Effect of Soluble Salt Loss via Spring Water on Irrigation-Induced Landslide Deformation

Landslide exposes the previously blocked groundwater discharge. High concentrations of soluble salt form salt sinters that can be observed near discharge passages. Based on existing laboratory investigation results of soil leaching and shearing reported in the literature, the effect of the soluble salt loss via spring water on irrigation-induced landslide deformation was studied under large-scale conditions. During our field investigation of landslides in the Heitai terrace of the Yellow River’s upper reaches in Gansu Province, China, 35 spring outlets were found, and the Heitai terrace was divided into five subareas, based on the difference in spring flow. Deformation data for the terrace were obtained by small baseline subset technology (SBAS-InSAR). These data were analyzed in combination with the amount of soluble salt loss, to explore the correlation between the deformation of the landslide and the soluble salt loss in the loess irrigation area. The results showed that the cumulative deformation and the loss of soluble salt were increasing continuously in the terrace. Although the increasing intensity of each subarea was different, the changing intensity of the two during the corresponding monitoring period was highly consistent. The statistical analysis revealed a strong positive correlation between the accumulated loss of soluble salt via spring water and the accumulated displacement of the terrace edge (p < 0.01). After the slope k between the two was tested by the Grubbs test and t-test, the k was no abnormality (α = 0.05) and difference (Sig > 0.05), further providing the basis for confirming the existence of this positive correlation. When the loss of soluble salt in rock and soil increased gradually, the accumulated deformation of the terrace edge also increased continuously. The findings of this study are of great significance for understanding the formation mechanism of landslides and the identifying landslide revival in irrigation areas of the Loess Plateau

Evaluation of the Effects of Forest on Slope Stability and Its Implications for Forest Management: A Case Study of Bailong River Basin, China

Previous studies have shown that the mechanical effects of vegetation roots on slope stability can be classified as additional cohesion effects and anchorage effects. The present study investigated the combined mechanical effects (additional cohesion effects and anchorage effects) of vegetation on a slope with coarse-grained soil in the mountainous region (significantly prone to slope failure) of Gansu Province, China. A detailed survey of tree density, root system morphology and slope profiles was conducted, and we also assessed the soil cohesion provided by the root systems of monospecific stands of Robinia pseudoacacia growing in different locations on the slope. The measured data were incorporated into a numerical slope model to calculate the stability of the slope under the influence of trees. The results indicated that it was necessary to consider the anchoring effect of coarse roots when estimating the mechanical effects of trees on slope stability. In particular, the FoS (factor of safety) of the slope was increased by the presence of trees. The results also demonstrated that vegetation increased slope stability. The reinforcing effects were most significant when the trees were planted along the entire slope. Although the reinforcing effects contributed by trees were limited (only 4–11%), they were essential for making optimal use of vegetation for enhancing slope stability. Overall, vegetation development can make a major contribution to ecosystem restoration in the study region

Impact of Water Level Fluctuations on Landslide Deformation at Longyangxia Reservoir, Qinghai Province, China

The construction of Longyangxia Reservoir has altered the hydrogeological conditions of its banks. Infiltration and erosion caused by the periodic rise and fall of the water level leads to collapse of the reservoir banks and local deformation of the landslide. Due to heterogeneous topographic characteristics across the region, water level also varies between different location. Previous research on the influence of fluctuations in reservoir water level on landslide deformation has focused on single-point monitoring of specific slopes, and single-point water level monitoring data have often been used instead of water level data for the entire reservoir region. In addition, integrated remote sensing methods have seldom been used for regional analysis. In this study, the freely-available Landsat8 OLI and Sentinel-2 data were used to extract the water level of Longyangxia Reservoir using the NDWI method, and Sentinel-1A data were used to obtain landslide deformation time series using SBAS-InSAR technology. Taking the Chana, Chaxi, and Mangla River Estuary landslides (each having different reservoir water level depths) as typical examples, the influence of changes in reservoir water level on the deformation of three wading landslides was analyzed. Our main conclusions are as follows: First, the change in water level is the primary external factor controlling the deformation velocity and trend of landslides in the Longyangxia Reservoir, with falling water levels having the greatest influence. Second, the displacement of the Longyangxia Reservoir landslides lags water level changes by 0 to 62 days. Finally, this study provides a new method applicable other areas without water level monitoring data

Distribution and characteristics of large landslides in a fault zone: A case study of the NE Qinghai-Tibet Plateau

© 2021 Elsevier B.V. The NW-SE-striking fault zone in the Bailong River Basin in the northeastern margin of the Qinghai-Tibet Plateau have the most densely distributed, large complex landslides in China. However, the failure of large complex landslides along the fault zone and the causes of their complex geomorphic characteristics are unclear. The purpose of this study was to explore the relationship between the fault zone and the spatial distribution, direction of movement, and geomorphic characteristics of large landslides. We inventoried 29 large landslides in the middle reaches of the Bailong River and described their characteristics. Statistical analysis revealed differences in the spatial relationship between the faults and landslides of different scales. Almost all of the landslide bodies with an area > 1 km2 are distributed on the faults; in addition, the strike of the faults was found to constrain the direction of movement of the landslides to the WNW-ESE direction. Statistical results show that the cross sections of landslides in the study area are asymmetric arc, corresponding to which there are significant differences in the geomorphological characteristics of the north and south sides of landslides. The geometric characteristics, physical properties (i.e., material weakness) of the fault zone and rapid uplift of the hanging wall were responsible for the asymmetric shape of landslide cross sections and the geomorphic difference. We present a conceptual model based on the relationship between the fault zone and landslides, which facilitates an improved understanding of the relationship between the fault zone and landslide evolution