Understanding and Reducing Landslide Disaster Risk

Shear strength is an essential component of slope stability analyses and necessary for the design of landslide repair and prevention works. This paper provides an in-depth review of the shear strength of soil pertinent to landslide analysis—fully softened shear strength and the residual shear strength of soils. Methods currently used in practice to measures the fully softened and residual shear strengths are summarized along with their advantages and disadvantages. Specifically, this paper will present details regarding the methods used to measure these shearing resistances, such as direct shear, ring shear, triaxial compression and direct simple shear tests to measure the fully softened shear strength and the use of direct shear, ring shear and triaxial compression tests to obtain the residual shear strengths. Pertinent information and discussions are provided regarding the interpretation of the shear envelopes developed from these testing methods focusing on the use of linear and non-linear (or curved) failure envelopes along with the interpretation of the strengths in terms of the secant friction angles. The various forms of curved linear envelopes presented in the literature are discussed. The paper also includes details of several commonly used correlations to estimate both the fully softened and residual shear strengths. Recommendations by the authors on the use, measurement and interpretation of both the fully softened and residual shear strengths are also included.

This paper describes and explains the large mobility of the 2014 Oso Landslide, which caused significant fatal consequences. This landslide occurred in two phases, characterized by significantly different material behaviour, strengths, and runout. A portion of the first phase underwent significant undrained strength loss (liquefaction) and travelled over 1.7 km over a nearly horizontal valley surface and devasted a residential community. The second phase underwent brittle failure with much less strength loss and runout than the first phase. The first phase slide mass is composed of insensitive, overconsolidated glaciolacustrine silt and clay, material not traditionally recognized as susceptible to a large undrained strength loss or liquefaction. A new rheology, appropriate for liquefied overconsolidated glaciolacustrine silt and clay, is presented and used in the runout analyses. The large runout occurred in two directions, which allows various runout models to be compared. Three numerical runout models were used to investigate their applicability to similar landslide configurations and future hazard and risk assessments. These runout analyses show the importance of: (1) using a digital terrain model in the runout analysis, (2) modeling field representative shear strength properties and failure mechanisms, and (3) predicting runout distance, splash height, and duration for risk assessments and to improve public safety for this and other slopes.

Until recently geomechanical numerical modelling of slopes and landslides was mostly performed for academic research purposes and for the engineering design of high earth embankments. In recent years, the use of Finite Element and Finite Difference modelling packages has become commonplace, and allowed complex analyses to be performed by practicing engineers in firms of all sizes. Although these software packages have widespread use in geotechnical engineering, there are two applications that are particularly well-suited for slope stability and landslide modelling. The first one, is the analysis of slope repairs and landslide stabilizations that combine multiple structural elements (e.g., several rows of piles with tiebacks). The second is the seismic performance of slopes, e.g., designs where dynamic amplification and permanent seismic displacements are a major concern. This paper presents recent advancements for the practical design of slopes, the advantages for designers of performing geomechanical modelling, and provides guidelines for their use in modern slope engineering and landslide stabilization practice.

Landslides are among one of the most devastating natural disasters affecting millions of people, causing tens of thousands of deaths and resulting in millions to billions of dollars of damage annually. Examination of historical data suggests an increase in the number of slope failures along with an increase in the two major triggers—an increase in the number of significant earthquakes and wetter than average annual precipitations. These trends highlight the continued need to improve landslide science and understanding. This paper presents a summary of the recent advances in knowledge pertinent to the methods of slope stability and deformation analyses starting with the state of practice as detailed by Prof. J. Michael Duncan in 1996. Specifically, the paper focuses on the improvements to the computational and graphical capabilities with the widespread use and availabilities of computers, the ability to perform macro level stability analysis for regions, the advent of probabilistic slope stability analyses, developments in slope stability analyses of unsaturated slopes, and new methods to perform deformation analyses. Several case studies highlighting these advances are also included.

On 10 October and 3 November 2018, two large landslides occurred at Baige on the Qinghai-Tibet Plateau, and completely blocked the Jinsha River. Accordingly two landslide dams formed and breached sequentially, with the breaching of the 3 Nov. dam generating a flood larger than the 10,000-year return period flood over a river reach of approximately 400 km, endangering the serial cascade dams and towns along the river. These were two typical large-scale hazard chains originated by landslides. This paper presents a five-phase protocol to manage the risks of landslide hazard chains, which includes definitions, multi-hazard assessment, exposure assessment, multi-vulnerability assessment, and multi-risk assessment. The protocol is illustrated in the case of the Jinsha River landslide hazard chains. How the hazard chains developed in space and time are introduced. The major engineering measures for mitigating short-term and longer-term risks are described, including the use of a 15 m deep diversion channel to reduce the dam failure flow rate and flow quantity, removal of two cofferdams along the river to avoid flood amplification effects, flood regulation using six reservoirs over 630 km downstream, load relief at the crest of the instable slope to increase its stability, and removal of part of the residual landslide barrier to minimize future landslide dam risks. Finally, several scientific topics are suggested for further study.

Many researchers have been investigating the mechanism of rock avalanches in the laboratory using flume tests, where dry rigid blocks are released on an inclined chute and the motion of the blocks are monitored using video cameras supplemented by image-based processing technique. In this paper, a recently developed sensing technique, which consists of permanent magnets as trackers and magnetometers as receivers, is used to examine the behaviour of the blocks as they propagate downslope. For this purpose, a permanent magnet, whose density, shape and surface characteristics are adjusted to be similar to the other blocks, is incorporated into the pile of blocks at specific locations. Since a permanent magnet generates static magnetic field, its flux density is detected by the magnetometers positioned appropriately adjacent to the flume. From the readings obtained, the magnet’s location and orientation at any given time is determined using an optimisation algorithm. For various combinations of pile height, block volume and surface inclination, the displacements and orientations of the permanent magnet, representing one of the blocks undergoing movement, are monitored from which kinematic quantities are captured to highlight the behaviour of the blocks as they flow down the chute. For comparison purposes, the movement of the blocks were also monitored by video camera. The results obtained using the magnetic tracking system coincide very well with those monitored using image analysis from video camera. These highlight the capability of the proposed magnetic tracking system in capturing key kinematic quantities during the downslope motion of the blocks, including translations and rotations.

