Landslide Mobility Research Articles

The 3rd Hutchinson lecture: numerical modelling of forests with uprooting as a nature-based solution to mitigate flow-type landslides

AbstractTo protect human lives and infrastructure in mountainous regions from flow-type landslides, engineered countermeasures, such as rigid and flexible barriers, are installed along predicted flow paths. Over recent years, research efforts in physical and numerical modelling have helped advance the understanding of impact mechanisms involved and enabled the optimization of the design of engineered solutions. With the advent of sustainable engineering, attention has shifted towards the use and development of nature-based solutions to impede flow-type landslides. A simple nature-based solution is to consider the effects of forests on the mobility of flow-type landslides. However, to leverage forests, the complex flow-stem interactions and effects of uprooting need to be captured. In this paper, details and results of a new GPU-empowered MPM-LSDEM numerical solver that simulates the effects of flows through tree stems that can uproot are presented along with systematic evaluation of the solver. Simulations of flow-forest interaction with and without uprooting show that forests have profound effects on flow forest interaction. For dense forests, uprooted stems can push flow material to enhance its runout distance. Additionally, uprooted stems tend to concentrate near the front of the flows even if they were evenly distributed throughout the model forest at the beginning. The impact force exerted by a stem can be considered concentrated loading and can damage barriers along the flow path. Taken together, hazard assessment tools that can model the effects of uprooting are crucial to close predictions of hazard extent (i.e., runout distance) and the design of physical countermeasures such as barriers.

Hypermobility of a Catastrophic Earthquake-Induced Loess Landslide

Landslide mobility refers to how far and fast a landslide can move downslope. It controls landslide impact areas and damage power. Highly mobile landslides are often initiated on slopes steeper than 30°. However, on 18 December 2023, an earthquake-induced landslide (35°52′54″N, 102°51′10″E) exhibited extraordinary mobility, with an overall travel angle of 1.5°, breaking an on-land landslide record. The landslide originated on a gentle slope (3.6°), eroded an earth dam along its travel path, and finally destroyed 51 houses and claimed 20 lives. Remote sensing and field surveys were conducted to provide morphological characteristics of the hazard chain. A numerical program, EDDA (Erosion–Deposition Debris Flow Analysis), was employed to reproduce the flow dynamics and investigate the causes of hypermobility. The findings reveal three primary causes of hypermobility: (1) liquefaction of the saturated silty loess stratum due to the combined effects of irrigation activity and seismic loading, (2) the loose and macro-pore structure of loess, and (3) confined topography and icy channel bed. The mechanisms revealed have broad implications for understanding fluidized mass movements on gentle slopes in seismically active regions.

Assessing the influence of temperature on slope stability in a temperate climate: A nationwide spatial probability analysis in Italy

Among landslide controls, the role of temperature in temperate regions remains poorly understood. Experiments revealed thermo-hydro-mechanical effects in geomaterials; however, field evidence of temperature-controlled landsliding is scarce. This complexity hinders the formulation of a temperature-related variable, useable in modelling across scales. Here, we identified spatial correlations between temperature and shallow landslides in gentle clay slopes. Notably, the temperature in the shallow underground is controlled by that of the atmosphere, and clays are the most sensitive to temperature among all geomaterials. Exploiting the Italian Landslide Inventory, we constructed a slope unit-based Generalised Additive Model and utilised Land Surface Temperature (LST) data from MODIS, accessible in Google Earth Engine. Interestingly, we observed a stronger positive correlation between landslides and LST, particularly in southern Italy, where categorised widespread shallow instabilities are common. Although more experiments and site-specific studies are warranted, the observed pattern appears consistent with thermal soil weakening, which may enhance landslide mobility.

Granular Scaling Approach to Landslide Runout.

A main objective in landslide research is to predict how far they will travel. Landslides are complex, and a complete understanding in principle requires accounting for numerous parameters. Here we engender a simplification by investigating the maximum landslide runout using granular laboratory experiments and a scaling analysis. We find that correctly accounting for the fall height and grain size distribution not only yields an improved correlation of normalized runout, but also quantitatively unites laboratory and field data. In particular, we find that the mobility of landslides increases with the square root of the fall height and with the skewness of the grain size distribution.

