Shallow Slides Research Articles

Assessment of landslide susceptibility for civil protection purposes by means of GIS and statistical analysis: lessons from the Province of Modena, Italy

This paper is focused on the analysis of landslide susceptibility for civil protection purposes. A methodology was developed and applied to support measures aiming at landslide risk mitigation. It is based on GIS and the Weight of Evidence (WofE) method, which was preferred among several other statistical approaches because it is suitable for large areas, easy to interpret and simple to program. The latter feature is important for implementing a GIS tool aimed to facilitate Civil Protection in the updating of susceptibility maps. An application of the methodology was performed in a mountainous and hilly area of the Northern Apennines (Italy) located in the Province of Modena where landslides are a critical issue in terms of civil protection due to the recurrent damages to buildings, roads and infrastructures. According to the Region Emilia-Romagna Landslide Inventory Map (RER LIM), shallow slides and earth flows are by far the most widespread mass movement types. Hence, the susceptibility assessment concerned these two types of movements. The choice of the training set, based on active landslides, took into account possible limitations of the input data. The predisposing factors were lithology, slope, curvature, Slope Position Index, aspect, land use, distance from roads. The validation was conducted through the PRC and SRC curves, and direct checking (comparison with past occurrences, multi-temporal orthophotos and field surveys). The resulting models predicted the location of landslides in an acceptable manner. One map for each type of landslides was produced and afterwards they were combined in a single document to improve their intelligibility in a civil protection framework.

Topographical factor-based shallow landslide hazard assessment: a case of Dayi area of Guizhou Province in China

BackgroundThree groups of factors related to topography, geology and hydrology have influence on the triggering of shallow landslides in soil material. In this paper a single representative factor (T-factor) for the topography is proposed, which can be used to define threshold values for the possibility of shallow soil slides. This study was carried out in the Dayi area, Guizhou Province, China. During a heavy rainfall event on June 6, 2011, 230 shallow soilslides were triggered. In some slopes, no shallow landslides were triggered even though some of the topographical factors point to unstable high probability.ResultsWe isolated and analyzed the influence of the topography on the triggering of shallow landslides in catchments with almost identical hydrological and geological conditions and propose a new T-factor as a topographical indicator which is a combination of the slope angle, the upslope contributing area, the cross-section, and the free-face of a (potential) shallow landslide. Higher T-factor values are related to higher probabilities of shallow landsliding. The probability assessment with the topographical factor T was successfully validated in other areas of the USA and Japan.ConclusionsWithout information on the geological and rainfall conditions, a quick and primary prediction of shallow landsliding using the topographical factor T is proposed. Additionally a new R-factor is proposed as a rainfall indicator, which is a combination of the 1 hour rainfall and cumulative rainfall before the landslide event and the annual rainfall. Higher R-factor values are generally related to higher probabilities of shallow landsliding. The primary probability factor P, which is the combination of T and R, gives a final indication of the probability of shallow landsliding.

Combination of statistical and physically based methods to assess shallow slide susceptibility at the basin scale

Abstract. Approaches used to assess shallow slide susceptibility at the basin scale are conceptually different depending on the use of statistical or physically based methods. The former are based on the assumption that the same causes are more likely to produce the same effects, whereas the latter are based on the comparison between forces which tend to promote movement along the slope and the counteracting forces that are resistant to motion. Within this general framework, this work tests two hypotheses: (i) although conceptually and methodologically distinct, the statistical and deterministic methods generate similar shallow slide susceptibility results regarding the model's predictive capacity and spatial agreement; and (ii) the combination of shallow slide susceptibility maps obtained with statistical and physically based methods, for the same study area, generate a more reliable susceptibility model for shallow slide occurrence. These hypotheses were tested at a small test site (13.9 km2) located north of Lisbon (Portugal), using a statistical method (the information value method, IV) and a physically based method (the infinite slope method, IS). The landslide susceptibility maps produced with the statistical and deterministic methods were combined into a new landslide susceptibility map. The latter was based on a set of integration rules defined by the cross tabulation of the susceptibility classes of both maps and analysis of the corresponding contingency tables. The results demonstrate a higher predictive capacity of the new shallow slide susceptibility map, which combines the independent results obtained with statistical and physically based models. Moreover, the combination of the two models allowed the identification of areas where the results of the information value and the infinite slope methods are contradictory. Thus, these areas were classified as uncertain and deserve additional investigation at a more detailed scale.

