Slide Mass Research Articles

Evaluation of Seismic Slope Displacements Based on Fully Coupled Sliding Mass Analysis and NGA-West2 Database

AbstractIn this study, two predictive models for seismic slope displacements are developed based on an equivalent-linear fully coupled sliding mass model and 3,714 ground-motion recordings selected...

The Vaiont landslide: re-assessment of the evidence leads to rejection of the consensus

There appears to be a clear general consensus in the literature regarding four critical issues that define the problem of the October 1963 Vaiont landslide and its behaviour that are central to the disaster: (1) the 1963 failure was a reactivation of an ancient landslide; (2) failure took place along thin clay seams (already at residual strength); (3) the sliding surface had a ‘chair’ shape with a (sub)horizontal base; and (4) failure was triggered by inundation of the toe of the slide mass by rising reservoir levels. The key to understanding the Vaiont landslide is the failure surface geometry, which was controlled by the structural geology. It now appears that the so-called chair structure (that was assumed to define the shape of the failure surface) does not exist, and without it, the first consensual point is untenable, and the fourth may not contain the whole truth. We have systematically re-examined the published evidence and undertaken our own new research in order to test the logical and geotechnical validity of the four elements of the consensus. Glacial processes can account for the pre-failure morphology of the landslide site; the clay seams must therefore have been at peak shear strength as there was no ancient landslide. Tectonic processes can account for the failure surface geometry, which does not have a ‘chair’ shape, as well as small-scale structures; and rainfall appears to have been an essential element in the initiation and development of the landslide. Our findings largely contradict the consensus position and thus form the basis of a new overarching hypothesis for the landslide that should account for all of the observed and known features, events and data.

On the initiation, movement and deposition of a large landslide in Maoxian County, China

At 5 am 24th June 2017, a catastrophic landslide hit Xinmo Village, Maoxian County, Sichuan Province, China. The slide mass rushed down from an altitude of 3400m and traveled 2700 m in a high velocity. The 13 million m3 deposition buried the whole village and caused about 100 deaths. The source area of the landslide is located in a high steep slope, average slope angle is 40o and maximal angle is 65o. The strata are interbedded Triassic Zagunao Formation metamorphic sandstone and slate with the dip slope angle of 45°. Based on high-resolution satellite remote sensing image, UAV image, DEM data, and field investigation, failure mechanism, travel features, and deposit characteristics were analyzed. The results showed that this landslide was influenced by Songpinggou Fault zone. According to the topography before the failure, the landslide is located in the back scarp of an antecedent landslide induced by Diexi Earthquake in 1933. The bedding slope provided potential rupture surface. Historical seismic activities and long-term gravitational deformation caused rock mass accumulated damages. Weathering and precipitation weakened the rock mass and finally induced shearing and tension failure. A huge block detached from the top rock slope, pushed the past landslide deposits in the middle part, rushed out of the slope bottom in a high velocity and buried the Xinmo Village. The rapid movement entrained and brought the soil into the Songping Gully which recoiled with and bounced back from the opposite mountain.

Experimental study on impulse waves generated by a viscoplastic material at laboratory scale

This experimental study provides insight into impulse waves generated by a viscoplastic material. The viscoplastic material chosen is a stable polymeric gel called Carbopol Ultrez 10, which is approximately modeled as Herschel–Bulkley model. As observed from high-speed cameras, the viscoplastic material such as Carbopol moves as a long and thin train of material along the slope, and only a fraction of the sliding mass is engaged in generating the leading wave. Therefore, our primary objective is to study how much of the initial slide mass is able to contribute to the leading wave formation. For the sake of distinguishing the actual slide mass acting on the leading wave formation with the initial mass, we define the submarine slide mass when the leading wave reaches its maximum wave height as “effective mass”. In this work, we held the still water depth and slope angle constant, and varied the initial slide mass and slope length. Then, we measured the slide velocity, slide thickness, and slide mass at impact, as well as the wave amplitude and wave height. The results indicate that the effective mass is dependent on both the initial slide mass and the slope length. The ratio of the effective mass to the initial slide mass is less than 20% in our experimental range, and the ratio increases with larger initial mass. In addition, we also examined our experimental data with previous empirical equations developed from granular slides. By considering the effective mass instead of the initial slide mass, the prediction of impulse waves generated by viscoplastic material is significantly improved.