On the undrained shear behavior of sand mixtures with non-plastic fines subjected to large shear displacement

Fluidized landslides pose significant hazards owing to the catastrophic failure and flow-like behavior with high mobility and long traveling distances. Non-plastic fines can be abundant in many fluidized landslides with 30%–40% content of relatively fine-grained particles. However, the role of fine particles in the initiation and movement of these landslides is not well understood. To investigate the effects of non-plastic fines content (FC) on the undrained shear behavior of the mixture, undrained ring shear tests were performed on mixtures of silica sand (D50 = 0.16 mm) with varying weight proportions of non-plastic fines (D50 = 0.035 mm) with different initial densities. We showed that liquefaction potential increased as fines content increased and initial density decreased. Peak strength (τp), steady-state strength (τss), and total dissipated shear energy to the steady state (Wss) increased against increasing density of the sample. Given the same initial density, τp, τss, and Wss decreased with the increases of FC. Using intergranular void ratio (es) and equivalent intergranular void ratio (es⁎), we found that plots of τp, τss, and Wss against es⁎ merged to a relatively narrow domain, indicating es⁎ can serve as a comprehensive indicator for evaluating the FC's effects on undrained shear behavior. An optimum es⁎ existed for the mixtures, which corresponds to the minimal brittleness index IB, that is used for analyzing liquefaction associated with post-failure behavior. The Wss in the log scale continuously decreased with increasing es⁎. We inferred that the addition of fine particles could change the inter-particle force transfer. When the FC increases, a greater proportion of fines can actively engage in the forces transferring structure as active fine particles, resulting in increasing liquefaction potential and reducing the energy dissipation throughout the entire shearing process of the saturated mixtures, thereby facilitating the fluidization and mobility of landslides. This study provides an evaluation of the full liquefaction process of fines-rich mixtures and further explains the fines' role in the high mobility of fluidized landslides based on the energy dissipation view.

Energy evolution of gravitational-granular flows

The catastrophe of natural disasters such as landslides, is a prevalent phenomenon in natural terrain conditions in high mountainous areas; however, the mobility of such landslides has not yet well understood due to the discrete nature of material and the coming to play of water. In this paper, we numerically study the mobility of an unsaturated gravitational-granular flow, occurring on a slope-break system that contains two regions: inclined-upstream and horizontal-downstream areas, by using three-dimensional discrete element simulations. A sliding volume composed of spherical grains collapses on the first region, then plunges and deposits on the second one. The upstream-plunging length and the cohesive stress exerted on grains affect differently on the energy evolution not only in the whole process but also in different regions and directions depending on the inclination angle. These findings provide a deep understanding of the mechanism and mobility of landslides, leading to good predictions about the potential impacts of the catastrophic landslides on buildings and human lives.

Assessing the influence of non-plastic fines on rainfall-induced landslide initiation and propagation: Flume test findings

Numerous fluidized landslides with long runout distances and fast movements have been triggered by heavy rainfall under climate change. Non-plastic fines are frequently involved in many fluidized landslides. However, the role of fines in the initiation and movement of landslides has not been well understood. This study aimed to investigate the role of non-plastic fines in the initiation and movement of rainfall-induced landslides in a flume test setup. The experiments were conducted using mixtures of silica sand (D50 = 0.16 mm) with different non-plastic fines (D50 = 0.035 mm) content under different initial densities. The results demonstrated that the behavior of landsliding greatly depends on fines content (FC) and initial packing density (presented by density index, Id) of the soil layers in the flume. The landsliding phenomena could be classified into five failure modes, including slow and fast retrogressive individual sliding, sudden multiple sliding, and deep-seated and shallow fluidized sliding. As the FC increased or Id decreased, the landsliding behavior gradually evolved from slow retrogressive individual sliding to shallow fluidized sliding. For the tests with Id ≥ −0.06, the peak velocity (Vp) of the landsliding increased continuously with FC. Conversely, for the tests with Id ≤ −0.19, an optimal FC of 30 % was identified at which Vp reached its maximum. Additionally, for FC ≤ 10 %, Vp decreased with the increasing Id, while for FC ≥ 20 %, an optional Id existed at which Vp reached its maximum for a given FC, and the value of optimal Id (−0.2 ∼ −0.04) varied with FC (20 % ∼ 40 %). The peak pore-water pressure (PWP) (up) generally increased with the increase of FC. Furthermore, an optimal Id existed at which the PWP built up after landsliding occurrence (Δu) reached its maximum. The equivalent intergranular void ratio (es*) and equivalent interfine void ratio (ef*), which are calculated by considering both FC and void ratio, are found to be appropriate indices for evaluating and explaining the role of fines in the observed landsliding behavior. In conclusion, the addition of non-plastic fines can change the structure of test materials and result in different failure modes and mobility of landslides by affecting both interparticle contacts and PWP responses. These findings provide insights into the mechanisms of landsliding behavior and have implications for the assessment and mitigation of landslides in geotechnical engineering.