Detailed landslide susceptibility mapping (LSM) requires a skillful landslide model. Considering that translational landslide is the most type of landslides occurred in the world, a well-behaved translational model is sought. This study presents a simple physically-based distributed translational landslide model. In this model, the incident of landslide is detected from the value of factor of safety (FoS) which is computed based on Mohr–Coulomb failure criterion. In here, FoS is calculated as the ratio of shear strength and shear stress. The lower the FoS, the higher the possibility of a landslide to occur. The model input data consists of soil cohesion $${\varvec{c}}$$ c (kg/cm2), soil specific weight $${\varvec{\gamma}}$$ γ (g/cm3), depth of surface of rupture (m), slope of surface of rupture $${\varvec{\beta}}$$ β (degree) and friction angle $$\boldsymbol{\varphi }$$ φ (degree). Application of the model was performed in Sirampog and Kandang Serang, two subdistricts in Western Central Java that underwent the most frequent landslides in the region. Model validation was conducted by comparing the values of FoS of unsaturated and saturated soils and identifying FoS in the sites where landslide events recorded. Several goodness of fit indices to measure the model performance are accuracy (ACC), success index (SI), average index (AI) and distance to perfect classification (D2PC). Under unsaturated condition, the result shows that the number of grids having FoS less than 1 are 0% and 0.6% for Sirampog and Kandang Serang respectively, indicating no landslide occurrence. When the soil gets saturated, 17.6% and 36% of area have FoS less than 1 for Sirampog and Kandang Serang respectively. This shows that the landslide occurred in this region is rainfall-induced landslide. Overall, the model shows a good performance with ACC, SI, AI, D2PC values are 0.82, 0.58, 0.54, 0 and 0.64, 0.49, 0.49, 0 for Sirampog and Kandang Serang respectively.

Rainfall has been identified as one of the main causes of slope failures in areas where high annual rainfall is experienced. The slope stability is very important consideration in management and is often being the most critical safety issue or feasibility component of many civil engineering project. An integrated analysis of rainfall-induced landslides was carried out through a laboratory test, as well as laboratory and numerical analyses. A set of laboratory-scale soil slopes was subjected to instability through different modes of rainfall intensities and slope inclination to clarify the process of failure initiation. Hydrologic responses of the model slopes to the saturation process were recorded by volumetric soil moisture sensors and tensiometer. The results of the comprehensive investigations demonstrate that landslide activity is closely related primarily to rainfall and soil properties and slope geometry. A numerical analysis was also performed to confirm the effect of these factors on landslide occurrence. In addition, the changes in the factor of safety and the volume mass of the failure surface were compared and verified. From the results of the experiment and analyses, it is concluded that the unsaturated slope stability analysis, setting the initial conditions and boundary condition is important. If engineers use the measured porewater pressure or matric suction, the accuracy of the analysis can be enhanced. The real-time monitoring system of porewater pressure or matric suction can be used as a warning of rainfall-induced slope failure.

In order to prevent occupational accidents during slope excavation work, it is important to include slope stability in all aspects of construction design. In slope excavation work, the two major factors are the excavation height and the gradient, both of which are prescribed by some guidelines and laws. However, accidents often occur during slope excavation work, even with the required safety gradient, because existing guidelines fail to consider the effects of water. In this study, the stability of a slope with rising groundwater was examined for different excavation slopes. The results show that the slope was stable in the absence of water, but it collapsed when the groundwater rose. We also propose a method for predicting landslides using slope movement measurements. The method uses the standard deviation from past measured values to detect data abnormalities on current measurements. Predictions obtained by this method were classified under advisory, warning, or emergency warning based on the deviation rate between the moving average and standard deviation of past data. It was observed that slope failure can be reliably predicted using this method.

Ruptures of tailing deposits can exhibit flow-like behavior and cause major disasters. An extensive mass of tailings can be transported over large distances at high velocity and flood downstream villages, resulting in the loss of a large number of lives and huge property losses. We present a series of flume tests to observe the process of tailing slope failure when subjected to a water flow. Progressive flow slides were observed in a range of tailing deposits with varying relative densities, in which hydraulic conductivity reduced with increasing relative density. The generation of pore pressure caused a sudden collapse of the dam for very loose, loose and medium dense materials, and is also evident in seismic signals and acoustic emission signals. In dense tailing slopes, progressive failure occurred, with several successive sliding surfaces, and several seismic signals corresponding to rising acoustic emission signals. The water inflow into dense slopes is slower due lower hydraulic conductivity, resulting in successive sliding starting at the slope toe and progressing within the soil mass. The runout, internal displacement and peak flow velocity tend to be quite similar with an increase in relative density up to 0.35, and become less pronounced for denser tailings slopes. A relative density of 0.35 is a transitional density from a sudden overall failure to a progressive slope failure.

Vegetation plays in an important role in the amount of surface runoff or infiltration after a rainfall event, specifically on slopes. High infiltration or seepage reduce shearing resistance of soil through the reduction in matric suction of partially saturated slopes, ultimately causing slope instability. On the other hand, low infiltration increases surface runoff and velocity of surface flow, which ultimately causes soil erosion. In this study, three different slopes were prepared using fine sand, specifically at the same dry density and geometry, but with three different vegetation cover densities. The slopes were instrumented with tensiometers at different depths. The slopes were subjected to a rainfall event with an intensity of 30 mm/h and advancement of the wetting front of the seepage water and soil matric suction were recorded with time duration after the rainfall. The experimental result shows that up to certain threshold vegetation cover density, amount of surface flow increases causing soil erosion. For the vegetation density above that threshold, vegetation covers intercept the rainwater and the intercepted water is gradually passed to ground. Moreover, vegetation cover will ease the flow of surface runoff water. These actions, on the other hand, increase the seepage velocity. As such, less dense vegetation cover triggers more rainfall induced soil erosion and denser vegetation cover increases the instability associated with rotational or translational slides.