Comprehensive investigation of submarine slide zones and mass movements at the northern continental slope of South China Sea

Multi-beam bathymetry and seismic sequence surveys in the northern slope of the South China Sea reveal detailed geomorphology and seismic stratigraphy characteristics of canyons, gullies, and mass movements. Modern canyons and gullies are roughly elongated NNW–SSW with U-shaped cross sections at water depths of 400–1000 m. Mass movements include slide complexes, slide scars, and debris/turbidity flows. Slide complexes and slide scars are oriented in the NE–SW direction and cover an area of about 1790 and 926 km2, respectively. The debris/turbidity flows developed along the lower slope. A detailed facies analysis suggests that four seismic facies exist, and the late Cenozoic stratigraphy above the acoustic basement can be roughly subdivided into three sequences separated by regional unconformities in the study area. The occurrence of gas hydrates is marked by seismic velocity anomalies, bottom-simulating reflectors, gas chimneys, and pockmarks in the study area. Seismic observations suggest that modern canyons and mass movements formed around the transition between the last glacial period and the current interglacial period. The possible existence and dissociation of gas hydrates and the regional tectonic setting may trigger instability and mass movements on the seafloor. Canyons may be the final result of gas hydrate dissociation. Our study aims to contribute new information that is applicable to engineering construction required for deep-water petroleum exploration and gas hydrate surveys along any marginal sea.

Stability analysis of complex rock slopes reinforced with prestressed anchor cables and anti-shear cavities

To evaluate the stability of reinforced complex rock slopes, an evaluation method for slope stability is proposed in this paper. In the proposed method, the force equilibrium of the potential slide mass is analyzed by treating the traction on the potential failure surface as an external force. The potential sliding direction is assumed to be the opposite direction of the resultant shear force on the potential failure surface, and the factor of safety is defined as the ratio of the available resisting force to the actual mobilized force. Through classic cases, the proposed method successfully predicts the stability of a slope critical to failure, and is compared with the traditional methods. Finally, the proposed method is used for a stability analysis of the left bank slope of the Jinping first stage hydropower station, considering two main reinforcing measures, prestressed anchor cables, and anti-shear cavities. Results indicate that the effects of the anti-shear cavities are more positively significant than the effects of the prestressed anchor cables. The safety factor is remarkably increased by the anti-shear cavities, which validates the importance of anti-shear cavities on slope stability.

Is air pollution causing landslides in China?

Air pollution in China often exceeds “unhealthy” levels, but Chinese air is not only a threat from being breathed: the pollutants may also be causing fatal landslides. Very acid rain from severe air pollution falls widely in southwest China, where coal is a major energy source. We discuss where acid rain may provide an unsuspected link between mining and the fatal 2009 Jiweishan landslide in southwest China; it may have reduced the strength of a thin, calcareous, black sapropelic shale in Jiweishan Mountain by removing cementing carbonate minerals and sapropel matrix. Mining beneath the potential slide mass may not have directly triggered the landslide, but collapse of abandoned adits drained a perched aquifer above a regional black-shale aquiclude. Inflow of acid, oxygenated water and nutrients into the aquiclude may have accelerated the reduction of strength of the weakest rocks and consequently led to rapid sliding of a large rock mass on a layer of weathered shale left composed largely of soft, and slippery talc.