Mechanism and numerical simulation of a rapid deep-seated landslide in Van Hoi reservoir, Vietnam

At approximately 5:00 AM on December 16, 2016, a rapid and deep-seated landslide was triggered by intense rainfall in the Van Hoi irrigation reservoir in Binh Dinh province, Vietnam. The landslide generated an impulsive wave with a height of approximately 20 m, resulting in severe damage to the reservoir operation station. This study investigated the mechanisms behind the landslide's initiation and simulated its initiation and motion processes through site surveys, ring shear tests, and the LS-RAPID simulation model. The physical tests were conducted on two soil samples from the sliding zone to examine the landslide mechanism. The results indicated that only sample 2 (a sand sample of completely weathered gneiss rock) showed a high level of landslide mobility due to its liquefaction phenomena resulting in a rapid pore water pressure development and a significant strength loss.
 In contrast, sample 1 (a silty sand sample of residual soils) did not exhibit this behavior due to its high shear resistance value at a steady state. The findings suggest that the sliding plane of the Van Hoi landslide formed in the completely weathered gneiss layer, and the high mobility level of sample 2 is primarily responsible for its rapid movement. Notably, the LS-RAPID model successfully reproduced the landslide process using the geotechnical properties obtained in the ring shear experiments. The simulation showed that the Van Hoi deep-seated landslide was initiated from the lower middle slope at a critical value of 0.55 for the pore water pressure ratio and traveled at a high velocity of approximately 37.0 m/s. The consistency between the computer simulation results and the on-site evidence and recorded data highlights the reliability of the LS-RAPID model as a tool for assessing landslide hazards.

Power laws for accurate determination of landslide volume based on high-resolution LiDAR data

Landslide volume is critical in landslide risk management due to its close association with the landslide mobility and damage to elements at risk. Limited by accessibility, site conditions and availability of equipment, directly measuring the landslide volume on site is challenging. Instead, many empirical area-volume power-law models have been developed to estimate the landslide volume. Yet the validity of these power-law models for small-scale shallow landslides is in question considering the substantial uncertainty of field-estimated landslide volume data for developing these empirical power laws. In this study, two high-resolution LiDAR-derived digital terrain models taken in 2010 and 2020 are leveraged to interpret the volumes of 1326 shallow landslides that occurred in Hong Kong during the same period. The high precision of the digital terrain models ensures the accurate interpretation of landslides and the identification of landslide source and transport areas. On the basis of the interpreted landslide characteristics, new power-law models and a multivariate distribution model are proposed to accurately estimate the volumes of small-scale shallow landslides based on easy-to-obtain landslide source features such as source area, length, width or maximum depth. The multivariate distribution model rigorously expresses the conditional probability distribution of the landslide volume and quantifies the uncertainty of volume estimation. The models therefore enhance the capability of landslide risk assessment and management.

The Mobility of Landslides in Pumice: Insights from a Flume Experiment

Risk of landslide hazards strongly depends on how far landslide sediment travels, known as landslide mobility. Previous studies mentioned enhanced mobility of earthquake-induced landslides in volcanic deposits compared to those from other geologic/soil settings. A flume apparatus constructed at a 1:300 scale was used to examine the mobility of landslides with pumice. Four pumice samples were collected from landslides induced by the 2018 Eastern Iburi earthquake, Hokkaido, Japan. Laboratory tests confirmed the unique low specific gravity of the pumice (1.29–1.33), indicating numerous voids within pumice particles. These voids allowed pumice to absorb a substantial amount of water (95–143%), about 9–15 times higher than other coarse-grained soils. Our flume experiments using various saturation levels (0–1) confirmed the influence of this inner-particle water absorption on pumice mobility. Because a low value of specific gravity indicates a low strength of soil, grain crushing may occur on the pumice layer, causing water from the internal voids to discharge and fluidize the transported landslide mass. Our findings indicate that such earthquake-induced landslides can be as mobile as those induced by rainfall, depending on the initial water content of the pumice layers. These conditions might be associated with water accumulation from previous rainfall events and the water-holding capability on pumice layers.

