Search

China has a significant portion of land in landslide-prone areas, and remote sensing technologies are becoming a tool of choice to investigate and monitor landslides. Although much progress has been made with remote sensing technologies and their applications in China, there is no systematical summary report. Thus, we summarize Synthetic Aperture Radar (SAR), optical remote sensing, and laser technologies currently being used in China, and their associated platforms (space-borne, air-borne, and ground-based). Multi-temporal optical images and time series SAR are often used to detect active landslides at time scales of years and months. The latest optical images and SAR intensity images are usual adopted to map fresh landslides, especial for coseismic landslides. LiDAR technology has been widely applied to identify ancient landslides. Combining advantages and limitations of every technology, an integrated space-air-ground collaborative investigation strategy has been proposed for early identification and early warning of landslides. Additionally, a comprehensive landslide investigation integrating multidisciplinary approaches, including remote sensing, geology, and geophysical exploration, could be a further developing trend, because remote sensing technologies just provide surface information, while a complete understanding of landslides requires more than surface information – knowledge of geotechnical parameters, geological features, and field conditions is also needed. • SAR, optical remote sensing and laser technologies have been applied for landslide investigations in China. • China has proposed remote sensing strategies for different landslides. • China has carried out successful remote-sensing applications on different scales. • Multidisciplinary integration for landslide investigation should be the further trend. [ABSTRACT FROM AUTHOR]

Agricultural irrigation has increased the groundwater level in the Heitai terrace (part of the Heifangtai terrace) by 20 m over nearly five decades, which causes 3–5 landslides each year at the edge of the terrace. The Heitai terrace is of great interest in the study of loess-related landslides; but there is no unanimous agreement on the types of either the landslides in this study site or the loess-related slope failures in general. On the basis of aerial images (res. 5 cm), Digital Elevation Model (res. 10 cm), and field investigations, we analyzed the distribution and failure mode of the landslides in Heitai. The geological structure and characteristics of 69 landslides (vol. 5 × 10 3 –6 × 10 6 m 3 ) are studied. The preliminary results of groundwater recharge in the terrace and formation of the apparent spring lines on the slope surface are analyzed to better understand the failure modes. We divided the landslides in Heitai into two groups based on the location of the failure surface, i.e. loess landslide and loess-bedrock landslide, of which the development is governed by the angle between the principle direction of slope deformation and the dip of bedrock bedding. We further analyzed the failure mode of each type observed in Heitai, defined as follows: loess-bedrock planar slide, loess-bedrock irregular slide, loess flowslide, loess slide, and loess flow. The proposed types of loess-related landslide are to be incorporated in the Varnes classification (Varnes, 1978) in consideration of the engineering properties of loess, and to provide backward compatibility for Heitai and potentially other regions in the Loess Plateau of China. [ABSTRACT FROM AUTHOR]

The Heifangtai terrace is located in the arid loess area in northwestern China, where a large number of landslides was induced by agricultural irrigation on the terrace, resulted in slope retreat at the terrace edge at an estimated rate of 0.024 km 2 yr − 1 . On the basis of field investigation and monitoring, remote sensing and aerial images, and laboratory tests, we analyzed the characteristics of slope retreat and the failure mechanism of the loess flowslides. The retreat of slope is caused by the retrogressive behavior of the loess flowslide, of which new failure develops at the backwall of the preceding one. The groundwater level variation governs the failure process and mechanism of the flowslides. The observed loess flowslides were accompanied by rapid slope deformation, high velocity, and long runout distance exhibiting liquefaction and fluidization during the movement. In the event of a loess flowslide, a small-scale drained slope failure produces a concave recession first intensifies localized groundwater flow on the slope surface while the flow is being impeded by the deposit, which produces an undrained condition with increasing localized pore-water pressure, and in turn facilitates the subsequent flowslide. Results of the isotropically consolidated undrained triaxial tests (ICU) and constant shear stress drained triaxial tests (CSD) revealed the strain-softening behavior in the saturated reconstituted loess, and they showed that the excess pore-water pressure is associated with a small axial displacement and possibly facilitated by some alternations in the loess structure at the micro-scale. [ABSTRACT FROM AUTHOR]

Thick loess deposits are considered problematic soils due to their susceptibility to collapse suddenly and in large volumes upon increase of water content. In the past decades, a large number of landslides occurred in the Loess Plateau in Gansu Province, north-western China, triggered by the extensive irrigation. The increase of water content has been identified as a key factor controlling the loess strength. However, the role of long-term saturation and pore fluid chemistry changes has not been investigated systematically. This paper reports on an experimental study on loess samples from Heitai loess terrace (Yongjing, Gansu) carried out through chemical analyses, oedometer and ring shear tests. The natural pore fluid was found to be a concentrated saline solution in unsaturated soil condition. Upon saturation, the pore ion concentration drop can contribute to shear strength loss in the clay component and volume decrease. A prolonged exposure to the irrigation water might facilitate cement dissolution, which could result in further weakening. [ABSTRACT FROM AUTHOR]

Evaluation and prediction of displacement by specific models help in forecasting geo-hazards. Among the various available predictive tools, Least Square Support Vector Machines (LSSVM) model optimized with Genetic Algorithm, namely GA-LSSVM, is commonly used to empirically forecast landslide displacement due to its capability of processing non-linear complex systems. Another improved hybrid model composed of Double Exponential Smoothing (DES) and LSSVM considers measured displacement and precipitation time series to estimate the one-step ahead displacement evolution of rain-induced landslide. Here, the modelling process and accuracy of these two models are presented, and their predictive performances are evaluated by the root mean squared error (RMSE), mean absolute percentage error (MAPE), accuracy factor (AF), and correlation coefficient (R). A slowly-moving landslide on gently dipping rocky slope located in Sichuan Province of China was chosen as the case study for its deformation triggered by intense seasonal rainfall. The application results indicated that both GA-LSSVM and DES-LSSVM models were suitable for accurately predicting the landslide displacement on the basis of precipitation and displacement observations. Furthermore, comparison results show that DES-LSSVM model can provide the better predictive accuracy, with RMSE and MAPE values of 0.059 mm and 0.004%, respectively. [ABSTRACT FROM AUTHOR]

Large number of rain-induced landslides occurred on 16 September 2011 in Nanjiang, southwest of China. The typical depth of failure surface was from 1 to 5 m at the gently inclined interface between the superficial red silty clay and bedrock. In order to explain the failure characteristics of these shallow landslides, we conducted a rainfall infiltration simulation test, calculated rainfall infiltration depth using modified Green-Ampt (G-A) infiltration model as well as considered the atmospheric effects on the slope failures. Results show that the permeability of red clay is extremely low and the rainfall infiltration depth is limited to around 0.5 m during a rainstorm. The rainfall infiltration capacity can be enhanced within the depth of atmospheric influence, which is determined as 5.4 m in the study area. With the increase of soil depth and the lower degree of weathering, the void ratio and permeability are gradually reduced; thus, the rainfall infiltration continues following a decreasing trend until the bedrock is reached. Within the shallow landslides in the study area, under the condition of rainfall, the slope can keep in a stable state when the depth of wetting front is less than the thickness of soil layer. When the wetting front proceeds to the interface between the silty clay and bedrock, the potential slip surface can develop on such soil-bedrock interface, in relation to the increased pore water pressure and ground water level. Consequently, shallow failures will occur along the soil-bedrock interface in a depth of 1–5 m. [ABSTRACT FROM AUTHOR]

