Numerical investigation on the initiation mechanism of debris-flow under rainfall

Rainfall is an important factor to trigger the debris flow.Numerical simulation on the responses of slopes and the initiation of debris flow under rainfall was processed by using the software FLAC2D based on the soil parameters in Weijia Gully,Beichuan County,Sichuan Province,China.The effects of the slope angle,rainfall intensity,soil parameters on the developments of the stress and pore pressure and deformation of the slope were studied.It indicates that large displacements of the slope are mainly located near the slope toe.With the increase of the rainfall intensity the stability of the slope decreases and so the debris-flow is easy to occur.     

Field observation of debris-flow activities in the initiation area of the Jiangjia Gully,Yunnan Province,China

The Jiangjia Gully, which is located in Dongchuan District, Yunnan Province, China, is a watershed prone to debris flows and has long-term recorded data of debris-flow occurrence. However, the initiation mechanism has mainly been studied by experiments in this watershed. To further reveal debris-flow formation mechanism in the Jiangjia Gully, debris-flow activities in the initiation zone were observed with hand-held video cameras in the summer of 2016 and 2017. In these two years, six debris-flo...     

Morphodynamics and sediment connectivity index in an unmanaged,debris-flow prone catchment: a through time perspective

Torrential processes are among the main actors responsible for sediment production and mobility in mountain catchments. For this reason, the understanding of preferential pathways for sediment routing has become a priority in hazard assessment and mitigation. In this context, the sediment Connectivity Index(IC) enables to analyse the existing linkage between sediment sources and the selected target(channel network or catchment outlet).The IC is a grid-based index that allows fast computation of ...     

Field investigations and numerical modeling of a giant landslide in the region of Eastern Himalayan Syntaxis:Jiaobunong landslide

Eastern Himalayan Syntaxis (EHS) is a tectonically active region that undergoes continuous geomorphic changes.Large landslides are predominant in this region.A ...     

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

At 5 am 24 th June 2017, a catastrophic landslide hit Xinmo Village, Maoxian County, Sichuan Province, China. The slide mass rushed down from an altitude of 3400 m and traveled 2700 m in a high velocity. The 13 million m~3 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.     

Debris flows introduced in landslide deposits under rainfall conditions: The case of Wenjiagou gully

Debris flows often occur in landslide deposits during heavy rainstorms. Debris flows are initiated by surface water runoff and unsaturated seepage under rainfall conditions. A physical model based on an infinitely long, uniform and void-rich sediment layer was applied to analyze the triggering of debris-flow introduced in landslide deposits. To determine the initiation condition for rainfall-induced debris flows, we conducted a surface water runoff and saturated-unsaturated seepage numerical program to model rainfall infiltration and runoff on a slope. This program was combined with physical modeling and stability analysis to make certain the initiation condition for rainfall-introduced debris flows. Taking the landslide deposits at Wenjiagou gully as an example, the initiation conditions for debris flow were computed. The results show that increase height of surface-water runoff and the decrease of saturated sediment shear strength of are the main reasons for triggering debris-flows under heavy rainfall conditions. The debris-flow triggering is affected by the depth of surface-water runoff, the slope saturation and shear strength of the sediment.     

Effects of loose deposits on debris flow processes in the Aizi Valley,southwest China

Loose deposits, rainfall and topography are three key factors that triggering debris flows.However, few studies have investigated the effects of loose deposits on the whole debris flow process.On June 28, 2012, a catastrophic debris flow occurred in the Aizi Valley, resulting in 40 deaths.The Aizi Valley is located in the Lower Jinsha River,southwestern Sichuan Province, China. The Aizi Valley debris flow has been selected as a case for addressing loose deposits effects on the whole debris flow process through remote sensing, field investigation and field experiments. Remote sensing interpretation and laboratory experiments were used to obtain the distribution and characteristics of the loose deposits, respectively. A field experiment was conducted to explore the mechanics of slope debris flows, and another field investigation was conducted to obtain the processes of debris flow formation, movement and amplification. The results showed that loose deposits preparation, slope debris flow initiation,gully debris flow confluence and valley debris flow amplification were dominated by the loose deposits.Antecedent droughts and earthquake activities may have increased the potential for loose soil sources in the Aizi Valley, which laid the foundation for debris flow formation. Slope debris flow initiated under rainfall, and the increase in the water content as well as the pore water pressure of the loose deposits were the key factors affecting slope failure. The nine gully debris flows converged in the valley, and the peak discharge was amplified 3.3 times due to a blockage and outburst caused by a large boulder. The results may help in predicting and assessing regional debris flows in dry-hot and seismic-prone areas based on loose deposits, especially considering large boulders.     

