Natural Slope Failures Research Articles

Fiber bundle model applied to slope stability assessment: co-detection multi-threshold analysis for early warning

Forecasting the imminent failure of natural slopes is crucial for effective Disaster Risk Reduction. However, the nonlinear nature of geological material failure makes predictability challenging. Recent advancements in seismic wave monitoring and analysis offer promising solutions. In this study, we investigated the co-detection method, which involves real-time processing of micro-seismic events detected concurrently by multiple sensors, to provide easy access to their initial magnitude and approximate location. By studying the Fiber Bundle Model and considering the attenuation of seismic waves, we demonstrated disparities in the statistical behavior of various rupture types before global catastrophic failure. Comparing avalanches with attenuated seismic wave amplitudes directly measured at sensor locations, we observed differences in their evolution towards catastrophic rupture. Leveraging a network of seismic wave sensors, we showed that the co-detection method was effective in detecting precursory seismic events, even with weak signals, making it a valuable tool for monitoring and predicting unstable slopes. Additionally, we demonstrated that a multi-threshold analysis of co-detection activity allowed for instantaneous capture of the seismic activity structure on unstable slopes. These findings contribute to our understanding of slope stability and offer insights for improved hazard assessment and risk management.

Knowledge-driven method: a tool for landslide susceptibility zonation (LSZ)

ABSTRACT Gangtok, situated at the south-eastern part of the Sikkim state in India is the centre of the state’s administrative operations. Precambrian rocks comprising of foliated schists and phyllites are the major share of this city; slopes are therefore prone to regular landslides. There is a paradigm shift in disaster management policy of the city to emphasize disaster preparedness in order to ensure that human life and property are not harmed to the best possible. Apart from natural slope failure, now-a-days Gangtok city is more prone to frequent landslides as a result of recent road and building construction. Present research work deals with the development of Landslide susceptibility mapping (LSM) within the Gangtok Municipal Corporation (GMC) region by means of geospatial analysis. The weighted overlay method (WOM) is adopted for this purpose where, weights are assigned to various triggering factors based on expert opinion. Twelve triggering factors i.e., geology/lithology, slope morphometry, lineament density, water regime, rainfall, elevation, soil type, soil liquefaction, soil thickness, building density, relative relief, and land use/land covers (LULC) are considered for this analysis. Outcomes of LSM reveal that about 19 and 31 percent of the study area fall within very high and high susceptible zone respectively whereas, 30 and 18 percent of the city are categorized as medium to low susceptible categories respectively. The model generated LSM is further confirmed by using previous landslide events, yielding an overall accuracy of 80%.

Mechanical properties of Bermuda grass roots towards sandy and clay soil for slope reinforcement

Natural and man-made slope failure has been a phenomenon that has caused many deaths, destruction, and environmental damage. The use of bioengineering technique (grasses) has been widely approached for slope remediation work. However, slope failure still occurs even though it has been protected by a few grasses. Many previous findings have reported on root pull out and root tensile strength for different plant species. However, the type of soil was not taken into account. Therefore, this research was carried out to investigate the function of root mechanical properties in different types of soil. The dry and wet sieve analysis tests were performed to know the classification of the soil. In addition to that, the soil mineralogy test was also conducted to support the soil classification. Root tensile strength tests were carried out on well-grown and poorly-grown Bermuda grass toward sandy and clay soil in dry and wet conditions. The dry condition is considered the condition of Bermuda grass in hot weather, while the wet condition is the condition after the raining season. Bermuda grass was chosen since this type of grass is widely applied for slope stabilization. The site locations were chosen in Temerloh, Maran which consist of clay soil. The other locations chosen were Karak, Gambang, Kuantan, Dengkil, Batang Kali, Ulu Yam, Kuala Pilah, Gombak and Sabak Bernam consist of sandy soil. The results show that the single root of Bermuda grass has higher tensile strength in sandy soil with range values from 0.47 to 185 Mpa compared to clay soil with range values from 0.12 to 159.10 Mpa. In conclusion, the results indicate that soil is one of the factors that influence the growth of bioengineering techniques for slope reinforcement.