Coupled Infiltration and Kinematic-Wave Runoff Simulation in Slopes: Implications for Slope Stability

Shallow translational slides are common in slopes during heavy rainfall. The classic model for the occurrence of translational slides in long slopes assumes rising saturation above a slip surface that reduces the frictional strength by decreasing the effective stress along soil discontinuities. The classic model for translational slope failure does not conform well to the nature of homogenous soils that do not exhibit discontinuities propitious to create perched groundwater over the soil discontinuity or slip surface. This paper develops an alternative methodology for the coupled numerical simulation of runoff and infiltration caused by variable rainfall falling on a slope. The advancing depth of infiltration is shown to affect the translational stability of long slopes subjected to rainfall, without assuming the perching of soil water over the slip surface. This new model offers an alternative mechanism for the translational stability of slopes that are saturated from the slope surface downwards. A computational example illustrates this paper’s methodology.

A combined triggering-propagation modeling approach for the assessment of rainfall induced debris flow susceptibility

Rainfall-induced shallow slides can evolve into debris flows that move rapidly downstream with devastating consequences. Mapping the susceptibility to debris flow is an important aid for risk mitigation. We propose a novel practical approach to derive debris flow inundation maps useful for susceptibility assessment, that is based on the integrated use of DEM-based spatially-distributed hydrological and slope stability models with debris flow propagation models. More specifically, the TRIGRS infiltration and infinite slope stability model and the FLO-2D model for the simulation of the related debris flow propagation and deposition are combined. An empirical instability-to-debris flow triggering threshold calibrated on the basis of observed events, is applied to link the two models and to accomplish the task of determining the amount of unstable mass that develops as a debris flow. Calibration of the proposed methodology is carried out based on real data of the debris flow event occurred on 1 October 2009, in the Peloritani mountains area (Italy). Model performance, assessed by receiver-operating-characteristics (ROC) indexes, evidences fairly good reproduction of the observed event. Comparison with the performance of the traditional debris flow modeling procedure, in which sediment and water hydrographs are inputed as lumped at selected points on top of the streams, is also performed, in order to assess quantitatively the limitations of such commonly applied approach. Results show that the proposed method, besides of being more process-consistent than the traditional hydrograph-based approach, can potentially provide a more accurate simulation of debris-flow phenomena, in terms of spatial patterns of erosion and deposition as well on the quantification of mobilized volumes and depths, avoiding overestimation of debris flow triggering volume and, thus, of maximum inundation flow depths.

Spatial distribution of landslides induced by the 2004 Mid-Niigata prefecture earthquake, Japan

On October 23, 2004, an earthquake with a moment magnitude of 6.8 occurred in the Chuetsu area of Niigata prefecture in Japan. This earthquake is known as the 2004 Mid-Niigata prefecture earthquake; the event was followed by severe aftershocks and caused many types of landslides such as surficial slides, shallow slides, and deep slides. A large number of landslides occurred in the upland village of Yamakoshi, destroying the entire village; in addition, a huge number of houses collapsed in Kawaguchi town. This study investigates the correlations between each type of landslide and the bedding plane orientation and dip, and other geomorphologic conditions. The landslide occurrence ratio (LOR) is used as an index to determine the correlation between the 2004 Mid-Niigata prefecture earthquake-induced landslides and the slope angle, slope aspect, rock type, and bedding plane orientation and dip. This work also proposes a methodology to determine the geometric alignment between the topography and the orientation of geological bedding planes. The method provides an efficient means of estimating the topography/bedding plane relationship over large areas.