Reconstruction of debris-flow activity in a temperate mountain forest catchment of central Mexico

The use of dendrochronology to study and date geomorphic processes in volcanic environments is still incipient, even more so on the volcanic slopes covered by temperate forests in central Mexico. Mass movements, such as debris flows, often impact forest stands where they cause damage to individual trees, thereby generating growth disturbances(GD) in the tree-ring records. The identification and dating of GD enables reconstruction of the age of trees colonizing bare surfaces after major events, but also allows the assessment of the frequency or spatial distribution of past geomorphic process activity. Here we used increment cores from 65 Pinus leiophylla, Abies religiosa, and Alnus jorullensis trees growing in the Axal gorge, on the southern slopes of La Malinche volcano, to unravel past debris-flow activity both temporally and spatially. Based on the combination of GD records, a weighted tree response index(Wit), field evidence and hydrometeorological records, we reconstructed 23 debris flows since 1933.Interestingly, almost two-thirds of the reconstructed years with debris-flow activity in Axal gorge match with events recorded in Axaltzintle gorge located on the NE slopes of La Malinche. These findings suggest a regional triggering mechanism, most likely related to the occurrence of hurricanes. This research could be useful for disaster risk management of the La Malinche National Park.     

Effect of rainfall on a colluvial landslide in a debris flow valley

A colluvial landslide in a debris flow valley is a typical phenomena and is easily influenced by rainfall. The direct destructiveness of this kind of landslide is small, however, if failure occurs the resulting blocking of the channel may lead to a series of magnified secondary hazards. For this reason it is important to investigate the potential response of this type of landslide to rainfall. In the present paper, the Goulingping landslide, one of the colluvial landslides in the Goulingping valley in the middle of the Bailong River catchment in Gansu Province, China, was chosen for the study. Electrical Resistivity Tomography (ERT), Terrestrial Laser Scanning (TLS), together with traditional monitoring methods, were used to monitor changes in water content and the deformation of the landslide caused by rainfall. ERT was used to detect changes in soil water content induced by rainfall. The most significant findings were as follows:(1) the water content in the centralupper part (0~41 m) of the landslide was greater than in the central-front part (41~84 m) and (2) there was a relatively high resistivity zone at depth within the sliding zone. The deformation characteristics at the surface of the landslide were monitored by TLS and the results revealed that rainstorms caused three types of deformation and failure: (1) gully erosion at the slope surface; (2) shallow sliding failure; (3) and slope foot erosion. Subsequent monitoring of continuous changes in pore-water pressure, soil pressure and displacement (using traditional methods) indicated that long duration light rainfall (average 2.22 mm/d) caused the entire landslide to enter a state of creeping deformation at the beginning of the rainy season. Shear-induced dilation occurred for the fast sliding (30.09 mm/d) during the critical failure sub-phase (EF). Pore-water pressure in the sliding zone was affected by rainfall. In addition, the sliding L1 parts of the landslide exerted a discontinuous pressure on the L2 part. Through the monitoring and analysis, we conclude that this kind of landslide may have large deformation at the beginning and the late of the rainy season.     

