Effects of Road and Traffic Parameters on the Evaluation of Rockfall Accidents in Mountainous Areas

Rock falls cause extensive damage in mountainous areas. Many factors are responsible for this natural phenomenon amongst which earthquakes, active faults, atmospheric and climatic conditions, weathering etc…are the most important ones. From the falling potential point of view, all mountainous areas are not the same and there are differences in risk factors. These factors are evaluated using various parameters that are divided into three main categories; geological and rock mechanics, climatological, and traffic parameters. There are various methods for risk analysis of roads. Applying these methods may prevent or reduce the effects of natural disasters. Due to the fact that Iran is located on a risk prone zone from natural disasters point of view, also because of its population density and natural disasters high risk, prevention and mitigation of risk is of great importance. Knowing the types and potential of the rockfall at slopes is the main step for preventing hazards. The risk evaluation methods are divided into optical risk evaluation, risk evaluation by GIS data, tree risk analysis and RHRS method. Having studied all the methods and their comparisons, the RHRS is considered as the most comprehensive and accurate method for mountainous roads in Iran and used in this case study (Karaj – Chalous Route). In this method initially the various regional, geological and traffic data were gathered and then those parameters required for rating of risk evaluation of rockfall incidents were calculated and rated. Finally the total parameters were considered as the total rating of the terminals where the higher the rate, the higher is the risk of slopes rockfall. Results obtained from the rating of rockfall risk within the 20 Km danger zone of the mentioned route were as follows: Traffic parameters must certainly be considered in risk analysis and evaluation of rockfall accidents in mountainous areas. Aspects such as sight destination, speed of the vehicle, traffic volume and the road width have great influences on determination of rockfall risks.Usually by increasing the traffic parameters, the rokfall risk is also increased in various terminals. As long as the rockfall risk is the result of combination of many parameters, therefore, the increasing of traffic parameters adds to the total rating of rockfall risk at different terminals. By studying and comparing the total rating of various terminals, also considering the total traffic rating, it became clear for the researchers that half of the ratings related to rockfall risk in mountainous roads were due to traffic parameters, and the remaining half was related to geological and climatological parameters which shows the significance of these parameters in risk analysis of rockfall accidents in mountainous roads. Due to the low width of the road and the limited spacing between mountains that the road passes through, installation and construction of guardrail ditches was not possible in most locations of the road, therefore the rating of this parameter was considered as the worst (100) among others. In rating of rockfall risk, some other aspects like the existence of substitute roads, routes to the relief centers, weathering etc… were considered so that a more accurate investigation could be carried out for the area and the selected terminals.