Red mudstone landslides are widespread in southwest of China. The development and distribution of deep-seated landsides with slow inclination are closely related to the special soft rock properties of the red mudstone layers. Most previous studies focused on the failure mechanisms of rain-induced shallow landslides. Studies on deep-seated landslides in red layer zones are still limited. In order to ascertain the basic failure mechanisms of red layer landslides with a gentle inclination, a fatal landslide named as Shibangou landslide, which occurred in Sichuan, China, was investigated. This paper aims to (1) conduct laboratory tests on the reduction in shear strength of a red layer to identify the water–rock coupling effect; (2) investigate variations in the microscopic structure of the soft rock found within a red layer after rainfall infiltration; (3) discuss the failure mechanisms of red layer landslides with slow inclination. Results from shear test of mudstone from the Shibangou landslide revealed that there is a tendency that behavior of soft rock can be transferred to soil in different days of immersion. The delineation threshold of shear strength of the red layer is determined as 6 days of immersion. Microstructures of clay minerals become loose and porous due to the contacts between the particles transferred from the face–edges, face–face associations into edge–edge, and face–edge associations. Therefore, the intramolecular and cemented expansions of illite are the basic mechanisms which lead to structural damage, structural decay, and strength attenuation of soft rock in red layer under the condition of rainwater infiltration. [ABSTRACT FROM AUTHOR]

The Discrete Element Method (DEM) is one of the most common numerical methods employed for the study of landslide disasters. Herein, this study proposes a method addressing the challenges associated with the selection of contact parameters for DEM blocks (or particles) when simulating landslide hazards. In 2018, two landslides occurred successively at the same slope of Baige, in Tibet, China. To efficiently simulate the entire process of landslide dynamics, a Graphics Processing Unit (GPU) program for blocky DEM, named CoSim-DEM, is developed. Furthermore, a parameter inversion method for the DEM simulation considering the deformation and failure process of landslide is provided and used to obtain the contact parameters for DEM blocks based on the failure process of the first landslide. The failure process of the second landslide is also simulated with the parameters obtained. The geomorphic characteristics of the landslide dams of the two times lanslides obtained by CoSim-DEM are validated by the field investigations. Based on the numerical results, the landslide damming process is divided into five stages and the entire path of the landside is divided into three zones. The results of this study provide a method to construct a database of parameters for geomaterials by using an inversion method based on the previous landslide cases. The method will be important for the rapid assessment and study of landslide hazards in the future. • A higher efficiency blocky DEM based on GPU is developed. • A parameters inversion method for DEM based on the failure process of the landslide is provided. • Two landslides at Baige, Tibet, China in 2018 are reproduced based on the inversed parameters. • The dynamic process of the landslide damming process has been studied. [ABSTRACT FROM AUTHOR]

Abstract: Understanding the mechanisms of landslide failure and resulting damming processes is crucial for constraining the hazard chain associated with landslide damming events. On May 12, 2008, the Wenchuan earthquake caused a large number of secondary hazardous events such as landslides and collapses, most of which occurred in high mountain gorges. In these areas, the sliding distance of landsides is often very short, and the landslides are often characterized by high speed, short distance, and damming. Using the Tangjiashan landslide damming events induced by the Wenchuan Earthquake as a model, this paper reconstructs the three dimensional failure and associated damming caused by the landslide based on a detailed geological investigation of the landslide area and using the dynamic finite element technique. The study proposes a four-stage model for the failure and damming process of the Tangjiashan landslide: earthquake induction and progressive destruction of the slide body, destruction and high-speed sliding of the slide body, slide body impact, disintegration, and river blockage for the formation of a damming body, and vibration compression. The average speed of the Tangjiashan landslide reached a maximum value of 22m/s about 30s after the earthquake, and the landslide reached stability about 60s later. [Copyright &y& Elsevier]

Abstract: The 2008.5.12 Wenchuan Earthquake (seismic magnitude Mw 7.9 according to the USGS) triggered a great number of landslides. A spatial database of landslides is built by interpreting the remote sensing (RS) data which covers 11 counties severely damaged by the earthquake with area of about 31,686.12km2. The geological settings of the study area are detailed mapped including geologic structure and lithology. The digital elevation model (DEM) of the study area with resolution of 30m×30m is presented to address the topographic characteristics. Correlations between the occurrence of landslides with geological settings i.e. active faults (the coseismic surface ruptures), geological unit, slope gradient, slope elevation as well as slope aspect are analyzed using spatial modeling in GIS with the aids of field investigations. It can be concluded that the distance to the causative faults and slope gradient are much more important than other factors. Landslides are clustered distributed along the causative faults of F2 and F3, and landslides incidence are dramatically decreasing with the increasing of the distance to the causative faults. The landslides incidence has an obvious increase near the active faults i.e. F1. Landslide concentration (LC, landslides/km2) has an obvious exponent increase with slope gradient. However, LC has no obvious relationship with geological unit and slope elevation; the difference of LC value in each geological unit (each slope elevation category) maybe have been the result affected by slope gradient for each geological unit (each slope elevation category) and distance of each geological unit (each slope elevation category) to causative fault zone. Isoseismal map reflects the incidence of landslides in some degree, and LC increases dramatically with Intensity increasing, almost all landslides occurred in the region above VI degree. Statistics result also indicates that in the near field of causative faults, landslides tend to have the initial sliding direction similar to the movement of the causative faults. And preliminary study shows that landslides incidence varies in different slopes with different structure, and consequent slopes and obsequent slopes have a higher landslides incidence than other layered slopes. [Copyright &y& Elsevier]

Real-time monitoring and intelligent early warning system are crucial and significant to take mitigation measures and reduce casualties and property losses related to landslides. It is difficult to obtain entire monitoring data in the accelerated deformation phase in a landslide event, and hard to issue early warning information using a traditional monitoring approach with fixed and low sampling frequency. Displacement increments of loess landslides induced by agriculture irrigation on the Heifangtai terrace could be sudden and extremely rapid. Typical landslide types include loess flowslides and loess falls. It is of practical significance to develop a self-adaptive data acquisition monitoring technique and establish a real-time landslide early warning system (LEWS) to meet the needs for risk mitigation of rapid sliding slopes on the Heifangtai terrace. The monitoring technique can wirelessly transmit displacement data and the LEWS was devised using the new artificial intelligence. The LEWS could automatically release the warning information in advance of the event once the early warning parameters exceed default thresholds. In this study, the early warning procedures, real-time monitoring approach, intelligent LEWS, a multiple criteria warning model, warning release and emergency mitigation measures, and performance are introduced in detail. Six loess landslides at Heifangtai and eight landslides in other regions of China have been successfully warned since its implementation in 2012. This study proposed an effective and practical solution for the early warning of loess landslides at Heifangtai. Two typical loess landslides that had successful early warnings at Heifangtai were presented. The successful implementation could serve as a reference for global rapid slope failure cases, considering the complex nature of landslide behaviors and failure mechanisms. • A self-adaptive data acquisition technique was successfully developed to monitor sudden failure of loess landslides. • 3D WebGIS-based platform developed by SKLGP becomes more intelligent and accurate. • Multiple alert criteria model including deformation rate, the rate increment, and tangential angle, is established. • The LEWS with multiple alert criteria model has successfully forecasted six loess landslides since its implementation in 2017. [ABSTRACT FROM AUTHOR]

