Earthquake-induced Slope Failures Research Articles

Assessment of seismic slope stability of Rangamati Hill Tracts, Bangladesh

Slope stability is an essential aspect of geotechnical engineering. Unstable slopes or stable slopes influenced by external factors may result in a catastrophic disaster called a landslide. In seismically active areas with steep terrain, landslides commonly occur and are regarded as one of the most severe threats. Bangladesh has not suffered any destructive earthquakes in recent years but has a considerable risk of facing such earthquakes owing to its geological conditions. Although slope failures occurring in the Rangamati Hill Tracts of Bangladesh are mainly rainfall-induced, due to the seismic risk in Bangladesh, it is essential to assess earthquake-induced slope failure in vulnerable areas. In this study, the authors analyzed the seismic slope stability at three locations in the Rangamati Hill Tracts using pseudostatic approaches. The pseudostatic approach with the variation in seismic force based on the seismic coefficient was utilized to determine the critical conditions. Using Newmark’s rigid block method, the permanent displacements for various slope conditions were calculated for the Kobe earthquake. The analysis provided crucial insight into the state of the locations. One location has a low factor of safety (FS) value at a slope angle of 30° or greater, whereas the others have a risk of slope failure at a slope angle of 50° or greater. Newmark’s displacement analysis also showed that the slopes at location 3 have the highest displacement at a lower slope angle, with location 1 and location 2 showing relatively better results than location 3. Structural and bioengineered preventive measures are needed in this area to reduce the vulnerability of possible slope failure.

Probabilistic Analysis of Earthquake-induced Failure and Runout Behaviors of Rock Slopes with Discrete Fracture Network

Earthquake-induced rock slope failure is one of the most destructive geohazards, posing serious threats to human lives and properties. The potential hazard of a rock slope, under the loading of earthquakes, can be assessed from its failure and runout characteristics, which are however affected by inherent fractures. To simulate the randomness of these inherent fractures, the discrete fracture network (DFN) modeling technique that is based on the Monte Carlo simulation (MCS) is often employed. It is worthwhile noting that different realizations of DFN can be sampled from different MCSs; however, only one realization of DFN is considered and studied in the conventional analysis. There exist differences between the arbitrarily selected DFN and true DFN; as such, the conventional deterministic analysis could cause uncertainty in DFN modeling and the potential hazard of a rock slope cannot be accurately evaluated. In such a circumstance, this paper proposes a probabilistic analysis of earthquake-induced failure and runout behaviors of fractured rock slopes, in which multiple realizations of DFN that are systematically generated with MCS are taken as inputs to the discrete element method (DEM) modeling of slope behaviors, thus, the uncertainty induced by DFN modeling can be explicitly considered and evaluated.

Evaluating earthquake-induced widespread slope failure hazards using an AHP-GIS combination

Landslides and slope failures are often caused by earthquakes. This study proposes a method to map earthquake-induced slope failure hazards that uses the analytic hierarchy process (AHP) and a geographic information system (GIS) for four districts where many slope failures were induced by earthquakes (the 2018 Hokkaido Eastern Iburi, 2016 Kumamoto, 2008 Iwate-Miyagi Nairiku, and 2004 Mid Niigata Prefecture earthquakes). The assessment system, which was based on the National Research Institute for Earth Science and Disaster Resilience landslide distribution maps, was analyzed using the methods of previously published. We considered the relationships between the earthquake-induced slope failure distributions and landslide hazard factors (elevation, slope angle, slope type, catchment degree, geology, and vegetation). These relationships were utilized for pairwise comparisons of the factors in the AHP analysis. The slope angle, slope type, and catchment degree exerted the highest effects on the slope failure distribution in the four districts. The four earthquake-induced slope failure distributions were highly consistent with the slope failure hazard rank. These results provide a practical method for evaluating earthquake-induced slope-failure hazards.

Buffer Zone Prediction for Simulated Earthquake-Induced Slope Failures in Mesilou, Kundasang, Sabah, Malaysia

The research area is located at Mesilou, Kundasang, Sabah at 1400 meters to 2000 meters from the sea level. It focuses on slopes of Pinousuk Gravel Unit, tilloid deposits from the glaciation of Mount Kinabalu during Late Pleistocene age. Four slopes were chosen for the estimation of ‘buffer zone’ of earthquake-induced slope failures. The simulation of the earthquake is conducted by using shaking table method and the earthquake event occurred in the research area on year 2018. The analysis shows the location of the buffer zones are within 1.5 meters to 13.5 meters from the toe of the slope, where the run-out distance is farther with the increment of shaking’s duration and slope height. Simulation analysis shows that all slopes have detrimental impact of the settlement area of Kg. Mesilou, Kundasang but only 60% to 87% of respondents are still staying in the area. However, 74% to 84% of respondents are willingly to relocate if given new disaster-free settlements.

