Since 1972, when the Norwegian parliament assigned national responsibility for avalanche research to NGI, extensive research has been conducted into understanding avalanche mechanisms, their run-out distance, and the magnitude of forces an avalanche inflicts on objects that stand in the path of avalanche masses. At the Ryggfonn test site, in Strynefjellet in Western Norway, a full scale avalanche path has been developed. Avalanches can here be triggered, and the pressure and forces exerted against instrumented tubular masts in the avalanche path and on a 16-meter-high embankment dam in the bottom can be measured and monitored.

"In collaboration with the NVE (The Norwegian Water Resources and Energy Directorate), the Norwegian Public Roads Administration and a number of other participants, we have established the experimental Research field in Ryggfonn. Here we can study large avalanches and use the results in civic planning, to implement safety measures against avalanches for vital infrastructure, buildings and other installations", says Krister Kristensen, senior engineer and avalanche expert at NGI.

NGI

The full scale experimental test site at Ryggfonn is unique in the world and provides opportunities to study trigger factors, avalanche dynamics and the effects of the embankment dam in the avalanche path run-out area in the bottom.

Rules and regulations results in safe dwellings

A result of this extensive research and the understanding of avalanches, are the landslide/avalanche safety requirements in the prevailing Planning and Building Law (PBL). The safety requirements of the PBL do not permit new private homes to be located in areas in which the probability of landslides/avalanches per year is greater than 1:1000. The equivalent requirement for the construction of hotels, hospitals, kindergartens, etc. is 1:5000.

"In Norway, we have a very clear set of rules and regulations for where it is allowed to build in relation to landslide/avalanche safety. We have avalanche experts, for exaple from NGI, that can evaluate and determine the danger zones, and we have a national landslide authority, NVE, with the authority to make sure that the rules and regulations are complied with. Therefore, it is not likely that we will see a large avalanche that destroys a major building here in Norway", says Kjetil Brattlien, avalanche expert at NGI.

A tourist area protected with avalanche embankment protection

NGI has developed methods to secure objects against landslides and avalanches, and has also designed and specified Construction of such safeguards in many places in the country. This has done on assignments from NVE, municipalities or private companies that own objects or buildings in avalanche prone terrain.

At Loen in Stryn, in inner Nordfjord, Sogn og Fjordane county, NGI designed and followed up during construction of a protective measure to Ensure that the popular Hotel Aleksandra is able to satisfy the very stringent requirements related to avalanches in the PBL regulations. A landslide and avalanche risk assessment of the area revealed that the hotel was located within the area where the probability for an avalanche was higher than 1:5000.

NGI

The embankment wall directs and forces the snow masses from Gjølmunna away from the hotel and dwellings.

"We were asked to propose and design qualified protective measures and solutions, so that the hotel would satisfy the very stringent safety requirements. The solution was a large embankment wall in the slope fan above the hotel. The embankment wall is designed to withstand forces from landslides and avalanches, and will lead both snow and soil and debris material from Gjølmunna away from the hotel, houses and other exposed objects, "says Krister Kristensen, senior engineer and avalanche expert at NGI.

Already in January 2016, only 6 months after completion, the embankment wall proved its success to work as intended, when an avalanche occurred in Gjølmunna. The snow masses followed the embankment wall as planned and was led away from the hotel and other fragile infrastructure.

 

FACTS:

  • The construction of the embankment wall above the hotel in Loen was completed in 2015 and had a cost of about 20 million NOK. The facility is 520-metres long in total, the wall itself is 360 metres long and 22 metres at the highest.
  • NGI has been avalanche technical consultant and advisor and NVE has been the responsible client. NVE has contributed with 80 percent of the cost. The remaining amount was split between Hotel Alexandra and the commune/municipality of Loen.
  • Together with hospitals, kindergartens etc., hotels are subjected to the most stringent safety requirements for avalanches/landslide protection. According to the Norwegian planning and building law, PBL, hotels fall in security class S3, which states that the probability to be hit by an avalanche should be less than 1:5000.
  • The avalanche/landslide danger zone maps, which NGI prepares on assignment from the Norwegian authorities, are compiles in accordance with the safety zones set by the PBL. The security requirement of the class S2, for new residential buildings, requires that the probability of an avalanche to Reach the house should be less than 1:1000.
  • For objects (buildings and other vulnerable infrastructure) that do not satisfy the safety requirements of the PBL, measures must be implemented to reduce the risk of landslides and avalanches. Protective structures are the most common measure in such cases. Embankment walls that can lead any slide mass material (snow, soil, rock, and flow debris etc.) away from exposed objects, or retaining walls which stops the avalanche or landslide and thereby protect exposed objects are examples of such safeguards.