Heavy rainfall may increase the infiltration rate, raising the groundwater table after a short period time. Variation in the hydrostatic pressure on potential sliding surfaces and trailing edges of fissures in a rock slope may contribute to slope failure. The failure mechanisms of rainfall-triggered rock wedge slides have been widely studied in the literature. However, studies on the dynamic evolution of groundwater in rock failure are still limited. In this study, a typical rock wedge slide that occurred in Chengkou County, Chongqing, China is selected as a case study to analyze the stability of rock wedge with double planes and tension crack subjected to groundwater dynamic evolution. Model tests were designed and performed to reproduce the dynamic evolution of groundwater in the rock slope and analyze its role in wedge failure. Development and distribution characteristics of water pressure are investigated through monitoring the water pressure distributed along the surfaces of wedge failures. From the experimental study, it is found that the initial formation process of water pressure along the sliding surface consists of four types of distribution patterns, i.e., triangular distribution, Type I trapezoidal distribution, Type II trapezoidal distribution, and Type III trapezoidal distribution. Based on the model tests and theoretical analysis, the order of the calculated safety factors of the Chengkou rock wedge slide are: triangle > type I trapezoid > type II trapezoid > type III trapezoid. The existence of inflection points in the trapezoidal distribution mode significantly increases water pressure on both sides of rock wedge, which contributes instability. The new approach for investigation of the effect of dynamic evolution groundwater on stability of rock wedge slide is developed based on fundamental mechanism and experimental study. It can be adopted for stability assessment of similar rock wedge slides in other areas. • Development and distribution characteristics of water pressure for rock wedge slide are investigated by model tests. • Results of groundwater dynamic evolution along the sliding surfaces were adopted for stability analysis of the real event. • Initial formation process of water pressure along the sliding surface consists of four types of distribution patterns. • Maximum uplift pressure will be formed when the water pressure distribution is in a triangular pattern. [ABSTRACT FROM AUTHOR]

• A new transparent soil is proposed to act as a surrogate for cemented soil, especially for natural argillaceous sand or sandy clay. • The strength parameters and permeability of the transparent cemented soil can be adjusted by using the appropriate fumed silica contents. • The transparent cement soil has the unique advantage of showing shear band propagation. • The transparent cement soil offers cohesion sufficient for building irregular models in laboratory model test. • The transparent cemented soil is compatible with image-based techniques for the following deformation measurement. This paper introduces transparent cemented soil as a surrogate for the physical modelling of geotechnical problems. The transparent soil consists of fused quartz particles that form the soil skeleton combined with a mixture of hydrophobic fumed silica powder and mineral oil that forms the cement material. Conventional isotropically consolidated undrained compression (CIU) tests and falling head permeability tests were carried out, demonstrating that the proposed transparent soil has similar mechanical properties and hydraulic permeability to those of natural cemented soil with clay as cement. The same triaxial and permeability tests were carried out on transparent cemented soils with increasing fumed silica contents to investigate the cement content's influence on mechanical properties. The results show that transparent cemented soils with increased fumed silica content have more effective strength, stiffness and cohesive force. In addition, the increased fumed silica content reduces the permeability of transparent soil. To demonstrate the practicability of the proposed material in geotechnical model tests, a laboratory slope model test was conducted. The proposed surrogate has high transparency, with a visible depth of 20 cm, and is compatible with image-based techniques for the following deformation measurement. Moreover, the transparent cement soil has the unique advantage of showing shear band propagation, which is invisible in conventional physical modelling. [ABSTRACT FROM AUTHOR]

The Three Gorges Hydropower Station is the largest hydropower station worldwide and the largest project ever built in China. There are about 2619 ancient landslides affected by reservoir level fluctuation in the Three Gorges Reservoir (TGR) area. More than 670 landslides have been reactivated and eight landslides have failed since the impoundment of the reservoir in June 2003, which seriously threatens people's safety and property. In this study, taking a large number of re-active and failed landslides as statistical samples, the activity and displacements of the reservoir landslide with special regard to different sliding surface and permeability are analyzed and discussed. It is noted that a significant correlation between the landslide movement and the reservoir filling process. The re-active landslides are mainly concentrated in the initial stage of water storage, and the frequency of activation as well as the degree of deformation decrease gradually after the third phase of water storage (175 m). Then the four dominant combinations of the inducing factors of re-active landslide are presented: (a) drawdown of water level, straight line sliding surface, 20–40% degree of immersion, and weak permeability; (b) drawdown of water level, arc sliding surface, 40–60% degree of immersion, and medium permeability; (c) raising of water level, fold line sliding surface, 20–40% degree of immersion, and good permeability; (d) raising of water level, chair shaped sliding surface, 0–20% degree of immersion, and good permeability. Furthermore, when the rate of the reservoir level fluctuation is greater than the permeability coefficient, the shape of sliding surface is from the straight line - the arc - the fold line - the chair shaped, and the hydraulics effect of reservoir water on landslide shifts from the seepage pressure effect to the buoyant effect. Meanwhile, the impact of the reservoir water filling on the landslide reactivation changes from favorable to worse, and the impact of the reservoir water drawdown on the landslide reactivation changes from worse to favorable. • Reservoir landslides are easy to revive under the four conditions: • Filling water + chair shaped sliding surface + degree of immersion 0–20% + good or better permeability. • Drawdown water + straight line sliding surface + degree of immersion 20–40% + medium or weak permeability. • Drawdown water + arc sliding surface + degree of immersion 40–60% + medium or weak permeability. • Filling water + fold line sliding surface + degree of immersion 20–40% + good or better permeability. [ABSTRACT FROM AUTHOR]

The Heifangtai terrace located in Yongjing County of Gansu Province in northwest China is characterized by a large number of landslides with frequent failure events related to agricultural irrigation activities. Thus, it is a task of great importance to identify and monitor the active loess slopes and sort out the impact factors. In this study, we employed the time series InSAR method to map the active slopes in the Heifangtai terrace with two TerraSAR-X data stacks covering the year of 2016 and two Sentinel-1 data stacks from 2016 to 2018. The detected active spots are mainly distributed along the edges of the terrace. Time series displacements derived from TerraSAR-X and Sentinel-1 observations were validated by comparisons against GPS and crack gauge measurements. Good agreement between InSAR and GPS was achieved at slow moving locations, while unwrapping errors induced by sudden accelerations make InSAR underestimate the pre-failure displacements with respect to GPS measurements. The trends of InSAR-measured displacement and crack gauge measurements also match well with correlation higher than 0.75. InSAR-measured displacements at the Jiaojia landslide group were highly correlated with the bury of groundwater record, which suggested that the rising of groundwater level may seriously decrease the stability of loess slopes. • Unstable slopes in the Heifangtai terrace are mapped with TerraSAR-X and Sentinel-1 InSAR analyses from 2016 to 2018. • InSAR results are validated by comparisons with GPS and crack gauge measurements. • Displacement patterns of typical landslides within the study area are analyzed. • Intensive irrigation on the terrace significantly affects the stability of loess slopes. [ABSTRACT FROM AUTHOR]

The catastrophic Tangjiawan landslide, triggered by the 2008 Wenchuan earthquake, blocked the Duba River, impounding one of the most dangerous coseismic barrier lakes in Beichuan, China. The lake was drained by an artificial spillway within one month after the earthquake to minimize the potential dam-breach flooding risk. However, on September 5, 2016, this landslide was reactivated and dammed the river again, creating a 20-m high dam at the same location and resulting in the formation of a barrier lake with a volume of 0.6 million m 3 . The day after the event we carried out a field investigation of the landslide and obtained a high-resolution image and DEM using UAV. The satellite images from 2005, 2008, 2010 and 2015 were also collected to analyze the evolution of the landslide. Together with multi-temporal DEMs, the geometry and volumes of the displaced mass and the landslide dams and barrier lakes were calculated using image interpretation and 3D spatial analysis with GIS. This landslide is of great scientific interest, as it presents a good example of multiple reactivation of a pre-historical giant landslide under different triggering conditions: a reactivation of an older landslide during the Wenchuan earthquake, and a second reactivation during a rainfall event several years later. Meanwhile from the hazard assessment and prevention perspective, it is also representative as it dammed the river twice in 2008 and 2016, posing threats to both upstream and downstream areas. We infer that the successive landslides in this region could be caused by the strong tectonic activities: including earthquakes and high average uplifting rate. The results of landslide volume analysis using multi-temporal DEMs, contribute to the landslide mechanism analysis, and suggest that the landslide volume estimation is effected by the landslide type, landslide rupture surface location, and resolution of DEM. We also compare the performance of different empirical models of landslide stability and dam-breach flood parameters and discuss their application during the quick assessment of the potential hazard of the landslide dams. Generally, the successive landslide dams at the Tangjiawan site are caused by the successive landslide reactivations on an anti-dip slope controlled by strong tectonic activity and river erosion, involve with a mass of loose materials of previous landslide deposition, and possess high flood risk to the downstream area. The experience gained in this work can be used to assist the hazard assessment and the planning of the emergency measures for similar landslide dams in the future. [ABSTRACT FROM AUTHOR]