The hydrogeological attributes and mechanisms of a receding sedimentary terrain in the Anambra Basin, Southern Nigeria

This research investigated the hydrogeological aspects associated with severe gulling and landsliding on a vulnerable sedimentary terrain in the context of the newly identified deformation patterns and large numbers of recently discovered scars clustering slopes on identical coordinates. Results of field survey, remote sensing, vertical electrical sounding and experimental analyses were presented to explain the causes and mechanisms of the mass movements ravaging the terrain. A digital elevation model accurately captured the diverse geomorphologic elements including landslide scars, hills, ridges, valleys, plains and rivers that matched field observations. The model aided the identification of previously unknown steep incised channels, active headcuts, unstable side walls and a seasonal river flowing near the slopes having large number of landslide scars. It was observed that areas that lay on higher elevations where the clusters occur were dominated by fresh scars while the moderate to low elevations were dominated by older ones. Majority of the slope failures initiated within the sandstone as shallow slides (<1 m to the sliding surface) covering <104 m2 with short runout distances. Bigger landslides, although few, occurred as isolated individual events initiated at the sandstone–shale boundary on distinct slopes. The steepness of the slopes seemed controlled by slope morphology (concavity) which probably influenced the number and distribution of landslide events. The steeper slopes were more concave and had the highest concentration of scars. Shallow water table (4–11 m) and increased instability (brittleness index) under increasing over-consolidation ratio are the critical failure factors.

Quantifying the contribution of grapevine roots to soil mechanical reinforcement in an area susceptible to shallow landslides

Hilly slopes cultivated with vineyards are often affected by rainfall-induced shallow landslides that cause destruction and loss of the cultivations. For this reason, the assessment of mechanical contribution from grapevine roots is fundamental for slope stability analyses and consequently for the slope preservation. In this context, our work aims to quantitatively evaluate the soil reinforcement given by grapevine roots. The selected study area (13.4km2), located in the region of Oltrepò Pavese in Northern Italy, is characterized by a high shallow landslides density and is constituted by vineyards in steep slopes. The tested soils are Haplic Calcisols, Petric Calcisols and Calcic Gleysols, with silt loamy or silty clay loamy textures, from high to very high carbonate content and low organic carbon and nitrogen contents. The rootstock of the grapevine is a combination of Vitis berlandieri and Vitis riparia with root systems, which reach average depths of up to 1.5m. The grapevine root density (number of roots and Root Area Ratio) is rather variable and is strongly correlated to soil permeability. In fact, the results show that low permeable soils have small number of roots and occur near recent shallow slides. Despite the differences of soil features, type of bedrock, grapevine plants age, vineyards row orientation and season collection, a unique relationship between root diameter and root tensile strength has been identified. Root reinforcement, related to the grapevine root system and evaluated using Fiber Bundle Model, shows the lowest values in correspondence of sites characterized by the lowest soil permeability, as in the study case Calcic Gleysols. The sites with these soil features, actually, are also those most affected by shallow instability in the past, indicating that their great susceptibility to shallow landslides. The results of this study also highlight the role played by different amounts of grapevine root reinforcement on the slope stability during rainfall conditions, which could lead to triggering, on the study area.

