Landslides are considered as natural disasters that lead to many deaths and severe property damages worldwide. Therefore, it is necessary to investigate the effective factors in order to make urgent planning and to present management solutions for the sensitive regions. Massive movement of materials, such as a landslide, is one of the problematic hillslope 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. Moreover, it is considered as a threat for road traffic. The present study aims slope stability analyses and landslide hazard zonation applying the process-based model (Sinmap).

This research was done by both field and experimental methods. Research steps are summarized as following.

Geomorphologic, hydrologic and soil mechanic characteristics of slopes in the considered zone were the required information in this study. To obtain this information, at first, it was necessary to recognize sample slopes to measure the above- mentioned variables. Therefore, first of all, landslides distribution map was prepared in the considered area then, on this basin, sample slopes were selected to measure essential variables. Sample hillslopes were recognized as 12 hillslopes, 5 stable (lack of land sliding) and 7 unstable hillslopes (having land sliding mass). They were 1- 12 numbers. 1-5 hillslopes are stable and 6-12 unstable. After selecting sample hillslopes, necessary parameters were assessed as following:

Mechanical features of soil: soil sampling from each hillslope was done the mechanical features of soil, so 50 kg soil was removed from each slope, from 75 cm to 1cm depth. In order to sampling soft and coarse soils, a core cuter devise and shovel were used, respectively. Sampled soils were transferred to Kermanshah soil mechanic laboratory, Kermanshah provincial transport office and necessary parameters, including dry soil specific weight(γ d), wet soil specific weight (γt), hydraulic conductivity , soil internal friction angle(φ) ,soil cohesion , and soil porosity were determined by using direct shear test.

Determining the geometric parameters of slopes: except for using topography map, altitude numerical model (Dem) with a pixel size of 20 by 20 m and satellite images were used to determine morphology parameters and to identify various hillslope types. Applying GIS software, manual and laser tape measure, clinometer, slope geometry characteristics such as mean slope (beta), slope width (W), slope length (L) area, were extracted.

Model implementation

The model used in this study was Talebi (2008) model which was, in fact, an extended model of process-oriented (physically based) model, being a combination of geometry model, hydrology model (permanent condition) and infinite slope stability theory. After obtaining necessary parameters to get slope factor of security (F S) including laboratory, topography and hydrology parameters, Fs values for each slope were measured by Matlab software

Unstable slopes of the region mainly have the stability coefficient less than 1 which is classified as very high vulnerable class. They have low inner friction angle, less than 29 degrees, based on geo-mechanic properties of soil. Moreover, their gradient angle is more than 35 percent. In term of shape, most of them have concave profile curvature and convergent plan which lead to slower drainage, the increase of relative saturation saving of the soil, and the decrease of stability. The results of the landslide hazard zonation mapping indicate that the majority of the study area located in protection class includes 26 percent of the study area. The lowest percentage of study area belonging to middle stability and quasi-stable classes which constitute 9.2 and 6.2 precent of the study area respectively.

According to landslide hazard zonation applying the process-based model (Sinmap), it can be included that percentage of stability is less than percentage of instability in Javarood region. So that the highest percentage of area is located in the protective class (26 %) and high threshold of instability (15.9 %) and a lower percentage of the region is located as stable and quasi-stable (20 %).This results indicates that the susceptibility of the scope of the study area in terms of inherent instability. So that natural factors (concave longitudinal profile and low friction, high angle of slope and high saturation coefficient) in these areas will certainly cause the landslide phenomenon. Therefore, this hillslopes will unstable under the influence of human activities such as leveling hillslope for the construction of residential or their road cutting.