Earthquake-Induced Flow-Type Slope Failure in Weathered Volcanic Deposits—A Case Study: The 16 April 2016 Takanodai Landslide, Japan

The aim of this paper is to provide new insight into the catastrophic mobility of the earthquake-induced flow-type Takanodai landslide that occurred on 16 April 2016, which had fatal consequences. A geological and geotechnical interpretation of the site conditions and experimental investigations of the mechanical behavior of weathered Kusasenrigahama (Kpfa) pumice are used to characterize the landslide failure mechanism. The results of large-strain undrained torsional shear tests indicate that Kpfa pumice has the potential to rapidly develop very large shear strains upon mobilization of its cyclic resistance. To evaluate the actual field performance, a series of new liquefaction triggering analyses are carried out. The liquefaction triggering analyses indicate that Kpfa pumice did not liquefy during the Mw6.2 foreshock event, and the hillslope remained stable. Instead, it liquefied during the Mw7.0 mainshock event, when the exceedance of the cyclic resistance of the Kpfa pumice deposit and subsequent flow-failure type of response can be considered the main cause of the landslide. Moreover, the combination of large cyclic stress ratios (CSR = 0.21–0.35)—significantly exceeding the cyclic resistance ratio CRR = 0.09–0.13)—and static shear stress ratios (α = 0.15–0.25) were critical factors responsible for the observed flow-type landslide that traveled more than 0.6 km over a gentle sloping surface (6°–10°).

Centrifuge modeling and analytical validation of seismic amplification in a slope during earthquakes – Implications to seismic slope stability analysis

Earthquake-induced slope failure causes enormous damage to structures above and below the slope. The acceleration amplified within the slope directly degrades the stability of the slope. However, the seismic amplification characteristics within a slope during earthquakes remains poorly identified. This study explores seismic amplification of a slope during earthquakes through dynamic centrifuge tests. Comparison of the acceleration amplification patterns between a slope model and a flat ground model revealed that the acceleration was concentrated at the crest and near the slope surface. This phenomenon was verified through the analytical model developed based on a multi-degree of freedom mass-damper-spring system. In addition, the analytical model enabled the computation of the peak acceleration at each part of the slope and allowed examination of the factor of safety for slope stability. While various locations within a slope can be chosen to determine the representative acceleration as well as the free-field flat ground response, the use of the acceleration at the crest resulted in the lowest factor of safety value. Therefore, a conservative analysis would preferably use the accelerations at the crest and on the slope surface, rather than using the accelerations in a free-field flat ground. This study presents unique ground acceleration data from the well-controlled physical modeling of a slope and a simple but robust analytical model to predict seismic amplification in a slope, which provides better insight into determination of ground acceleration for slope stability analysis.

Monitoring the changing seismic site response of a fast-moving rockslide (Brienz/Brinzauls, Switzerland)

SUMMARYSeismic measurements on unstable rock slopes are a complementary tool to surface displacement surveys to characterize and monitor landslides. A key parameter is seismic amplification, which tends to scale with the degree of rock mass degradation. Amplification also provides a direct measure of how the wavefield is intensified during seismic loading, eventually leading to coseismic failure. Here we present the dynamic response of the fast-moving Brienz/Brinzauls rock slope instability in Switzerland (10 $ \times $ 106 to 25 $ \times $ 106 m3), which threatens settlements and infrastructure in the area. The rockslide shows strong seismic amplification at two resonant frequencies with factors of up to 11 and wavefield polarization influenced by the local fracture network orientation. We monitored the dynamic response over a period of 30 months using ambient vibrations and regional earthquake recordings. We observed a change in wavefield polarization of up to 50°, coinciding with a rotation of the relative surface displacement vector field measured by geodetic systems, highlighting the linkage between wavefield polarization and stress field (i.e. rock mass kinematics). For the analysis of secondary, relative surface displacements, we propose a singular value filtering of the displacement field to remove the principal component of landslide motion. In addition, we found increased seismic amplification values after periods of strong precipitation, providing empirical field evidence that the local precipitation history is a key parameter for assessing the hazard of earthquake-induced slope failure.