Rural earthen roads impact assessment in Phewa watershed, Western region, Nepal

This work describes current research being conducted in the Phewa watershed, near Pokhara in Nepal’s Middle hills, a moist sub-tropical zone with the highest amount of annual rainfall in Nepal (4,500–5,000 mm). The main purpose of this study is to focus on the increase and impact of rural earthen road construction in the Phewa watershed as part of land use changes over 30 years in one of Nepal’s most touristic regions. Research methods were interdisciplinary and based on a combination of remote sensing, field observations and discussions with community members. The study compared 30 year-old aerial photos with current high resolution satellite images to detect changes in the watershed road network. Secondly, 42 % of the watershed’s roads (138 km) were surveyed in order to inventory and quantify shallow landslide events. Using an erosion-characteristics grid, their main features were measured (location, size, type and dimensions of damaged areas, etc.) and a Geographic Information System data base was created. We then estimated economic impacts of these events in terms of direct agriculture lands losses and road maintenance. Results of the remote sensing analysis demonstrate that the road network increase is following an exponential trend, which enables us to predict future watershed road network scenarios. Field work investigations have demonstrated that unplanned road excavations are producing mainly embankment shallow planar soil slides and/or gullying which primarily affect roads themselves, wiping them out and blocking vehicle circulation, and secondly, destroying or burying agriculture lands. Along the 138 km surveyed, we calculated an amount of soil material released of about 70,000 cubic meters, which amounted to 99 cubic meters per kilometer annually. Of 179 cases of roadside erosion processes sampled, about 85 % directly impact roads or agricultural lands. The current mode of road construction which is currently occurring in Nepal is largely related with erosion and shallow landslide processes. Considering the exponential growth of rural earthen road networks, we would expect an increase of sediments released by roads and serious consideration must be taken if roads continue to be made without more careful methods. Through simple technologies using low cost and local resources along the lines of ‘green road’ or ‘eco-safe road’ approaches, it may be possible to reduce the impacts of rural road construction.

Learning distributed word representation with multi-contextual mixed embedding

Learning distributed word representations has been a popular method for various natural language processing applications such as word analogy and similarity, document classification and sentiment analysis. However, most existing word embedding models only exploit a shallow slide window as the context to predict the target word. Because the semantic of each word is also influenced by its global context, as the distributional models usually induced the word representations from the global co-occurrence matrix, the window-based models are insufficient to capture semantic knowledge. In this paper, we propose a novel hybrid model called mixed word embedding (MWE) based on the well-known word2vec toolbox. Specifically, the proposed MWE model combines the two variants of word2vec, i.e., SKIP-GRAM and CBOW, in a seamless way via sharing a common encoding structure, which is able to capture the syntax information of words more accurately. Furthermore, it incorporates a global text vector into the CBOW variant so as to capture more semantic information. Our MWE preserves the same time complexity as the SKIP-GRAM. To evaluate our MWE model efficiently and adaptively, we study our model on linguistic and application perspectives with both English and Chinese dataset. For linguistics, we conduct empirical studies on word analogies and similarities. The learned latent representations on both document classification and sentiment analysis are considered for application point of view of this work. The experimental results show that our MWE model is very competitive in all tasks as compared with the state-of-the-art word embedding models such as CBOW, SKIP-GRAM, and GloVe.

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.

Evaluation of storm wave-induced silty seabed instability and geo-hazards: A case study in the Yellow River delta

Models based on the theoretical framework of soil mechanics are presented to evaluate storm wave-induced silty seabed instability and geo-hazards through a case study in the Yellow River delta. First, the transient and residual mechanisms of wave-induced pore pressure are analyzed. Three typical models (i.e., elastic model, pore pressure development mode and elasto-plastic model) are proposed to calculate wave-induced stresses in the seabed. Next, mechanisms and calculation methods of wave-induced seabed instability modes such as scour, liquefaction, seepage instability and shear slide are proposed. Typical results of storm wave-induced excess pore pressure and seabed instability are given and relevant discussions are made. At last, the formation mechanism of geo-hazards in the Yellow River delta is analyzed based on the proposed mechanism and calculated results. Results and analysis indicate that both transient and residual mechanisms are important to storm wave-induced response of silty seabed and hence the elasto-plastic model is more appropriate. Complete liquefaction does not happen, while other types of instability occur mostly within 2–6m under the seabed surface. Wave-induced scour, seepage instability and shear slide are all possible instability modes under the 1-year storm waves, and scour is predominant for the 50-year storm waves. The formation mechanism of geo-hazards such as shallow slide and storm wave reactivation, pockmarks, silt flow and gully, disturbed stratum and hard crust in the Yellow River are well explained based on the proposed mechanisms and calculated results of storm wave-induced silty seabed instability.