Effect of geojute technique on density,diversity and carbon stock of plant species in landslide site of North West Himalaya

Mountainous regions of the globe experience landslides due to heavy rainfall and unplanned construction on slopes. Geojute is adopted globally as a landslide rehabilitation measure, but its impact on natural vegetation development is poorly understood. The present study was conducted to examine the impact of geojute application on vegetation restoration, ecology and carbon stock in a recently occurred landslide, during 2012. The results revealed that the geojute application improved the richness, diversity, density and basal area of plant species at the landslide site. Likewise, biomass production, carbon stock and carbon sequestration of plant species was observed significantly higher in geojute treatments compared to control (without geojute treatment). Moreover, significant improvement in soil moisture was recorded beneath the geojute treatments. Further, results showed that the geojute is highly effective in controlling soil erosion at the landslide site. The findings of this study revealed ecological and environmental benefits of geojute application in term of improvement in vegetation recovery processes, species diversity and carbon sequestration at the landslide site. The scientific outcome of this study can be helpful for planning the rehabilitation measures in landslide affected regions of the globe.     

Hydrodynamic processes and depositional styles of glacier-associated deposits in the Moxi basin,Southwest China

This study aims to understand the particle size distribution and depositional styles of glacier-associated deposits in the Moxi basin in southwest China. Based on field surveys, 28 samples from glacier-associated deposits (including glacial till, fluvioglacial, debris flow, river and lake deposits) were collected and tested in the laboratory. The results showed that the glacier-associated deposits can be differentiated based on particle gradation, particle size distribution and accumulated percentages. We evaluated the evolution of a former dammed lake in the Moxi basin based on glacier-associated deposits. The results of this study also indicated that the Moxi Platform was not formed by a single depositional process but is composed of both fluvioglacial and debris flow deposits. This research shows that the depositional style analysis is useful in identifying different glacier-associated deposits in high mountain regions. Moreover, the evaluation of the differences in particle sizes of the glacierassociated deposits is useful in reconstructing geohazard events in periglacial regions, and this information can help in identifying and reducing the potential risks associated with geo-hazards.     

Study on stability and reinforcement of a landslide on Ji''an-Dandong highway

This study clarified the failure mechanism of a landslide on Ji'an-Dandong highway, through the detailed analysis of its geological condition. Then based on the back analysis of the broken landslide, take limit equilibrium method to evaluate the stability of the potential landslide. The result shows that the landslide is lack of safety stock, so anchor rope is designed to reinforce the landslide.     

Study on stability and reinforcement of a landslide on Ji''''an-Dandong highway

This study clarified the failure mechanism of a landslide on Ji'an-Dandong highway,through the detailed analysis of its geological condition.Then based on the back analysis of the broken landslide,take limit equilibrium method to evaluate the stability of the potential landslide.The result shows that the landslide is lack of safety stock,so anchor rope is designed to reinforce the landslide.     

Failure analysis on a heavy rainfall-induced landslide in Huay Khab Mountain in Northern Thailand

On 28 th July 2018, a massive landslide occurred in a mountainous area in Northern Thailand. The landslide after ten days of heavy rainfall generated the movement of uphill mountain soil into the populated village. This study presents a comprehensive failure analysis of local rainfallinduced landslides based on topographical and geological information. Rainfall measurement data were gathered from two rainfall stations close to the study area. The rainfall records show that the total monthly rainfalls in 2018 were significantly higher than the average monthly rainfalls over the past decade. Site investigation started with an unmanned aerial photogrammetric survey to generate a digital elevation model. Then, dynamic probing test, microtremor survey, and electrical resistivity survey were carried out along undisturbed soils beside the failed slope to evaluate the thickness of the soft soil cover on top of the rock basement. During the site survey, residual soil samples were collected to determine engineering properties in the laboratory. Finally, a slope stability analysis was performed to assess the landslide hazard based on the results of aerial photogrammetric survey, field exploration, and laboratory tests. The slope stability analysis and rainfall records revealed that the Huay Khab landslide was mainly caused by an increase in the water content of residual soils due to the prolonged rainfall which led to a sharp decrease in the shear strength. This leads to the conclusion that the proposed landslide investigation program could be used to assess the potential of landslide failure due to prolonged rainfall on a local scale.     