SIMULATING EARTHQUAKE-INDUCED SLOPE FAILURES USING A SOLID-FLUID COUPLING MODEL BASED ON THE SMOOTHED PARTICLE HYDRODYNAMICS FRAMEWORK

Various numerical analysis methods have been developed to simulate earthquake-induced slope failures. Simulations of earthquake-induced slope failures require capabilities to reproduce some factors, including the trigger level of an input ground motion and a travel distance of debris. For reproducing a trigger level of an input motion, the finite element method based on solid mechanics has been used. For reproducing a travel distance of debris, simulation methods based on the fluid dynamics have been applied. This study presents a new approach to simulate an earthquake-induced slope failure, coupling the solid mechanics and the fluid dynamics, based on the framework of the smoothed particle hydrodynamics (SPH). The presented approach allows us to simulate an earthquake-induced slope failure from its triggering stage to its accumulation stage. The presented approach demonstrated its capabilities to reproduce the trigger level of ground motion and a travel distance of debris through several simulation cases. The paper concluded that the presented approach could be a promising method to simulate earthquake-induced slope failures.

EVALUATION OF EARTHQUAKE-INDUCED SLOPE FAILURE DISTRIBUTION USING THE AHP METHOD AND GIS

Landslides or slope failures are often caused by earthquakes. The 2018 Hokkaido Eastern Iburi Earthquake and the 2016 Kumamoto Earthquakes in Japan caused many slope failures that were distributed both widely and densely. This study proposes an earthquake-induced slope failure hazard mapping method that uses the analytic hierarchy process (AHP) and a geographic information system (GIS) for specific districts, the Atsuma district in Hokkaido and Minamiaso district in Kumamoto. The earthquakeinduced slope failure hazard assessment system used here is based on the landslide distribution (NIED catalog, Japan), which includes tens of thousands of locations in the Atsuma and Minamiaso districts. We considered the relationships between landslide distribution and landslide hazard factors (elevation, slope angle, slope type, catchment degree, geology, and vegetation). These relations were introduced to pairwise comparisons of factors in the AHP method. The AHP method was applied to evaluate the slope failure hazard rank. An earthquake-induced slope failure hazard map was created based on slope failure hazard ranks of I–V. As a result, slope angle, slope type, and catchment degree were found to exert maximum effects on slope failure distribution due to earthquakes in both the Atsuma district in Hokkaido and the Minamiaso district in Kumamoto. The two earthquake-induced slope failure distributions are almost consistent with the slope failure hazard rank. These results provide a practical method for evaluating earthquake-induced slope failure hazards.

Ground motion prediction equations for Arias Intensity using the Kik-net database

In seismic design, intensity measures are selected on the basis of how well these parameters correlate with the damage caused by earthquakes and on our ability to predict these intensity measures for a given earthquake scenario. As an index for the energy content of ground motions, Arias Intensity has proved to be efficient in several applications, including the prediction of earthquake-induced slope failure and damage in structures, and to a lesser extent liquefaction triggering. In this article, the Kiban-Kyoshin network (KiK)-net database is used to present ground motion prediction equations (GMPEs) for Arias Intensity of shallow crustal and subduction zone earthquakes. The proposed GMPEs are applicable for M 4-9. The predictive models incorporate the average shear-wave velocity over the upper 30 meters (VS30) for the prediction of site effects. The proposed relationships include additional attenuation for paths that cross the volcanic fronts and different attenuation for forearc and backarc regions of Japan.

Hazard-Consistent Earthquake Scenario Selection for Seismic Slope Stability Assessment

Design ground shaking intensity, based on probabilistic seismic hazard analysis (PSHA) maps, is most commonly used as a triggering condition to analyze slope stability under seismic loading. Uncertainties that are associated with expected ground motion levels are often ignored. This study considers an improved, fully probabilistic approach for earthquake scenario selection. The given method suggests the determination of the occurrence probability of various ground motion levels and the probability of landsliding for these ground motion parameters, giving the total probability of slope failure under seismic loading in a certain time interval. The occurrence hazard deaggregation technique is proposed for the selection of the ground shaking level, as well as the magnitude and source-to-site distance of a design earthquake, as these factors most probably trigger slope failure within the time interval of interest. An example application of the approach is provided for a slope near the highway in the south of Sakhalin Island (Russia). The total probability of earthquake-induced slope failure in the next 50 years was computed to be in the order of 16%. The scenario peak ground acceleration value estimated from the disaggregated earthquake-induced landslide hazard is 0.15g, while the 475-year seismic hazard curve predicts 0.3g. The case study highlights the significant difference between ground shaking scenario levels in terms of the 475-year seismic hazard map and the considered fully probabilistic approach.