Seismic performance of loess-mudstone slope by centrifuge tests

In this paper, we study the effect of the amplitude of input shaking on the dynamic response of a loess-mudstone slope through a series of staged centrifuge tests, including different amplitude earthquake excitations, in which the seismic performance of the slope models was analyzed and investigated. The derived outputs were processed to study the earthquake acceleration amplification effect and to assess the induced deformation mechanism in terms of the resulting displacements and deformation mode. The test results indicated that the amplification factors of peak ground acceleration (PGA) increased with increasing slope height, reaching maximum values at the crest. The amplification effect was also demonstrated on the slope surface. In addition, the predominant amplitude of the input seismic excitation was critical to the response of the slope. The results proved that the displacements in the loess layer were much larger than those in the weathered mudstone. Tensile cracks were formed mainly on the crest and the upper part of the slope, and failure modes were dominant at the slope surface. The location of the slide plane in the model was consistent with the location of maximum acceleration. A continuous shallow slide plane was formed in the loess layer. The analysis provides good information for identifying both surface movement and mass movement.

Initiation processes for run-off generated debris flows in the Wenchuan earthquake area of China

The frequency of huge debris flows greatly increased in the epicenter area of the Wenchuan earthquake. Field investigation revealed that runoff during rainstorm played a major role in generating debris flows on the loose deposits, left by coseismic debris avalanches. However, the mechanisms of these runoff-generated debris flows are not well understood due to the complexity of the initiation processes. To better understand the initiation mechanisms, we simulated and monitored the initiation process in laboratory flume test, with the help of a 3D laser scanner. We found that run-off incision caused an accumulation of material down slope. This failed as shallow slides when saturated, transforming the process into debris in a second stage. After this initial phase, the debris flow volume increased rapidly by a chain of subsequent cascading processes starting with collapses of the side walls, damming and breaching, leading to a rapid widening of the erosion channel. In terms of erosion amount, the subsequent mechanisms were much more important than the initial one. The damming and breaching were found to be the main reasons for the huge magnitude of the debris flows in the post-earthquake area. It was also found that the tested material was susceptible to excess pore pressure and liquefaction in undrained triaxial, which may be a reason for the fluidization in the flume tests.

Landslides triggered by the 3 August 2014 Ludian earthquake in China: geological properties, geomorphologic characteristics and spatial distribution analysis

On 3 August 2014, an earthquake of Mw 6.5 happened in Ludian County, Yunnan Province, China. This earthquake triggered hundreds of landslides of various types, dominated by shallow slides, deep-seated slides, rock falls, debris flow and unstable slopes. Using field investigations and remote sensing images, 413 landslides triggered by the Ludian earthquake were statistically analyzed. Statistical analyses show that most of the landslides are shallow slides with a small volume. Most of these landslides are concentrated near the epicentre with distances ranging from 6–12 km, especially at the upper slope along the river valley. The number of landslides increased with increasing distance from the epicentre (0–9 km) and then decreased with increasing distance from the epicentre (>9 km). The landslides decreased in density with increasing distance from the fault rupture. More than 70% of the landslides occurred on the right side of the Xiyuhe-Zhaotong fault, when viewed from Southwest (SW) to Northeast (NE). Slope aspect and gradient had a substantial influence on the landslide distribution and landslide density increased with increasing slope gradient. Approximately, 65% of the landslides happened at the back slope with respect to the earthquake epicentre.

