Progressive Failure of Offshore Slopes due to Construction in Upslope Areas

2015 ◽  
Author(s):  
Rajib Dey ◽  
Bipul Hawlader ◽  
Chen Wang
Keyword(s):  
Large Scale ◽  
Strain Softening ◽  
Progressive Failure ◽  
Limit Equilibrium ◽  
Shear Bands ◽  
Submarine Landslides ◽  
Limit Equilibrium Methods ◽  
Triggering Factor ◽  
Potential Failure ◽  
Clay Layers

Human activities such as construction loading in upslope areas could be a potential triggering factor for many offshore landslides such as the 1979 Nice landslide. Post-slide investigations show that the existence of marine sensitive clay layers might be one of the potential causes of many large-scale submarine landslides. In this paper, a finite element (FE) modeling technique is developed to analyze the failure of a slope in undrained condition. Nonlinear strain softening behaviour of undrained shear strength of marine sensitive clays is incorporated in the FE analysis. Strain localization in narrow zones (i.e. shear bands) could be successfully simulated. The formation of shear bands and their propagation could explain some potential failure mechanisms. The FE results show that large-scale catastrophic failure of submarine slopes might have occurred due to shear band propagation through strain softening clay layers, which cannot be explained using the traditional limit equilibrium methods for slope stability analysis. Effects of different factors, such as thickness of the marine clay layer and its sensitivity, on stability of submarine slope are also examined.

scholarly journals Factor of Safety Reduction Factors for Accounting for Progressive Failure for Earthen Levees with Underlying Thin Layers of Sensitive Soils

2013 ◽  
Vol 2013 ◽  
pp. 1-13 ◽  
Author(s):  
Adam J. Lobbestael ◽  
Adda Athanasopoulos-Zekkos ◽  
Josh Colley
Keyword(s):  
Finite Element ◽  
Strain Softening ◽  
Progressive Failure ◽  
Limit Equilibrium ◽  
Thin Layers ◽  
The Finite Element Method ◽  
Element Analysis ◽  
Limit Equilibrium Methods ◽  
The Stability ◽  
Reduction Factors

The effects of progressive failure on flood embankments with underlying thin layers of soft, sensitive soils are investigated. Finite element analysis allows for investigation of strain-softening effects and progressive failure in soft and sensitive soils. However, limit equilibrium methods for slope stability analysis, widely used in industry, cannot capture these effects and may result in unconservative factors of safety. A parametric analysis was conducted to investigate the effect of thin layers of soft sensitive soils on the stability of flood embankments. A flood embankment was modeled using both the limit equilibrium method and the finite element method. The foundation profile was altered to determine the extent to which varying soft and sensitive soils affected the stability of the embankment, with respect to progressive failure. The results from the two methods were compared to determine reduction factors that can be applied towards factors of safety computed using limit equilibrium methods, in order to capture progressive failure.

scholarly journals Overview of Retrogressive Landslide Risk Analysis in Sensitive Clay Slope

Geosciences ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 279
Author(s):  
Blanche Richer ◽  
Ali Saeidi ◽  
Maxime Boivin ◽  
Alain Rouleau
Keyword(s):  
Numerical Methods ◽  
Risk Analysis ◽  
Numerical Modelling ◽  
Progressive Failure ◽  
Limit Equilibrium ◽  
Strength Reduction ◽  
Critical Parameters ◽  
Limit Equilibrium Methods ◽  
Sensitive Clay ◽  
Analytical Limit

Sensitive clays are known for producing retrogressive landslides, also called spread or flowslides. The key characteristics associated with the occurrence of these landslides on a sensitive clay slope must be assessed, and the potential retrogressive distance must be evaluated. Common risk analysis methods include empirical methods for estimating the distance of potential retrogression, analytical limit equilibrium methods, numerical modelling methods using the strength reduction technique, and the integration of a progressive failure mechanism into numerical methods. Methods developed for zoning purposes in Norway and Quebec provide conservative results in most cases, even if they don’t cover the worst cases scenario. A flowslide can be partially analysed using analytical limit equilibrium methods and numerical methods having strength reduction factor tools. Numerical modelling of progressive failure mechanisms using numerical methods can define the critical parameters of spread-type landslides, such as critical unloading and the retrogression distance of the failure. Continuous improvements to the large-deformation numerical modeling approach allow its application to all types of sensitive clay landslides.

scholarly journals Comparative analysis of large scale scenario-based landslides hazard zonation maps. A case study in Iasi City, Romania

2017 ◽  
Vol 19 (1) ◽  
pp. 145-154
Author(s):  
COMAN Cristina Magdalena ◽  
MANEA Sanda ◽  
OLINIC Ernest ◽  
BOȚI Ioan
Keyword(s):  
Comparative Analysis ◽  
Safety Factor ◽  
Large Scale ◽  
Deterministic Model ◽  
Hazard Analysis ◽  
Limit Equilibrium ◽  
Stability Factor ◽  
Northwestern Part ◽  
Engineering Software ◽  
Limit Equilibrium Methods

