Flow Slides Research Articles

Shear strength parameters identification of loess interface based on borehole micro static cone penetration system

BackgroundLoess is prone to large deformation and flow slide due to natural and artificial interfaces inside. The strength of these interfaces controls the mechanical properties of loess. Obtaining their mechanical parameters through in-situ testing is essential for evaluating the mechanical stability in loess engineering with interfaces.MethodsBy developing a borehole micro static cone penetration system and creating various types of loess with interfaces, extensive borehole penetration model tests were conducted to observe changes in cone tip resistance during penetration. The response surface method was used to analyze the impact of various test conditions on the calculated resistance. A three-dimensional surface fitting method was employed to establish the relationship between penetration parameters and shear strength parameters, which was validated through in-situ testing.ResultsThe developed borehole micro static cone penetration system achieves overall miniaturization while providing significant penetration power and ensuring an effective penetration distance. Cone tip resistance development during penetration can be divided into three stages: initial, rapid increase, and slow increase. The transition times between these stages vary for different soils. Calculated resistance is positively correlated with dry density and normal stress and negatively correlated with water content. A quadratic positive correlation was established between calculated resistance and shear strength parameters during penetration. In composite soils, the interaction between water content and normal stress is strong. Compared to intact soil samples, the shear strength parameters of composite soils are more prominently influenced by water content.ConclusionA system for testing interface mechanical parameters was innovatively developed, fulfilling the need to obtain interface shear strength parameters for deep soil. This study can provide support for ensuring the long-term stability of the loess slope or subgrade with interfaces.

Prediction of retrogressive landslide in sensitive clays by incorporating a novel strain softening law into the Material Point Method

Sensitive clays, when subjected to large strains, exhibit a unique strain-softening behavior, transforming into a remolded liquid with remarkably low shear strength. When a slope fails, this behavior leads to the remolded clay moving away from its original position, triggering subsequent failures and catastrophic outcomes. To accurately predict such scenarios, it is crucial to incorporate realistic strain-softening characteristics into the constitutive soil model. This paper presents a novel yet practical strain-softening law developed by the authors that effectively captures the post-peak behavior of sensitive clays down to their remolded strength. The softening law is implemented in an elastoplastic Mohr-Coulomb model and incorporated into Anura3D, an open-source software that uses the Material Point Method to simulate large deformations. The constitutive model is calibrated by simulating the stress-strain behavior through direct shear tests conducted at three sensitive clay landslide locations. The accuracy of the overall numerical framework is assessed by predicting the post-failure movements of these landslides. Notably, two of the landslides, Sainte-Monique (1994) and Saint-Jude (2010), have previously been analyzed using other numerical tools, allowing for a comparative analysis with the method presented here. The third landslide, the Saint-Luc-de-Vincennes landslide, representing a composite flow slide and spread, has been numerically simulated for the first time. The post-failure behavior observed in the landslide events is compared with field observations and other numerical analyses. The results show that the MPM models with the proposed strain-softening law can reasonably predict post-failure retrogression and runout distance, which are crucial parameters for determining the risk of landslides in sensitive clays.

Numerical analysis of downward progressive landslides in long natural slopes with sensitive clay

Landslides occurring in sensitive clay often result in widespread destruction, posing a significant risk to human lives and property due to the substantial decrease in undrained shear strength during deformation. Assessing the consequences of these landslides is challenging and necessitates robust numerical methods to comprehensively investigate their failure mechanisms. While studies have extensively explored upward progressive landslides in sensitive clays, understanding downward progressive cases remains limited. In this study, we utilised the nodal integration-based particle finite element method (N-PFEM) with a nonlinear strain-softening model to analyse downward progressive landslides in sensitive clay on elongated slopes, induced by surcharge loads near the crest. We focused on elucidating the underlying failure mechanisms and evaluating the effects of different soil parameters and strain-softening characteristics. The simulation results revealed the typical pattern for downward landslides, which typically start with a localised failure in proximity to the surcharge loads, followed by a combination of different types of failure mechanisms, including single flow slides, translational progressive landslides, progressive flow slides, and spread failures. Additionally, inclined shear bands occur within spread failures, often adopting distinctive ploughing patterns characterised by triangular shapes. The sensitive clay thickness at the base, the clay strength gradient, the sensitivity, and the softening rate significantly influence the failure mechanisms and the extent of diffused displacement. Remarkably, some of these effects mirror those observed in upward progressive landslides, underscoring the interconnectedness of these phenomena. This study contributes valuable insights into the complex dynamics of sensitive clay landslides, shedding light on the intricate interplay of factors governing their behaviour and progression.