A Case Study on the Energy Capacity of a Flexible Rockfall Barrier in Resisting Landslide Debris

Landslides frequently occur in forest areas with a steep hillside, especially when severely disturbed by human activities. After sustained heavy rainfall, a landslide occurred near the Tianwan tunnel entrance of the Chongqing-Huaihua railway in China. Fortunately, the landslide debris was successfully intercepted by a flexible barrier originally installed to stop rockfalls, which is, to date, the first publicly reported case of landslide debris having been successfully intercepted by a flexible barrier without any damage, in mainland of China. A field investigation was first conducted, and then a back analysis of the landslide mobility and the interaction between the landslide and the flexible barrier was carried out. The back analysis showed that the impact energy was three-times larger than the rated energy capacity of the flexible barrier. It also showed that the elongation of the brake rings and the deflection of the flexible barrier from the numerical simulation was comparable to that from the field measurements. The fact that these brake rings were not elongated to their limit indicated that the capacity of the flexible barrier still had a surplus. Finally, to investigate the maximum energy capacity of a flexible rockfall barrier in resisting landslide debris, parametric analyses of a flexible barrier impacted by landslide debris with different impact energies and velocities were carried out using a coupled ALE-FEM modeling technique. The results showed that the flexible barrier dissipated less than 40% of the total energy of the landslide debris. With an increase of impact energy, the energy dissipation ratio of the flexible barrier decreased linearly. The maximum energy capacity of a flexible rockfall barrier in resisting landslide debris is four-times that of resisting a rockfall.

Do standing trees affect landslide mobility on forested hillslopes in Japan?

AbstractLandslide mobility likely changes in response to the effects of standing trees on the landslide runout. However, the properties of standing trees that influence landslide runout are not well understood. In this study, the relationships between the properties of landslides and the heights of standing trees and the runout distances of rainfall‐induced landslides (primarily 101–103 m3 in volume) in the Hiroshima Prefecture, Japan, were examined to investigate whether the heights of the trees around the runout area change the landslide mobility. The results indicate that the landslide runout was constrained not only by the landslide area and volume but also by the tree height around the runout area. Tall but sparse standing trees did not prevent landslide runout, whereas dense standing trees resulted in relatively low landslide mobility, irrespective of whether the trees were broadleaf or coniferous. A comparison between our landslide inventory and previously reported landslides showed that the landslide mobility was lower in areas with standing trees than in areas without standing trees, such as under experimental conditions and for landslides in Martian and submarine environments. Therefore, differences in the heights of the trees around the runout area can result in variations in the extent of landslide‐related hazards and disturbances.

Distribution and Mobility of Coseismic Landslides Triggered by the 2018 Hokkaido Earthquake in Japan

At 3:08 on 6 September 2018 (UTC +9), massive landslides were triggered by an earthquake of Mw 6.6 that occurred in Hokkaido, Japan. In this paper, a coseismic landslide inventory that covers 388 km2 of the earthquake-impacted area and includes 5828 coseismic landslides with a total landslide area of 23.66 km2 was compiled by using visual interpretations of various high-resolution satellite images. To analyze the spatial distribution and characteristics of coseismic landslides, five factors were considered: the peak ground acceleration (PGA), elevation, slope gradient, slope aspect, and lithology. Results show more than 87% of the landslides occurred at 100 to 200 m elevations. Slopes in the range of 10~20°are the most susceptible to failure. The landslide density of the places with peak ground acceleration (PGA) greater than 0.16 g is obviously larger than those with PGA less than 0.02 g. Compared with the number and scale of coseismic landslides caused by other strong earthquakes and the mobility of the coseismic landslides caused by the Haiyan and Wenchuan earthquakes, it was found that the distribution of coseismic landslides was extremely dense and that the mobility of the Hokkaido earthquake was greater than that of the Wenchuan earthquake and weaker than that of the Haiyuan earthquake, and is described by the following relationship: L = 18.454 ∗ H0.612. Comparative analysis of coseismic landslides with similar magnitude has important guiding significance for disaster prevention and reduction and reconstruction planning of landslides in affected areas.

