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CONCEPT OF AVALANCHE HAZARD AND RISK
An avalanche is a mass of snow that falls by effect of the force of gravity after being set in motion, instantly, as a result of disruptions due to natural or accidental causes of the conditions of equilibrium of the snow cover on slopes with a sufficient incline. Nearly all alpine and high altitude valleys are likely to be affected by falling avalanches.
The warning of "avalanche hazard" is understood as the possibility of the occurrence of a hazardous event, perhaps in a remote and uninhabited high altitude area devoid of buildings or constructions: there is a hazard but there is no risk of damage.
The concept of "avalanche risk" implies on one hand the existence of a real hazard, and on the other hand the presence of persons and/or things potentially in harm's way.
The use of numerical indices or adjectives for the definition of the avalanche hazard in the snow bulletins is now a consolidated practice in every country. The standardized scale includes 5 degrees of hazards with an adjective that summarizes all the peculiarities of the hazard (low, moderate, marked, strong, very strong).
The violence of snow masses rushing downhill can cause considerable harm to buildings and or infrastructures at lower elevations, and is a serious menace to the life of the mountain communities.
POSSIBLE PREVENTIVE MEASURES
To effectively counter the avalanche hazard, efficient protective systems of "active defence", consisting of particular infrastructures perfectly suitable for the solution of the problem, have been studied and used for decades.
These protective systems belong mainly to two types:
- Snow fences of wire-rope nets;
- Steel or wood snow barriers.
The snow fences of wire-rope nets built by Artigiana Costruzioni respect the parameters set down by the Davos Institute for the Study of Snow and Avalanches.
The fences are installed in rugged and scarcely visible areas without plant cover, and, being unobtrusive, they have a minimal impact on the environment. They also have the function of boulder fences during the summer season, thanks to their elastic structure.
The principle of operation is very simple: the panels of triangular net joined in a modular arrangement form a homogeneous surface of variable length, usually not greater that 50-60 m, also to allow the passage of persons and animals. This creates a kind of dam effect that allows the snow to accumulate while it prevents the snow mass from sliding downhill.
The forces generated by the weight of the snow are elastically absorbed by the net and transmitted to the anchoring means by the supports and the guy ropes.
Therefore the anchoring means, made with a double spiroid rope, are the elements that demand a particular care and attention during the drilling and injection phase.
The structure is made up of tubular galvanized steel element provided with a series of fairleads in the head that make it possible to adjust the ropes based on the angle of the slope. The tubular support is itself supported on a plate through a ball joint, and the plate is in turn fixed to the ground by means of micropiles and log bolts anchored to a concrete plinth.
All the materials used are new, certified and protected by zinc plating against corrosion.
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