. Within a return period of 25 years it is assumed that the critical snow height on the
south-facing hillside would not exceed two metres measured normal to the ground,
corresponding to approximately 2.3−3.0 metres measured vertical on slopes of 30−45 degree.
In some locations, a maximum depth of two metres is expected.
Accordingly, the vertical height of posts and strength of structure was designed for 2.0, 2.5
and 3.0 metres of low density snow (200 kg/m 3 ), respectively and 1.3, 1.7 and 2.3 metres of
high density snow (400 kg/m 3 ). The design snow loads were calculated in accordance with
the Swiss guidelines with some adjustments to account for verified creep and glide conditions
of Norwegian snow.
The design of the retention structure was based on the forces acting on posts, tendons and
mesh from the calculated loads. An example of estimated section forces between post and
tendon is shown in Figure 3.
The ideal location for the fix point between tendon and strut as well as dimensions of posts,
are shown in Table 1.
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