Large-scale landslide inventory and their mobility in Lvliang City, Shanxi Province, China

Landslides are one of the most destructive geological disasters that threaten people's lives and property. With the high-resolution satellite images from Google Earth and the method of visual interpretation, we develop a large-scale landslide inventory in Lvliang City in the east of the Loess Plateau. The inventory includes a total of 12,110 landslides, and the area of each individual landslide ranges from 0.03 to 1.35 ​km2. The landslide area ratio (LAR) is used to measure the influence of several geological factors on landslides, including stratigraphic chronology, elevation and slope. From Paleozoic to Cenozoic, LAR generally shows an increasing trend. With the increase of elevation, LAR initially increases and then decreases, reaching the peak value in the elevation range of 1000–1100 ​m. With the increase of slope angle, LAR also increases first and subsequently decreases, and reaches the peak value in the range of 15–20°. In addition, we analyze the landslide mobility level (H/L) of 12,110 landslides in the study area, and observe a linear relationship between landslide height and sliding distance. Landslides with larger areas exhibit high mobility, manifested as the fact that H/L decreases with the increase of the landslide area. Meanwhile, both slope angle and aspect exert obvious effects on the mobility of landslides.

Rheological characteristics of marine sediments from the Ulleung Basin, East Sea to estimate the mobility of submarine landslides

In estimating the geohazards posed by submarine landslides, the rheological properties of marine sediments are of significant importance for their postfailure dynamics. We report an experimental study of the rheological behavior of marine sediments taken from the Ulleung Basin, East Sea and their influence on numerical simulations of debris flow runout. Marine sediments exhibit a typical yield stress behavior, such as that of low-activity clays. For the materials examined, different yield stresses are observed depending on the shearing methods. Steady-state and oscillatory shear tests were conducted for different volumetric concentrations of sediment. According to the test results, the Bingham yield stresses under controlled shear stress and shear rate range from approximately 100 Pa to 1500 Pa, but the yield stresses under oscillatory shear loads range from approximately 25 Pa to 3500 Pa for a given sediment concentration. In the latter cases, the value obtained in the elastic region is approximately doubled. Experiments under steady-state and oscillatory shear loads can be helpful in determining the yield points in the elastic and viscous regions and in explaining changes in the structure of the soil sample due to shear. We apply the range of measured yield strength values to numerical simulations of debris flow runout using a Herschel-Bulkley model and find that only the lowest values of yield strength, despite the low sediment concentrations, could account for the observed runout and thickness distribution. We infer that significant wetting must occur during debris flow motion to attain the observed runout.

An Arbitrary Lagrangian Eulerian (ALE) finite difference (FD)‐SPH depth integrated model for pore pressure evolution on landslides over erodible terrains

AbstractEntrainment of saturated bed material increases the mobility of fast landslides. The distribution of excess pore pressures changes in the body of the landslide, as the material entering it has much lower effective confining stresses which results on much smaller apparent basal friction angles. The purpose of this paper is to enhance the Finite Differences depth integrated SPH model developed by the authors to cope with material which is flowing up the FD meshes. The model is set within an Arbitrary Lagrangian Eulerian framework (ALE), and the resulting excess pore pressure evolution model will include now advective terms in addition to the diffusive and source terms. In order to assess the importance of the proposed modification, we introduce a basal Péclet number which relates two non dimensional reference times of consolidation and erosion.

The influence of slope gradient and gully channel on the run-out behavior of rockslide-debris flow: an analysis on the Verghereto landslide in Italy

Rockslide-debris flow may cause catastrophic damages because of its high speed and long run-out distance. The influences of slope gradient and gully channel on the entrainment, deposition, and run-out behavior of this type of landslide were not sufficiently investigated by previous studies. To achieve a better understanding toward this type of landslide, a recent rockslide-debris flow that occurred in the Northern Apennines of Italy is studied through field investigation and numerical simulation. The run-out process of this landslide is simulated by an improved depth-averaged model, paying special attention to analyzing the influence of slope gradient and gully channel. The simulation results are compared with the detailed field data of entrainment and deposition distributions. It shows that the depth-averaged model can reasonably simulate the entrainment and deposition characteristic of this landslide by adopting different basal friction strengths for the rockslide region and debris flow region. Entrainment occurs in both high and low slope gradient zones. However, entrainment can only be observed in the high slope gradient zones, while in the low gradient zones, the post-failure topography shows accumulation and deposition. The simulation results also demonstrate that the presence of a gully channel is a key factor in determining landslide mobility and run-out distance. In comparison to a landslide with similar size and geological settings but without a gully channel, the run-out distance is much less, and the landslide does not develop into a flow.