High alpine geotechnical real time monitoring and early warning at a large imminent rock slope failure (Hochvogel, GER/AUT)

Monitoring and early warning systems based on process dynamics gain importance to cope with an increasing number of alpine hazards. The imminent Hochvogel rock slope failure (up to ca. 260,000 m3) is paradigmatic of natural carbonate slope failure dynamics and a benchmark site for developing an effective monitoring and early warning system. The analysis of process dynamics shows constant movement rates (12 mm/a) over the last 3 years but also a response of specific cracks to heavy precipitation events resulting in factor 5 higher movement rates during wet periods. Here, we show valuable lessons learnt during the development of a reliable monitoring system under challenging environmental conditions. The insights into pre-failure slope dynamics acquired at the Hochvogel will help to detect precursors of a final failure and to warn early.

Effectiveness of filter gabions against slope failure due to heavy rainfall

Slope failures due to heavy rainfall events are phenomena that can cause serious damage to social infrastructures and the loss of lives. Based on previous studies, natural slope failures are generally shallow and originate at the slope toe where infiltrated rainwater has accumulated and saturated it. Hence, it is extremely important to prevent these initial failures from inducing entire slope failures. In the present study, firstly, 1 g model tests, called G series tests, were conducted. In the tests, a gabion filled with filter materials was placed at the slope toe of each model for reinforcement and to drain the accumulated rainwater from the slope toe. Filter gabions have been found to shrink the failure regions and to significantly extend the time until slope failures occur. The failure mechanism in the G series tests was almost similar to that in cases without filter gabions if focus was placed on the slope above the filter gabions. However, the drainage effect was small. Secondly, P series tests, in which a filter gabion with a pipe was introduced for each model, were conducted. The results of these tests indicated that the displacements significantly decreased as the diameter of the pipe and the depth of the pipe’s insertion to the surface layer increased. Water did not discharge through the pipe until the pore water pressure around the pipe reached positive values. The failures always started when a phreatic surface appeared on the slope surface. Thus, it is very important to prevent a phreatic surface from forming on the slope surface. The adequate arrangement of a filter gabion with a drainage pipe may increase the potential for slope stability.

Experimental study on failure of temporary earthen slope triggered by intense rainfall

In practice, intense rainfall is one of the major factors contributing to slip failure of man-made or natural earthen slopes, in particular in sandy strata. To explore the failure mechanism of the man-made earthen slope caused by intense rainfall, extensive indoor rainfall experiments in combination of DIC image technology were carried out. The rainfall-triggered slip failure modes were investigated with respect to shot-concrete covering the slope surface (scenario A), the paved roadway on the slope crest (scenario B), and exposed excavation slope (scenario C), respectively. Although the instability evolution mechanisms of these slopes were different for the three rainfall infiltration patterns, the sandy slopes had the same slip failure characteristics of linearity. Generally, the slope faced the highest risk of losing stability in scenario C; scenario A was more dangerous than scenario B at the same rainfall intensity. These results are helpful for professionals to understand the failure development of earthen slope triggered by intense rainfall and then implement appropriate remedial measures to mitigate relevant hazards.

Mechanism of the progressive failure of non-cohesive natural dam slopes

Progressive failure, which begins in the downstream slopes of dams, is one of the main failure modes for natural dams in the field. However, this failure mode lacks attention in the scientific literature, especially regarding its formation mechanism. In this paper, flume tests were conducted to simulate the progressive failure of a natural dam. The results show that the progressive failure process is induced by seepage water discharging on the downstream slope, including the erosion of individual soil particles, repeated minor slip failures, upward head-cutting erosion of the dam crest, and finally the collapse of the dam when the processes have evolved sufficiently. This study focuses on analyzing the initiation mechanism of soil particle migration. The influence of seepage and interflow stresses on the incipient erosion of soil particles is analyzed. In addition, the buoyancy of soil particles on the downstream slope surface is not considered in the vertical direction in this paper but in the direction perpendicular to the downstream slope surface. The paper also discusses how to estimate the occurrence of the progressive failure of a natural dam. In the estimation method, the stress of the interfacial flow, the seepage flow stress, and the friction stress of the soil particles are considered when the phreatic line reaches the downstream slope surface.

