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Typhoons are recurring meteorological phenomena in the southeastern coastal area of China, frequently triggering debris flows and other forms of slope failures that result in significant economic damage and loss of life in densely populated and economically active regions. Accurate prediction of typhoon-triggered debris flows and identification of high-risk zones are imperative for effective risk management. Surprisingly, little attention has been devoted to the construction of physical vulnerability curves in typhoon-affected areas, as a basis for risk assessment. To address this deficiency, this paper presents a quantitative method for developing physical vulnerability curves for buildings by modeling debris flow intensity and building damage characteristics. In this study, we selected the Wangzhuangwu watershed, in Zhejiang Province of China, which was impacted by a debris flow induced by Typhoon Lekima on August 10, 2019. We conducted detailed field surveys after interpreting remote sensing imagery to analyze the geological features and the mechanism of the debris flow and constructed a comprehensive database of building damage characteristics. To model the 2019 debris flow initiation, entrainment, and deposition processes, we applied the Soil Conservation Service-Curve Number (SCS-CN) approach and a two-dimensional debris flow model (FLO-2D). The reconstructed debris flow depth and extent were validated using observed debris flow data. We generated physical vulnerability curves for different types of building structures, taking into account both the degree of building damage and the modeled debris flow intensity, including flow depth and impact pressure. Based on calibrated rheological parameters, we modeled the potential intensity of future debris flows while considering various recurrence frequencies of triggering rainfall events. Subsequently, we calculated the vulnerability index and economic risk associated with buildings for different frequencies of debris flow events, employing diverse vulnerability functions that factored in uncertainty in both intensity indicators and building structures. We observed that the vulnerability function utilizing impact pressure as the intensity indicator tends to be more conservative than the one employing flow depth as a parameter. This comprehensive approach efficiently generated physical vulnerability curves and a debris flow risk map, providing valuable insights for effective disaster prevention in areas prone to debris flows. [ABSTRACT FROM AUTHOR]

This paper aims to provide a framework for simulating the formation process of melt-driven debris flow for use in the risk assessment of hazard. According to field research, the formation process of melt-driven debris flows consists of three stages including snow melting, soil infiltration, and runoff/debris flow propagation. From this point of view, an integrated model of melt-driven debris flows is developed, coupling three corresponding physical models through some common variables while considering the effects of temperature variations and entrainment. For the evaluation of the erosion rate of loose materials while considering the presence of fine particles, a relationship between critical shear stress and surface fine-particle proportion is introduced. This integrated model is employed to retrospectively analyze the formation process of the 2010 melt-driven debris flows in the Tianmo catchment, China. The numerical results show that the melt-driven debris flow formation process is effectively described by reproducing the behaviors at each stage based on the proposed model. Furthermore, the hourly temperature variation and sediment characteristics (e.g., coarse particle size and initial soil moisture content) are discussed in detail as factors affecting runoff and entrainment. [ABSTRACT FROM AUTHOR]

As the global climate warms, the frequency of soil slope failures induced by snowmelt is gradually increasing, especially loess landslide disasters in seasonally frozen areas. Landslide disasters in seasonally frozen areas pose a serious threat to human lives and engineering constructions and are gradually drawing greater public attention around the world. However, the mechanism that regulates deformation and failure processes, resulting in snowmelt-driven landslides, remains elusive. The Yili River Valley in Xinjiang, China, is an ideal location for exploring the mechanism of snowmelt-driven landslides. Based on detailed field surveys, remote sensing image identification, meteorological data analysis and loess characteristic tests, this paper takes a representative high-level loess landslide in north-west China as a case in order to explore its evolution history, movement process and resurrection mechanism. It was found that this loess slope had suffered two large-scale sliding failures and different degrees of inherited slope deformation had been found between the two slope failures. The 32 surface cracks identified have a total length of 3,505.10 m, and the total area of the landslide was found to be 135,462m2. The average thickness of the sliding body was about 30 m, and the volume was approximately 504,000 m3. The actual movement time lasted for 32 s with an average moving speed of about 15 m/s. Human grazing activities dominate the formation and development of slope surface cracks in the early stage. The strong water sensitivity of distinctive loess controls soil strength deterioration in the slip zone. Rapid snow removal and infiltration, driven by an abnormal temperature rise in Spring, is the most important triggering factor for slope deformation, evolution and failure. As regional grazing activities increase and global warming intensifies, the potential for resurrection landslides will increase. The results provide essential information for a comprehensive understanding of early warning systems and risk assessment for snowmelt-triggered landslides in cold areas. [ABSTRACT FROM AUTHOR]