Prediction of landslide runout based on influencing factor analysis

Landslide runout predictions are essential for producing hazard maps and siting mitigation structures. Data from 55 catastrophic historical landslides in the mountainous area of China are used to determine how topography, material, triggering factors, volume, and initial posture of the slide mass influence runout. Plots and regressions between slide mobility, expressed in terms of the equivalent coefficient of friction (ratio of the fall height to the runout distance), and the slide volume show the necessity to exclude data from zones where motion is blocked by steep orthogonal slopes (“T-type topography”) in defining meaningful empirical relationships. Landslide material exerts strong control on runout, with colluvium showing the strongest dependence on slide volume. Rainfall-induced rockslides have higher mobility than gravity-induced rockslides, but rockslides triggered by great earthquakes may have lower mobility than gravity-induced rockslides. The extra sum of squares analysis results demonstrate that slide volume is the dominant predictor for estimating runout, with posture also influencing the runout distance of non-seismic rockslides. These results provide the basis for our new, multiple-factor predictive method for runout distance. The predicted runout distance in the test case was about 115% of the actual distance. This method may enhance the accuracy of runout distance estimates for landslides in the mountainous area of China.

Sedimentology and geomorphology of a large tsunamigenic landslide, Taan Fiord, Alaska

On 17 October 2015, a landslide of roughly 60×106m3 occurred at the terminus of Tyndall Glacier in Taan Fiord, southeastern Alaska. It caused a tsunami that inundated an area over 20km2, whereas the landslide debris itself deposited within a much smaller area of approximately 2km2. It is a unique event in that the landslide debris was deposited into three very different environments: on the glacier surface, on land, and in the marine waters of the fjord. Part of the debris traversed the width of the fjord and re-emerged onto land, depositing coherent hummocks with preserved source stratigraphy on an alluvial fan and adjacent moraines on the far side of the fjord. Imagery from before the landslide shows that the catastrophic slope failure was preceded by deformation and sliding for at least the two decades since the glacier retreated to its current terminus location, exposing steep and extensively faulted slopes. A small volume of the total slide mass remains within the source area and is topped by striated blocks (>10m across) and standing trees that were transported down the slope in intact positions during the landslide. Field work was carried out in the summer of 2016, and by the time this paper was written, almost all of the supraglacial debris was advected into the fjord and half the subaerial hummocks were buried by glacial advance; this rapid change illustrates how highly active sedimentary processes in high-altitude glacial settings can skew any landslide-frequency analyses, and emphasizes the need for timely field investigations of these natural hazards.

Oso, Washington, Landslide of March 22, 2014: Dynamic Analysis

This paper describes and explains the spectacular mobility of the 2014 Oso landslide, which was the cause of its fatal consequences. A geomorphic interpretation of the site conditions is used to reconstruct the landslide failure mechanism. Two numerical models are used to conduct an inverse runout analysis. The models implement a newly defined rheology appropriate for liquefied soils. It is shown that this landslide occurred in two phases, characterized by different material strengths. Although the temporal sequencing of the two phases remains somewhat ambiguous, it is clear that the distal phase underwent significant undrained strength loss (liquefaction) and travelled more than 1.4 km over a nearly horizontal surface. The proximal phase underwent brittle failure, with much less strength loss than the first phase. The parent material forming the slide mass was composed of insensitive, overconsolidated glaciolacustrine silt and clay, material not traditionally recognized as liquefiable. It is hypothesized that a substantial volume of liquefaction-prone soil was formed by colluvial softening of the parent material during the process of slope development prior to 2014.

Kinetic characteristics of debris flows as exemplified by field investigations and discrete element simulation of the catastrophic Jiweishan rockslide, China

The Jiweishan rockslide of June 5, 2009 in China provides an important opportunity to elucidate the kinetic characteristics of high-speed, long-runout debris flows. A 2D discrete element model whose mechanical parameters were calibrated using basic field data was used to simulate the kinetic behavior of this catastrophic landslide. The model output shows that the Jiweishan debris flow lasted about 3min, released a gravitational potential energy of about 6×10^13J with collisions and friction dissipating approximately equal amounts of energy, and had a maximum fragment velocity of 60–70m/s, almost twice the highest velocity of the overall slide mass (35m/s). Notable simulated characteristics include the high velocity and energy of the slide material, the preservation of the original positional order of the slide blocks, the inverse vertical grading of blocks, and the downslope sorting of the slide deposits. Field observations that verify these features include uprooted trees in the frontal collision area of the air-blast wave, downslope reduction of average clast size, and undamaged plants atop huge blocks that prove their lack of downslope tumbling. The secondary acceleration effect and force chains derived from the numerical model help explain these deposit features and the long-distance transport. Our back-analyzed frictions of the motion path in the PFC model provide a reference for analyzing and predicting the motion of similar geological hazards.