Borehole monitoring of thermo-hydro-mechanical rock slope processes adjacent to an actively retreating glacier

Most natural rock slope failures result from long-term strength degradation. It is often hypothesized that glacial retreat leads to enhanced progressive damage accumulation in adjacent rock slopes, due to mechanical unloading and changes to the thermal and hydraulic boundary conditions. However, direct observations of subsurface processes in a rock slope subject to glacial retreat are rare. In this paper, we present the design, implementation, and performance of a new borehole monitoring system installed on a rock slope in fractured crystalline rock located beside the glacier tongue of the retreating Great Aletsch Glacier (Valais, Switzerland). The three vertical, 50 m deep boreholes were instrumented to continuously monitor groundwater pressure, temperature and deformation at high resolution, in order to investigate thermo-hydro-mechanical coupled slope processes that drive progressive rock mass damage. We show that the system is capable of measuring both reversible and irreversible displacements along single fractures at magnitudes ranging between 0.001 mm to >2 mm in the studied rock slope, and that it is often possible to identify drivers of these deformation signals. The transient subsurface temperature field shows clear indications of former ice occupation in form of cold temperatures preserved at depth and superimposed annual temperature cycles penetrating down to a depth of about 17 m. The variability of the pressure head in the slope is driven by annual snowmelt infiltration cycles, rainfall events, and the assumed connection to englacial water of the temperate glacier. The new and continuously growing dataset presented here will enable us to relate the changing boundary conditions caused by glacial retreat and fatigue from daily to annual thermal and hydraulic loading cycles to progressive rock mass weakening, which may ultimately result in rock slope failure.

Shear behavior of unsaturated intact and compacted loess: a comparison study

Understanding the shear behavior of unsaturated intact and compacted loess is essential for analyzing rainfall induced failure of man-made and natural loess slopes. So far, comparison studies on the shear behavior of unsaturated intact and compacted loess are still incomplete. This study aims to investigate the shear behavior of intact and compacted loess under unsaturated conditions. To achieve this objective, consolidated-drained triaxial tests were carried out with 36 intact and compacted loess. Results show that the failure envelope of intact and compacted loess at different dry densities and suctions could be unified through the effective stress concept of unsaturated soil together with the Mohr–Coulomb failure criteria. Comparing with intact loess, compacted loess shows a unified failure envelope with a 15% larger slope (corresponding to a 14% larger friction angle). As evidenced from Scanning Electron Microscope (SEM) observations, significant amount of aggregates was developed during the preparation of compacted loess. Those aggregates may enhance the interlocking in the compacted loess and hence result in a relatively large friction angle. On the other hand, suction contribution to the effective stress of compacted loess is more significant than that of intact loess. This can be explained by the fact that the compacted loess contains larger amount of air–water interface and contact area between water and soil particle because of higher water retention capacity. Therefore, the effective stress contributed by the surface tension (i.e., air–water interface) and the negative pore-water pressure acting on the contact area is higher for compacted loess.

The 30 November 2018 Mw 7.1 Anchorage Earthquake

AbstractThe Mw 7.1 47 km deep earthquake that occurred on 30 November 2018 had deep societal impacts across southcentral Alaska and exhibited phenomena of broad scientific interest. We document observations that point to future directions of research and hazard mitigation. The rupture mechanism, aftershocks, and deformation of the mainshock are consistent with extension inside the Pacific plate near the down‐dip limit of flat‐slab subduction. Peak ground motions >25%g were observed across more than 8000 km2, though the most violent near‐fault shaking was avoided because the hypocenter was nearly 50 km below the surface. The ground motions show substantial variation, highlighting the influence of regional geology and near‐surface soil conditions. Aftershock activity was vigorous with roughly 300 felt events in the first six months, including two dozen aftershocks exceeding M 4.5. Broad subsidence of up to 5 cm across the region is consistent with the rupture mechanism. The passage of seismic waves and possibly the coseismic subsidence mobilized ground waters, resulting in temporary increases in stream flow. Although there were many failures of natural slopes and soils, the shaking was insufficient to reactivate many of the failures observed during the 1964 M 9.2 earthquake. This is explained by the much shorter duration of shaking as well as the lower amplitude long‐period motions in 2018. The majority of observed soil failures were in anthropogenically placed fill soils. Structural damage is attributed to both the failure of these emplaced soils as well as to the ground motion, which shows some spatial correlation to damage. However, the paucity of instrumental ground‐motion recordings outside of downtown Anchorage makes these comparisons challenging. The earthquake demonstrated the challenge of issuing tsunami warnings in complex coastal geographies and highlights the need for a targeted tsunami hazard evaluation of the region. The event also demonstrates the challenge of estimating the probabilistic hazard posed by intraslab earthquakes.