基于双重注意力机制的滑坡识别方法优化

随着计算机视觉技术的发展,通过卫星图像深度学习进行滑坡识别的研究正在逐步展开。通过引入双重注意力机制,提出了一种基于卷积神经网络的滑坡图像识别优化算法。基于统计的2 200张滑坡图像数据集,探讨了10种网络结构及4种注意力机制对滑坡识别结果的影响,并通过比例为4∶1的训练集和测试集进行滑坡识别,验证了本文方法的有效性。结果表明：ResNet结构相较于其他网络结构表现更为优秀,就该算例而言,ResNet-101结构具有最高的召回率、精确率和F1度量。融入了双重注意力机制的卷积神经网络相较于单个神经网络而言,滑坡识别的精确率更大,且滑坡边界分割结果更接近于真实的滑坡边界,其中,ResNet-101+DAN模型为最优模型。相较之下,单个神经网络无法克服图像噪声的影响,图像分割结果不佳。     

Model test of the influence of cyclic water level fluctuations on a landslide

Many landslides in reservoir areas continuously deform under cyclic water level fluctuations due to reservoir operations. In this paper,a landslide model, developed for a typical colluvial landslide in the Three Gorges Reservoir area, is used to study the effect of cyclic water level fluctuations on the landslide. Five cyclic water level fluctuations were implemented in the test, and the fluctuation rate in the last two fluctuations doubled over the first three fluctuations. The pore water pressure and lateral landslide profiles were obtained during the test. A measurement of the landslide soil loss was proposed to quantitatively evaluate the influence of water level fluctuations. The test results show that the first water level rising is most negative to the landslide among the five cycles. The fourth drawdown with a higher drawdown rate caused further large landslide deformation. An increase of the water level drawdown rate is much more unfavorable to the landslide than an increase of the water level rising rate. In addition, the landslide was found to have an adaptive ability to resist subsequent water level fluctuations after undergoing large deformation during a water level fluctuation. The landslide deformation and observations in the field were found to support the test results well.     

Formation mechanism of a rainfall triggered complex landslide in southwest China

This case study is about a landslide that occurred after 4 days of heavy rainfall,in the morning of June 29,2012,in Cengong County,Guizhou Province of China,geographical coordinated 108°20′-109°03′E,27°09′-27°32′N,with an estimated volume of 3.3×106 m3.To fully investigate the landslide process and formation mechanism,detailed geotechnical and geophysical investigations were performed including borehole drilling,sampling,and laboratory tests coupled with monitoring of displacement.Also,a combined seepage-slope stability modeling was performed to study the behavior of the landslide.After the heavy rainfall event,the sliding process started in this area.The landslide development can be divided into different parts.The man-made fill area,spatially distributed in the south side of the landslide area with low elevations,slid first along the interface between the slope debris and the strongly weathered bedrock roughly in the EW direction.Consequently,due to severe lateral shear disturbance,the slope in the main sliding zone slid next towards the SW direction,along the sliding surface developed within the strongly weathered calcareous shale formation located at a depth of 25-35 m.This means it was a rainfall triggered deep-seated landslide.Finally,retrogressive failure of a number of upstream blocks occurred,which moved in more than one direction.The initial failure of the man-made fill area was the‘engine’of the whole instability framework.This artificial material with low permeability,piled up in the accumulation area of surface and sub-surface and destroyed the drainage capacity of the groundwater.The numerical modeling results agreed with the analysis results obtained from the laboratory and field investigations.A conceptual model is given to illustrate the formation mechanism and development process of the landslide.     