Detection of potential slope instabilities across wide areas using SAR interferometry (InSAR) techniques can aid prevention and mitigation of landslide disasters. Nevertheless, the low spatial density of coherent radar targets detected by conventional time series InSAR methods in mountainous areas with complex topography and vegetation cover introduces considerable uncertainties into the deformation measurements, and thus results in a high probability of omissions for landslide detection. In this study, a new time series InSAR method named Coherent Scatterers InSAR (CSI) is proposed to solve this problem through the joint exploitation of Persistent Scatterers (PS) and Distributed Scatterers (DS) to increase the quantity of Measurement Points (MPs) in rural environments. We applied this approach to detect potentially unstable slopes at a catchment scale, delineate sliding boundaries, and measure the deformation of major landslides. The archived ALOS PALSAR and ENVISAT ASAR data stacks covering the Danba County in the upper reach of the Dadu River Basin in southwest China, were processed. The PALSAR-measured deformation rate map revealed 17 suspected landslides and their sliding boundaries. By contrast, only six out of these 17 landslides were detected from the ASAR results, as the other 11 landslides were undetected due to the much lower density of coherent points. These detection results were indirectly verified by two different approaches. Two differential interferograms for recently acquired L-band ALOS-2 PALSAR-2 data pairs were visually inspected to check whether these landslides are still in active deformation. The reliability of the InSAR results was further evaluated by comparisons against field survey and in-situ GPS measurements. The spatial and temporal patterns of surface displacements at several slow-moving landslides were analyzed in detail, and general guidelines on the application of the CSI method for landslide investigations were discussed and summarized. [ABSTRACT FROM AUTHOR]

Bedding-controlled landslides in alternated mudstone and sandstone beds in cataclinal slopes are common in the Sichuan basin and in the Three Gorges area in China. They are characterised by very gentle dip angles of the beds (<10°), and usually exhibit slow creep movements throughout the year. However, during the rainy season, they can have sudden accelerations and undergo large displacements. In this work, the influence of saturation degree, displacement rate and stress state on the shear strength of the shear-zone soil was investigated. The results of the displacement-controlled ring-shear tests show a rate-weakening behaviour even at low rates of displacement. Dually, the shear-controlled tests show that the displacement rate can increase dramatically in response to a slight increase of the shear stress. The threshold stress that triggers large displacement is equal to the rate-dependent residual shear strength of the soil. [ABSTRACT FROM AUTHOR]

Landslides of the flow type are among the most destructive mass movements due to their potential high mobility, long runout distance and capacity of entraining further material during movement. Generation of positive pore pressure excess is considered to be a fundamental triggering mechanism which, in some cases, can produce stress state instability and fluidization of both fine-grained and granular deposits, resulting in extremely fast and catastrophic events. Several experimental works and theoretical studies have been carried out so far to investigate the initiation mechanism and runout of flowslides. However, efforts are still needed to improve the understanding, for instance, of the role of the soil grading on the initiation and evolution of the movement. To this aim, a series of flume tests has been carried out using granular mixtures of coarse and small particles. High temporal resolution data acquisition has been used to investigate the onset of failure in terms of pore pressures, surface and internal displacements and vibration signals. By means of shear-controlled triaxial tests and permeability tests, the hydraulic conductivity has been found to be a controlling factor in the landslide initiation, whereas the uniqueness of the instability line – the lower bound of potentially unstable stress states – regardless of the soil grading, suggests that pore pressure measurement in the field can serve as a reliable indicator in early-warning systems. [ABSTRACT FROM AUTHOR]

This paper studies the run-out of earthquake-induced landslides. There are more than 20 mechanical models to explain long run-out of rapid landslides including some earthquake-induced landslides. However, notably few of them considered the effect of seismic loading on the run-out of landslides. In a previous study, we have proposed a model, which is called the multiplex acceleration model (MAM), to interpret the long run-out mechanism, and a shaking-table test has been performed to verify the MAM. Because the previous MAM is a conceptual model and only a single stone has been examined under sine waves by the shaking-table test, the MAM needs to be extended and further verified. In this paper, the MAM was extended by introducing the movement change that was induced by the so-called trampoline effect of earthquake loading, and the latest practical numerical simulation program, discontinuous deformation analysis (DDA), was used to verify the mobility of earthquake-induced landslides. After a conceptual landslide model was used to verify the effect of seismic loading on the mobility, the Donghekou landslide, which was a typical long run-out landslide that was induced by the 2008 Wenchuan earthquake, was analyzed. The results show that: the seismic loading could be one of the factors that could eventually help increase the run-out of landslides. [ABSTRACT FROM AUTHOR]

The quantitative risk assessment of landslides requires the spatial impact probability of their run-out processes to conduct vulnerability assessments and prioritize mitigation measures. Hence, a general framework for three-dimensional (3D) probabilistic landslide run-out hazard evaluation is presented in this paper. In the proposed framework, a continuum mechanics concept-based dynamic numerical model, called Massflow, is used to conduct run-out analyses. A multi-observation Bayesian back analysis method with Markov chain Monte Carlo simulation is used to calibrate the uncertainties of the input parameters based on a past landslide event, which integrates the prior information, observation information, and model bias factor to yield posterior distributions of the input parameters. Then, the posterior distributions are used as inputs for a future event to estimate the exceedance probabilities of run-out intensities (i.e., maximum run-out height and velocity) on a 3D terrain and produce run-out hazard maps for quantitative landslide risk assessments purposes. To improve the computational efficiency of the proposed framework without losing accuracy, a multi-response Kriging-based surrogate model with a sequential adaptive sampling strategy is developed for both the back analysis and forward prediction. Finally, two sequential slides of landslide CJ#8 located in the Heifangtai terrain, Gansu, China are employed to test the performance of the proposed framework, with its advantages and potential drawbacks discussed in detail. Results show that the proposed framework can effectively calibrate the model input parameters to evaluate the run-out hazard of similar landslides, and the predicted results can be employed in landslide risk assessments and mitigations. • A 3D probabilistic landslide run-out hazard evaluation framework is proposed. • A multi-observation-based Bayesian framework is employed to calibrate input parameters. • Run-out intensity exceedance probability curves are calculated to produce probabilistic run-out hazard maps. • Multi-response Kriging-based surrogate models are used to significantly improve computational efficient. • Results can be employed for quantitative landslide risk assessment. [ABSTRACT FROM AUTHOR]

Shear zone is widely observed in natural faults and landslides as well as laboratory experiments on granular material. Understanding the shear-zone evolution process in granular materials is crucial in studying the dynamics of the landslides and faults. However, it is still not well understood. To this end, we conducted a series of ring-shear experiments to investigate the evolution of strain localization and shear-zone internal structure in cohesive and non-cohesive granular materials. The quantitative evaluation was conducted by using high-solution X-ray computed tomography (CT). The analyses included visualization of shear-zone internal structure and quantification of particle shapes, orientations, and grain-size distributions at different shear strain levels. We found that with the increase of shear displacement, the large particles inside the shear zone became more and more rounded, but without an orientation, wear and attrition resulted in an abundance of nanoparticles within the shear zones. We also found fine-particle layers (nanoparticle layers) formed on either side of shear zones during shear localization, implying that shear development progressed from a shear zone to an interface. These findings offer some new understanding of the evolution of shear zones in granular materials. • The temporal evolution of the shear-zone internal structure was examined by X-ray computed tomography (CT). • The shear developed progressively from an initial zone of finite thickness into a shearing interface. • Abundant nanoparticles were formed in the shear zone due to wear and attrition. [ABSTRACT FROM AUTHOR]