Seismic response of the Lengzhuguan slope caused by topographic and geological effects

Earthquake-induced slope failure often results in a large loss of life and property, and thus, understanding how a slope responds to seismic shaking can reveal the mechanism and movement of this kind of phenomenon. After the 2008 Wenchuan earthquake, a dense array of strong earthquake seismographs were deployed along the Lengzhuguan slope, Luding County, Sichuan Province, Southwest China, to study the seismic response of the slope. Three main shocks were recorded in 2014 and 2015, with epicenter distances between 34 km and 70 km. Observation data show that the ground motion was polarized in the direction perpendicular to the elongation direction of the ridge (near 50° azimuth from North), with an amplification coefficient >10 and a ground motion amplification frequency band between 1.5 and 2.5 Hz. The results of a series of numerical simulation experiments conducted using the finite difference method indicate that the observed seismic response characteristics of the Lengzhuguan slope can be reproduced only by a heterogeneous model containing a loose deposit layer with a thickness of 30 m. It was found that geological and topographic conditions resulted in complex slope seismic response characteristics that were coupled in both time and frequency, and the geological conditions dominated the seismic response of the slope. In terms of co-seismic landslide hazard, more attention should be given to subsurface lithology and rock mass structure.

Dynamic centrifuge model tests and material point method analysis of the impact force of a sliding soil mass caused by earthquake-induced slope failure

Dynamic centrifuge model tests and associated analyses are carried out to develop a procedure for simulating the slope failure process during earthquakes and to evaluate the force of a sliding soil mass impacting a structure. This impact force is successfully measured in the dynamic centrifuge model tests using a slope height of 50 m in the prototype scale. The results of a pseudo-static limit equilibrium analysis, assuming a circular failure plane, show that a stability analysis can be an effective tool for evaluating the critical acceleration under which the slope failure starts, although it is not applicable for evaluating the runout distance or the impact force of the sliding soil mass to the structure. Therefore, an attempt is also made in this study to examine the applicability of empirical equations for evaluating the impact force by comparing the evaluated impact force using Hertz’s equation and an empirical equation based on fluid mechanics with the measured ones. The comparison reveals that these simple equations would not be able to estimate the impact force well, even though parameter setting is required for applying the equations. On the other hand, it is also found from a relevant analysis that the material point method (MPM) is an effective tool for simulating the failure behavior of a slope and for evaluating the impact force of a sliding soil mass induced by a slope failure.

A Field Data Acquisition Method and Tools for Hazard Evaluation of Earthquake-Induced Landslides with Open Source Mobile GIS

The PARSIFAL (Probabilistic Approach to pRovide Scenarios of earthquake Induced slope FAiLures) method was applied to the survey of post-earthquake landslides in central Italy for seismic microzonation purposes. In order to optimize time and resources, while also reducing errors, the paper-based method of survey data sheets was translated into digital formats using such instruments as Tablet PCs, GPS and open source software (QGIS). To the base mapping consisting of Technical Regional Map (Carta Tecnica Regionale—CTRs) at the scale of 1:10,000, layers were added with such sensitive information as the Inventory of Landslide Phenomena in Italy (Inventario dei Fenomeni Franosi in Italia—IFFI), for example. A database was designed and implemented in the SQLite/SpatiaLite Relational DataBase Management System (RDBMS) to store data related to such elements as landslides, rock masses, discontinuities and covers (as provided by PARSIFAL). To facilitate capture of the datum on the ground, data entry forms were created with Qt Designer. In addition to this, the employment of some QGIS plug-ins, developed for digital surveying and enabling of quick annotations on the map and the import of images from external cameras, was found to be of considerable use.

Evaluation of Isolation Risk in Mountainous Region Considering Road blockages Caused by Earthquake-induced Slope Failures: Application to 2004 Niigata-ken Chuetsu and 2016 Kumamoto Earthquakes

Evaluation of Isolation Risk in Mountainous Region Considering Road blockages Caused by Earthquake-induced Slope Failures: Application to 2004 Niigata-ken Chuetsu and 2016 Kumamoto Earthquakes

Probabilistic Approach to Provide Scenarios of Earthquake-Induced Slope Failures (PARSIFAL) Applied to the Alcoy Basin (South Spain)