Assessing vulnerability of elevated cities to earthquake induced landslides based on landslide mobility

Earthquake induced landslides in seismically active steep terrain pose a threat to human lives. Urban settlements in such terrain are exposed to widespread destruction due to these sudden slope movements. Predicting slope failures using Newmark algorithm has been a traditional way of estimating landslide distribution in the aftermath of a strong shallow focus earthquake. Mobility of the slope as represented by the equivalent coefficient of friction is a strong indicator of the destruction caused by the landslides. In this work we evaluate the vulnerability of urban settlements to earthquake induced landslides using a relation developed for mobility of rock slides caused by earthquakes. Seven landslide sites that were identified by field survey after the devastating earthquake of magnitude Mw 6.9 in the Indian state of Sikkim, were used as a case study to assess the mobility and predicted displacement. Results suggest that larger landslides have a higher mobility and are more destructive than smaller rockslides. Landslide with a friction coefficient value of 0.8403 was responsible for severely damaging and blocking the highway. A preliminary model that correlated volume and Newmark’s displacement is obtained from the data in this study however, this model needs to be validated with a larger dataset for better accuracy. We propose that the mobility of landslides can be used to assess the vulnerability of urban settlements to earthquake induced landslides in steep terrain. Software that predicts the ground motion and generate reliable strong motion data can be integrated with automated disaster warning system in smart cities.

Investigation of the characteristics and long-runout movement mechanisms of the Luanshibao landslide on the eastern margin of the Qinghai-Tibet Plateau

The Luanshibao (LSB) ancient landslide is a typical long-runout landslide that occurred on the eastern margin of the Qinghai-Tibet Plateau. To examine the long-runout mechanism of the LSB landslide, a detailed field investigation and a series of saturated soil triaxial and ring shear tests were carried out. The field investigation results revealed that the flat and broad Maoyaba (MYB) basin provides the required topographic conditions for the long-runout movement of the LSB landslide. The shallow deposit of the MYB basin is mainly composed of saturated weathered granite sand, which plays a key role in resulting in the high mobility of landslides. The results of the triaxial tests reveal that the soils show the characteristics of shear contraction first and then dilatation under static loading, and cyclic mobility occurs under cyclic loading. The results of the ring shear test reveal that the pore water pressure of the sample has undergone three stages of increase-decrease-increase. Finally, the pore-water pressure ratio increases to a constant of approximately 0.79, and the shear resistance decreases significantly. Grain crushing results in pore-water pressure generation and the liquefaction of saturated weathered granite sand for long shear displacement. It is proposed that sliding surface liquefaction is the main reason for the formation of complex surface landforms and the long-runout movement of LSB landslides.

The mechanics of landslide mobility with erosion

Erosion can significantly increase the destructive power of a landslide by amplifying its volume, mobility and impact force. The threat posed by an erosive landslide is linked to its mobility. No mechanical condition has yet been presented for when, how and how much energy erosive landslides gain or lose. Here, we pioneer a mechanical model for the energy budget of erosive landslides that controls enhanced or reduced mobility. Inertia is related to an entrainment velocity, is a fundamentally new understanding. This ascertains the true inertia of erosive landslides, making a breakthrough in correctly determining the landslide mobility. Erosion velocity, which regulates the energy budget, determines the enhanced or reduced mobility. Newly developed energy generator offers the first-ever mechanical quantification of erosional energy and a precise description of mobility. This addresses the long-standing question of why many erosive landslides generate higher mobility, while others reduce mobility. We demonstrate that erosion and entrainment are different processes. Landslides gain energy and enhance mobility if the erosion velocity exceeds the entrainment velocity. Energy velocity delineates distinct excess energy regimes. Newly introduced mobility scaling and erosion number deliver the explicit measure of mobility. Presented dynamical equations correctly include erosion induced net momentum production.