The Assessment of Natural Hazards of Khorramabad-Pol-e-Zal Freeway with the Passive Defense Approach

Document Type : مقاله پژوهشی


Lorestan University


1. Introduction
Transport network, as a basic infrastructure, is of economic, social, and political importance to any country. Among the various ways of transport (that is, road, rail, air, and sea), road transport, due to its unique features, basically is known to be the most commonly used one. Nowadays, one of the important ways to bring down an under-attack country is to seriously damage its vital arteries (i.e. roads and transportation ways). Therefore, in order to defend a country against such attacks, it is imperative to know how to deal with them. Passive defense, as one of the influential factors in many projects, is one of the most effective and sustainable ways to defend against such threats. It refers to a number of strategies, utilization of which in the design and construction of facilities and biological buildings, automatically increases the defense power of the construction without pressuring the human resources, and, as a result, decreases the possibility of crisis.
One of the factors contributing to passive defense is paying attention to geological features when locating and routing facilities and constructions. Slope instabilities are among such phenomena that are related to geological features; in addition to road blockage, these instabilities cause the parts on which facilities and structures are built to move and be displaced. Based on the aforementioned argument, it is imperative to consider the geological features while building infrastructures such as roads; it is also crucial to evaluate active geological forms and phenomena, having passive defense in mind, when locating and routing such infrastructures in order to minimize the risk of damage made by geological movements to them. In this regard, Khorram abad-Pole Zal Freeway as the main south-north road artery of the country that has a diverse range of natural hazards due to its geological characteristics is studied using the passive defense approach.
Khorrram abad-Pole Zal Freeway, the area of study, as part of Tehran-Bandar Imam Khomeini’s route, has a length of about 104 km. The freeway extends from some parts of Lorestan Province (that is, Dore-Chegeni and Poldokhtar) to Andimeshk in Khuzestan Province. The path starts from the latitude of 33˚ 25′ and the longitude of 48˚ 12′ east and ends at the latitude of 33˚ 48′ North and the longitude of 48˚ 03′ east.
2. Material and Methods
The present study has used an applied research type; moreover, for the research method of the study, the analytical field studies method was employed. Data were gathered using data from both library and field studies methods. Library resources were tapped on in order to make theoretical assessments and to develop a theoretical framework of the research literature. In the field studies that form the fundamentals of the present research, the freeway was firstly studied to identify the natural hazards that endanger the path. Afterwards, using GPS, hazardous places along with places were landslides had occurred were identified. The rest of the qualitative and quantitative data from hazardous points were collected in field studies. In the present study, physical tools such as geological maps of 1: 100000, topographic maps of 1: 25000, digital elevation model with a resolution of 30 meters, satellite images (Landsat-Sensor TM and ETM), images of Google Earth, conceptual tools such as software Arc GIS, ENVI, Google Earth, and other similar software were used to create a database; satellite imagery, spatial analysis and map drawing have also been employed in the study.
After providing the basic information, the hazardous places along with the identified hazardous points, according to the data gathered from the field studies, were prioritized using Delphi method and the opinion of experts in Geological Sciences. Finally, the hazards were analyzed after dividing them into different sections according to their risk level.
3. Results and Discussion
The survey of Khorram abad-Pole Zal Freeway and its surrounding areas indicated that mass movements, landslides, and collapses occur frequently in the given areas. Based on the field studies, 21 active landslide zones threaten the road. Most landslides occurred in the north side of the freeway in poor resistant limestone formations; the geological formation, trenching, and tilt have been the most important factors in these occurrences. The study of the position of active landslides on the route showed that the most dangerous parts of the freeway in terms of landslide risk are from km 1.5 to km 36 and from km 56 to km 62. Landslides either have not occurred in other parts of the roads or have only had non-threatening volumes. Prioritizing the risks of 21 active landslides, based on the considered factors, indicated that 11 landslides have the highest amount of risk, 3 are highly risky, and 7 are of a moderate risk. These landslides are mainly observed in two sectors of the route – the first part is from km 16 to km 36 and the second is from km 57 to km 60. According to the risk of landslides, the 104 km freeway is divided into 5 sections. The first section has a length of 1.5 km and is located in the area that has no risk. The second section has a length of 36 km and is in a dangerous area. The third section has a length of 19 km and is in an area that, in terms of being risky, ranges from slight to moderate. The forth section has a length of 6.5 km and is in a dangerous area. The fifth, and the last section has a length of 41 km and is located in an area of no risk. Thus, in terms of landslide risk, 42.5 km of the freeway is located in dangerous areas and 42.5 km of it is situated in areas that have no risk of landslide.
The risk of rockfall in the freeway was also studied as another natural hazard to the road. Based on the field studies, 30 areas of active rockfalls were identified. Most of the active rockfalls have occurred in the north slopes with weathered, and mixed soil, bedrock and mainly in limestone formations combined with other stones. The identified rockfall areas are of high frequency of occurrence in two parts of the freeway. The first section is located in the distance between km 13 to km 20 of the freeway and includes 12 points of rockfall. In this section, rockfalls mainly consist of big rocks. The second part is located in the distance between km 23 to km 39 of the freeway and includes 12 points of rockfall. Rockfalls occur sporadically in other parts of the freeway. The prioritized areas of active rockfall, based on the hazard level, indicated that 6 points are of great danger, 18 points involve a high risk of rockfall, and 6 points are of medium risk level. Out of the 6 highly dangerous areas, 4 are located in the first part of the route (i.e. from km 30 to km 36), and the other two points are located in the second part of the freeway (i.e. from km 63 to km 93). The area of high risk of rockfall is located in the first part of the freeway (i.e. from km 13 to km 19.5) and in the second part of it (i.e. from km 25 to km 39). The areas with medium risk of rockfall are located in different parts of the road, especially at the beginning of the freeway.
4. Conclusion
Based on the passive defense approach, the survey of Khorram abad-Pole Zal Freeway indicated that natural hazards such as landslides and rockfalls have a high frequency of occurrence in the area and that these phenomena are serious threats to the 104 km freeway as well as to structures such as tunnels, electric towers, etc. The study and mapping of landslides along the freeway indicated that the landslides are of more abundance and density in two specific sections of the route. The length of the route, considering active and dangerous landslides, is 42.5 km which includes 21 active landslide zones.
Active areas of rockfall are also of serious threat to the freeway. The classification of the route into 7 different sections, based on the risk of rockfalls, showed that 3 sections involve no risk, 2 are of medium risk, and 2 are dangerous and highly risky. Accordingly, 17.2 km of the freeway is located in the risk-free zone, 63.1 km in the zone with moderate risk, and 27.3 km in the danger zone. Moreover, out of the 30 active areas of rockfall along the freeway, 6 points are highly dangerous, 18 have a high risk level, and 6 are of medium risk. Hence there are 24 active areas of rockfall that are of actual risk to the road.
The results of the study showed that Khorram abad-Pole Zal Freeway is not in an acceptable condition from a passive defense point of view. The main reason for this is that the geological feature of the area have not been taken into account when designing the freeway. Natural hazards such as landslides and active rockfalls, due to overlooking the geological features of the area, have blocked, and destroyed, parts of the freeway and structures alongside it.


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