Triggering and evolution of static liquefaction in submarine slopes with quasi-saturated sand

Liquefaction flow slides of submarine slopes with quasi-saturated sand have been frequently observed in engineering practice. That instability can be attributed to a decrease in resistant shear strength caused by static liquefaction. However, the triggering of static liquefaction in submarine slopes has received limited attention. To address this gap, a state-dependent constitutive model for quasi-saturated sand with entrapped air is employed that can represent the effects of compression and dissolution of gas accurately. Moreover, the soil model enables the evaluation of the triggering of static liquefaction based on second-order work. To study the triggering mechanism of static liquefaction, a submarine slope model is established using the material point method. The static liquefaction area is detected by the vanish of second-order work. Results indicate that static liquefaction initially arises at the slope surface and gradually expands towards the interior of the slope as the rapid loading at the top of the slope increases. Furthermore, the presence of entrapped gas within the slope can effectively enhance the resistance to slope instability caused by static liquefaction. It significantly alters both the location where static liquefaction is initially triggered and the subsequent evolution pattern, in comparison with saturated submarine slopes.

Numerical modelling of downward progressive landslides in sensitive clay

Landslides in sensitive clays are catastrophic events that threaten life and property. When plastic strain occurs in sensitive clays, there is a significant reduction in the undrained shear strength. Consequently, even minor triggers can lead to multiple progressive landslides, causing extensive devastation. Investigating landslides in sensitive clay presents challenges, necessitating robust numerical methods to comprehend failure modes and collapse behaviors, particularly in the post-failure phase. Although several numerical methods have been utilized for simulations, most have primarily focused on upward progressive landslides. In this study, we adopted the nodal integration-based particle finite element method to simulate downward progressive landslides triggered by surcharge loads from an embankment near the crest in sensitive clay on a long slope. We also considered nonlinear strain softening in sensitive clays. The effects of the strain softening rate and strength gradient of the sensitive clay layer on the failure mechanisms and destruction extent were investigated. The simulation results reveal that a downward progressive landslide initiates with a localized flow slide surrounding the embankment and usually involves a combination of various failure modes.

Modeling large-deformation features of the Lower San Fernando Dam failure with the Material Point Method

The Material Point Method (MPM) is used to model the well-known case study of the earthquake-induced Lower San Fernando Dam failure. This upstream flow slide, leaving only 1–2 m freeboard, emphasized the importance of seismic hazard analyses of earthen dams. This study expands on the Chowdhury (2019) nonlinear seismic deformation analysis, which successfully captured liquefaction initiation and engineering failure characteristics. It could not, however, fully capture the large-deformation behavior and post-failure equilibrium cross-section due to mesh entanglement limitations of the Finite Difference Method. This MPM model initializes post-shaking and simulates the large-deformation undrained behavior of both liquefied sands and shear-softened clays. Several novel features implemented in the MPM advance modeling capabilities, including a nonconforming traction boundary to model reservoir pressure, and an adhesion boundary to model the reservoir bottom sliding interface. Compared to previous studies, the current study predicts improved kinematic behavior and post-failure cross-sectional features. Qualitative highlights include well-defined shear banding, sharp heel scarp features, blocky features, a toe bulge, and shear separation of the leading slide mass. Quantitative highlights include 1.5 m remaining freeboard, 20 m crest loss, and 66 m upstream toe runout, versus field observations of 1.2–1.8, 20, and 65 m, respectively.