Submarine slopes are subject to a variety of failure styles, ranging from large, long runout landslides to both shallow and deep-seated landslides with limited down-slope displacements. The upper continental slope off the east coast of the North Island of New Zealand, hosts numerous landslides which vary in size, volume and runout characteristics. The region is located on an active subduction zone experiencing regular earthquakes and is close to the base of gas hydrate stability. Consequently, both seismic loading during earthquakes and over-pressure in the slope from the migration of free gas may be plausible movement mechanisms for both shallow and deep landslides but their potential behaviour during earthquakes and in response to elevated pore fluid pressures remains poorly constrained. We conducted a series of experiments in a Dynamic Back Pressure Shearbox on sediments recovered from the Hikurangi subduction margin to simulate the complex stress conditions in submarine landslides and explore their potential movement mechanisms in response to elevated pore fluid pressures and seismic loading. Our experiments successfully simulated a range of landslide behaviour that advances our understanding of the variety of landslide types observed on active continental margins. The movement behaviours observed provide credible mechanisms to explain how some submarine landslides may be subject to episodic movement without undergoing catastrophic failure as a result of over pressuring by free gas and seismic loading during earthquakes.

Each year, rainfall events trigger a large number of landslides causing damage and victims. The study and forecast of rainfall-induced landslides is a field of great importance. Many research activities aim to understand landslide processes and to improve early warning systems. Infiltration processes and underground water circulation have an important role to define failure processes characteristics. In this work, some results from tests performed with a physical slope model are reported. Some experimental tests were conduced, using pyroclastic soil from Sarno area (Southern Italy—near the volcano Vesuvio), affected by landslide events on 5 May 1998. In these places the stratigraphy are composed from limestones covered by layers of pyroclastic deposits. These soils are the product of different eruptions of more volcanoes like Somma-Vesuvius, Flegrei fields and other volcanoes present in the Region no longer active. Generally, they are incoherent deposits with variable granulometry that range from sands, silty sands and silts (ashes) until sands with gravel (pumice) and gravels. Some tests considering both homogeneous and stratified deposits of ash and pumice were carried out. During the tests, both during evaporation and infiltration processes, suction and volumetric water content at different depth were measured by using the appropriate sensors. By comparing and analysing all the collected data it was possible to study the infiltration processes that lead to the failure and the difference between the stratified and the homogeneous deposit.

Fragmentation in a rockfall event influence the total number of fragments, the mass distribution, and the impact energies and runouts. Then, the probability of impact and hazard characterization should consider fragmentation. A fractal fragmentation model has been proposed in order to reproduce the phenomenon. The Rockfall Fractal Fragmentation Model has been implemented in a 3D rockfall propagation simulator named RockGIS. We present the analysis of a fragmental rockfall that occurred in Mallorca, Spain. Fieldworks are carried out in order to obtain the block size distribution of the rockfall deposit. A 3D terrain model is obtained using UAV surveys and digital photogrammetric techniques. The obtained 3D point cloud is cleaned of vegetation and used to create a Digital Elevation Model (DEM). The fragmentation model parameters and the propagation simulator coefficients have been calibrated to accomplish both, the resultant block size distribution and the runout distance of the blocks. The obtained results show a good reproduction of the fragmental rockfall studied. After the calibration is accomplished, older and future rockfalls in the cliff may be analyzed, considering thousands or single blocks simulations with or without fragmentation.

The present paper describes the elaboration of 3D surface and geological models generated for a series of landslide sites, zones marked by large incipient slope failures, or those presenting structural characteristics of an ancient giant mass movement. For both, surface and geological models, high-resolution satellite or drone imagery was draped on the digital elevation model constructed from the same imagery or using Radar or LiDAR data. The geological models further include geophysical data, supported by differential GPS measurements, complemented by georeferenced geological and tectonic maps and related geological sections. The soft layer thickness information and borehole data are typically represented in terms of logs inside the model. For several sites also slope stability analyses were performed, either in 2D or in 3D. Inputs for those analyses were directly extracted from the 3D geomodels, outputs were again represented in the models.Some of those models, such as the one produced for the right-bank slopes of the Rogun Dam construction site can be quite complex and we clearly could notice that an immersive analysis using VR technology helps understand their internal structure and perform a better slope stability analysis. Still these analyses have their limits, as a study in Virtual Reality is purely individual (at present time, the visiting researcher is separated from the rest of the World). Therefore, we suggest that a real advancement can only be achieved if the technological developments go along with a stronger collaboration between scientists from the various geo-domains, who could also be immersed in the same virtual model (~collaborative VR).

Flow-like landslides commonly happen in mountainous areas and may cause economic and human life losses in the impacted areas. Computer modelling has become an effective tool for landslide risk assessment and reduction. Models based on discrete element method (DEM) have been widely used for landslide prediction; however, this method is computationally too demanding for large-scale applications. Depth-averaged models (DAMs) have been widely reported for simulating run-out and deposition of flow-like landslides over large spatial domains due to its relatively higher computational efficiency. To combine the advantages of both types of modelling approaches, this work introduces a novel landslide model developed by coupling a DEM model with DAM for simulation of flow-like landslides, in which the DEM is employed in the landslide initiation area to better simulate the failure mechanism of slope, and the DAM is adopted in the landslide runout and deposition phase, where the landslide has developed into flow-like landslide with fluid-like behaviour. Finally, the new coupled model is validated against an experimental test case. Satisfactory results have been obtained, demonstrating that the coupled model is able to accurately capture the detailed dynamics of flow-like landslides.

Anticipation of complex cascading landslides, important to inform risk management, requires the use of advanced modelling approaches. Such approaches have become increasingly available during the last decade, and have been successfully applied for the back-calculation of well-documented test cases. These back-calculations have helped to identify the needs for further research in terms of making reliable predictive simulations possible. This paper summarizes the key challenges in doing so as well as the resulting ongoing and planned model enhancements. Thereby, the focus is put on the propagation and interaction of flow processes. The main challenges are related to the understanding of the physical processes, the numerical implementation, and model parameterization. Some important needs for enhancement are the better representation of (1) landslide-reservoir interactions and (2) entrainment, deposition, and stopping; (3) an improved numerical scheme; (4) consideration of “slow motion”; (5) interfaces to fall models; (6) guiding parameter sets; and (7) the dynamic adaptation of key parameters to flow dynamics. Further important issues, which are not the focus of this work, are landslide triggering and release as well as the communication of uncertain model results.