Understanding the triggering mechanism and possible kinematic evolution of a reactivated landslide in the Three Gorges Reservoir

More than 5000 landslides or potential landslides have been induced in the Three Gorges Reservoir (TGR) region since the impoundment in 2003, which have caused great damage and remain a huge threat to the dam and people living in the reservoir area. Understanding the deformation characteristics and failure mechanism of the landslides can be helpful in stability evaluation and landslide prediction. The primary aim of this study is to research the characteristics of the landslide motion and its relationships with environmental triggers, taking the Quchi landslide, a large, slow-moving, reactivated landslide in the TGR region, as an example. The instability clearly showed visible signs of movements since 2002, and after that, the slope has been experiencing persistent deformation. By combining 4 years of meteorological, hydrological data with displacement measurements from open fractures, deep boreholes, and surface points, as well as in situ observations, this paper reports the geological and geotechnical investigations performed to define the movement. The deformation is believed to be governed by reservoir water levels, while the precipitation has a minor effect. Seasonally, the slope movement has a very distinctive pattern with large deformation starting abruptly right after reservoir drawdown in June and lasting into late summer (September). Then there is a rapid transition to constant deformation (almost no displacement) as the reservoir level rises. The slope displacements appear to gradually increase every year, which suggests very high possibility of the large and overall failure of the slide. Both monitoring results and geomorphological observations have highlighted that the two active slide masses Q1 and Q2 would probably collapse in different kinematic evolution modes, i.e., the multistage failure and whole sliding motion.

The formation of the Wulipo landslide and the resulting debris flow in Dujiangyan City, China

The Wulipo landslide, triggered by heavy rainfall on July 10, 2013, transformed into debris flow, resulted in the destruction of 12 houses, 44 deaths, and 117 missing. Our systematic investigation has led to the following results and to a new understanding about the formation and evolution process of this hazard. The fundamental factors of the formation of the landslide are a high-steep free surface at the front of the slide mass and the sandstone-mudstone mixed stratum structure of the slope. The inducing factor of the landslide is hydrostatic and hydrodynamic pressure change caused by heavy continuous rainfall. The geological mechanical model of the landslide can be summarized as “instability - translational slide - tension fracture - collapse” and the formation mechanism as “translational landslide induced by heavy rainfall”. The total volume of the landslide is 124.6×104 m3, and 16.3% of the sliding mass was dropped down from the cliff and transformed into debris flow during the sliding process, which enlarged 46.7% of the original sliding deposit area. The final accumulation area is found to be 9.2×104 m2. The hazard is a typical example of a disaster chain involving landslide and its induced debris flow. The concealment and disaster chain effect is the main reason for the heavy damage. In future risk assessment, it is suggested to enhance the research on potential landslide identification for weakly intercalated slopes. By considering the influence of the behaviors of landslide-induced debris flow, the disaster area could be determined more reasonably.