Landslide disasters are associated with severe losses on the Loess Plateau of China. Although early warning systems and susceptibility mapping have mitigated this issue to some extent, most methods are qualitative or semi-quantitative in the site-specific range. In this paper, a quantitative spatial distribution model is presented for site-specific loess landslide hazard assessment. Coupled with multi-temporal remote sensing images and high-precision UAV cloud point data, a total of 98 loess landslides that have occurred since 2004 on the Heifangtai terrace were collected to establish a landslide volume-date and retreating distance database. Eleven loess landslides are selected to construct a numerical model for parameter back analysis, and the accuracy of the simulation results is quantitatively evaluated by the centroid distance and overlapping area. Different volumes and receding distance rates of landslides are fitted to determine the relationship between cracks and potential volume, and different volumes and parameters are combined to simulate the spatial distribution of potential loess landslides. The results of this study reveal that landslide volumes mainly range between 1 × 103 and 5 × 105 m3, and the historical occurrence probability reaches 0.551. The optimal parameters are estimated by the maximum likelihood method to obtain a uniform distribution parameter value probability model, and the results show that the error of the estimated length within a range of 0.05 from the optimal parameter does not exceed 15%. In the selected slope slide case, farmland near the toe of the slope primarily includes exposed hazards with probabilities greater than 0.7. This work provides a useful reference for local disaster reduction and a theoretical methodology for hazard assessments. [ABSTRACT FROM AUTHOR]

Mitigation works are very essential for mitigation of debris-flow hazards in mountainous areas. Usually, it is difficult to assess the effectiveness of existing mitigation works in a catchment. This paper presented a method for quantitative assessment of debris flow mitigation measures by using Kanako system, a user-friendly GUI-equipped debris flow simulator that allows good visualization and easy interpretation. Kanako 2D (Ver. 2.04) was applied to a case study at Caijia Gully, Sichuan Province, China. Mitigation works including check dams, drainage channel, and deposition basin were constructed in the gully in 2001 and 2006. Kanako 2D can simulate debris flow from steep area to alluvial fan. 1D simulation was applied for assessing the effect of the check dams at the lower part of the gully, and 2D simulation was applied for the effect of the drainage channel and deposition basin on the alluvial fan. The simulation results indicate that debris flow will cause great damage to residential area on the alluvial fan if mitigation measures were not implemented in the gully. For old dams which have been filled up with deposits of previous debris flows, the results show that they still have the function for controlling debris flow due to the gradient reduction of the channel bed in front of the dams by the trapped debris flow deposition. After the comprehensive control of debris flow including trapping, drainage, and deposition in the gully, the simulation results indicate that the risk on the alluvial fan can be reduced to an acceptable level. [ABSTRACT FROM AUTHOR]

During the dry season of December 2020, two sliding subzones of the Qingliu landslide in southwest China slid out of stability, severely damaging the buildings on the slope. To investigate the mechanism and movement of landslides in the dry season, we employed high-resolution unmanned aerial vehicle mapping, electrical resistivity tomography, on-site union boreholes, groundwater detection, deep displacement monitoring, and numerical simulation to analyze the deep geotechnical structural characteristics, groundwater runoff paths, and destabilization range and movement processes at different times. Preliminary analysis showed that the slow infiltration of rainwater during the rainy season and infiltration of snow melt in winter, topography, and loess clay layers of the slide zone type are related to the triggers of landslide instability. Four layers of rock-soil stratification interfaces with different resistivity values, revealed by electrical resistivity tomography, comprising loess-like pulverized clay, gravelly pulverized clay, and bedrock, existed at different burial depths in the longitudinal section. Borehole and displacement monitoring revealed the existence of a primary slip surface and several secondary slip surfaces, with an average thickness of 16–22 m and a maximum daily displacement at the slip surface of approximately 2.29 mm. The deepest groundwater level of the water-bearing section in the borehole was 25.8 m, and it percolates and drains through fractures in the loess-like layer. Startup acceleration, deceleration pileup, front-edge pileup stopping, and middle- to rear-edge pileup stopping are the four primary discrete element simulation movement phases. The findings help deepen the understanding of similar dry-season landslides and their disaster-causing effects. [ABSTRACT FROM AUTHOR]