Recent submarine mass failures that generated tsunami have caused people to pay more attention because of the resultant casualties. A submarine landslide tsunami requires more computer time for the simulation because of the high spatial resolution and associated short time steps even though the computational domain is smaller than that of a seismic tsunami. To reduce the resources to forecast tsunamis, reciprocal Green’s functions have been proposed and the forecast results are verified by comparing with direct numerical simulations of a tsunami model COMCOT. However, due to features different to seismic tsunamis, some precautions should be taken in applying this approach in submarine landslide tsunamis. Possible solutions to overcome difficulties using this approach are also recommended. Finally, suggestions based on reciprocal Green’s functions are advanced to build a practical forecast system for submarine landslide tsunamis.

The identification of the slope deformation characteristics upon rainfall plays an important role in providing early warning information and implementing emergency remedial actions before landslide occurs. In this study, a coupled hydro-mechanical formulation of finite element analysis was performed to investigate the displacement behaviour of slopes triggered by rainfall infiltration. The simulation results showed in good agreement with experiment result. The model study was then carried out to investigate the hydraulic and deformation response of the shallow slope. The numerical results revealed that the developed slope displacement with time can be divided into three stages, namely constant, accelerated, and critical deformation stages, corresponding to various rates of slope movement and porewater pressure development stages. Finally, the relationships of slope displacement magnitude with the factor of safety that established from this study can be seen as a good indicator for shallow landslide hazard assessment.

Recently, deep-seated landslides, DSLs, have become more frequent due to heavy rain events. Due to DSLs, there have been some cases of landslide dam formations in mountainous regions. When landslide dam outburst occurs, large scale debris flow might devastate the downstream area. Therefore, debris flow scenarios, arising from landslide outbursts, are studied to predict and prevent the damages in the downstream regions. In this study for the purpose of simulation, we applied the Hyper KANAKO system with the digital elevation model, DEM, taken before and after the landslide dam formation. First, we simulated the landslide dam outburst scenario by comparing it with the downstream deposition. When the sediment diameter and the fluid phase density were set to 0.2 m and 1,000 kg/m3, respectively, the results were satisfactory. Then, we considered an effective countermeasure installation in the torrent by setting one closed type sabo dam with an effective height of 15 m. We found that setting the sabo dam in the downstream side of the torrent prevented the sediments from moving downstream; this setup effectively prevented the damage. Therefore, simulations are useful for landslide dam outburst hazard mapping and for effective countermeasure implementation.

In this work we describe a first version of the simulation tool developed within the SMART-SED project. The two main components of the SMART-SED model consist in a data preprocessing tool and in a robust numerical solver, which does not require a priori identification of river beds and other surface run-off areas, thus being especially useful to provide accurate input data to more localized landslide and debris-flow models. Furthermore, a geostatistical tool is available to downscale SoilGrids particle size fractions (psf) data to a given resolution. The psf data is employed also within the SCS-CN method, used to model the infiltration process. The results of a complete numerical simulation are reported and possible future developments of the model are discussed.

One of the most disastrous landslide events happened in Myanmar was Chin state landslides due to abnormal heavy rainfall in July 2015. The landslides destroyed and damaged nearly 3,000 buildings and killed 5 people. In particular, a deep-seated landslide occurred at Mt. Rung, Hakha city on 27 July 2015 was a serious event in the history of the Chin state with about 500 m wide and 1,000 m long. On the day of the landslide occurrence, an intense rainfall of 180 mm fell within a short time span in the Hakha area. This research aims to assess the potential rainfall-induced landslides of the remained body on the slope of July 2015 landside based on assumed pore pressure ratio (ru), soil parameters from the ring-shear tests and computer simulation. In the simulation, pore pressure ratio ru was gradually increased from 0 (no groundwater) to 0.5 (groundwater table at ground surface) to simulate two potential cases of rainfall-induced landslides with the depths of 30 and 60 m. The landslides started when pore pressure ratio reached 0.35 and 0.39 which are corresponding to the groundwater level height equal to 71 and 80% of the total thickness of the sliding layers. The volumes and velocities as well as the affected areas of the landslides were also calculated. The method would provide an assessment of landslide hazard triggered by rainfall and the result would be of great help for the authorities in the management of slope disasters.

Urbanization has been related to natural disasters such as landslides and debris flows that can cause fatality, destruction of infrastructure and environmental impacts. From 19 to 20 August, 2014, heavy rainfall occurred in Hiroshima city causing many landslides and debris flows. This disaster killed 74 people, 255 houses damaged and a total of 4,576 houses were affected reported by the Ministry of Land, Infrastructure, Transport, and Tourism of Japan (MLIT). The cumulative rainfall from 8:30 PM of August 19 until 04:30 AM of August 20 reached 248 mm at Miiri rain gauge station in Hiroshima. This is the main reason caused the Hiroshima disasters. Although intense rainfall in the short time was the trigger, urbanization into the foot of steep mountain slope lead to increase the loss of life. This paper presents the adverse effects of urbanization on basis of site investigation and multi-temporal satellite images and estimate hazard zoning causing by a potential landslide using the ring shear tests and integrated simulation model.

The results of material entrainment analysis in RAMMS debris flow software, as well as numerical models of final flow heights for two case studies from the Republic of Serbia are presented. Both cases were triggered after extreme rainfall period in May 2014. These debris flow processes started with initial sliding of huge volume block, prolonging to behave as flowing process. They are situated in different regions of country and quite different in sense of geology, gravel size, geometry etc. Results of the analysis showed that entrainment material affects final results of transportation model, runout distance, deposition area and volume of debris flow. In both cases entrainment volume is very huge, but it is much less than initial volume (about 11% of total volume in both case studies). Final results are validated with pre- and post- event DEMs (Digital Elevation Models and analysis of ERT geophysical results.

Creeping landslides are one of the major natural disasters in mountainous regions. Therefore, study of the creeping behavior of a landslide and associated Geotechnical issues are important. This study has addressed and evaluated the creeping behaviour of a the Tomuro landslide Gunma, Japan induced by snow melt water using the 2D-FEM based elasto-viscoplastic constitutive model as a case study. Two new control constitutive parameters were incorporated in the numerical model for the first time to better understand the creeping behaviour of a landslide. Such control constitutive parameters were estimated based on the relation between the total factor of safety, calculated by the various Limit Equilibrium Methods such as Ordinary Method of Slice (Fellenius 1936) (case I), Bishop’s Method (1955) (case II), Janbu’s Simplified Method (1973) (case III), and Finite Element Method (case IV), and the field monitoring displacement rate of the Tomuro landslide. In addition, the snowfall precipitation was also considered during the calculation of total factor of safety using both limit equilibrium methods and finite element method. Others required material parameters for landslide simulation were calculated based on the field investigation and laboratory tests of the collected blocked samples. First, the predicted and measured time histories of horizontal displacement of the Tomuro landslide was compared for the validity of the proposed numerical model and found in good agreements with each other. Then, the simulation results of deformation pattern and shear strain pattern were presented and discussed. Finally, the possible failure mechanism along the slip surface of a landslide induced by snow melt water was discussed.

