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
Figure 4 An instrument for measuring tension in the Geobrugg net row (left) and a broken
top loop in a wire rope anchor from the same row (right).
Figure 5 shows the tension recorded by one of the two instruments in rows II for the eleven
winters since the start of the experiment. The tension increases with increasing snow depth in
the early part of the winter and typically reaches a maximum between 150 and 350 kN in
March to April. The maximum tension varies from year to year, depending mainly on the
maximum snow depth of the winter. The onset of melting, typically in the beginning of May,
leads to a sharp decrease in the tension. There are no indications of an increase in the loading
due to deformation or gliding introduced by melting.
Figure 6 shows the compressive force and the moment from the winter 1997/1998 computed
from the strain recorded by four vibrating wire sensors that are mounted about 1 m above the
ground on a post in the Geobrugg nets in row II. The maximum force and moment of the
winter are found to be 160 kN and 19 kNm, respectively.
Figure 5 Measured tension in an uphill anchor in the Geobrugg and EI nets in Siglufjörður
from eleven winters, 1996/1997 to 2006/2007. Note that a d-link shackle connecting
the instrument to the anchor broke in the winter 2000/2001 resulting in the
abrupt drops in the tension for the curve from that winter.
Jóhannesson and Hopf 147