Preliminary investigation of the 20 August 2014 debris flows triggered by a severe rainstorm in Hiroshima City, Japan

In the early morning of 20 August 2014, a high-intensity/low-duration rainstorm occurred in Hiroshima City, in southwest Japan. Within 3 h, the rainfall exceeded 200 mm, which is more than twice the monthly-average for this area. This heavy rainfall triggered 107 debris flows and 59 shallow slides, which caused 44 injuries, and 74 deaths. 133 houses were destroyed and an additional 296 houses were severely damaged. Most of the debris flows occurred in heavily weathered granite slopes, while others occurred in weathered hornfels slopes. A field investigation on two of the gullies in which the debris flows occurred was conducted in order to better understand the characteristics of the debris flows. The main purpose of this investigation was to understand the geomorphological and geological conditions, the soil properties, and the initiation/traveling mechanisms of the debris flows. The longitudinal and cross-sectional profiles along the two gullies were measured, beginning at the source areas and ending at the downstream limits of the deposition areas. For soil property determination, disturbed and undisturbed soil samples were collected for laboratory tests which included in-situ density measurement, grain size distribution analysis and triaxial compression tests. In the triaxial compression tests, consolidated-undrained compression tests under different confining stresses were conducted to measure the strength parameters of the strongly-weathered granite. Pore-water pressure controlled triaxial test was conducted to simulate the failure process of the slope given an increase of the pore-water pressure. Chemical analyses of the granite samples were also conducted in order to understand the degree of weathering of the granite in the debris flow gully. A high intensity, short duration, localized rainfall event initiated debris flows in very steep slopes. These were initiated as a thin sliding mass in weathered coarse-grained granite and hornfels, and became two different types of debris flow after traveling down the slopes. The slope angle and the cross section of the gully, and the grain size of the debris significantly controlled the motion behavior of the debris flows.

Database and spatial distribution of landslides triggered by the Lushan, China Mw 6.6 earthquake of 20 April 2013

On 20 April 2013, an earthquake with Mw 6.6 (Ms 7.0) hit Lushan County, Sichuan Province of China (30.3°N, 103°E), only 85km southwest of the 2008 Wenchuan Mw 7.9 event. The Lushan shock triggered a large number of landslides with various types, including highly disrupted shallow slides and rock falls, deep-seated landslides and large-scale rock avalanches. Post-earthquake high resolution aerial photographs and satellite images, as well as a series of pre-earthquake high resolution satellite images were collected to construct a detailed, accurate, objective, and complete coseismic landslide database/inventory, which was validated by field investigation in selected areas. Based on the aerial photographs (0.2 or 0.6m resolution) that partly cover the affected area and pre-earthquake satellite images, 14,580 coseismic landslides were recognized and mapped. In those areas without post-earthquake aerial photographs coverage, we mapped 7,948 more coseismic landslides based on post-earthquake satellite images (Rapideye images with 5m resolution and ZY-3 images including panchromatic images with 2.1m resolution and multi-spectral images with 5.8m resolution) and pre-earthquake satellite images. The 22,528 coseismic landslides, with a horizontal projection area of 18.88km2 and an estimated total volume of 41.56×106m3, were distributed in a nearly elliptic area of about 5,400km2. Correlations between coseismic landslide abundances and topographic, geologic, and seismic factors were analyzed on 15,546 landslides of area ≥100m2. Scatter plots between regional slope angle and landslide abundances in generalized homogeneous lithology combinations show no obvious relationship is present between them, which challenges the conclusions of previous studies. Combining the Lushan earthquake-triggered landslides with other events on reverse and/or thrust faults such as the 1999 Chi-Chi and 2008 Wenchuan shocks, we found that coseismic landslides tend to occur in areas enveloped by two or more imbricated reverse and/or thrust faults, rather than only along the seismogenic fault. The Lushan event shows a higher ability of triggering landslides compared with other earthquakes of similar magnitudes, which is likely due to the steep and rugged topography and fractured and densely jointed lithology resulted from long-term tectonic activity. The blind reverse seismogenic fault is likely also another significant factor. Based on detailed coseismic landslide inventory maps and databases of several recent major earthquakes such as the 2008 Wenchuan, 2010 Haiti, 2010 Yushu, and 2013 Lushan temblors, we suggest that the empirical correlations between earthquake magnitude and coseismic landslides need to be updated.