As a natural earth-surface process, mass movements (e.g., rock avalanches) typically entrained a large amount of bed material in their pathway, increasing volume and run-out distance. Many authors attribute the increased mobility of these fast gravity flows to the total or partial fluidization of the path material due to the rapid undrained loading. A question raised here is whether any other entrainment mechanisms are involved in this process. In this study, we conducted a series of flume experiments to simulate rock avalanches overriding a saturated bed material. Experimental results showed that the overriding flow fluidized the bed material into a viscous state. We also found that the rapid loading by the overriding debris leads to an increase in pore pressure at the bottom, but does not bring it to the level of fluidization. We tested the rheological properties of the bed material and found significant shear-thinning rheology, with its viscosity decreasing rapidly with increasing shear strain rate. Therefore, we think that the excess pore pressure at the basal layer and the shear-thinning rheology at the flow mass simultaneously contributed to the bed-material fluidization and long-runout distance. This finding provides a possible natural explanation of the hypermobility of rock avalanches. This finding can also help improve the accuracy and reliability of the numerical simulation of rock avalanche entrainment by using the viscous model obtained from the experiments. • A series of flume experiments have been conducted to understand the entrainment mechanisms of debris avalanches. • The overriding flow fluidized the bed material into a viscous state rather than liquefying it. • The mechanism of shear thinning of the flow mass plays an important role in the long-runout phenomenon. [ABSTRACT FROM AUTHOR]

Quantifying building vulnerability under landslide run-out impacts is a pivotal aspect of landslide quantitative risk assessment (QRA). The degree of loss of buildings exposed to landslides (i.e., vulnerability) is dictated by the interplay between landslide run-out impacts and the resistance capacity of the building. However, the current link between landslide run-out and building capacity evaluations in landslide QRA is weak. Furthermore, uncertainties regarding both landslide run-out and building response must be quantified via suitable methods to enhance the trustworthiness of vulnerability evaluations. This study proposes a probabilistic framework to evaluate building vulnerability under landslide run-out impacts. The framework comprises a numerical model, which integrates dynamic run-out computations (for simulating the landslide run-out process) and finite element computations (for evaluating the resistance capacity of the building under lateral loading), aiming to assess the damage inflicted on buildings by landslide run-out impacts. Considering the uncertainties of the landslide run-out process and building structural response, a probability density evolution method (PDEM) is employed to calculate the exceedance probabilities of different limit states of building capacities. Ultimately, building vulnerability under landslide run-out impacts is ascertained by combining the probabilities of different damage states with their respective loss ratios. The proposed methodology is illustrated in a scenario where a flow-type loess landslide impacts a five-story reinforced-concrete (RC) frame building. The results indicate that the PDEM effectively estimates the exceedance probabilities with tolerable computational errors. Moreover, the vulnerability results link the failure probability of landslides and the cost of building damage within the QRA framework of individual landslides whose run-out affects nearby buildings. • A probabilistic framework is developed to evaluate building vulnerability under landslide run-out impacts • The uncertainties regarding both the landslide run-out and the building structural response are considered • A probability density evolution method is used to significantly improve computational efficiency • The probabilities of landslide intensities exceeding different levels of building capacities are calculated • Results can be directly employed for quantitative risk assessment of individual landslides [ABSTRACT FROM AUTHOR]

Strong earthquakes can trigger extensive landslides, generating abundant loose deposits that are prone to be remobilized as debris flows by subsequent rainfall events. The magnitude-frequency distribution of post-earthquake debris flows often changes significantly over time. However, the key parameters controlling the post-earthquake debris flow activity and magnitude were poorly understood. In this study, we selected a representative catchment in the Wenchuan earthquake-hit region to study the activity of debris flows from 2008 to 2020, as well as the changes in parameters due to material depletion, grain size coarsening and vegetation recovery. Samples were collected from the field in different years after the earthquake and were tested in the laboratory to obtain their geotechnical properties. A numerical model was improved by considering the changing properties to fit better to dynamic conditions after the earthquake. We found that the particle size of the loose material gradually coarsened, the shear strength showed an increasing trend, while the erodibility coefficient of loose material showed a decreasing trend. The evolution of these parameters controlled the magnitude-frequency of post-earthquake debris flows and also changed their behavior from slope failures in the first few years after the earthquake to concentrated surface runoff erosion (channel erosion) in later years. The results have an important implication for risk assessment and prediction of future debris flows in earthquake-prone regions. • An improved numerical model simulates multiple debris flows after earthquake. • The parameters that control the magnitude-frequency of debris flows chang over time after the earthquake. • The post-earthquake debris flow activity is impacted by source material depletion, grain size coarsening, and revegetation. [ABSTRACT FROM AUTHOR]

Abstract A large amount of debris was generated by the co-seismic mass wasting associated with the 2008 M w 7.9 Wenchuan earthquake. The abundance of this loose material along the slopes caused more frequent debris flows, triggered by less intense and/or shorter rainfalls. However, both the triggering rainfall and the debris flow frequency seem to have normalised progressively during the past decade. Although changes of rainfall thresholds for post-seismic debris flows were recorded after several major earthquakes, the factors controlling these changes remain poorly constrained. With the aid of a virtual experiment, we investigate the roles of material depletion, grain coarsening and revegetation of the co-seismic debris on the propagation and deposition of debris flows initiated by runoff, as well as their influence on the triggering rainfall thresholds. We employ a Geographic Information System (GIS)-based simulation of debris flow initiation by runoff erosion, which we first calibrate on the 14th August 2010 Hongchun gully event that occurred near the Wenchuan earthquake epicentre. We obtain, by investigating each of the aforementioned processes, changing critical rainfall intensity-duration thresholds for given debris flow runout distances. Grain coarsening appears to play a major role, which is consistent with published laboratory experiments, while material depletion and revegetation do not seem able to account alone for the actual quick decay of debris flow frequency. While the virtual experiment has proven useful in identifying the first-order controls on this decay, model improvements and verification over multiple catchments are needed to make the results useful in hazard assessments. Highlights • Soon after the Wenchuan earthquake there was an increase of debris flows and a reduction of the critical rainfall thresholds. • The frequency of remobilisations and the critical rainfall seem to have normalised in 2015. • We analyse the influence of material depletion, grain coarsening and revegetation, of the co-seismic deposits. • We calibrated a physically-based model at Hongchun gully. • Grain coarsening has been found to be the most limiting factor for the generation of debris flows. [ABSTRACT FROM AUTHOR]

Abstract A catastrophic debris flow occurred in Zhouqu County, Gansu Province, Northwestern China, at midnight on 7 August 2010, resulting in damage to >390 buildings. Assessment of the vulnerability of buildings to debris flow hazards is essential to quantify the risk of debris flows. This paper presents a new family of physical vulnerability curves to assess the damage to buildings by debris flows based on extensive observed data of building damage and simulated debris flow intensity. A database of damaged buildings in the affected area of the Zhouqu debris flow was reconstructed. Numerical simulations using FLO-2D were conducted to determine the intensity of debris flows. A series of physical vulnerability empirical models for assessing the building damage has been proposed using various hazard intensity measures. Since buildings of different structural types have different resistances to debris flows, the vulnerability functions were developed for two typical types of structures, i.e. brick-concrete structures and reinforced concrete-frame structures. The proposed vulnerability functions are comparable with those for debris flows in Switzerland, Italy and Austria. The buildings may be completely destroyed when the debris flow depth is more than one half of the building height for both types of building structures. Highlights • A family of new physical vulnerability models has been developed to assess building damage by debris flows. • A database of damaged buildings by the Zhouqu debris flow was constructed. • The intensity of the debris flow was reproduced by numerical simulations. • The vulnerability models relate the degree of building damage to hazard intensity indices. [ABSTRACT FROM AUTHOR]

