## 4 Results and Discussion
### Application of the VR Model
Stronger rocks are more resistant to the driving force of landslides and less prone to damage than weaker rocks [40]. The main lithology units of the study area consisted of Jurassic sandstone and Quaternary loses. Vertical joints, structural joints, collapse joints, and weathering joints of loess are generally developed, which are potential geological factors leading to geological disasters such as loess slides and falls. The deformation and failure caused by loess colmissibility provide a channel for precipitation collection and rapid infiltration, and often lead to geological disasters such as landslides. The vertical joints and weathered joints of sandstone in the slope zone are developed, and the development and expansion of joint cracks form the dangerous rock mass of slope is seen, which often leads to fall disasters [25]. The joints in all the study area are very developed. From the VR values, it is seen that the high landslide volume occurred in the lithological units of sandstone with the VR value of 1.4640, followed by the lithological unit of loess with the VR value of 0.8152. The Jurassic sandstone had a higher value because it is mainly in the valley area; as the drainage area, the hydrological conditions are more complicated. The stability of the soil mass might be harmed by road cutting caused by slope excavations. As a result, one of the influencing elements for landslides is closeness to a road. In the case of distance to roads, distance to roads of 0-50 m had the highest VR values, while the VR value in the distance to roads of 300-500 m had saltation. The result may be that the population density is high in the study area [41], and thus the road net is also density. In the range of 300-500 m, large collapses had occurred. However, the overall trend is that the VR value decreased as the distance increased, indicating that the distance to roads has a high influence on landslide occurrence and scale. Actually, the amount of landslide occurrence within 150 m of the road accounted for more than 78% in the study area. There are reverse correlations between landslide volume and parameters based on the VR value of the distance to river. In the study area, 89% of the landslide occurredwithin 150 m of streams. At the same time, the hydrographic axes of the third and fourth order streams are considered to be the main factor of the occurrence of landslides [28]. This is because the scouring effect of river flow will erode the slope. At the same time, the seepage effect of water flow makes the slope soil saturated. A large amount of free water is accumulated in collapsible loess, and the shear strength of soil is reduced, which has a negative impact on the slope stability. In addition, human activities are mostly distributed in the valley, which reduces the slope stability and is also the cause of frequent disasters and serious landslide erosion on both sides of the river. Profile curvature measures the rate of change of slope, which controls erosion and deposition by affecting the acceleration and deceleration of the flow across the surface. Convex surface is positive and concave surface is negative [42]. For the profile curvature, 44% of the landslide occurred on the concave slopes, while 56% occurred on the convex slopes, and the VR value for convex slope (1.0505) is greater than that of the concave slope (0.9567), indicating that the convex slope has a little more effect on the volume of landslides. The concave slope easily collects rainwater, and rainwater infiltrates along the slope, which reduces the shear strength of soil and causes the instability and deformation of soil. At the same time, the potential energy of convex slope soil is closer to the limit value of mechanical equilibrium, and is also vulnerable to stronger weathering, which may also lead to the occurrence of slope instability. Stochastic statistics of 300 unstable slopes in China have shown that the instability of convex slopes is better than that of concave slopes [43].