Deterministic and Probabilistic Analysis of Liquefaction for Different Regions in Bihar

The built environment and human life have been regularly affected by earthquakes. One of the most catastrophic earthquake hazards is liquefaction causing failure of embankment, earth structures, foundations, natural slopes and superstructures. In this paper, three methods have been used to predict the liquefaction susceptibility of some of high seismically active regions of Bihar such as Darbhanga, Samastipur, West-Champaran and Araria Sangram. The first method is based on semi-empirical approach, given by Idriss and Boulanger (in: Proceedings of 11th International conference on soil dynamics and earthquake engineering and 3rd International conference on earthquake geotechnical engineering vol 1, pp 32–56, 2006). The stress reduction factor (rd), overburden correction factor for cyclic stress ratios Kσ, earthquake magnitude scaling factor for cyclic stress ratios (MSF) and recently modified relations has been considered in this approach. The result is obtained in form of factor of safety at particular depth beneath the ground surface. The second approach is based on Muduli’s probabilistic method (2013) and third is on relevance vector machine (RVM) method developed by Karthikeyan et al. (Eur J Environ Civ Eng 17(4):248–262, 2013). RVM model has been used to determine the liquefaction potential of soil based on standard penetration test (SPT) blow count. The SPT data has been used as input parameter for the analysis. Site coming under high seismic zone is more susceptible to liquefaction during earthquake. This concludes that earthquake magnitude plays very important role for the assessment of liquefaction, irrespective of soil type and water table of the site. This paper contains the deterministic and probabilistic analysis of liquefaction behavior of soil.

INFLUENCE OF MATRIC SUCTION ON INSTABILITY OF UNSATURATED SILTY SOIL IN UNCONFINED CONDITIONS

Rainfall has been recognized as one of the main causes of natural or manmade slope failure inmany tropical areas of the world. In order to reduce and mitigate rainfall-induced slope failures, there is a needto develop an understanding of reduction in shear strength of soil due to water infiltration. This research aimedat understanding the influence of matric suction on water infiltration and transformation of shear strength inunsaturated soil in unconfined condition. In the present study, two types of test series have been performedusing modern triaxial test apparatus: (1) shear-infiltration test, and (2) pre-wetting shear test. From test results,it was concluded that water infiltration causes the excessive deformations and softening which decreases thecohesion and hence reduces the shear strength of the soil. The more decrease in shear strength was witnessedin case of pre-wetting shear tests and maximum reduction observed was 85% against 36cm3 of infiltrated water.

Storm Water Scouring Simulation Analysis on Vegetated Slope

The ecological concept has become more widespread and biotechnical slope protection has been accepted by more people as environmental policies become more stringent. Biotechnical slope protection has become widely used because of its unique features, which include wave resistance, waterproof flow-scour protection, greening and landscaping effects, environmental friendliness, and positive social benefits. Slope surfaces are exposed to and affected by natural conditions, particularly storm-water scouring, which has an obvious impact on slope instability. However, most previous studies have focused on soil reinforcement by plant root systems in non-saturated soil conditions, and soil reinforcement in saturated soil conditions after rainfall has rarely been studied. In this study, we conducted laboratory-based storm-water scouring experiments to assess the erosional effect of storm-water scouring on slopes, reveal the mode and process of failure of natural and vegetated slopes under storm-water scouring, and develop and refine the mechanism and theoretical understanding of soil reinforcement by plants.