A promising protocol for the endothelialization of vascular grafts in an instrumented rotating bioreactor towards clinical application

Pre-endothelialization of a tissue-engineered vascular graft before implantation aims to prevent thrombosis and immunoreactions. This work demonstrates a standardized cultivation process to build a confluent monolayer with human aortal endothelial cells on xenogenous scaffolds. Pre-tested dynamic cultivation conditions in flow slides with pulsatile flow (1 Hz) representing arterial wall conditions were transferred to a newly designed multi-featured rotational bioreactor system. The medium was thickened with 1% methyl cellulose simulating a non-Newtonian fluid comparable to blood. Computational fluid dynamics was used to estimate the optimal volume flow and medium distribution inside the bioreactor chamber for defined wall-near shear stress levels. Flow measurements were performed during cultivation for constant monitoring of the process. Three decellularized porcine arteries were seeded and cultivated in the bioreactor over six days. 1% MC turned out to be the optimal percentage to achieve shear stress values ranging up to 10 dyn/cm2. Vascular endothelial cells formed a continuous monolayer with significant cell alignment in the direction of flow. The presented cultivation protocol in the bioreactor system thus displays a promising template for graft endothelialization and cultivation. Therefore, establishing a key step for future tissue-engineered vascular graft development with a view towards clinical application.

LABORATARY STUDY OF THE VERTICAL RETREATING SAND WALL OBSERVED IN COASTAL FLOW SLIDES

Coastal flow slides have been reported around the world (Mastbergen et al., 2019; Nédélec et al., 2022), often at over-steepened banks subject to strong tidal flows, pose threat to coastal communities and infrastructure (Lulla, 2017). With sea level rise caused by climate change, these flow slides are expected to occur more frequently in more sites worldwide. Amity Point Beach, North Stradbroke Island (27o 23’ 35’’S, 153o26’23’’E), about 40 km from Brisbane, Australia, have experienced regular coastal flow slides for more than 40 years (Eberhardt, 1978). Together with observations at Amity Point beach field site, small-scale flow slides are simulated in laboratory by tilting metal box filled with sand and fluid.

Centrifuge and Numerical Modeling of Liquefied Flow and Nonliquefied Slide Failures of Tailings Dams

Centrifuge and Numerical Modeling of Liquefied Flow and Nonliquefied Slide Failures of Tailings Dams

Landslide Classification and Prediction of Debris Flow Using Machine Learning Models

Landslides are unpredictable and destructive calamities that motivated the development of early warning systems to alert people and save their lives and property. A novel two-layer architecture is proposed to classify and predict landslides and types. The research is carried out in the Idukki district, Kerala, India, covering an area of 4358 km2. Layer-1 uses topographical, hydrogeological, and meteorological features collected from various sources. The binary classifier in this layer classifies and predicts the probability of landslide occurrence. Layer-2 classifies landslides into debris flow, rockfall, and surficial slides and predicts debris flow through a multi-class classifier. To achieve better prediction accuracy, the landslide features that significantly influence the landslide occurrence of layer-1 are combined with layer-2. The Synthetic Minority Oversampling Technique is used to balance the database of minority categories. Classification and prediction are achieved using machine learning models such as the support vector machine, decision tree, random forest, and extreme gradient-boosting, and their performances are compared. The feature score for every feature of the model is calculated using the feature importance technique. The machine learning models are validated using the Area Under the Receiver Operating Characteristics curve and F1-score. On comparison, Extreme Gradient-Boost is found to perform well. Based on the prediction probability, the debris flow is classified into high-risk, medium-risk, and low-risk regions. This favored in identifying vulnerable areas and appropriate mitigation measures to reduce life loss and damage to infrastructure.

An Integrated Bayesian Risk Model for Coastal Flow Slides Using 3-D Hydrodynamic Transport and Monte Carlo Simulation

