Hazard assessment of loess landslide based on soil moisture content and supported by slope unit in Qingjian City, Shaanxi Province

Landslide hazard assessment is one of the important measures for disaster reduction and prevention. Field investigations show that 138 landslides are developed along the slopes around the city area in Qingjian, which seriously threaten the safety of the city. In order to accurately evaluate the hazard of landslides in Qingjian City, the authors divided the slope zone of Qingjian City and surrounding areas into 925 slope units according to the development of river valleys and the integrity of topography. The slope units were calculated according to different slope gradients, slope heights and slope patterns under different soil moisture values. The calculation results show that, with the gradual increase of the soil moisture content of slope, the area of the stable slope gradually decreases, and the area of the unstable slope gradually increases. According to the monitoring data of soil moisture content of loess slope in northern Shaanxi, the probabilities of occurrence of soil moisture content (w) were analyzed and calculated. The probability of occurrence of w ≤ 0.15 is 0.622 (very high probability), that of 0.15 < w ≤ 0.2 is 0.2963 (high probability), that of 0.2 < w ≤ 0.25 is 0.0816 (medium probability), and that of w>0.25 is 0 (low probability). The hazards of slope units were assessed in combination with the slope stability calculation results and the soil moisture content occurrence probability. The assessment results show that the very high hazard area is 3.27 km², which includes 112 slope units and 92 landslides; the high hazard area is 4.19km², which includes 128 slope units and 36 landslides; the medium hazard area is 8.75 km², which includes 251 slope units and 6 landslides; the low hazard area is 15.20km², which includes 434 slope units and 4 landslides.