Slope stability analysis using artificial intelligence techniques

Natural and man-made soil slope failures are complex phenomena and cause serious hazards in many countries of the world. As a result, public and private property is damaged worth millions of dollars. It is necessary to understand the processes causing failure of slopes and prediction of its vulnerability for proper mitigation of slope failure hazards. Various attempts have been made to predict the stability of slope using both conventional methods such as limit equilibrium method, finite element method, finite difference method and statistical methods. Artificial intelligence (AI) methods like artificial neural networks, genetic programming and genetic algorithms, and support vector machines are found to have better efficiency compared to statistical methods. The present study is an attempt to use recently developed AI methods such as functional networks (FNs), multivariate adaptive regression splines (MARS), and multigene genetic programming (MGGP) to predict factor of safety of slope using slope stability data available in the literature. Prediction model equations are also provided, which can be used to predict the factor of safety of a slope. The performances of these AI techniques have been evaluated in terms of different statistical parameters such as average absolute error, maximum absolute error, root mean square error, correlation coefficient, and Nash–Sutcliff coefficient of efficiency. Of the available models, MARS model had better prediction performance in comparison with MGGP and FN models in terms of the above statistical criteria.

Trends in large-deformation analysis of landslide mass movements with particular emphasis on the material point method

Traditional geotechnical analyses for landslides involve failure prediction (i.e. onset of failure) and the design of structures that can safely withstand the applied loads. The analyses provide limited information on the post-failure behaviour. Modern numerical methods are able to simulate large mass movements and there is an opportunity to utilise such methods to evaluate the risks of catastrophic damage if a landslide occurs. In this paper, various large-deformation analysis methods are introduced and their applicability for solving landslide problems is discussed. Since catastrophic landslides often involve seepage forces, consideration of the coupled behaviour of soil and pore fluid is essential. Two approaches to model soil–pore fluid coupling in large-deformation analysis using the material point method (MPM) are introduced. An example simulation is presented for each approach; one on a model levee failure and the other on a natural cut slope failure (the Selborne experiment conducted by Cooper and co-workers in 1998). In the levee failure case, MPM simulation was able to capture a complex failure mechanism including the development of successive shear bands. The simulation was also able to predict excess pore pressure generation during the failure propagation and the subsequent consolidation stage. The simulations demonstrated the importance of the dilation characteristics of soil as well as changes in geometry for the post-failure behaviour. In the Selborne case, MPM was able to simulate the progressive failure of brittle, overconsolidated clay. The evolution of shear stresses along the failure surface was also captured by the MPM. The changes in the pore pressure and the actual shape of the failure surface were simulated by the MPM. The importance of accurately modelling the shear band within the MPM framework is highlighted.

1G場での振動実験による斜面模型の崩壊挙動の分析

1G場での振動実験による斜面模型の崩壊挙動の分析

Laboratory and modelling investigation of root-reinforced system for slope stabilisation

Most natural slope failures are induced by seepage and/or rainfall. Soil bioengineering is an environmentally friendly method which employs vegetation to reinforce the soil in sloping terrain. The vegetation can contribute to slope stability in two ways, mechanical and hydrological. This paper demonstrates the effect of a vegetation root matrix on a soil slope and focuses on mechanical reinforcement using an example of vetiver grass. Vetiver grass (Vetiveria nemoralis A. Camus) specimens, grown for under a year, were used in this study. The investigation programme includes root observations, direct shear tests and centrifuge model tests. The growing rate of the vetiver roots and the root area ratios were observed during the tests. The cohesion and angle of internal friction of root-reinforced soils were determined from a standard direct shear apparatus and a large direct shear apparatus. A series of centrifuge tests was carried out to demonstrate the effect of vegetation on seepage- and rainfall-induced slope failures. The results indicate that the vetiver roots showed rapid growth within a year and that the shear strength of the root-reinforced soil was significantly increased by the bundle of roots. The results also reveal that the bundle of root fibres in the centrifuge model tests helped to reduce the deformation of the soil slope due to instability by increasing the shear strength of the slope.