Mt. Fuji is the largest polygenetic volcano in the Japanese archipelago. Its last eruption was Hoei in 1707. Since it has been dormant for over 300 years, not only people live near Mt. Fuji, but the area supports many economic activities in Japan. Because volcanic eruptions are accompanied by sediment movements, debris flow occurs due to heavy rainfall after ash fall, snow-melting volcanic mud flow, etc. Debris flow occurs frequently and intensively when ash has accumulated. Herein we simulate debris flows caused by rainfall after an eruption with ash fall using a method that combines Cellular Automaton (CA) and Multi Agent (MA) Systems. The CA/MA method can realize high-speed calculations because large-scale simultaneous equations do not need to be solved and the results can be easily imaged. Although local rules must be set experimentally and calibrated, the CA/MA method can easily reflect knowledge and experiences of experts such as geologists, geomorphologists, and geotechnical engineers.

The undercutting method applied together with the cut-and-fill technique has been realized through open-pit coal mining. To predict the time of slope failure, a method of forecasting slope failure time by the inverse velocity of slope surface proposed by Fukuzono (1985 in A new method for predicting the failure time of a slope. Japan Landslide Society, Japan, pp. 145–150) is employed in practice. However, the characteristics of slope movements in undercut slopes are different from those of typical slopes due to arch action across the pit; therefore, more investigations are required to examine whether this method can be effectively used to predict the failure time for an undercut slope. In this study, the undercut slope failure prediction technique following this approach was examined via geotechnical centrifuge modelling. The movement distributions of the slope surface were recorded by a high-speed VDO camera and analysed by the image processing software. This study confirms that the inverse of the average surface velocity is qualitatively valid for a centrifuge model of undercut slope.

The Material Point Method (MPM) is an emerging computational tool to simulate the complex dynamic process of rainfall-induced landslide. In this field, hydraulic boundary conditions play an important role. In recent researches, the average relative velocity of pore water with respect to the solid skeleton is considered as Darcy’s velocity usually. Hence, rainfall intensity (mm/h) can be assigned to the node of the mesh as a velocity boundary directly. However, the evolution of true velocities of liquid and solid phases has missed so far in the investigation of the landslide process. In order to keep the information of true velocities in the simulation, this paper provided a new solution to estimate the true velocity of the liquid phase at the node of the boundary layer and has been implemented a coupled hydro-mechanical model using MPM. The validation of such implementation was achieved by simulating a 1D infiltration problem and comparing with the MPM results with those obtained through the commercial software PLAXIS. With the help of this newly implemented boundary condition, rainfall-induced landslides can be better investigated using MPM.

Earthquakes can cause landslides on many scales in mountainous areas and pose danger to the residential area at the bottom of mountains. In some areas where the earthquake intensity is not high enough to cause large soil movement, the shaking effect on the stability of slopes during the following rainfall is not significant. However, in certain areas, shaking-caused large cracks on the slope surface play an important role in the stability of slopes subject to the following rainfall. The effect of pre-shaking on the slope stability when the slope is subject to rainfall is still not fully studied. In this study, centrifuge model tests on slopes subject to earthquakes and rainfall were carried out and due to insufficient shaking intensities and soil suction in the unsaturated slope, cracks were not seen on the surfaces of the slopes after shaking and only small displacement was induced, which made it difficult to specify the influence of earthquakes on the stability of slope subject to the following rainfall. The soil displacement and mobilization patterns of two slopes in this study were similar and the negative contribution of shaking to the slopes were not thoroughly investigated. However, the intensity and duration were the main factors that affected the occurrence and mode of the slide caused by rainfall; a uniform rainfall distribution is also necessary to validate the triggering mechanism of slide in the model tests.

Safety estimations of nuclear facilities must assess the risk of earthquakes stronger than that assumed in the original design. We propose a simple model using the discrete element method to evaluate the traveling distance of a collapsed rock mass when slope collapse occurs. We introduce a new parameter, rotational friction, to evaluate the reach distance and the accumulation state of collapsed soil. We also present the range value of rotational friction and its evaluation method.

Rainfall-induced shallow landslides of flow-like type are very common in ash-fall pyroclastic soils originated from explosive activity of the Somma-Vesuvius volcano (southern Italy). Over the last few centuries, these phenomena have frequently affected pyroclastic soil-mantled slopes of mountain ranges that surround the volcano causing hundreds of casualties. Many researches have been focused on this topic, especially after the occurrence of the deadly debris flow events of May 1998, which hit Sarno Mountains causing 160 victims. Among the various aspects studied, aimed at the assessment and mapping of hazard to landslide initiation and propagation, the estimation of shear strength of ash-fall pyroclastic soils still deserves to be advanced. This is especially due to the relevant spatial variability of geotechnical properties which are controlled by complex stratigraphic settings. According to such a research focus, the present paper deals with physical and shear strength laboratory characterizations of ash-fall pyroclastic soils and the estimation of the inherent variability. A total number of 97 direct shear tests, supported by grain size and Atterberg’s limits analyses, were carried out. The high number of tests allowed to perform a statistical analysis based on quantile regression approach and aimed at considering the uncertainty related to the high variability of Mohr–Coulomb’s shear strength parameters. The results obtained show values, especially for the drained friction angle (ϕ′), generally higher than those considered in literature. Outcomes of the study and the approach proposed can be conceived as a benchmark for further analyses aimed at the assessment of hazard to initiation of this type of landslides or related physically-based rainfall thresholds.