The literature suggests two forms of flow slides: breaching and liquefaction. Both forms of failure have comparable ultimate circumstances, but the progression and sand movement mechanisms of breaching failure diverge from those of liquefaction. The first type, breaching, occurs in densely packed sand and is characterized by slow sand grain discharge throughout the dilation of the failing soil particles and negative excess pore pressures. The latter form, known as liquefaction, is the process by which a mass of soil abruptly begins to behave like a flowing liquid, and as a result, it can flow out across overly mild slopes. The process begins in compacted sand and is linked to positive surplus pore water pressures that are caused by the compaction of the sand. Despite the available literature on flow slide failures, our understanding of the mechanisms involved remains limited. Since flow slides often begin below the water surface, they can go undetected until the collapse reaches the bank above ground. The complexity of flow slides requires the use of cutting-edge technological instruments, diving equipment, advanced risk assessment, and a variety of noteworthy probabilistic and sensitivity analyses. Hence, we developed a new sensitivity index to identify the risk of breach failure and vulnerable coastal areas to this risk. In addition, we developed a sophisticated hybrid model that allows for all possibilities of flow slides in sync with random variables used in this new sensitivity index. In this new hybrid model, three distinctive models exist. The 3D Hydrodynamic Model addresses waves, wind, current, climate change, and sediment transport. The Monte Carlo Simulation is responsible for sensitivity analysis, and the Bayesian Network focuses on joint probabilities of coastal flow slide parameters of this new index that incorporates all environmental parameters, including climate change. With the assistance of these three models, researchers aim to: (a) expand the application scope by presenting a method on coastal flow slides; (b) consider different particle diameters corresponding to critical angle slope failure; (c) analyze variables that can play a pivotal role in the flow slides; and (d) present a methodology for coupling coastal flow slide projections with reliable outcomes. The hybrid model incorporates random variables of retrogressive breach failures, and the new risk index considers their ranges to control the simulation. The use of such a hybrid model and risk index offers a robust and computationally efficient approach to evaluating coastal flow slides.

Stabilizing and Destabilizing Breaching Flow Slides

As a result of the dilation of soil matrix, dense submarine sand slopes can temporarily be steeper than the natural angle of repose. These slopes gradually fail by the detachment of individual grains and intermittent collapses of small coherent sand wedges. The key question is whether steep disturbances in a submarine slope grow in size (destabilizing breaching) or gradually diminish (stabilizing breaching) and thereby limit the overall slope failure and resulting damage. The ability to predict whether the breaching failure is stabilizing or destabilizing is also crucial for the assessment of safety of submarine infrastructure and hydraulic structures located along rivers, lakes, and coasts. Through a set of large-scale laboratory experiments, we investigate the validity of an existing criterion to determine the failure mode of breaching (i.e., stabilizing or destabilizing). Both modes were observed in these experiments, providing a unique set of data for analysis. It is concluded that the existing method has limited forecasting power. This was quantified using the mean absolute percentage error, which was found to be 92%. The reasons behind this large discrepancy are discussed. Given the complexity of the underlying geotechnical and hydraulic processes, more advanced methodologies are required.

Compressibility and permeability of weathered, sensitive volcanic ash (tephra) deposits at the Omokoroa flow slide, New Zealand

Volcanic ash (tephra) deposits from the Omokoroa flow slide, New Zealand, exhibit a high concentration of the secondary clay mineral halloysite being responsible for high sensitivities in these soils. Sensitivity is the ratio between intact and remoulded undrained strength at the same water content. So far, compressibility and permeability have not been studied for halloysite-rich sensitive soils. Here, we found that oedometer compression behaviour of intact tephras depended on the sensitivity. Compression behaviour of remoulded tephra seemed to be independent of sensitivity and halloysite morphology but varied with liquid limit. Compression lines of remoulded tephras were less steep and, thus, exhibited an overall smaller compressibility, then those determined from remoulded sedimentary clays. Permeabilities of remoulded tephra samples were generally smaller than permeabilities of remoulded sedimentary clays. For halloysite-rich tephra, it was found that permeabilities of remoulded samples were smaller than those of intact samples. A new parameter was introduced, the permeability sensitivity, which quantifies the difference in permeabilities between intact and remoulded tephras. We found a fairly strong positive relationship (R2 = 0.89) between the permeability sensitivity and the sensitivity. The halloysite morphology seemed to be moderately correlated with the permeability sensitivity (R2 = 0.45). Our findings have implications for progressive slope failure in sensitive soil but are limited by means of the indirect method of analysing time–settlement curves of step-loaded oedometer tests to derive permeability and re-orientation of samples to allow horizontal drainage in a conventional oedometer cell.