The Longxi river basin with the city of Dujiangyan, in the Sichuan province of South West China, belongs to the seismic area of the May 12, 2008 Wenchuan earthquake. Lots of loose co-seismic materials were present on the slopes, which in later years served as source material for rainfall-induced debris flows. A total of 12 debris flows, were triggered by heavy rainfall on August 13, 2010 in the study area. The FLO-2D numerical analysis software was adopted to simulate debris flows intensity, including movement velocities and maximum flow depths. A comparison of the measured fan spreading with the simulation results, the evaluation parameter Ω was used to verify accuracy of simulation, the results show Ω values ranging between 1.37 and 1.65 indicating relative good simulation results. This study also estimated the flood hydrograph for various recurrence intervals (20, 100, and 200 years, respectively) to perform scenario simulations of debris flows, and followed Swiss and Austrian standards to establish a debris flow hazard classification model on the basis of a combination of the debris flow intensity and the recurrence period. This study distinguishes three hazard classes: low, medium, and high. This proposed approach generated a debris flow hazard distribution map that could be used for disaster prevention in the Wenchuan earthquake-stricken area, South West China. [ABSTRACT FROM AUTHOR]

Massive rockslides are recognized as one of the most catastrophic hazards due to their rapid sliding velocity and high destructiveness. This study focuses on the progressive failure analysis of translational rockslides (PFTRs) on a cataclinal dip slope, whose shear failure develops mainly along the bedding plane of the underlying strata from the head to the toe of the rockslide. A force and energy equilibrium-based analytical method (FEE) is proposed, combining shear failure propagation and strength degradation, to analyse the stability based on static equilibrium and displacement based on energy equilibrium. A representative translational rockslide, the Shanshucao landslide in the Three Gorges Reservoir, China, is used as a case study. The results of the FEE are validated by comparison with the revised rigid limit equilibrium method (RLEM) and numerical simulation (NS). According to the RLEM and NS, when the shear failure of the slide surface develops to a position with a horizontal distance of approximately 225 m, the rockslide steps into the critical state from partial progressive deformation to failure of the entire rockslide. The FEE obtains a similar result, and the corresponding horizontal distance is 200 m. The rockslide displacement calculated by the FEE agrees well with the results of the NS. Before the critical state, the rockslide displacement is less than 0.05 m; afterwards, the displacement of the entire rockslide obviously increases. In addition, it is proven that the hydrostatic pressure in subvertical tension cracks and the post-failure shear surfaces are the primary impetus for accelerated deformation of rockslides and further development of failure surfaces. The validated results indicate that the FEE is a straightforward and effective method to analyse both the stability and displacement of PFTR, which is significant for rockslide early warning and risk mitigation. In addition, the FEE still has limitations with regard to generalization of the landslide geo-mechanical model and the method validation with observational data of historical events. [ABSTRACT FROM AUTHOR]

The Hongshiyan rock avalanche is a remarkable landslide disaster with approximately volume of 12 × 106 m3, triggered by the 2014 Ms. 6.5 Ludian earthquake in Yunnan Province, China. This study conducted a comprehensive analysis by the model based on discrete element (DEM-based) numerical simulation to understand the transport process and mechanism for this rock avalanche. The simulation results showed that the transport process of the rock avalanche depends on the input seismic duration and motion. The average velocity of the rock avalanche sharply increases to peak value of 27 m/s and then gradually decreases to zero, and 64% and 36% of the total energy are dissipated by collision and friction, respectively. In this process, the progressions from simple disintegration along pre-existing discontinuities to fragmentation that creates new fracture surface are documented, and gradual increase of the fragmentation degree over time results in the decrease of fragment size and the formation of well-graded and narrower-interval gradation. This fragmentation evolution creates a conductive condition to the development of internal shear, and is closely associated with the dense flow regime that dominates the main body of the rock avalanche but presents discontinuous distribution along the flow thickness direction. In addition, further analyzing the simulated results indicates that more likely effects of fragmentation on mobility of rock avalanches depend on fragmentation-induced special flow structure, which makes a rock avalanche in a flow state with lower friction and lower energy consumption. [ABSTRACT FROM AUTHOR]

