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
Barrier built up with geo-cells, under
construction, Siglufjörður 2006.
Barrier built up with geo-cells, after
completion, Siglufjörður 2006
It is important to note that the top width must be sufficient to operate machinery, especially if
the leeside slope is steep. The 3m usually allocated for the top width is very narrow. At least
6m are needed for trucks to maneuver one the top so usually the final two meters of fill are
built up with an excavator.
5. GROUNDWATER
Groundwater levels in both cut and fill areas are very important. It is essential to lower the
groundwater levels under the dams and barriers as much as possible to increase their stability
and take some measures to maintain these levels and ensure that water has a safe passage out
from under the constructions. For this purpose trenches have been excavated under the dams
that have been filled with highly permeable material wrapped in geotextile. The most
effective fill materials are stones that can be screened from the scree material. The final
positioning of these trenches is best selected and adjusted to conditions encountered when
construction has started, rather than specifying a grid of trenches. This will allow them to be
positioned where water is actually flowing. The photographs below show typical trenches.
Drainage trench, Siglufjörður, 1999. Drainage trench, Flateyri, 1997.
194 Avalanche protection – some aspects of design and construction