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The triggering mechanism and movement evolution of loess-red clay landslides, which occurred frequently along the contact between the loess and red clay on the Loess Plateau, are closely related to the mechanical properties of the contact surface. This work presents an experimental investigation on loess, clay and loess-red clay interlaminar (LRCI) samples obtained from a typical loess-red clay landslide in northern part of Shaanxi province of China, using a series of ring shear tests, microscopic observation and scanning electron microscopy tests, in an attempt to explore the mechanical behavior of loess, clay and LRCI samples with variation in moisture content, normal stress and shear rate. The results revealed that for all specimens, both the peak shear strength τ p and the residual shear strength τ r decreased with increasing moisture content, among which, moisture content has the greatest influence on the τ p and τ r of red clay, followed by the LRCI specimen, and the loess specimen is least affected by moisture content. Meanwhile, exponential functions describing the correlations between shear strength and moisture content of LRCI, red clay and loess specimens were proposed. Furthermore, the macroscopic morphological characteristics and the microstructure of shear surface obtained from the LRCI specimens showed that a localized water accumulation was built up within the shear surface as the water content increases to some extent, and a high degree of liquefaction developed within shear surface when the moisture content reached to the saturate degree. The microstructural observation on LRCI specimen suggested that the shear surface became smoother and the larger percentage of small-sized pores was observed with moisture content. Accordingly, the built-up excess pore water pressure during shearing is difficult to be dissipated due to a close structure of small-sized pores. Due to the low permeability, high pore-water pressure built up within the shear zone and the increase in the fine particle content, the LRCI soils with a high saturation degree shows the potential for the localized liquefaction within shear zone, which further provides a scientific explanation for the triggering mechanism of loess-red clay landslides with high-speed and long- run out. [ABSTRACT FROM AUTHOR]

Under the heavy rainfall risk due to global warming, a new trend has emerged in geological disasters of loess, which have often evolved into a chain form of disaster chain of loess (DCL) in recent years. The DCL is characterized by multiple, hidden, catastrophic, and complex characteristics that seriously affect the construction and operation of large-scale infrastructure on the Loess Plateau. To understand the formation mechanism of a disaster chain of loess, we took the Shiyangpo DCL, a typical disaster chain occurring recently on the Loess Plateau, as an example to investigate the geomorphic features and deformation characteristics of DCL using new technologies and methods such as Unmanned Aerial Vehicle (UAV) mapping and Geographic Information Systems (GIS) spatial analysis technology. A series of special laboratory tests considering the vibration of the loess subgrade was conducted to explore the changes in physical and mechanical properties of loess samples in the study area under natural, saturated, and vibration conditions. Additionally, the trigger factors and evolution process of this DCL were analyzed, and the formation mechanism of recently emerging typical DCL was revealed as well. The triggering factors of the disaster were summarized as follows: loess nature, heavy rainfall, irrigation, irrational excavation, incomplete drainage channels, and long-term vehicle vibration of roadbeds. Furthermore, extreme rainfall was identified as the primary inducing factor of Shiyangpo DCL. Finally, the development and evolution of Shiyangpo DCL were divided into five stages: the formation of the loess sinkhole stage, the occurrence of the loess subsidence stage, the occurrence of the loess collapse stage, the occurrence of the loess landslide stage, and the formation of river-blocking and dammed lake stage. This study reveals the cause and evolution process of the newly emerged DCL in the Loess Plateau, and the new techniques and methods involved can provide references for the theoretical research and prevention of loess geological disasters in other places. • The typical disaster chain of loess (DCL) was investigated using new methods. • The geomorphic features and failure characteristics of typical DCL were analyzed. • The triggering factors of typical DCL were explored. • The evolution process and formation mechanism of typical DCL were revealed. [ABSTRACT FROM AUTHOR]

The present study aims to investigate the distribution and size of landslides in relation to relative relief. For this, a landslide inventory map of the area was developed from the interpretation of satellite images and detailed field survey. From this we could map 331 landslides in Ningqing County (Shaanxi Province). By using GIS and statistical approaches, we studied the coupling between landslide size distribution and relative relief. From this the control of relative relief on the rollover effect of the size distribution of landslides is obtained. The result shows that the landslide frequency-relative relief distribution is unimodal, with majority of landslides occurring in areas with relative reliefs in between 300 and 400. The relative number density of landslides decreased with the increase in the relative relief; on the contrary, the average area, average length and average width of landslide increased with the increase in relative relief. The percentage of large-scale landslide increased with the increase of relative relief or vice versa. In addition, the cumulative frequency-area distributions of these landslides empirically agree well with a power-law relation with an exponent of 1.776 above a certain size threshold. Below this value, it exhibited an obvious rollover effect. Further analysis has shown that landslide cumulative frequency-area curve is strongly influenced by relative relief. The rollover effect is more obvious with the increase of relative relief. The exponent of power law correlation gradually increased from 0.993 to 1.872 with increasing relative relief. [ABSTRACT FROM AUTHOR]

• Landslide path dependence has been proved in loess environment. • The influence of landslide clusters on the dynamic evolution of South Jingyang Tableland is revealed. • The hydrogeological structure of the study area is investigated. • Multi-disciplinary methods are applied to loess landslide investigation. Recently, the concept of landslide path dependence has been proposed and well confirmed in landslide studies in central Italy and the Nepal Himalaya, providing a novel perspective for understanding landslide activity patterns and assessing susceptibility. Previous studies have shown that landslides in some loess tableland regions of China have obvious clustering effect, but whether landslides in these regions also have path dependence have not been well discussed. From the perspective of landslide path dependence, multidisciplinary survey methods (including remote sensing, satellite interpreting and monitoring, geographic information system mapping, terrestrial laser scanner survey, electrical resistivity tomography survey, remote online monitoring, physical experiments, numerical simulations, mathematical statistical analysis, and geomorphic change detection, etc.) were jointly applied in the study of landslide clusters in the South Jingyang Tableland, Shaanxi Province, China. We reveal the temporal-spatial distribution and deformation law of landslide clusters in the study area, analyze the effect of consecutive landsliding on the geomorphic evolution of the loess tableland and its triggering mechanism, and find the evidence of the existence of landslide path dependence in loess environment. The results show that the rise of groundwater level caused by human activities is the main culprit for the landslide clusters formation in the study area. Different path dependent models (reactivation or continuation landsliding, local activation landsliding, and remote activation landsliding) repeatedly acted alone or interacted with each other, leading to the formation of large-scale landslide clusters, and continuously remodeled the landscape of the loess tableland, thus accelerating the evolution process of the loess tableland. This study provides a scientific basis for further understanding the distribution law, sliding mode, clustering effect and formation mechanism of landslide clusters in loess tableland. [ABSTRACT FROM AUTHOR]