Soil moduli E depends on soil skeleton, particle shape and size, void ratio, moisture content, dry density and stress history. Residual soil contains more silica with inorganic clay compounds and soil structure depends on its parent rock and weathering state. Undisturbed soil samples were collected from two different rainfall precipitation zones of 2500 mm and above 5000 mm subjected to frequent cycles of wetting and drying. Our study explored the numerical relationships between standard soil physical properties such as void ratio, dry density and the elastic parameters such as Young’s moduli, E and secant moduli E50 and E70 of residual soil. We found that void ratio and dry density are fully dependent on formation characteristics of their parent materials and strongly impact on soil Young’s moduli, E and secant moduli, E50 and E70. The soil moduli of residual soil with void ratio and dry density relationships were derived. However, soil dry density had less influence than the void ratio. The study indicates residual soil is subjected to different precipitation and can have the same dry density but different soil skeleton, like loose or dense, and thus have different moduli. This may help in the evaluation of complex forms of slope instability.

To investigate the friction characteristic of root-soil interface and to quantitatively evaluate the contribution of shrub roots on soil shear strength, a new aspect of generalized equivalent confining pressure (GECP) was considered in the terms of the function of plant roots in reinforced soil was equivalent to confining pressure. Indigofera amblyantha was selected as the test plant of which the roots were sliced and the root surface roughness were calculated. In order to evaluate the influence of root diameters and soil moisture content no friction characteristics of root-soil interface, and different root distribution patterns were launched to analyze the influences on the shear strength of soil-root composites. Pull-out friction tests and triaxial shear tests were conducted on the soil-root composites prepared by sieving and remolding. The results showed that there was no significant difference in surface roughness of Indigofera amblyantha roots with the gradual increase of root diameter. The pull-out shear stress of roots in soil-root composites presented a downward trend with the increase of soil moisture content, which concentrated in 15–25 kPa. Under the CU condition, GECP of complex roots (CR) is 1–2 times that of vertical roots (VR) and 2–5 times that of horizontal roots (HR). GECP of plant roots augmented by 20–50%, when confining pressure increased from 50 to 150 kPa. The research results are great guiding significance to use shrubs plants to improve the stability of slope soil structure and prevent soil erosion and other geological disasters.

Mae Moh lignite mine is the largest open-pit mine in Thailand. The current mine operation is with over 250 m depth. The mine has been operated for over 50 years and would have a plan for the further operation of the next 20 years approximately. With a much deeper mine operation, this open-pit mine would be unavoidably to deal with more stress condition complexity of slope stability analysis, in particular for the long-term(time-dependent) stability. The long-term slope stability generally relates to the material “creep behavior” of which the time-dependent effect of a small deformation scale continually takes place under the constant stress condition. The main component of the Mae Moh open-cut slope is “claystone” which can be classified as the soft rock. It has properties in between soil and rock, causing difficulties in setting an appropriate test facility and determining a constitutive model to investigate its creep behavior. This study aimed to investigate the use of the soft soil creep (SSC) model to describe the creep behavior of the Mae Moh claystone based on a series of test results obtained creep tests from an own customized triaxial creep test facility designed to suit with the soft rock-like material. Plaxis 3D, the powerful commercial finite element program, was also used to simulate such creep behavior using the SSC model, one of its build-in constitutive material models. The Mohr-Coulomb (MC) model was also used as a benchmark in the finite element simulation. Results showed the SSC model could better simulate the time-dependent deformation of the Mae Moh claystone than using the MC model. It could be noticed that the SSC model would be an option to describe the creep behavior of the soft rock, using derived inputs based on the soft rock properties as it can be seen from a good agreement between test results and simulation of the slope of this study.

The 2016 Kumamoto earthquakes, Japan, caused a large numbers of slope failures, especially a large—scale flow—type landslide was induced in the area near the Aso Volcanological Laboratory of Kyoto University in Takanodai, Minamiaso Village Kumamoto, Japan. From the field observation, sliding surface was the tephra layer of Kusasenrigahama fallen pumice (Kpfa) which was deposited by the volcanic activity (around 30,000 years ago, Miyabuchi et al. in VSJ 48(2):195–214, 2003). This tephra layer (Kpfa) was a key soil to understand the mechanism of this large-scale flow-type landslide, then some soils from this tephra layer were retrieved from the sliding surface in the field. This study is focused on the physical properties, monotonic and cyclic direct shear behaviour for the tephra layer (Kpfa) to understand the mechanism of this landslide during earthquake. Constant vertical stress and constant volume cyclic direct shear tests were performed to study the cyclic behaviour of the tephra layer (Kpfa). From the constant vertical stress test, strain hardening behaviour was observed. From the constant vertical stress test, shear displacement increased largely during cyclic loading, despite the tephra layer being in an unsaturated state, which were similar to the behaviour of saturated sand during liquefaction. In the future, this research will be developed considering the study of particle breakage on Kpfa.

This paper presents the effect of shear rates on residual strength of four typical clay soils having high to low plasticity in its soil natures. The shear rates were fixed in a range of 0.073–0.586 mm/min. A series of tests were performed by means of ring shear apparatus. The effect of shear rates on residual strength of the high plasticity soils, medium plasticity soils and low plasticity soils were compared. The results showed that hardly increases in the strength from the residual-state of shear after the shear rate of 0.233 mm/min.

Rainfall-induced landslides in Southern Italy often affect the pyroclastic soils produced by the past explosive activity of Vesuvius volcano. Along hilly zones these soils are mostly unsaturated and characterized by a metastable structure, which can experience static liquefaction upon shearing. Several authors studied the mechanical behaviour and the wetting-induced collapse through triaxial tests and direct shear tests. Here, a new series of tests is performed—on remolded specimens—through the Suction Controlled Simple Shear apparatus, which is particularly suitable to reproduce the in-situ stress–strain hillslope conditions and the strain/stress paths induced by rainfall during the failure and post-failure mechanisms. The results are discussed in terms of shear strain, axial strain and saturation degree.

The loss of shear strength in a soil subjected to cyclic loading resulting from a reduction in the effective stress is known as cyclic mobility. Although the occurrence of cyclic mobility can have disastrous consequences including the loss of lives due to landslides and structural failure as well as substantial damages, quantitative evaluation of strength loss as a result of cyclic loading is not well described in the literature. In this study, eighteen laboratory prepared mineral mixtures composed of powdered montmorillonite and kaolinite clay minerals mixed with ground quartz are used to perform static and cyclic simple shear tests to establish the degradation in undrained shear strength that results from cyclic loading. The results are used to establish a relationship between the normalized undrained strength ratio and the post-cyclic effective stress ratio. This relationship is then used to examine the expected reduction in undrained shear strength and corresponding factor of safety against landslide at a post-earthquake landslide site in the Lokanthali region of Nepal after the 2015 Gorkha earthquake. The estimates from the proposed relationship are within 10% of the measured values.