Crustal stress changes and characteristics of damage to geo-engineering structures induced by the Great East Japan Earthquake of 2011

T he Great 2011 Earthquake of East Japan, with a moment magnitude of 9.0, occurred off the shore of the Tohoku Region of Japan. Although seismologists anticipated an earthquake with a magnitude of 7.5 in the source area, the magnitude of this earthquake was much greater than anticipated. Furthermore, the level of the tsunami induced by this earthquake also exceeded expectations. Therefore, damage caused by the tsunami was tremendous and more than 18,000 people perished due to insufficient counter-measures. The author first presents characteristics of the earthquake and its associated tsunami and then describes damage to some geo-engineering structures. The final part of the article describes lessons learned from this earthquake and proposes recommendations. Changes in crustal stress occurred as forecasted by computations and in situ stress measurements. However, it is expected the orientation of the maximum principal stress would remain almost the same as those prior to the earthquake. The scale and number of slope failures were much larger on the hanging wall side of the earthquake fault as compared to those on the foot-wall side. It has also become clear that the scale of natural slope failures is much larger than that of cut-slopes (man-made) and, therefore, more attention should be given to potential natural rock slope failures. In addition, slope failures may also be induced by tsunamis, thus necessitating further studies on the effect of tsunamis on rock slopes, with consideration of their structural geological features. Strong ground shaking induced the collapse of semi-underground tunnel portals in the abandoned Oya quarries. In addition to potential caving of abandoned mines and quarries during earthquakes due to either pillar failure and/or roof failure, groundwater may present additional impacts on immersed mines. Sinkholes are thought to be due to ground rupture induced by the sloshing of groundwater in inclined shafts. Tsunami waves inundated many tunnels on the Onagawa, Minami-Sanriku and Kesennuma railways, although they did not cause any major structural damage. However, consideration should be given to the impact of high internal hydrostatic water pressure on conventional tunnels when they are located in tsunami-prone areas.

Study on mechanism of retrogressive slope failure using artificial rainfall

Many slope failures have been observed in the mountainous environments of the world due to rainfall events. However, studies related to the correlation of rainfall intensity, sliding initiation time and the position of slip surface head are still lacking. Studies on the mechanisms of retrogressive slope failure that may occur in a series and the down-slope displacement of failure mass are also rare. In this study, slope failure experiments were performed using medium-grained silica sand S6 to prepare the model slope in a 5m long, 30cm wide and 50cm deep rectangular flume. The experiments consisted of detailed observations of failure process consisting series of failures successively, with particular emphasis on the time of failure; shape, size and position of the slip surface; and final shape of the model slope after down-slope displacement of the failure masses. Moisture profiles at different points within the model slope soil domain and the profile of surface-water forefront were also reported. The observations showed that the slope failure initiating once at the region near the toe results in successive sliding failures in a series, thereby propagating an unstable zone toward the up-slope. When the slope failure initiates at the region toward the head reach, the successive failures may propagate toward the down-slope first, and then again toward the up-slope. This study also noticed a strong correlation between rainfall intensity, sliding initiation time and the position of its slip surface head. The relationship might depend on the shape and size of the model slope and the type of material used in the formation of the model slope. However, the results indicate the possibility of finding a relationship among rainfall intensity, sliding initiation time, and the position of its slip surface head in a natural slope failure prone zone. A landslide model test and application in real field, based on the similarity theory, may reveal the relationship more realistic. Then it would have a significant impact on policy making to mitigate the probable catastrophe during extreme rainfall-induced landslide disaster.

Controls on the size and geometry of landslides: Insights from discrete element numerical simulations

We use numerical two-dimensional discrete element method (DEM) to study the controls on the size and geometry of an individual landslide. This method allows us to analyze the temporal and spatial evolution of slope failure and landsliding from the intact, pre-failure slope to the restabilized, post-failure slope.The size of our simulated landslides reflects the amount of disintegrated material available for sliding, which is controlled by the peak strength of the slope material and to a lesser degree by the pre-failure slope angle. The observed size of natural landslides, therefore, reflects mainly the local natural material strengths. We hypothesize that the observed global characteristic landslide size is a result of the limited thickness (generally up to a few meters) of disintegrated and weathered material that exists on hillslopes, poised and ready for sliding. The primary controls on the landslide geometry, quantified as the ratio of their thickness to length t/l, prove to be the residual friction angle of the slope material and the original slope angle. The t/l is observed to be unchanged for a given initial slope angle and independent of the slope material peak strength or the slope height. We suggest that the narrow range of observed natural t/l is a result of narrow ranges of mechanical properties and initial slope geometries involved in natural slope failure.