On January 27, 2021, a small-scale loess landslide occurred in Dangchuan Village, Yongjing County, Gansu Province, China. Timely monitoring and warning helped to prevent any casualties. The sliding mass of the Dangchuan landslide fell in two stages with an interval of 24 s and lasted for a total of 31 s. Eventually, the Dangchuan landslide had a descent height of approximately 120 m and a sliding portion stretching approximately 350 m. The landslide volume was approximately 3 × 104 m3. Based on the investigation of different stages of the Dangchuan landslide and the characteristics of the deposition area, the induction of this landslide was attributed to the effect of frozen stagnant water. Following field investigation of the landslide source and crack areas, a potential sliding mass model with a volume of 5 × 104 m3 was obtained via calculation. To predict the disaster scope of potential landslides, we first used DAN3D software to invert this Dangchuan landslide. Then, based on the numerical model parameters obtained from the inversion, the sliding accumulation process of the potential slide mass was simulated. The results showed that the maximum disaster scope of the potential slide mass would be larger than that of the Dangchuan landslide. The new deposit would cover an area of approximately 3.5 × 104 m2, with a thickness in the range of 0–6 m. The new deposition area would expand by approximately 50 m in the long-axis direction compared to the Dangchuan landslide, impacting the houses and roads. The DAN3D prediction results of the disaster scope will help residents in the potential danger zone evacuate in advance, reducing unnecessary damage. [ABSTRACT FROM AUTHOR]

Runout prediction and deposit characteristics investigation for the long runout rock landslides are challenging and interesting problems nowadays. On a practical level, the landslide is a critical issue around the world which could lead to catastrophic consequences. One of the current typical instances is the successive Baige landslides in Tibet, China, where massive damages to infrastructure constructions led to evacuation of more than 86,000 people. The work is specially aimed at investigating the dynamic behaviors of the long runout rock landslides and predicting the potential impact region by numerical simulations. The focus is on the representation of the interaction between the constituent blocks and macro-scale response of landslides. In this case, the distance potential-based discrete element method is adopted to solve the above problems and reproduce the sliding process of the Baige landslides. Before applied in modeling the Baige landslides, performances of this method are firstly validated by two well-known benchmark experiments. The simulation results agree well with the existing experimental measurements and reported observations. It is proved that the method could predict a quantitative accumulation area of related landslides and provide a reference of hazard mitigation. [ABSTRACT FROM AUTHOR]

The damming of rivers by landslides resulting in the formation of a lake was one of the typical secondary geological hazards triggered by the Wenchuan earthquake which occurred on May 12, 2008. Some landslide-dammed lakes were at a high risk of causing further damage since the rainstorm season was expected soon after the earthquake. Understanding the dynamic processes in the formation of landslide-dammed lakes is helpful in planning the mitigation measures. The Yangjiagou landslide-dammed lake was selected as a case study to investigate the typical processes of dam formation. The dynamic simulation of the formation of the Yangjiagou landslide-dammed lake was divided into two steps: the landslide step and the overflow/overtopping step. Two-dimensional discrete element method (DEM) was adopted to investigate the mechanics of the Yangjiagou landslide. The landslide process was found to be controlled by the bond strength and residual friction coefficient of the DEM models. Computational results show that the formation of the landslide dam took approximately 35 s. The maximum velocity of a typical particle was approximately 26.8 m/s. The shallow-water equation and finite difference method were used to analyze the hydrodynamic mechanisms of the overflow process of the landslide-dammed lake. Computational results show that overflow would have occurred 15.1 h after the river was blocked, and overtopping failure occurs for the landslide dam in the rainstorm season when the water flow is large enough, causing a major disaster. [ABSTRACT FROM AUTHOR]