Rapid landsliding phenomena demonstrate that their constituent grains can flow with extremely low friction along their runout paths. Over the past several decades, many studies have been motivated to reveal such kind of unusual physical process; however, the progressive maturation of these events is still lack of enough scientific evidence. Modern insight into the granular dynamics indicates that the force fluctuations may be in behaviour of abrupt perturbations of internal forces and release of strain energy. Remarkably, such energy release events are manifested in the generation of elastic waves, termed acoustic emissions (AE), which deliver invaluable information concerning the granular deformations. We thus employed a high frequency range of AE sensor to capture the elastic waves and examined the relationships between characteristics of AE and fluctuations of shear resistance. Our results suggested that there was a strong correlation between shear resistance drops and AE events; the characteristics and occurrence rates of generated AE events were influenced not only by shear velocity but also by particle size. The drops of shear resistance and the amplitude of AE waveforms were greater with increase of particle size, and the AE rates increase with increase of shear velocity.

In open cut works in landslide areas, caisson type piles suffer much more severe deformation than predicted. The site was studied based upon additional geological surveys. From ground measurement results and back analysis, measures were considered necessary to prevent loosening associated with excavation at an early stage. In this project, as part of open cut works, the early closure method that has been proven to be effective in controlling deformation in mountain tunnels was used. In order to replicate the 3D restraint effect of natural ground, an appropriate construction method was planned from 3D FEM analysis. As a result, not only the rebound of the excavated bottom was suppressed, but also displacement of the pile and increase in rebar stress could be restricted. We believe that this method proved to be an effective construction method and established a prediction study method, and that this construction method can be used as a reference for similar construction.

Rock slopes can be affected by weathering and human activities. Depending on the type of the rock, the impact of weathering and excavation can change. This leads some strength reductions and consequently some stability problems. Limit equilibrium analyses are widely used to assess slope stability but empirical methods are also very useful and quick. Basic quality (BQ) system is very popular method which is developed in China to assess slope stability of the rock slopes. Generally it leans on strength and rock soundness/GSI to determine slope stability. In this study, rock slope stabilities were assessed with limit equilibrium method and BQ system. 55 cut slopes located in Western Black Sea Region of Turkey were used to evaluate the stability conditions. 39 of the cut slopes are located in flysch deposits consisting mudstones and sandstone/limestone alternations. Other rock types are granite, basalt, andesite, granodiorite, serpentinite and tuff. According to the field observations, degree of weathering of most of the cut slopes are moderate (38), and the rest are slightly (10) and highly (7). Uniaxial compressive strength, point load strength index and Schmidt hammer tests were applied to find strength values. According to the tests, most of the rocks are in the category of weak and medium strong (5–50 MPa) throughout the study area. The field observations revealed that all cut slopes are stable except surficial failures due to weathering and excavation. According to limit equilibrium analyses, all cut slopes are stable, but only surficial failures were observed due to degradation which is completely coherent with the field observations. However, BQ System revealed that most of the results are not coherent with the field observations and limit equilibrium results. It is concluded that rocks stronger than 50 MPa can be assessed properly by BQ System in the study area.

Rainfall-triggered landslides are an ‘everyday risk’ to Small Island States, such as Saint Lucia in the Caribbean, and have the potential to destroy or damage buildings and disrupt lifelines such as roads and pipelines. To better evaluate these landslide hazards, efforts have been made to develop decision-support tools linking rainfall scenarios to stability for different types of road cut slope. Many thousands of stochastic simulations can be performed using a combined hydrology and slope stability model (CHASM) which requires inputs of slope cross-sectional geometry, soil and hydrological parameters which allows representative rainfall-triggered landslide scenarios to be produced. To use CHASM for this purpose the statistical variation of the relevant geotechnical properties such as friction angle needs to be assessed. This paper presents the analysis of an updated database for Saint Lucian soils that has been compiled using data supplied by the Government of Saint Lucia Ministry of Infrastructure, Port Services and Transport. The Coefficient of Variation values of the key soil mechanics parameters are reported and previously developed transformation models for estimating effective friction angle are updated. The Weibull statistical distribution is shown to be the best fit to the friction angle data.

Mt Gamalama is a volcanic island which has a history of tsunamigenic volcanic eruptions with known events in 1608, 1840, and 1871, where tsunami generation is suspected due to landslides or sector collapse of the steep flanks entering the Molucca Sea threatening the coastal population and infrastructure. The potential landslides were investigated by applying a limit equilibrium method and the generalized Hoek–Brown failure criteria. This resulted in a so-called factor of safety (FoS) which describes the Mt Gamalama slope stability level. The critical FoS values ranging from 1.945 to 3.361 have been obtained for the four sections of the Mt Gamalama edifice—the north, south, west, and east sides and are considered in a relatively stable condition. These values hold for a static condition only under gravity and in the absence of any volcanic activity. The application of so-called seismic loads kh of 0.103, and 0.155, 0.457, and 0.685, and magma pressures of 2–17 MPa due to vertical and tilted dyke intrusion decreases FoS values (FoS < 1.000) in all sections. We show that these additional factors destabilize the Mt Gamalama slopes and even lead to failure.

The cyclic fluctuations of matric suction and its influence on unsaturated soil mechanics in the active zone is largely disregarded in many slope stability calculations. However, the depth of the unsaturated zone can be significant, especially in semi-arid to arid climates where large portions of the slope are not governed by saturated soil mechanics. Additional tools are used to characterize historical climate and compare several factors that have resulted in changing landslide movement rates and magnitude. Infiltration of precipitation and snowmelt directly contributes to matric suction losses in the head scarp and is exacerbated by the presence of tension cracks. While groundwater levels are primarily correlated to changing movement rates in the Thompson River valley, seasonal changes in matric suction can influence the degree to which movement rates change. Climatic events and trends over the past few years alter the long-term soil water accumulation in the valley. By accounting for the additional strength or potentially rapid losses in strength due to increasing water content, it may be possible to develop a more complete understanding of the climate change mechanisms driving changing movement rates in the translational, metastable earthen slides that dominate the Thompson River valley.

