To provide engineers with a better tool, we have developed a program for avalanche computation. After a brief description of the mathematical model and the assumptions, we describe influence of physical and numerical parameters, which allows a better understanding of the physical phenomenon which we call an avalanche. The satisfactory agreement between computations and observations allows us to assume that the model is well founded; further experiments will allow us to improve this simulation tool.
Drifting snow creates problems which have practical effects in France in two situations. The first situation is when the result of wind action on snow is to cause accumulation of this snow on mountains, leeward of crests, and consequently to create the potential hazard of avalanche. The second is when the result is to pile up snow in flat regions wherever there are obstacles such as road cuttings and vegetation. This paper focuses on the second type of problem, which affects large areas of central and north-eastern France. We explain how we have chosen our test site, which initial experiments we have conducted in order to assess the general geometrical features which a snow fence must possess in order to function most effectively in collecting snow, and how subsequently we have assessed the properties and costs of different fencing systems.
This paper reports the present stage in our research programme. We have used two very different models : (i) A numerical model treating the avalanche as a Newtonian liquid with a free surface; this model describes qualitatively the velocity fluctuations both of avalanche particles and of the front and gives some quantitative predictions, but much experimentation is needed to determine the large number of parameters involved. (ii) An analogue model in which powder avalanches have been simulated in an underground tunnel, taking account of the densimetric Froude number; this model reproduces the pressure rise which precedes the visible front, and also the pressure wave as the front passes which causes so much damage to engineering works—and human beings. These models have been applied to two cases—a bridge and a snow shed.The interplay between models and experimentation is discussed and the need for improved data on the mass output of an avalanche, of its detailed velocity history, and of the force on large objects is emphasized. Methods being used to try to supply this information are discussed ; gamma-ray measurements for specific mass, high-speed stereophotogrammetry for velocity, and various pressure sensors for the force. The possibility of releasing real powder avalanches to enable such measurements to be made more reliably is being investigated.
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