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Landslides which occur at unexpected locations and times, and which have unrecognizable risk areas, often cause mass casualties. Despite there being few preceding landslides in the same season, the catastrophic Qijiaba landslide occurred in the new government-selected settlement of Wufu village, Sichuan Province, China, on September 5, 2021, killing three people and destroying 13 houses. In this paper, the landslide features and causes are discussed based on field investigations, remote sensing interpretations, and laboratory-based soil experiments. The results showed that it was a typical soil landslide within a geomorphic hollow of the slope with a volume of 20,230 m3, recurrence interval of at least 69 years, and runout distance of 137.5 m. This type of landslide is difficult to predict. The soil strength in the sliding surface decreased suddenly as the water content increased, and the soil's rich clay mineral and high clay particle contents determined its high mobility (Heim's ratio of 0.44). The occurrence time of the Qijiaba landslide lagged 1.3 days behind the peak rainfall, and the 2-day cumulative rainfall was a crucial factor in the landslide occurrence. Finally, the large water confluence area behind the main scarp was determined to be 3.9 times the area of the landslide itself, thereby providing abundant water conditions to induce failure. The factors underlying the casualties included inappropriate site selection, insufficient awareness of potential landslides, and failure to evacuate in time. The results of this study provide a basis for future prevention, mitigation, and early warning of similar landslides. [ABSTRACT FROM AUTHOR]

On 5 April 2021, a high-position landslide occurred in Tiejiangwan, Liujiang Town of Hongya County, Sichuan Province, China. The detached mass transformed into a debris avalanche traveled about 1300 m with an elevation difference of 665 m and caused three fatalities. Then landslide deposits were initiated by continuous rainfall and evolved to a debris flow five days later, forming a secondary disaster chain. The rapid characterization of a landslide-debris flow chain (LDC) is a critical step in remediation works and future early warning of failure. This paper proposes a rapid disaster information integration and assessment method for providing information on LDC occurrence, failure mechanisms, and potential hazard-affected areas via examining and characterizing the Tiejiangwan LDC based on multi-method including geomorphological mapping, structural characterization, kinematic analysis and numerical simulation. The results suggested that the first landslide initiated from a mountain ridge that experienced historical deformation extended over the fractured argillaceous siltstones. Constrained by three discontinuity sets, the failure mode was determined as planar failure along a sub-vertical defect. The cause of first landslide can be attributed to a jointed effect of structural plane, tectonic activity, terrain and slope structure, while rainfall is the dominating triggering factor. Deposits with loose structure subjected to persistent rainfall and gully topography contribute to the occurrence of secondary debris flow. Using UAV and LiDAR identification, the unstable elements in the surrounding cliffs of the source area are derived and a three-dimensional simulation was implemented to detect the energy, velocity, height and reach of detached blocks. The proposed method leads to rapid characterization of LDC and assists the evaluation of cliff instability of these environments. Highlights: We proposed a rapid and integrated assessment system for landslide-debris flow chain occurrence, failure mechanisms, and potential hazard-affected areas identification. Quantitative study was conducted on the evolution from landslide deposits to debris flow. 3D simulation was performed to reveal the runout behaviors of surrounding potential dangerous rockfall areas. [ABSTRACT FROM AUTHOR]

A rainfall-induced catastrophic landslide occurred at UTC + 8 03:50 local time on August 21, 2020, in Zhonghaicun village (N 29°20′30″, E 102°41′40″), Hanyuan County, Sichuan Province, China, resulting in damage to 6 buildings and 9 casualties (7 fatalities and 2 missing). In this paper, multitemporal remote sensing images, comprehensive field investigations, drilling holes, deformation monitoring, and numerical simulations are used to identify the main characteristics and the formation mechanism of the event. The results showed that long-term intensive rainfall in 2020 played an essential role in the failure of the Zhonghaicun landslide and that strong earthquakes in Wenchuan County (Ms 8.0, on 12 May 2008) and Lushan County (Ms 7.0, on 20 April 2013) also exerted a negative influence on the evolution process of this catastrophic landslide. Several traction zones appeared after the occurrence of the landslide. Fortunately, no evident deformation was observed and these slopes were in a stable state. In addition, a large-scale potential sliding slope, four small-scale landslides, and a debris flow were found in the study area. [ABSTRACT FROM AUTHOR]

This paper reports on a recent landslide event, which occurred in Yanyuan County at Xichang City, Sichuan Province, China, on 19 July 2018. Due to the continuous and heavy rainfall between 8 July 2018 and 18 July 2018, approximately 18 million m3 of soil detached from an ancient landslide and buried 65 buildings, the entire sliding process lasted for several minutes. Here, based on field investigations and unmanned aerial vehicle (UAV) photography, we describe the characteristics and failure mechanism of this landslide. The results showed that the landslide was triggered by the continuous and heavy rainfall. Additionally, during the first post-failure stage, the motion of this landslide involved typical successive movement, and over time, the style of movement progressively turned flow-like, which can be classified as debris slide by using the 1978 Varnes classification scheme. The landslide event described here is an outstanding case for landslide studies. In particular, this landslide represents a good illustration of the transform mechanism of landslide movement from sliding to flow-like. [ABSTRACT FROM AUTHOR]