The Indian Himalaya is very prone to landslides due to its complex geology and tectonic set-up along with high intensity rainfall and aggravated slope conditions as a result of anthropogenic activities. Landslide hazard assessment is very essential before any hill development construction activity begins. Engineering geological investigation forms the primary basis for any slope stability assessment leading to plan for any construction so that landslide occurrences are minimized. Engineering geological data for rock slope stability assessment can be very easily collected from the field. These data can be used for rock mass characterization and classification such as Geological Strength Index (GSI), Rock Mass Rating (RMR) and Slope Mass Rating (SMR). The paper describes these rock mass classification techniques and presents some field examples. The paper also presents application of these techniques to derive some relevant geotechnical parameters for numerical analysis to determine the stability of slopes in terms of factor of safety.

This paper contains the first results of an ongoing research dealing with post-fire mass movements in Italy. Although the attention of the scientific community is increasing worldwide, very few geo-hydrological processes occurring in burned areas are reported for Italy. As the probability of occurrence and magnitude of wildfires is expected to increase in the future because of climate change, more efforts should be made to deepen knowledge on interacting disturbances. Here, we present a case study regarding the erosional response after fire recurrence in a watershed located in NW Italy, where multiple flow processes occurred after six months since the last wildfire, as a consequence of different rainstorms. It contains a description of the geological and geomorphological background, the burn severity assessment together with the analysis of the triggering rainfalls and the outline of the main geomorphic effects that affected people and lifelines.

The development of a sports hall in the Unika Soegijapranata Campus in Central Java is constrained by geological conditions. At the time of land preparation, a crack appears on the fence of the sports hall foundation that was predicted as a sign that they have a soil creep. This condition has threatened the implementation of such development. Therefore, it is necessary to know the subsurface conditions, especially the sliding surface location and pattern of the existing cracks in the ground. This information is beneficial to avoid soil creep risk. In order to support the information, both the geological survey and seismic refraction were conducted in this location. According to the survey, it is found that the sliding surface was identified as volcanic breccia with the depth from 5 m up to 20 m. There are many faults found based on the seismic data, and many cracks appear on the surface, which suspected as the creep crown. Some areas of the sports hall are located in the soil creep crown. According to the drilling data and geo-electrical survey, the sliding surface location of the soil creep was identified within volcanic breccia layers. It is recommended to shift the planned location of the sports hall in order to avoid or minimize the soil creep risk.

Landslides are a common and widespread phenomenon in Slovenia, as they are in most European countries. Because we cannot avoid the risk of landslides and must live with it, it is important to understand and predict landslide dynamics. Research on landslide dynamics forms the basis of landslide hazard prevention and serves as a basic requirement for the development of prediction models and for defining prevention and mitigation measures. The principal aim of this study is to form a basis to predict real-time dynamics of landslides that have been posing a direct threat to settlement Koroška Bela (with approximately 2200 inhabitants) for centuries. Prediction modelling is based on monitoring and recognition of displacement triggering mechanisms and their interactions. The study area is located above the settlement of Koroška Bela (NW Slovenia, Karavanke) which exhibits a number of deep-seated landslides (the Urbas and Čikla landslides) in weathered siltstone and claystone.

Quantitative risk analysis is valuable tool in risk management, yet the calculation of risk is often hampered by a lack of quality spatial input data, particularly landslide event inventories. These event inventories provide information to determine the number, size and spatial location of landslides triggered by discrete events such rainfall or earthquakes. This paper presents an approach whereby we use historical New Zealand earthquake-induced landslide inventories to estimate the landslide hazard for the Franz Josef and Fox glacier valleys, West Coast, South Island, New Zealand, as no pre-existing complete earthquake-induced landslide inventories exist for this area of New Zealand. We outline a methodology for the calculation of earthquake-induced landslide magnitude-frequency relationships from the 2016 Mw 7.8 Kaikōura earthquake, the 1968 Mw 7.1 Inangahua earthquake, and the 1929 Mw 7.8 Murchison earthquake to determine the probability of a given volume of landslide occurring for different levels of ground shaking.

Natural terrain covers over 60% of the land area of Hong Kong. With the close proximity of developments to hillsides and high annual rainfall, Hong Kong is under a constant threat from natural terrain landslides. Over the past years, the Geotechnical Engineering Office (GEO) of the Civil Engineering and Development Department of the Hong Kong Special Administrative Region Government has applied state-of-the-art remote sensing techniques, for example, laser scanning, photogrammetry and interferometric synthetic aperture radar, in landslide risk management. These include landslide hazard identification and monitoring, post-landslide responses and residual risk management, design of landslide prevention and mitigation measures etc. This paper discusses the advantages of remote sensing technology and their applications to enhance the slope safety of Hong Kong. Pilot studies applying machine learning on identification of geological features from aerial imageries and further studies being/to be conducted are also covered.

The Hokkaido Eastern Iburi earthquake was occurred at 3:07 on 6th September 2018, the southern part of Hokkaido, Japan. At the same time, many mountain areas have slope failures in Atsuma. It is necessary to assess the mechanisms of the landslide from geological and topographic factors, rainfall, seismic motion, vegetation. The objective of our study investigates the relationship between slope failure and vegetation of the slope in Atsuma. This study compares the slope failure data with vegetation distribution data and DEM data. The whole analysis area is located in the watershed along the Habiu river. The vegetation distribution is investigated in the whole analysis area within the collapsing slope using spatial analysis of GIS. As a result, vegetation on the slope of the whole analysis area mainly distributed with Hardwood’s natural forest and Coniferous plantation, Weed. We do not fully clarify the classification of the vegetation distribution on the collapsing slope of the whole analysis area. Then, we focus on some small watershed to consider the classification of the vegetation distribution on the collapsing slope. The collapsing slope area in the study area is mainly covered with Coniferous plantations. The no collapsing area in the study area is mainly covered with Hardwood’s natural forest. Therefore, it is a possibility that the collapsing slopes of the Atsuma region are affected by the vegetation on each slope.

The International Consortium on Landslides (ICL) and The Global Promotion Committee of the International Programme on Landslides (GPC/IPL) have been responsible for organizing the World Landslide Forums (WLFs) every three years since 2008.