Snow-supporting structures in permafrost

Snow-supporting structure (snow bridge) damaged by rock fall

Row of snow-supporting structures which was deformed due to pronounced creep of the underlying permafrost. Photo: S. Margreth (SLF)

Permafrost occurs above 2300-3000 m in the Swiss Alps, depending on slope aspect. Snow-supporting structures are increasingly being built in areas where the ground is perennially frozen and may contain varying amounts of ice. They are erected on steep avalanche slopes (30-50°), which are generally covered with an unstable layer of scree in high mountain areas.

SLF is investigating whether and how snow-supporting structures can be built in permafrost areas and whether there are thermal interactions between the steel structures and the underlying frozen ground which could induce thawing and slope instability and therefore cause damage to the structures.

The anchors of the snow-supporting structures penetrate the problematic, potentially unstable active layer, which displays positive temperatures in summer and in which frequent and numerous phase changes occur. This layer can be subject to creep. The snow-supporting structures also modify the temporal and spatial distribution of the snow cover and induce a pronounced delay in spring snow melt.

Technical investigations have shown that snow nets are best adapted to creeping permafrost conditions and that special measures need to be taken during construction in permafrost. The various technical measures, such as anchor types, grout types and grout injection methods have been published in new guidelines for the construction of snow-supporting structures in permafrost, which were developed at SLF.

Various measurements have been made on experimental snow-supporting structures since 1996, in order to determine how the structures are adapted to permafrost conditions. Ground temperature, slope stability, snow cover distribution and the temperature of the anchors are monitored. SLF also measures the temperature and stability of other structures such as chairlift pylons to determine their stability on steep permafrost slopes.

Literature

• List of publications on permafrost

Contact

• Marcia Phillips