Long-term kinematics and mechanism of a deep-seated slow-moving debris slide near Wudongde hydropower station in Southwest China

Long-term kinematic research of slowmoving debris slide is rare despite of the widespread global distribution of this kind. This paper presents a study of the kinematics and mechanism of the Jinpingzi debris slide located on the Jinsha river bank in southwest China. This debris slide is known to have a volume of 27×106 m3 in active state for at least one century. Field survey and geotechnical investigation were carried out to define the structure of the landslide. The physical and mechanical properties of the landslide materials were obtained by in-situ and laboratory tests. Additionally, surface and subsurface displacements, as well as groundwater level fluctuations, were monitored since 2005. Movement features, especially the response of the landslide movement to rainfall, were analysed. Relationships between resisting forces and driving forces were analysed by using the limit equilibrium method assuming rigid-plastic frictional slip. The results confirmed a viscous component in the long-termcontinuous movement resulting in the quasioverconsolidated state of the slip zone with higher strength parameters than some other types of slowmoving landslides. Both surface and subsurface displacements showed an advancing pattern by the straight outwardly inclined(rather than gently or reversely inclined) slip zone, which resulted in low resistance to the entire sliding mass. The average surface displacement rate from 2005 to 2016 was estimated to be 0.19~0.87 mm/d. Basal sliding on the silty clay seam accounted for most of the deformation with different degrees of internal deformation in different parts. Rainfall was the predominant factor affecting the kinematics of Jinpingzi landslide while the role of groundwater level, though positive, was not significant. The response of the groundwater level to rainfall infiltration was not apparent. Unlike some shallow slow-moving earth flows or mudslides, whose behaviors are directly related to the phreatic groundwater level, the mechanism for Jinpingzi landslide kinematics is more likely related to the changing weight of the sliding mass and thedownslope seepage pressure in the shallow soil mass resulting from rainfall events.     

Field and laboratory observations on predation and prey selectivity of the scyphomedusa Chrysaora cf. caliparea in Southeast Indian waters

Chrysaora cf. caliparea, one of the most abundant medusae species in India, seems to be an important predator in the coastal waters of Bay of Bengal. The ability of Chrysaora cf. caliparea to feed at maximum rate in high prey concentrations implies that this jellyfish can efficiently exploit dense prey patches, at least for a short period. This study presents preliminary information regarding digestion and feeding rate upon copepods in a warm water environment. The ingestion rate of the average-sized medusae Chrysaora cf. caliparea is well balanced in nature, which in turn implies that this jellyfish is tuned for optimal utilization of available prey resources. Comparison with earlier research indicates that prey escape speed is one important factor governing which prey will be captured. A full understanding of predation mechanics awaits further investigation of both predator and prey behavior. However, because of the scarcity of long-term quantitative population data most insights have to be made indirectly. Nevertheless, low abundance of Chrysaora cf. caliparea in the water column during summer (May 2007) and the overall annual abundance seem not to considerably affect the zooplankton population, especially copepods. The present work contributes to the knowledge of prey-predator relationship of the forgotten fauna in Indian waters, which is especially crucial for understanding the process of ecological recovery of coastal water environment.     

Numerical simulation of a high-speed landslide in Chenjiaba,Beichuan, China

High-speed landslide is a catastrophic geological disaster in the mountainous area of southwest China. To predict the movement process of landslide reactivation in Chenjiaba town, Beichuan county, Sichuan province, China, we simulated the movement process of two landslide failures in Chenjiaba via rapid mass movement simulation and unmanned aerial vehicle images(UAV), and obtained the movement characteristic parameters of the landslides. According to a back analysis, the most remarkable fitting rheological parameters were friction coefficient(μ=0.18) and turbulence(). The parameter of landslide pressure was applied as the zoning index of landslide hazard to obtain the influence zone and hazard zoning map of the Chenjiaba landslide. Results show that the Duba River was blocked quickly with a landslide accumulation at the maximum height of 44.14 mwhen the Chenjiaba deposits lost stability. The hazard zoning map indicated that the landslide hazard degree is positively correlated with the slope.This landslide assessment is a quantitative hazard assessment method based on a landslide movement process and is suitable for high-speed landslide. Such method can provide a scientific basis for urban construction and planning in the landslide hazard area to avoid hazards effectively.