The 2008 M w 7.9 Wenchuan Earthquake (Sichuan, China) was possibly the largest and most destructive recent earthquake as far as the geo-hazards are concerned. Of the nearly 200,000 landslides triggered originally, many remobilized within a few years after the initial event by rainfall, which often caused catastrophic debris flows. The cascades of geo-hazards related to the Wenchuan Earthquake motivated research worldwide to investigate the triggering and mechanisms of co-seismic landslides, their rainfall-induced remobilization, the generation of debris flows, the evolution of their controlling factors, and the long-term role of earthquakes in shaping the topography. On the eve of the 10th anniversary of the 2008 Wenchuan Earthquake, we present a short review of the recent advances in these topics, discuss the challenges faced in the earthquake-related geo-hazards mitigation practice, and suggest priorities and guidelines for future research. [ABSTRACT FROM AUTHOR]

On 8th August 2017, a catastrophic Ms. 7.0 earthquake with a focal depth of 20 km struck the Jiuzhaigou County in Sichuan Province, China. It exerted a strong influence on the slope stability within the surrounding areas and triggered numerous secondary geohazards including rockfalls and other co-seismic landslides, which incurred drastic surface changes, and thus can be easily identified from cloud-free high-resolution optical imagery. Most of such landslides became stabilized shortly after the earthquake while others moving very slowly for years. In contrast, some slopes were destabilized without significant surface change into slow-moving landslides, which may pose long-term potential threats to people's life and property. Therefore, it is crucial to accurately identify these slow-moving landslides and regularly monitor their post-seismic activity. In this study, we employed the synthetic aperture radar interferometry (InSAR) techniques to detect and monitor slow-moving landslides after the earthquake in the Jiuzhaigou area, and analyzed the impacts of the earthquake on these landslides through integration of multi-source data (InSAR, Lidar, optical image, and field survey). As a result, 16 slow-moving landslides were detected by InSAR in the Jiuzhaigou area, including several historical landslides. The results of time-series InSAR analyses enabled identification of three kinds of landslide evolution modes affected by the earthquake, i.e. acceleration of deformation of pre-existing landslides, reactivation of dormant landslide, and remobilization of earthquake-triggered landslide. Each mode is supported by detailed analyses of multi-source data. The results demonstrated that satellite InSAR combined with high-resolution Lidar and optical data can provide a cost-effective approach of post-earthquake geohazards detection and monitoring. • 16 slow-moving landslides identified by InSAR analyses in Jiuzhaigou earthquake area. • InSAR measurements combined with Lidar DSM and optical image for landslide interpretation. • Effectiveness of slow-moving landslide identification results validated by field survey. • Three types of seismic-induced landslide evolution mode inferred from multi-epoch InSAR results. • Joint analyses of co-seismic and slow-moving landslides revealed earthquake influence pattern. [ABSTRACT FROM AUTHOR]

In mountainous areas of Southwestern China, debris flows occur every rainy season in recent years and have become one of the main threats to human life and properties. After a giant debris-flow event on August 13, 2010 in Sichuan province, the need to deploy a real-time monitoring network and early warning system (EWS) in this region with high potential risk became of paramount importance. This paper, therefore, presents a proposal for a 3D WebGIS-based platform combined with wireless sensor network (WSN) for debris-flow monitoring, analysis of rainfall thresholds for potential debris-flow gullies, and preliminary criteria for automatic and continuous monitoring and alert of debris flows. The choice of a WSN environment simplifies data collection, especially for the combination of various monitoring data provided by different sensor terminals. Warning thresholds stored in the database can easily be modified to improve the prediction of debris-flow occurrence, and there is a user-friendly 3D graphical interface which allows an almost real-time solution for decision-makers. The automatic computer-based EWS applied in the case study proves to be useful for debris-flow early warning, and improvements expected from continuation of this study could ultimately reduce the losses caused by such type of natural hazard. [ABSTRACT FROM AUTHOR]

The construction of mine goafs as an underground reservoir to store and utilise mine water can effectively alleviate the contradiction between coal and water in the arid mining areas in western China. Understanding the effects of water on the mechanical properties and micro-structure of coal is essential for the stability design of coal pillar dams subjected to repeated water erosion. In this study, ultrasonic, X-ray diffraction, scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), and uniaxial compression tests were conducted on coal samples with zero to five dry–wet cycles to investigate the changes in water absorption characteristics, pore structure, microscopic morphology, and mechanical properties as the number of dry–wet cycles, n , increased. Moreover, the connection of the pore structure and microscopic morphology with the mechanical damage was established. The results showed that the peak stress and elastic modulus were negative exponential functions of n. As n increased, the moisture content saturation and homogeneity of the coal sample increased, the number of pores increased, and tiny pores within the coal converted to medium-to-large pores. Further, the peak stress had a good negative linear fit to the porosity and internal damage defined by the integrated area of the T 2 curve. According to the SEM test results, the coal underwent five stages during a dry–wet cycle: uniform and dense original structure, particle aggregation, pore development, fracture sprouting, and overall structural fragmentation, with a gradual decrease in structural integrity. The damage variable, D , was defined by the fractal dimension, F , of the SEM images, enabling the quantitative characterisation of the coal microscopic damage during the dry–wet cycle; moreover, D / F was an exponential function of n. Finally, the damage mechanism of coal samples was interpreted from both macroscopic (i.e. NMR) and microscopic (i.e. SEM) perspectives, and they showed good agreement. Our results could provide a reference for the long-term stability assessment and design of coal pillar dams. • Connection of pore structure/microscopic morphology with coal mechanical properties. • Calculation of coal microscopic damage using SEM image fractal dimension. • Coal damage mechanism explained and verified macroscopically and microscopically. [ABSTRACT FROM AUTHOR]

The extremely strong Wenchuan earthquake triggered thousands of landslides in Sichuan Province, China. Flow-like landslides, such as the Tangjiashan, Wangjiayan, and Donghekou landslides were among the most destructive, causing many casualties and serious economic damage. It is therefore important to identify the flow mechanisms and investigate the specific characteristics of these flow-like landslides. This paper presents a three-dimensional model based on smoothed particle hydrodynamics (SPH) to simulate rapid landslide motion across 3D terrain. The Navier–Stokes equations in a CFD framework are used as governing equations, and artificial viscosity is incorporated into the pressure terms in the momentum equation to dissipate energy to avoid numerical oscillation and particle penetration, thus improving the stability of the numerical results. A non-Newtonian fluid model, the Bingham model, has proven suitable for describing the relationship between the shear strain rate and the shear stress in highly deformed soil materials. In the proposed model it is used as the constitutive model to describe the fluidization characteristics of flow-like landslides combined with the Mohr–Coulomb yield criterion. The model incorporates a no-slip boundary condition, to consider the effect of a solid boundary on slope movement. Ghost particles are created and assigned an artificial velocity. The viscous force caused by the solid boundary is calculated using the relative velocities between the fluid and the boundary particles. Open Multiprocessing (OpenMP), an API for multi-platform shared-memory parallel programming, is used to improve the efficiency of the SPH code running. To show the validity of the proposed approach, a benchmark problem of 3D dam break was simulated. The calculated distances of the surge front at different times agree well with the test results. Numerical modeling of the propagation of the Tangjiashan, Wangjiayan, and Donghekou landslides was performed by the application of SPH models to real flow-like landslides. The whole flow processes of these flow-like landslides across the 3D terrain are represented. The landslides change direction, split or join in, and spread or contract in their flow path in response to the local topography. Time-history curves of the velocity and displacement were obtained to analyze the movement characteristics of the landslide mass. The shapes of the deposition zones after slide occurrence were investigated. Comparisons of the SPH simulated geometry and the surveyed landslide configurations for the Tangjiashan, Wangjiayan and Donghekou landslides were conducted, and show a high degree of similarity. This indicates that the proposed 3D SPH model can accurately represent the evolution of the final slide shape. The prediction of the fluidization characteristics of earthquake-induced flow-like landslides can notably reduce sudden loss of life, as it provides a means for mapping hazardous areas, for estimating the hazard intensity, and for identification and design of appropriate protective measures. [ABSTRACT FROM AUTHOR]