The PARSIFAL (Probabilistic Approach to pRovide Scenarios of earthquake-Induced slope FAiLures) approach was applied in the basin of Alcoy (Alicante, South Spain), to provide a comprehensive scenario of earthquake-induced landslides. The basin of Alcoy is well known for several historical landslides, mainly represented by earth-slides, that involve urban settlement as well as infrastructures (i.e., roads, bridges). The PARSIFAL overcomes several limits existing in other approaches, allowing the concomitant analyses of: (i) first-time landslides (due to both rock-slope failures and shallow earth-slides) and reactivations of existing landslides; (ii) slope stability analyses of different failure mechanisms; (iii) comprehensive mapping of earthquake-induced landslide scenarios in terms of exceedance probability of critical threshold values of co-seismic displacements. Geotechnical data were used to constrain the slope stability analysis, while specific field surveys were carried out to measure jointing and strength conditions of rock masses and to inventory already existing landslides. GIS-based susceptibility analyses were performed to assess the proneness to shallow earth-slides as well as to verify kinematic compatibility to planar or wedge rock-slides and to topples. The experienced application of PARSIFAL to the Alcoy basin: (i) confirms the suitability of the approach at a municipality scale, (ii) outputs the main role of saturation in conditioning slope instabilities in this case study, (iii) demonstrates the reliability of the obtained results respect to the historical data.

Earthquake-induced slope failure susceptibility in eastern Nepal

Nepal is considered as one of the earthquake-prone countries in the region. Earthquake is a major concern of Nepal because of rapid population growth, poor land use planning, precarious settlement patterns, and poorly implemented building code. Earthquakes in Nepal have been reported since 1255 while major earthquakes were recorded in 1408, 1681, 1810, 1833, and 1866, 1934, 1980, 1988, 2011, and 2015. An earthquake in September 18, 2011 measuring 6.9 in Richter scale, killed 6 people and injured 30 people in Nepal. There were many roadside slope damages near the epicenter area. To assess the roadside slope damages after this earthquake, a field visit was conducted and a landslide inventory map along the roadside slope was prepared for most damaged area. This paper provides a comprehensive information about earthquake-induced slope failures occurred in the Mechi Highway of eastern Nepal and also discusses an approach of earthquake-induced slope failures hazard mapping in Nepal.

Hazard analysis of seismic submarine slope instability

To assess the risk associated with a submarine landslide, one must estimate the probability of slope failure and its consequences. This paper proposes a procedure to estimate the probability of earthquake-induced submarine slope failure (hazard) based on probabilistic seismic hazard analyses, ground response analyses and advanced laboratory tests. The outcomes from these analyses are treated in a probabilistic framework, with analytical simulations using mathematical techniques such as the first-order reliability method, Monte Carlo simulation and Bayesian updating. Fragility curves of slope failure during the earthquake (co-seismic) and after the earthquake (post-seismic) were developed in this study, and were shown to provide a clear and well-organized procedure to estimate the annual failure probability of a submarine slope under earthquake loading.

What we can learn about slope response to earthquakes from ambient noise analysis: An overview

Earthquake induced slope failures are responsible for a significant amount of life loss and damage, and their effective mitigation requires further advancements in our comprehension of slope behaviour under seismic shaking. One source of uncertainty in seismic landslide susceptibility assessment is the phenomenon of enhanced amplification of ground motion along down slope directions. This implies a strength demand beyond that estimated by standard slope stability analysis. An extensive accelerometer monitoring of slope dynamic response in areas exposed to seismic landslide hazard is unfeasible. An alternative approach can take advantage of recent development of reconnaissance techniques based on the analysis of ambient noise recorded by portable instruments. The most popular technique, known as Nakamura or HVNR method, consists in analysing H/V spectral ratios between Horizontal and Vertical components of Noise Recording, and allows the recognition of site resonance frequencies. The application of HVNR to complex site conditions typical of marginally stable slopes is often difficult and requires the development of “ad hoc” procedures both for acquisition and analysis of noise recording. Tests in different geologic and geomorphic settings show that an analysis of azimuthal variation of spectral ratios can reveal the presence and orientation of directional resonance, whereas the recognition of main resonance frequencies requires a proper selection of signals to be analysed. Efforts to evaluate amplification factors currently rely on numerical simulations, which in turn require S-wave velocity of slope materials. Ambient noise analysis in terms of velocity models can contribute through the inversion of H/V spectral ratios and surface wave velocity dispersion curves derived from the processing of multiple simultaneous noise recordings. However these applications require a correct identification of the nature of surface waves present in the noise recording.

A probabilistic evaluation of the size of earthquake induced slope failure for an embankment

The seismic design method for earth structures considers only the safety factor, subsidence and sliding displacement. However, the estimation of the size of slope failures is necessary to judge the remaining function of an embankment after an earthquake event. The size of slope failures due to an earthquake is investigated by considering the heterogeneity of the ground strength and was based on slope stability analysis of two case histories: the 2001 Geiyo Earthquake (Mj6.7) and 2009 Suruga Bay Earthquake (Mj6.5). As a result, we propose a method for slope failure size estimation based on the maximum slip surface. The proposed method enables a rational assessment of the functional loss of an embankment in terms of the slope failure size.