Presentation a Risk Model of Avalanche Points in Mountainous Roads (Case Study: Chalous- Karaj Road)

Falling avalanche is one of incidents that may happen during cold months of winter in Iran. This event may lead to closure of some main roads of the country. Road closure is a challenging issue، particularly on roads connecting Tehran capital to the northern cities. Detecting avalanche prone locations on roads is usually conducted by data gathering، surveying and investigating aerial photos. Field investigation usually requires collecting regional data including slope stability، geology and number and repetition of road traffic. In this study importance of each parameter was determined By an AHP method. After interviewing experts، importance of each parameter was determined pair wise. Final weights for each parameter were also determined using Expert Choice software. Searching for important contributing parameters and methods for measuring risk of avalanche in mountainous roads in the literature، main parameters of falling avalanche were selected and used in this study. It is obvious that many of recognized parameters should be considered in every effort of measuring danger. That is why such parameters are similarly used in most methods. The most important reference for categorizing the methods of risk measuring was guidelines on preventing falling stones and avalanche published by US National Institute of Highways and the Main Office of Highways. In these guidelines، traffic repetition is taken as an important factor increasing the risk after a falling event happens. This study framed the experts’ opinions and optimized risk analysis with regards to local geotechnical and geologic conditions in Iran. Experts selected the snow depth، hillside slope، vegetation condition on hillside and number and repetition of the road traffic. Importance of parameters were calculated as 44. 1% for traffic number and repetition، 19. 1% for the hillside slope، 17. 2% for vegetation، 15. 6% for snow depth and 4% for traffic rate. These parameters were selected as the factors contributing in avalanche. In continue each parameter was rated in a four level category (very high، high، medium and low). Model of avalanche danger calculates the avalanche risk in every point in a road network and all roads can be evaluated in terms of the danger of potential avalanche. For example the model was applied on Karaj-Chalus highway connecting Alborz to Mazandaran provinces. This highway is an important arterial between the capital and the northern cities. Using the method، 15 dangerous avalanche prone locations were determined and prioritized. They are located at 65، 73 and 60 km from Karaj. Preventive efforts should be taken for maintaining these locations and keeping them safe against potential avalanches