Experimental Study on Failure Mechanism and Mode of Fly-Ash Dam Slope Triggered by Rainfall Infiltration

The fly-ash dam is used to store the fly ash discharged from the thermal power plant. A fly-ash dam is a special slope built with fly ash, and rainfall infiltration is an important reason to induce the landslide of this kind of slope. In this paper, the laboratory tests of different slope ratios and initial seepage fields under rainfall were carried out, aimed at studying the failure mechanism, failure mode, triggering mechanism, and influence factors for the slope instability of the fly ash dam slope under rainfall infiltration. The results show that: (I) Three failure mechanisms were found in the tests: sliding failure, runoff erosion, and flow-slide failure. Due to the low density of fly ash, runoff erosion is more likely to occur under rainfall. Differently from clay slope, flow slide is an important failure mechanism of fly ash slope under rainfall. (II) Local erosion damages caused by runoff erosion and flow slide are the important triggering factors of the fly-ash dam slope failure under rainfall. (III) Three failure modes were observed in the test: the overall sliding failure of the slope, the retrogressive landslide caused by multi-stage local sliding, and the gradual erosion failure of the slope (caused by the combined action of runoff erosion and flow slide). (IV) The slope ratio has an important influence on the failure mode. With the decrease in slope ratio, the failure mode evolves from sliding failure to flow-slide failure and runoff erosion failure. The greater the slope ratio, the more obvious the sliding failure characteristics; the lower the slope rate, the greater the runoff erosion damage. The existence of an internal seepage field in the slope intensifies the occurrence of flow slide.

An assessment of the mechanical performance of a novel sand bentonite-glass fiber composite for the avoidance of catastrophic landfill failure

• Octahedral shear stress increased higher at the fiber aspect ratio than at the fiber dosage. • At peak and residual stress, bearing capacity factors improved significantly. • Negative excess pore waster pressure increased with an aspect ratio of 40. • Energy absorption capacity was the function of fiber dosage and fiber aspect ratio. Compacted sand bentonite (CSB) blend is one of the finest materials for landfill construction. CSB mixes with a strain-softening tendency may fail abruptly, increasing soil permeability. Water movement over the shear zone can induce flow slides, triggering a catastrophic collapse. Waste glass fiber was added to the CSB mixture (90:10) in various fractions (0.5 %, 1, and 1.5 %) and aspect ratios (l/d = 40, 80, and 120) to prevent the soil structure from collapsing. A full-scale consolidated undrained (CU) test was conducted to assess (i.e., c-phi-analysis) the load-carrying capabilities of waste fiber soil composite. The octahedral shear stress was increased significantly for both stress level (i.e., peak and residual stress). Positive pore water pressure (PWP) increased progressively after initial yield, while negative PWP reduced as the aspect ratio increased from 80 to 120. Fiber dosage and fiber aspect ratio improved bearing capacity factors (N c ,N q ,N ϒ ) and undrained bearing capacity. The EAC (Energy absorption capacity) was determined using a numerical integration approach through MATLAB (version14), and the use of waste fiber resulted in a considerable improvement. Several variables contributed to the principal stress and soil modulus. Accordingly, they were framed with all the variables and built a model that matched the experimental results well.

Breaching and liquefaction in subaqueous retrogressive flow slides

Although retrogressive flow slides in subaqueous sandy slopes can be very large and cause substantial damage, the failure mechanisms of such slides are not very clear yet. This study analyses two well-monitored flow slides in a shoal margin in the Western Scheldt estuary in the Netherlands: a natural flow slide that eroded 300 m into the edge of the shoal and an artificially induced flow slide that was triggered by dredging and eroded only 30 m of the shoal margin. Both slides were simulated with a newly developed numerical model that describes the physics of slow retrogressive breaching and the much faster retrogression of statically liquefied fine to medium (silty) sands. The simulations show that the differences in trigger and size can be explained by assuming that in the larger slide both retrogressive breaching and static liquefaction took place, while in the smaller one only breaching occurred. The main contribution of retrogressive liquefaction to the larger slide was the generation of a temporary high-erosive density flow that proved sufficient to create such a high, near-vertical slope that the breaching process could continue over a long period and distance. It is therefore likely that both breaching and static liquefaction play a role in large natural flow slides.