Assessment of the Evolution of a Landslide Using Digital Photogrammetry and LiDAR Techniques in the Alpujarras Region (Granada, Southeastern Spain)

In this work a detailed analysis of the temporal evolution of the Almegíjar landslide is presented. It is a rock slide located in the Alpujarras region (Granada, Spain) that has developed over the last 30 years. Six datasets and photogrammetric flights corresponding to the years 1956, 1984, 1992, 2001, 2008, and 2010 were surveyed. The more recent flight of 2010 combined an aerial digital camera and a LiDAR sensor and was oriented by means of in-flight data and tie points. This 2010 flight allowed for the generation of a reliable and high-precision Digital Terrain Model (DTM). The other flights were oriented using second-order ground control points transferred from the 2010 flight, and the corresponding DTMs were prepared by automatic matching and subsequent editing from the stereoscopic models. After comparing the DTMs of different dates, it has been observed that the landslide was triggered after 1984 and since then has evolved in an irregular pattern with periods of variable activity. On average, the ground surface dropped more than 8 m in depleted zones and rose nearly 4 m in the accumulation zones, with a velocity catalogued as very slow (about 15–30 cm/year) over a time span corresponding to a degree VIII of diachroneity. The total volume of the mobilized mass of this large contemporary slide was about 300 × 103 m3.

Stabilisation of the Jackfield slope at Ironbridge Gorge, Shropshire

The Ironbridge Gorge in Shropshire, UK, is young in geological terms and is generally prone to slope instability. Jackfield is an area on the banks of the River Severn that has a record of known slippages; these are put into geological and historical context. A scheme was proposed to stabilise the slope, adopting a hybrid method of analysis and design. The evolution of this scheme is outlined with particular emphasis on the design of the piles that were a fundamental part of the solution. Piles were used to stabilise the landslide by mobilising available passive resistance in the underlying stable ground mass and transmitting that resistance into the overlying slide mass, adopting the Viggiani method. The difference between the approaches of the geotechnical and structural aspects of the design is discussed in some detail as the design team was careful to avoid compounding factors of safety; this is illustrated by a numerical example. The determination of pile strength is outlined and a worked example for ascertaining pile spacing is included along with installation details.

Stability analysis of the sliding process of the west slope in Buzhaoba Open-Pit Mine

To study the stability of the west slope in Buzhaoba Open-Pit Mine and determine the aging stability coefficient during slide mass development, the deformation band of the west slope and the slide mass structure of the 34,600 profile are obtained on the basis of hydrology, geology, and monitoring data. The residual thrust method is utilized to calculate the stability coefficients, which are 1.225 and 1.00 under sound and transfixion conditions, respectively. According to the rock damage and fragmentation and the principle of mechanical parameter degradation, the mechanical models of the slide mass development of the hard and soft rock slopes are established. An integrated model for calculating the slope stability coefficient is built considering water, vibration, and other external factors that pertain to the structural plane damage mechanism and the generating mechanism of the sliding mass. The change curve of the stability coefficient in the slide mass development is obtained from the relevant analyses, and afterwards, the stability control measures are proposed. The analysis results indicate that in the cracking stage of the hard rock, the slope stability coefficient decreases linearly with the increase in the length Lb of the hard rock crack zone. The linear slope is positively correlated to rock cohesion c. In the transfixion stage of the soft rock, the decrease speed of the stability coefficient is positively correlated to the residual strength of the soft rock. When the slope is stable, the stability coefficient is in a quadratic-linear relationship with the decreased height Δh of the side slope and in a linear relationship with anchoring force P.

Deformation and failure of the Xiaochatou Landslide under rapid drawdown of the reservoir water level based on centrifuge tests

The deformation and failure mechanism of landslides caused by reservoir water operations is a significant problem that is being addressed by researchers. The Xiaochatou Landslide in the Wudongde Reservoir area is taken as an example for the performance of centrifugal model tests under gravel conditions with the rapid drawdown of the reservoir water level. The data concerning the displacement and pore water pressure during this process show that the Xiaochatou Landslide, which is a complex landslide containing a shallow slide mass, middle slide mass and deep slide mass, is extremely sensitive to the rapid drawdown of the water level. The centrifuge tests show that the shallow slide mass will fail and that the middle slide mass will suffer a large displacement after a rapid decrease in the reservoir water level. Furthermore, the Xiaochatou Landslide exhibits the characteristics of retrogressive failure.

