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On August 14, 2020, it occurred a landslide-induced debris flow in Wangcang County, Sichuan Province, Southwest China, three people killed, and two houses destroyed. Behaved as a typical geohazard chain, it originated from a rockslide in marlstone, controlled initially by structural planes in rock mass, and evolved into a debris flow through successive geophysical process. This debris flow reached a run-out distance of 2050 m in the horizontal and 628 m in vertical direction. Remote sensing analysis, field survey, and laboratory tests were conducted to investigate its failure mechanism and dynamic characteristics. The results found that the source zone in the gully was 16.32 × 103 m2, with a volume of 317.52 × 103 m3. Interbedded marlstone with dense structural planes was one of controlling factors for the landslide failure. The continuous rainfall up to 315 mm during the previous 24 days and 32 mm at the date before the incident directly motivated rock slope failure. The contributions of topography, rock fragmentation, entrainment, and flow discharge for this process were discussed. It is found that changes in slope from 11° to 40° provided tremendous potential energy for the rock mass sliding with high speed and then disintegrating in traveling. Entrainment in the channel increased the fine content of the moving rocky mixture. In addition, the flow discharge changed the rheological properties of the mixture by adding seepage. These factors significantly affected the transformation process. Notably, the turning relief or confluence site may be accelerating this process. This research may provide references for further research on geohazard chains. [ABSTRACT FROM AUTHOR]

On July 23, 2019, a large-scale landslide occurred in Jichang town, Shuicheng County, Liupanshui City, Guizhou Province in China. The landslide, which moved along two gullies, resulted in strong punching-shear, induced scarping on vegetation and large destruction of houses, and finally formed a deposit with a volume of 2 × 106 m3. This research aims to understand the effect of topography on landslide kinematics. To achieve this aim, a detailed field investigation was first carried out with an unmanned aerial vehicle (UAV) aerial photography survey, resident interviews, and field sampling. The rainfall analysis indicates the effective rainfall within 7 days before landslides was 70.14 mm which exceeded the rainfall threshold of 54.3 mm in this region, which finally triggered the landslide. Traditional soil mechanic tests were then performed to identify the soil properties of the source material. Combined with numerical simulation using the nonlinear shallow water equation, the whole process of landslides was divided into four stages: instability stage, acceleration stage, transformation stage, and impact and accumulation stage. The simulations results show the landslide block slid with a low velocity of 8 m/s for about 100 m. Then, Froude number of landslide increases from 2 to 3 when passing the high and steep terrain, indicating that landslide change to inertial dominated with potential same Froude behavior of classic debris flow. The rupture mass slid with the peak velocity of 23 m/s and diverged in two gullies and ran out for about 600 m. The maximum velocity is 23 m/s in east gully while only 15 m/s in west gully. Compared with deep and incised valleys in the west, shallow and straight valley in the east decreases the deposit depth and further increases the velocity of landslide material with increased runout distance. This research may provide a fast flow path of back analyzing geo-hazards on complex terrain and serve as a basis for future research on long runout landslides. [ABSTRACT FROM AUTHOR]

Bed entrainment changes the rheology of the sliding mass and the topography of the sliding surface, finally influencing the propagation of flow-like landslides. In previous studies, both empirical methods and physically based methods have been used to simulate bed entrainment. However, the influences of bed entrainment on the rheology and topography of flow-like landslides were not deeply explored. In this paper, the physically based model proposed by Fraccarollo and Capart (J Fluid Mech 461:183–228, 2002) is adopted to calculate the bed entrainment rate, and a new method is proposed to consider the rheology change associated with bed entrainment in flow-like landslides. The new rheology change method and the Fraccarollo and Capart model are incorporated into a quasi-3D finite difference code to analyze an ideal case and two typical flow-like landslides. The two real landslides are the Dabaozi landslide and the Dagou landslide in the Chinese Loess Plateau. They represent two different bed entrainment scenarios: the erodible mass is relatively thick in the Dabaozi landslide, while that of the Dagou landslide is relatively thin. The results show that both the topography and rheology changes have a significant influence on the propagation of flow-like landslides: (1) the rheology change mainly influences the run-out distance of a landslide, while the topography change mainly impacts the lateral spreading; (2) entraining soft materials can significantly increase the run-out distance of a flow-like landslide; (3) the topography change can obviously constrain the lateral spreading of those landslides when the erodible mass is relatively thick. In addition, it shows that the rheology change and topography change influence each other in the propagation of a flow-like landslide, and the proposed rheology change method in this paper can properly reflect this interactive process. [ABSTRACT FROM AUTHOR]

The fluctuation of the water level in a reservoir may induce various types of slope movements. Some of these movements are new, whereas others are old but reactivated. Many ancient landslide accumulations are distributed in the deep valleys of the eastern Qinghai-Tibet Plateau margin in China and will likely be reactivated after the completion of reservoirs and pose a risk to reservoirs, dams, facilities, and towns near mountainous areas. The Shuangjiaping ancient landslide, located in the Dadu River, Sichuan Province, China, is an example of this case. Since August 2010, the western part of the accumulation body has seen the gradual appearance of deformations. The Pubugou reservoir water level rises and inundates the front edge of the accumulation body, thus threatening the safety of the national highway G108 and 37 houses on it. This study is based on field work investigation, drilling work, aerial photography, and profile survey. The site-scale investigation shows that the deformation area is only a part of an ancient landslide accumulation, with an area of approximately 50.4 × 10 m and a volume of ca. 956 × 10 m. Boundary and deposit characteristics of landslide accumulation are specified, which could be divided into four zones, namely, zones A and C, which are an avalanche accumulation area mainly composed of large blocks with diameter ranging from 1 to 3 m (some blocks have a diameter ranging from 5 to 10 m), zone B, a residual integrated rock mass accumulation area with 'fake bedrock,' and zone D, a fine material accumulation area. A conceptual model is proposed to explain the mechanism and sliding process of this ancient landslide. The model includes translational sliding, stopping and hanging in air, avalanche accumulating, and transforming. The saltation of topography, material structure, and kinematic characteristics is the evidence used to identify the ancient landslide in deeply incised mountain areas. The current activity is found to be a surficial deposit displacement, and the whole landslide accumulation is stable or quasi-stable. [ABSTRACT FROM AUTHOR]