Geological hazards, especially landslides and mudslides, are frequent in Caoke County, Sichuan Province, China. In September 2022, the mechanical parameters of the soil were obtained through a basic investigation of the landslide characteristics of Ni changgou. Upon that, the finite element-discrete element method was used to reconstruct the three-dimensional numerical model of the landslide on the right bank of Ni changgou, and the initiation mechanism of rainfall on landslide and the formation of debris flow impact dam process were simulated. Furthermore, the pore pressure, stability coefficient as well as displacement of the landslide body were analyzed. It turned out that with the increase of rainfall intensity, the pore water pressure value also increases, where pore water pressure rises rapidly. the slope is close to the unstable edge, Eventually, it tends to one under rainfall conditions, and due to gravity, the slide of the landslide is induced. The duration of landslide movement is about 200 s, the maximum average velocity of the landslide reaches 4.85 m/s, and the average movement distance is close to 500 m. In addition, this method is applied to the Chutougou debris flow, and the corresponding hazard analysis is added which could better show the treatment and application of debris flow in actual engineering. [ABSTRACT FROM AUTHOR]

Globally, but especially in Sichuan Province (Southwest China), landslides are considered to be one of the most common geological hazards. The purpose of the current study is to develop a novel model based on fractal theory, GeoDetector, and random forest, namely, the "GD-FFR-RF" model, for landslide susceptibility modeling and identifying areas prone to landslides with a case study of Sichuan Province, China. On this basis, fourteen landslide conditioning factors, including slope angle, slope aspect, relief amplitude, surface roughness, cutting depth, elevation, river density, rainfall, stream power index, road density, plan curvature, profile curvature, peak ground acceleration, and lithology, are selected. The information gain ratio is used to determine the significance of different conditioning factors. The overall performance of the three resulting models is assessed using the area under the receiver operating characteristic (ROC) curve (AUC) and several statistical indices. The GD-FFR-RF model yields better overall performance and more accurate results than the FFR-RF and FR-RF models. Therefore, in conclusion, the GD-FFR-RF model can be applied as a promising comprehensive model for the spatial prediction of landslide occurrence in subsequent studies. The generated landslide susceptibility maps will be useful for developing strategies for landslide hazard prevention and mitigation. [ABSTRACT FROM AUTHOR]

The failure of the 2017 Xinmo catastrophic rockslide in Maoxian County, Sichuan, Southwest China was a combined effect of long-term and short-term triggering factors. Field investigation, historical data collection, laboratory tests, chemical and microstructure analysis and numerical simulations were adopted herein to reveal the initiation and failure mechanism of the Xinmo rockslide. The analytical results showed that this failure involved the coupling of several triggering factors. The initial cracks in the rock mass were induced by historical earthquakes due to the convex topography and the direction effect. Rock masses from the source area of the Xinmo rockslide contain water-sensitive minerals, i.e., albite and chamosite, and the easily oxidized chemical element Fe, resulting in obvious strength deterioration under the action of water. The scanning electron microscopy (SEM) experimental results indicated that the internal structure of the rock mass is conducive to weathering. The compressive and shear strengths of the rock mass were reduced due to freeze-thaw cycles and weathering. The antecedent rainfall further deteriorated the stability of the slope, and stress and deformation accumulated continually in the locked section. Finally, the locked section sheared out, and the slope failed. An entrainment effect was observed in the Xinmo rockslide due to the presence of old landslide deposits and the antecedent rainfall, resulting in an amplification of the catastrophic rockslide. A simplified three dimensional analysis model was established in this study to reveal the influence of the triggering factors on the failure mechanism of the Xinmo rockslide. [ABSTRACT FROM AUTHOR]

At approximately 3:50 a.m. (UTC + 8) on August 21, 2020, a massive rainfall-induced landslide occurred in Zhonghaicun, Fuquan town, Hanyuan County, Sichuan Province, China, forming an approximately 40.85 × 104 m3 landslide accumulation, burying eight houses and approximately 100 m of roads, and causing long-term traffic interruptions. The landslide was comprehensively evaluated through field investigation, UAV photography, borehole drilling, and laboratory tests. According to movement and accumulation characteristics, the landslide is divided into the main sliding zones (the source area, impact sliding area, shoveling-accumulation area, and accumulation area) and landslide-affected zones. The deformation and failure of the Zhonghaicun landslide are related to the lithology (existence of a weak interlayer), geomorphology (microrelief changes), and antecedent rainfall. However, the main trigger of the landslide is continuous rainfall, which increases the landslide saturation and pore water pressure and reduces the mechanical strength of the weak layer. The landslide failure mode is complex. The upper slope is affected by rainfall and loses stability first. Under the impact of the sliding mass, sliding of the lower slope is triggered. This study of the Zhonghaicun landslide characterizes the evolution process of a complex rainfall-induced landslide and provides ways to mitigate landslide disasters. [ABSTRACT FROM AUTHOR]

A giant soil landslide named Boli landslide occurred on the right bank of Taozi Gully, a branch of the Jiami River in Taozi town, Sichuan Province, China, at approximately 5:40 am local time on 19 July 2018. The landslide destroyed 186 houses and nearly 300 acres of agricultural land in Boli village. Real-time evacuation was successfully implemented to avoid casualties of 281 people among 65 settlements due to the effective warning. This study revealed the typical characteristics, the cause, and the failure mechanism of Boli landslide on the basis of multi-temporal remote sensing images, field investigation, and analysis of the landslide soils. A simple, effective, and scalable community-based early warning system was also proposed in the study on the basis of real-time evacuation in response to landslide hazards in mountain in near future. Moreover, the experience and the effective risk avoidance mode of this study can be used by the concern parties to improve the disaster prevention and countermeasures of poor mountainous areas. [ABSTRACT FROM AUTHOR]