The reduction of friction in long runout landslides as an emergent phenomenon

AbstractCampbell et al. (1995) modeled long runout landslides as granular flow using a soft particle code. Their model essentially simulates landslides from first principles, and although no fluid or obvious mechanism for reduction of friction is included, the model successfully reproduced many field observations of landslides (e.g., the preservation of source stratigraphy in the final slide mass and a decreasing effective friction with increasing slide volume). We extend the work of Campbell et al. (1995) with a focus on the mechanism that reduces friction in these slides. We find sliding preferentially occurs when the overburden is relieved by pressure variations in the slide. Further analysis shows that our results are very similar to the predictions of the acoustic fluidization hypothesis. Moreover, we determine that for long runout landslides the wavelength of vibrations associated with acoustic fluidization is determined by the size of the rock fragments in the slide.

Stability analysis of stratified rock slopes with spatially variable strength parameters: the case of Qianjiangping landslide

Jurassic strata prone to slope failure are widely distributed in the Three Gorges Reservoir region. The limit equilibrium method is generally used to analyze the stability of rock slopes that have a single failure plane. However, the stability of a stratified rock mass cannot be accurately estimated by this method because different bedding planes have variable shear strength parameters. A modified limit equilibrium method is presented with variable water pressure and shear strength used to estimate the stability coefficient of a sloping mass of stratified rock and to identify the potential sliding surface. Furthermore, an S-curve model is used to define the spatial variations of the shear strength parameters c and ϕ of the bedding plane and the tensile strength of the rock mass. This model can also describe the variation of strength parameters with distance from the slope surface, which depends on the reservoir water level. Also, it is used to evaluate the stability of the Qianjiangping landslide, located at Shazhenxi Town, Zigui County, Three Gorges Reservoir area, China. The results show the most probable sliding surface is the interface between a slightly weathered layer and subjacent bedrock. When reservoir water rises above the elevation of the slide mass toe, the stability coefficient of the slope declines sharply. When the reservoir water level is static at 135 m, the stability coefficient decreases gradually as the phreatic line changes as a result of heavy rainfall.

Assessing post-failure mobility of submarine landslides from seismic geomorphology and physical properties of mass transport deposits: An example from seaward of the Kumano Basin, Nankai Trough, offshore Japan

A prominent paleo-landslide in the Slope Basin seaward of the Megasplay Fault in the Nankai Trough was emplaced by a relatively high-mobility mudflow based on analysis of physical properties and seismic geomorphology. Post-failure behavior of submarine landslides is a critical variable that determines amplitude of slide-generated tsunami but is historically difficult to constrain due to the wide variety of post-failure styles of submarine landslides. In recent controlled laboratory experiments, the ratio of the shear stress to yield strength (defined as the Flow Factor) controls a wide spectrum of mass movement styles from slow, retrogressive failure to rapid, liquefied flows. Here, we apply this laboratory Flow Factor approach to a natural landslide in the Nankai Trough by constraining pre-failure particle size analysis and porosity. Several mass transport deposits (MTDs), were drilled and cored at Site C0021 in the Nankai Trough during International Ocean Discovery Program (IODP) Expedition 338. The largest, MTD B, was encountered at 133–176m below seafloor and occurred approximately 0.87Ma. Slide volume is 2km3, transport distance is 5km, and average deposit thickness is 50m (maximum 180m). Pre-failure porosity was estimated from shallow sediments at Site C0018 (82%). Grain size distribution was measured directly from samples with the hydrometer method with the following averages: 37% clay-sized, 60% silt-sized, and 3% sand-size particles. Together, the porosity and clay fraction define the Flow Factor to be 3.5, which equates to a relatively high-mobility slide. We interpret that the landslide that created MTD B was a single event that transported the slide mass relatively rapidly as opposed to a relatively slow-moving cohesive style, landslide. This is supported by the observation in three-dimensional seismic data of a completely evacuated source area with no remnant blocks or retrogressive head scarp and an internally chaotic seismic facies with large entrained blocks. This back-analysis approach can be extended to other field settings characterized by fine-grained siliciclastics and where water content and clay percentages are known.