Seabed morphology and sedimentary processes on high-gradient trough mouth fans offshore Troms, northern Norway

Trough mouth fans (TMF) situated at the mouths of formerly glaciated cross-shelf troughs are important paleoclimatic archives. Whereas the sedimentary processes of large, low-gradient TMFs have received considerable interest, little attention has been paid to the other end member of this landform class, i.e. TMFs with higher slope gradients. Detailed swath-bathymetric data and seismic profiles from the continental margin offshore Troms, northern Norway cover three high-gradient TMFs (the Andfjorden, Malangsdjupet and Rebbenesdjupet TMFs; slope gradients generally between 1° and 15°), as well as inter-fan areas, which include two submarine canyons (the Andøya and Senja Canyon) and the Malangsgrunnen inter-fan slope. The present-day morphologies of the Andfjorden and Malangsdjupet TMFs have evolved from sediment transport and distribution through gully-channel complexes. The Andfjorden TMF has later been affected by a large submarine landslide that remobilized much of these complexes. The Rebbenesdjupet TMF is dominated by a number of small and relatively shallow slide scars, which are inferred to be related to small-scale sediment failure of glaciomarine and/or contouritic sediments. The canyons cut into the adjacent TMFs, and turbidity currents originating on the fans widened and deepened the canyons during downslope flow. The Malangsgrunnen shelf break and inter-fan slope acted as a funnel for turbidity currents originating on the upper slope, forming a dendritic pattern of gullies. A conceptual model for the high-gradient TMFs on the Troms margin has been compiled. The main sediment input onto the TMFs has occurred during peak glacials when the Fennoscandian Ice Sheet reached the shelf edge. The overall convex fan form and progradational seismic facies show that these glacigenic deposits were repeatedly distributed onto the fan. On the Andfjorden and Malangsdjupet TMFs, gully-channel complexes occur within such deposits. It is thus inferred that the steep slope of these TMFs promoted rapid transformation from small-scale slumps and debris flows on the upper slope, into partly erosive turbidity currents. These flows continued into the deep sea, thus promoting efficient sediment by-pass across the TMFs. This model can be applied to other TMFs situated at the mouths of other glaciated cross-shelf troughs. In contrast, low-gradient TMFs are found to be dominated by glacigenic debris flow deposits. Furthermore, gully-channel complexes demonstrating the presence of erosive turbidity currents on high-gradient TMFs are rare on low-gradient TMFs. Large submarine landslides occur at both high- and low-gradient TMFs.

Rain-triggered slope failure of the railway embankment at Malda, India

The common slope stability analysis is incapable of accurately forecasting shallow slides where suction pressures play a critical role. This realization is used for elaborate stability analyses which include soil suction to better predict rainfall-induced slides at railway embankment at Malda where three known cases of slope failures and train derailments occurred after heavy rainfall. The relationship between the soil–water content and the matric suction is established for the embankment soil. It is then used in the coupled analyses of seepage and slope stability to estimate performances of the embankment at different intensity and duration of rainfall. The numerical simulations are performed with the FE code Geo-Studio. The numerical results show significant reduction in the factor of safety of the railway embankment with the increase in the intensity and duration of rainfall. The effectiveness of the proposed mitigation measures including placement of 2 m-wide free draining rockfill across the slopes and drilling 5-m-long sheet pile wall at the toe of the embankment is studied numerically. The study confirms that the proposed mitigation measures effectively increase the factor of safety of the embankment and stabilizing it even in case of a heavy rainfall of 25 mm/h over 12 h.

Use of Live Poles for Stabilization of a Shallow Slope Failure

AbstractSoil bioengineering methods consisting of live poles and brush layers were used to stabilize shallow slides and control erosion on an embankment slope in eastern Ohio. Plant survival rates, slope movement, soil moisture content, and soil suction were measured. Load tests were performed to evaluate resistance of the poles, and results were used to estimate the stability of the repaired slope. Seven years after the repair was completed, vegetation is well established and the slope is stable, which is in agreement with calculated safety factors. This study indicates that soil bioengineering methods can be used for stabilization of shallow failures; however, the method may not be immediately effective, and the time of installation and soil moisture conditions are important for survival of the poles.