Time-Lapse Camera Monitoring and Study of Recurrent Breaching Flow Slides in Cap Ferret, France

In this paper, we present a low-cost method designed to monitor recurrent breaching flow slides that impact the security of a beach. This beach, located in France at the inlet of Arcachon Bay, connects a sand spit to a tidal channel while ending at the toe of a coastal defense. Monitoring is based on capturing images and intends to add continuous information to intermittent direct observations so that triggering and influencing factors can be assessed more precisely. The method is based on time-lapse picture collection and processing. The field of view shows successive emerged manifestations of flow slide phenomena, as well as some possibly related environmental elements. On-site application for 576 days provides important indications and details on flow slide event progress and beach recovery. A simple but quantitative analysis of the influence of sand spit topographic changes is proposed as a preliminary approach of the method’s suitability for studies of environmental processes in conjunction with coast protection.

Loess Is More: Field Investigation and Slope Stability Analysis of the Tanana 440 Landslide, Interior Alaska

ABSTRACT Landslides are geologic hazards that threaten human life, property, and infrastructure. Proper mitigation requires knowledge of where landslides occurred in the past. Until recently, no landslide inventory maps had been published for any area of Alaska. Here, we present a short overview of landslide mapping within the Fairbanks North Star Borough (FNSB), Alaska, and a focused investigation of the Tanana 440 (T440) landslide. We mapped 1,679 landslides and field-verified 51 landslides within the FNSB. These landslides vary in age, movement type, and material. We present the results of in-depth mapping; subsurface exploration; soil engineering properties, including results of direct shear testing; and slope stability analysis of the T440 landslide, which we determined is a flow slide in loess that occurred during the late Pleistocene to mid-Holocene. We modeled seven slope stability scenarios for the T440 landslide by varying water table position and seismic load. Our modeling results suggest that thawing permafrost and/or seismic loading were likely possible triggers for the T440 landslide. To our knowledge, we present the first comprehensive direct shear testing of non-plastic silt with a variation in moisture content and the first comparison of direct shear and field vane shear measurements of silt. The average cohesion and internal friction angle of the wetted remolded silt were 3.0 kPa and 23.1°, respectively. These values did not significantly change with increasing moisture content. The direct shear and vane shear strengths of silt had low correlation (R2 = 0.20), unlike the strong correlation that is typical of clay soils.

Quantitative physical model of vulnerability of buildings to urban flow slides in construction solid waste landfills: a case study of the 2015 Shenzhen flow slide

Quantitative physical model of vulnerability of buildings to urban flow slides in construction solid waste landfills: a case study of the 2015 Shenzhen flow slide

ОПОЛЗНИ ТЕЧЕНИЯ: РОЛЬ СТРОЕНИЯ МАССИВОВ ГРУНТОВ В ИХ ФОРМИРОВАНИИ, ОСОБЕННОСТИ РАЗВИТИЯ И ТИПИЗАЦИЯ

The flow («dry», plastic, viscoplastic, viscous) is one of the main mechanisms of landslide displacement. The paper discusses the features of the formation and development of landslides, the displacement of which occurs in the form of a flow caused by soils saturated. The flow slides formation is associated with the excess of the creep threshold by the shear stresses acting in the slope massif with the transition of deformations from decaying to irreversible, progressive ones. When classifying slope processes, most researchers classify flow slides (under various names) into a separate class. Flow slides usually refer to the displacement (in subaerial or subaqueous conditions) of the moist mass or saturated clay, sandy-clay or rubble-clay soil, which moves along an inclined surface. It is shown that the formation of flow slides can occur either for a long time, with the gradual development of plastic deformations, or very quickly, with an almost instantaneous transition of soils to a fluid state (liquefaction). The main features with reference to which typical types of the flow slides is carried out are: 1) the capture depth of the massif by landslide deformations and the location of the flow zone; 2) morphometric characteristics, including the shape of the landslide body (in plan); 3) the type of soils involved in displacement and the mechanism of the transition of soils into a «fluid» state; 4) features of the displacement mechanism, including depending on the consistency of the landslide masses, due to the ratio in the composition of the moving mass of the solid (debris, clay) component and the water component. The features of the development and differences of surface landslides and «deep» flow slides, including the features of their displacement, morphology and structure, are characterized. The sequence of the landslide deformations development is described. The existing approaches to the typification of flow slides are considered. Summary typical types of flow slides of a current on the initiation and mechanism of displacement is prepared. It is concluded that it is necessary to take into account the features and differences of flow slides in the course of their study.