# Factors Affecting the Stability of Loess Landslides: A Review
## 2 Relevant Measured Parameters
### The Effect of Water  
Researchers have also studied the effects of water on landslides in loesses, including changes in water content that affect factors such as water table and liquefaction, as well as changes in water content due to rainfall and spatial and temporal variations of water. Researchers generally agree that irrigation has a significant impact on landslides. Erosion of the sliding surfaces and layers, water table fluctuations, cracks formation, liquefaction under static conditions, effects on the shear strength, and changes in the morphology of landslides have been the main focus of research into the damage caused by irrigation-induced loess landslides. These effects are all interrelated, and variations in different parameters have a direct or indirect effect on the stability of loess slopes. Improper irrigation and drainage practices can exacerbate the damage to loess slopes and become important factors in triggering loess landslides [4; 22]. Irrigation can cause static liquefaction, leading to the formation of localized slip surfaces which then lead to landslide movement [68; 69]. The resistivity of the soil body shows a slow decreasing trend with increasing water content when the water content of the soil body is greater than its optimum water content [59]. Compared to rainfall, diffuse irrigation has a greater effect on loess water content and, consequently, groundwater [70]. As soil moisture increases and diffuse irrigation raises the water table, the shear strength of the loess decreases. In addition, concave slopes are more susceptible to irrigation-induced soil moisture. Landslides are more likely to occur in gullies or on the backs of landslides [71]. Finally, the detrimental effects of irrigation-induced high-speed landslides in remote areas of loesses are also worth mentioning [72]. Rainfall has been extensively studied as an important factor in triggering loess landslides. Previous studies have demonstrated the significant influence of rainfall on landslides by extensively investigating the effects of natural rainfall and the use of artificial rainfall for controlled purposes. [PERSON] et al. [73] concluded that the strength of loesses is more sensitive to variations in water content than other soil types, based on artificial rainfall experiments conducted on natural loess landslides. An increase in water content results in a significant reduction in the strength of the loess, which in turn triggers landslides in loesses [37]. Furthermore, the time taken for water migration in the sample to reach an essentially steady state under rainfall conditions gradually increases as the compaction of the loess sample increases [66]. Hydraulic equilibrium disturbance of a loess landslide was modelled by [PERSON] et al. [74]. As shown in Figure 4, the model indirectly changes irrigation location by the changing of landslide geometry. Rainfall intensity has a relatively small effect on the collapse mode, although it influences slope deformation and landslide development in the long term [30]. Consequently, sustained rainfall is the main trigger for landslide formation [20]. ERT is mainly used to study the spatial and temporal dynamics of water. The spatial and temporal distribution of water movement within loess slopes can be visualized using this technique. ERT is an invaluable tool for assessing landslide stability as there is currently no alternative method that provides the same insights into the temporal distribution of subsurface moisture. In areas of unsaturated loesses, shallow infiltration depths can cause soil liquefaction. As water content increases, drainage at the base of a slope can be impeded, leading to landslides [75]. The maximum value of the slope in the apparent resistivity curve, together with the portion of the ERT curve, provides an accurate estimate of the maximum variation in water content within the loess layer, particularly near the water table boundary [76].