عنوان مقاله [English]
Worldwide cause landslides are considered as natural disasters, which to many dead and intense damage. So, it is important to examine the impressive factors for urgent planning and presence management solutions for sensitive regions. A landslide based on geological and geomorphological factors, hydrological, and biological and human; but only the trigger or external factor is a key factor to start a landslide. Intense storm, fast snow shrinking, sudden changes in groundwater level, earthquake, and fast erosion are regarded as the most important trigger factors for landslides (Sidle & Ochiai 2006(. Rainfall is considered as the most common trigger factor in the occurrence of landslides (Crozier1999; Jacob 2003). The event of a landslide relies on various factors, for example, geological, geomorphological, hydrological, biological, and human. However, the basis in making a landslide is mainly a trigger factor where precipitation is recognized as the most common one. Therefore, recognition of natural factors and human activities, causes and intensifiers of landslides, on the other hand slope stability analysis largely experts will help determine the most appropriate way to integrate slopes slippery. Whether old or new in this region, the slopes of folded Zagros in the range of studying area are sensitive to slippery movements, proved by numerous landslides. Massive movement of materials, like a landslide, is one of the problematic slope processes in Javanrood located in the northwest of folded Zagros, for this phenomenon leads to demolition of forest lands, farms, and pastures of the region. In addition, it is considered a threat to road traffic. Current study to the threshold of critical rainfalls in the occurrence of landslides in the Javanrood basin using a physically based model set. Physical models need accurate and comprehensive information on soil characteristics and hydrology slope. Operations such as the pattern of rainfall and groundwater level changes modeled mathematically in physical models of landslides
Application of materials in this research was Javanrood s 1. 50000 topographic maps, 1; 100000 geological maps, 1; 55000 spatial images, Google earth satellite images, GPS, 20m altitude numerical models, Arcgis and Matlab softwares and laboratory parameters, including dry soil specific weight(γd), wet soil specific weight (γt), hydraulic conductivity, soil internal friction angle (φ), soil cohesion, and the porosity of the soil.
This research was completed through the fields, and empirical methods. Search steps are summarized as following: In the present study, 12 slopes of Javanrood, including 7 unstable slopes, and 5 Stable slopes, were chosen as the samples. All the alternatives of slope stability analyses were found using field studies, experimental studies, and topographic analysis of the landslides. The model utilized as a part of this research was the model of Talebi (2008) which was indeed, an amplified model of a physically-based model, being a blend of geometry model, hydrology model (perpetual condition), and unending slope stability theory. This model is used to study shallow landslides in slopes with different topography in regards to arrange shape (concave, convex, parallel), and profile curvature (concave, convex and direct). It considers the impacts of slope morphology on saturation storage of plan shape and length profile. At the end, with a reverse method of the safety coefficient decreased on the stability of the 1 and the critical rainfall was determined for each slope
3. Results and Discusion
The results showed that this model efficiently determine enough to critical precipitation. It was found that vulnerable slope slip less critically needed precipitation as the stable. According to the calculations, the amount of critical rainfalls for unstable landslides is less than 50 mm per day, although it is more than 100 mm / day for the stable. In addition, a safety factor in various periods return indicates that as the return period increases decreases the amount of stability slop. On the other hand, the return period increases for some instable slopes, will reduce their instability.
The objective of this study was to determine the critical rainfall in the occurrence of shallow landslides by the famous process-based model (Talebi 2008) in Javanrood. The results of factor values stability and critical rainfall of slopes study demonstrates that the model efficiency enough to identify critical rainfall. In accordance with the precise information about the soil and the hydrology of slope, can mathematically model the process as rainfall and water level changes on the land, and merge with penetration models and analysis of stability of slope. So, are able to assess the necessary rainfall for show landslide. According to the findings of significant rainfall in the region, it can be said that critical rainfall for the slopes of the region depend on the amount of the stability of the slope. Stability of slope is under the influence of morphological and hydrological factors and soil of them mechanical. So, the slopes with low safety factor needs less critical rainfall to define these landslides than stable ones.