Rapid gravitational flows such as debris avalanches and debris flows may entrain significant amounts of in situ material along their tracks, increasing their volume. Interactions between rapid gravitational flows and bed material are complicated. Especially, the physical mechanism of the fluidization has remained a mystery up to now. To gain a better understanding of the fluidization mechanism and influencing factors, we conducted flume experiments simulating the process of a flow overriding saturated bed material. Results showed that the overriding flow fluidized the bed material into a viscous state rather than liquefying saturated bed material. We also carried out a rheometer test on the saturated bed material. It revealed shear-thinning of the bed material. We deduced that shear thinning, and not liquefaction, was the principal mechanism for bed-material fluidization. Based on these results, a two-layer flow model was proposed using the classical depth-integrated approximation and the Saint Venant equation. It was assumed that both the dry rock avalanche and the impacted saturated bed material behaved as visco-plastic flows with different apparent viscosities. The model's two viscosity parameters were calibrated using the experimental run-out times and distances. We conclude from comparison of the tests and simulations, that our model well simulates the entrainment process. • The overriding flow fluidized the bed material into a viscous state rather than liquefying saturated bed material. • Instead of liquefaction, shear thinning was the principal mechanism for bed-material fluidization. • The proposed two-layer flow model can well simulate the entrainment process. [ABSTRACT FROM AUTHOR]

Abstract: Tests were carried out to investigate some propagation mechanisms involved in rapid, dry, granular flows and to identify factors influencing mass-front velocity in a large flume with two slopes by analyzing image records, as a step in understanding the behavior of rock avalanches. The varied test conditions were gradation and volume of materials, shape and initial arrangement of blocks, consecutive releases, obstacles, and bottom roughness. Flume test results show that the mass-front velocity varied with the characteristics and concentration of particles. The velocity was high and its fluctuation was also great along the upper slope for the cobbles. The velocity increased with the volume for mono-materials. The composite of cubes and gravel with a large volume displayed a rather lower mobility than the mono-material of cubes and of gravel with a small volume. The velocity for the composite of cobbles and gravel with a large volume was almost the same as the mono-material of cobbles and of gravel with a small volume. The velocity also depended on macro- and micro-topography. The velocity decreased by about 25% when the granular flow changed the direction of movement near a concavity for all cases. Two peak velocities were showed in those cases with a convexity. The materials decelerated when it encountered the convexity, and then accelerated greatly after they took a ballistic trajectory from the vertex of the convexity and briefly lost contact with the base of the flume. The mean velocity along the lower slope reduced by 29.4% due to the resistance of a model forest, and increased by 26.2% without matting. [Copyright &y& Elsevier]

Empirically derived rainfall thresholds of debris flows are used for regional-scale early warning. However, triggering rainfall intensities of post-seismic debris flows evolve with time, causing high false alarms since thresholds estimated by conventional methods ignore the uncertainty of non-triggering rainfall events. Based on 172 triggering rainfalls and 2396 non-triggering rainfalls from 2008 to 2013 after the Wenchuan earthquake, we analyzed the evolution of probabilistic rainfall thresholds for post-seismic debris flows using a Bayesian technique. We found, rainfall thresholds significantly decrease compared with pre-earthquake events initially and later tend to increase annually. Meanwhile, the triggering rainfall characteristics tend to gradually change from a short-duration high-intensity pattern to a long-duration and low-intensity pattern. We also checked the effect of antecedent precipitation on debris flows by defining an IET (inter-event time). Our results suggest the antecedent precipitation plays an important role in low-intensity long-duration rainfall-induced debris flows and has little effect on the short-duration high-intensity rainfall-induced debris flows. The characteristics of triggering rainfall for debris flows after the Wenchuan earthquake can be best reflected by IET = 7 h. By employing a Naïve Bayes algorithm, uncertainties of three rainfall threshold models, I-D (mean intensity-duration), I T -D (triggering intensity-duration), and I T -E (triggering intensity-cumulative rainfall) were investigated, and the I T -D model was found to perform best. The characteristics and evolution of debris flow rainfall thresholds over the years after the Wenchuan earthquake was best presented by the Bayesian probabilistic rainfall thresholds. We believe the results can be used to improve the precision of an early warning system for post-seismic debris flows. • We present probabilistic rainfall thresholds for debris flows post-Wenchuan earthquake using a Bayesian technique. • Antecedent precipitation is significant to trigger debris flows by low-intensity long-duration rainfall. • Thresholds significantly decreased post-earthquake, then increased annually, not yet returned to the pre-earthquake level. [ABSTRACT FROM AUTHOR]

The input parameters of dynamic numerical models for landslide run-out distance simulations cannot be measured accurately, which results in significant uncertainties in the predictions obtained using these models. To address this issue, a novel framework combining probabilistic back analyses and probabilistic predictions of landslide run-out distance is developed in this study, with the aim of ensuring the reliability of run-out predictions in risk assessments. First, a probabilistic back analysis method is applied to calibrate the input parameters and quantify their uncertainties; the calibrated parameters are then used for a probabilistic forward run-out prediction. Unlike the trial and error calibration approach, the back analysis method is implemented probabilistically by modeling the input parameters as random variables and efficiently improving their distributions through Markov chain Monte Carlo-based Bayesian inference using the observed run-out distance of a previous landslide event. These improved posterior distributions are employed to obtain the run-out distance exceedance probability curve of a potential landslide similar to the previous event; this curve can be used to estimate the probability of the run-out distance being exceeded at different locations along the landslide's path. By selecting different threshold values for the exceedance probabilities, a landslide hazard zoning map can be generated, serving as a valuable tool for landslide risk assessment and management. Moreover, a Kriging-based surrogate model is used to approximate the dynamic numerical model employed in this study, which significantly improves the computational efficiency of the proposed methodology. Finally, two sequential landslides that have occurred in the Heifangtai terrace of Gansu Province, China, are considered as a case study to demonstrate the performance of the proposed methodology. • Propose a probabilistic framework for reliable landslide run-out distance modeling. • Probabilistically calibrate the numerical model using observed run-out distance. • Assess landslide run-out distance exceedance probability with the calibrated results. • Kriging-based surrogate model significantly improves computational efficiency. • Results can be employed in quantitative risk assessment of individual landslides. [ABSTRACT FROM AUTHOR]

Landslides are one of the commonly natural disasters triggered by rainfalls, earthquakes, and human activities, which cause fatalities, damage to properties, and economic losses in the world. Early warning method may predict landslide occurrence and reduce the risk. In this paper, we propose a self-developed site-specific landslide early warning system (LEWS), which has been progressively designed and accomplished over the past decade in Southwest China. The warning model for the prediction of slope instability is focused on multiple thresholds, including deformation rate, rate increment and tangential angle related to surface displacement measurement. The debris-flow initiation is determined by critical rainfall thresholds integrated with the topographic and geological conditions at a catchment scale. The recent Xingyi rockslide, Baige debris slide and debris flows in Zoumaling catchment are selected to explain the specific process of landslide early warning in a real-time operating system. The performance of the presented warning system is evaluated by comparison with the inverse-velocity model (INV) and gradient model (SLO) in the prediction of slope failure time. The Receiver Operator Characteristic (ROC) analysis is used to prove its feasibility and reliability in the debris-flow initiation prediction. The presented warning model and system can be applied to other regions in landslide early warning and to be useful to mitigate landslide losses and damages. • Provide a successfully real-time landslide early warning system. • Warning model and warning system can be applied in an emergency response to mitigate landslide losses. • Comparing with the SLO, INV model and using ROC analysis to evaluate the performance of the warning system. [ABSTRACT FROM AUTHOR]

Devastating landslides were frequently triggered by earthquakes and caused severe damage and human losses. More than 25,000 people were killed by the Wenchuan earthquake-induced landslides. A proper model for estimating loss of lives is important in quantifying the human risks posed by earthquake-induced landslides. This paper presents a new model for quantitatively estimating the human vulnerability to earthquake-induced landslides using Bayesian networks. A database incorporating information of fatal landslides induced by the Wenchuan earthquake is established. A Bayesian network is constructed according to a logic structure of loss-of-life mechanisms by considering four types of key factors, i.e., deposit thickness, building damage, evacuation, and resistance capacity. The probabilities of the nodes (factors) and the arcs (inter-relationships) of the network are quantified according to statistical data, judgment based on experiences, and existing physical or empirical models. The human vulnerability to earthquake-induced landslides is quantitatively estimated through constructing a systematic structure considering the uncertainties of the control factors and their inter-relationships. Comparison between the recorded fatality rate and predicted fatality is conducted to verify the proposed model. Finally, sensitivity analysis is conducted to identify the most important parameters that lead to loss of lives. • A database of fatal earthquake-induced landslides in the Wenchuan earthquake area was constructed. • A vulnerability model for assessing the loss of lives by earthquake-induced landslides has been developed. • The vulnerability model relates the human resistance capacity, evacuation and time to hazard intensity indices. • The human fatality rate can be quantified using Bayesian networks based on the fatal landslide database. [ABSTRACT FROM AUTHOR]

Under rainfall conditions, the characteristics of hydraulic changes related to the failure evolution of fill slopes are critical to the early warning of slope failure. In this study, a series of model tests are carried out on loess fill slopes with different slope types. The matric suction, volumetric moisture content, pore water pressure and deformation of the slope are monitored in real time during the rainfall process. Meanwhile the development of cracks and the failure modes of the slope are analyzed, and then the early warning strategy of fill slope failure induced by rainfall is studied. The results show that loess landslides induced by rainfall exhibit a hysteresis. However, the volumetric water content and the matrix suction respond earlier than the pore water pressure. The slope failure is produced when the volumetric water content and the matrix suction are respectively at their maximum and minimum values. The evolution mechanism of cracks on the slope starts when tensile cracks are first generated near the leading edge surface and then extend backwards. In the next stage, shear fracture is produced near the flanking of the slope and finally, the trailing edge produces a transfixion tensile crack from the top to toe of the fill slope, which not only provides the advantage of an infiltration channel to control the hydrological process, but also evolves into the trailing edge boundary of each failure of fill slope. With the increase of rainfall duration, the filling slope presents different failure characteristics, revealing the hydraulic behavior of a partially saturated slope. In addition, combined with the infinite slope stability analysis in Mohr–Coulomb soil, the matrix suction and volumetric water content thresholds of the fill slopes with different slope angle are determined. The early warning threshold model for rainfall induced slope instability is proposed and a new framework of early warning is provided. • Model testing in the loess fill slope with typical slope shapes (such as nearly vertical and terraced) induced by rainfall has been conducted for the first time. • It is observed that the tensile cracks on the top of the fill slope control the hydrological process and evolve into the trailing edge boundary of each failure. • It is important to note that the sliding surface of the overall failure is not the interface between the fill slope and original slope. • It is concluded that the critical matric suction, critical volumetric water content, and early warning threshold model of the fill slope can be a reliable approach for failure forecast. [ABSTRACT FROM AUTHOR]

A large and catastrophic rock avalanche occurred at the Xinmo village in the Maoxian county of the Sichuan province of China on June 24, 2017. The avalanche destroyed 64 houses and killed 10 people, and 73 people were reported to be missing. In this study, we focused on the contributions of six historical earthquakes to the collapse of rocks in the source area and the landslide amplification caused by the entrainment of pre-existing deposits on the landslide path. The historical earthquakes in this area contributed different levels of damage on the source rocks; particularly, the 1933 Diexi earthquake induced a few initial cracks in rocks at the crest of the steep hillslope. Under the combined time-effects of long-term weathering and gravity, the rock blocks in the source area were detached from the crest along the intersecting cracks and over-dip soft layer (namely, the sliding surface). The avalanche was amplified by the entrainment of colluvium on its path. The influence of the colluvium on the movement process of the Xinmo landslide was modelled by the GPU-based parallel discontinuous deformation analysis (DDA) method, and the effect of the impact and entrainment in the debris flow was rigorously analysed. The results indicate that the impact and entrainment can continuously increase the volume of debris flow, and the thickness of the colluvium was established to be in the range of 25.9–33.9 m based on the analysis of the deposit pattern and movement duration of the avalanche. There were numerous unstable rocks induced by historical earthquakes, at the crests of steep hill slopes in the earthquake-stricken area. With long-term damage caused by environmental factors and gravity, the failure of unstable rocks with high potential energy is likely to cause severe disasters. The excess pore water pressure likely to be present in the colluvium or deposits during impact and entrainment can considerably reduce the effective stress and degrade friction resistance along the runout path. As a result, the landslide can be intensively amplified owing to the effect of impact and entrainment under a lower friction resistance • The volume of rock avalanche sharply increased by entrainment effects. • The rocks at the source were damaged by historical earthquakes. • The colluvium exerts different influences on the movement of the avalanche with an increase in its thickness. • Numerous earthquake-damaged rocks at the summit of mountains are hazardous. [ABSTRACT FROM AUTHOR]

The Huangnibazi landslide in Li County of southwest China, began to slide rapidly since 8 August 2017. It received little attention before the failure event. The fast motion of the slope posed great threats to the safety of nearby villages and the national highway G317 at the foot of the mountain. In this study, Synthetic Aperture Radar (SAR) datasets collected by C-band Sentinel-1 and X-band TerraSAR-X (TSX), as well as optical images acquired by Sentinel-2 Multi-Spectral Instrument (MSI) over the landslide site were analyzed to characterize the evolution of the slope before and after the failure event. Firstly, the surface change of the sliding area was qualitatively evaluated using the Sentinel-2 true-color images and pseudo-colored TerraSAR-X amplitude images. Next, the slow movement of the slope before the failure event was detected by interferometry using both TerraSAR-X and Sentinel-1 data stacks. The maximum displacement rate estimated was larger than −45 mm/year along the radar line of sight (LOS) direction. Finally, the large post-failure displacements of the landslide were successfully retrieved with meter-level accuracy from TerraSAR-X observations using adaptive amplitude offset tracking method. The maximum displacement decreased from about 30 m in 11 days in August 2017 to 1–2 m in 22 days in January 2018 in both LOS and azimuth directions. According to the recent measurements of surface displacement, the landslide body is becoming stabilized gradually, which suggests that the risk of catastrophic collapse of the slope has been largely reduced. • Failure-induced slope surface changes revealed by Sentinel-2 and TerraSAR-X images. • Pre-failure landslide surface displacements detected by time series InSAR analyses. • Large post-failure displacements retrieved by adaptive POT from TerraSAR-X images. • Time series post-failure displacements suggest reduced risk of catastrophic collapse. [ABSTRACT FROM AUTHOR]