Large-scale landslides hazard analysis is based, among other methods, on the numerical evaluation of the safety factor using physical and mechanical parameters measured in the field. The safety factor is determined as the ratio between the forces acting in the favor of sliding phenomenon and the resistance of the earthen massive. The main purpose of the paper is to create two bi-dimensional models of landslides hazard assessment based on the estimation of the stability factor, under different degrees of soil saturation and considering different scenarios of seismic acceleration. Slope stability analysis allows the simultaneity of two exceptional loads such as saturation and earthquake. The first model follows the methodology provided by the national law. In this case, the safety factor is determined by applying limit equilibrium methods using specific geotechnical engineering software. The second model aims to create a deterministic model for safety factor assessment implemented in a GIS system. This one is based on the infinite slope model. The secondary objectives of the paper are: providing theoretical principles, attaining the comparative analysis between the methodologies mentioned above, identifying the critical points of the created models and the reciprocal validation of the results. The study area is a hilly area located in the NorthWestern part of the Iasi City, Romania. The geotechnical parameters were obtained from the laboratory tests carried out on samples taken from 22 boreholes. The geomorphological parameters resulted from the high quality digital elevation model with 1m resolution. The final maps representing the spatial distribution of the safety factor values are reclassified using a common scale. Similarity analysis of the results indicates a good mutual validation.

scholarly journals Error Source Analysis and Precision Assessment of Limit Equilibrium Methods for Rock Slopes

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Xiaofan An ◽  
Ning Li ◽  
Peng Zhang ◽  
Wenbo Sun
Keyword(s):  
Finite Element ◽  
Evaluation Method ◽  
Progressive Failure ◽  
Limit Equilibrium ◽  
Influence Factors ◽  
Source Analysis ◽  
Rock Slopes ◽  
Error Source ◽  
Sliding Surfaces ◽  
Limit Equilibrium Methods

The approximate assumptions of limit equilibrium methods are the fundamental cause of the deviation between their calculation results and actual situation. This study proposes a new finite-element evaluation method to reflect the progressive failure characteristics of rock slopes. By comparing the results of limit equilibrium and finite-element methods, the influence factors of stability for planar landslides are systematically studied. The factors include the plastic parameters of sliding surfaces in progressive failure, the elastic parameters of sliding mass, the elastic deformation of sliding beds, and excavation stress release. Moreover, the stress distribution rules on sliding surfaces and the diversity of safety factors are explored. Finally, the error source and calculation accuracy of the limit equilibrium method in slope analysis are obtained. The study provides scientific references for analyzing and evaluating the stability of such slopes.

scholarly journals Large-deformation finite-element modelling of earthquake-induced landslides considering strain-softening behaviour of sensitive clay

2019 ◽  
Vol 56 (7) ◽  
pp. 1003-1018 ◽  
Author(s):  
Naveel Islam ◽  
Bipul Hawlader ◽  
Chen Wang ◽  
Kenichi Soga
Keyword(s):  
Finite Element ◽  
Large Deformation ◽  
Large Scale ◽  
Slope Failure ◽  
Strain Softening ◽  
Limit Equilibrium ◽  
Fe Analysis ◽  
Plastic Shear ◽  
Fe Modelling ◽  
Sensitive Clay

Large-scale landslides in sensitive clays cannot be explained properly using the traditional limit equilibrium or Lagrangian-based finite-element (FE) methods. In the present study, dynamic FE analysis of sensitive clay slope failures triggered by an earthquake is performed using a large-deformation FE modelling technique. A model for post-peak degradation of undrained shear strength as a function of accumulated plastic shear strain (strain-softening) is implemented in FE analysis. The progressive development of “shear bands” (the zone of high plastic shear strains) that causes the failure of a number of soil blocks is simulated successfully. Failure of a slope could occur during an earthquake and also at the post-quake stage until the failed soil masses come to a new static equilibrium. Upslope retrogression and downslope runout of the failed soil blocks are examined for varying geometries and soil properties. The present FE simulations can explain some of the conditions required for different types of seismic slope failure (e.g., spread, flowslide or monolithic slides) to be triggered, as observed in the field.

Progressive failure of the Carsington Dam: a numerical study

1992 ◽  
Vol 29 (6) ◽  
pp. 971-988 ◽  
Author(s):  
Z. Chen ◽  
N. R. Morgenstern ◽  
D. H. Chan
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Factor Of Safety ◽  
Progressive Failure ◽  
Limit Equilibrium ◽  
Equilibrium Analysis ◽  
Element Analysis ◽  
Limit Equilibrium Analysis ◽  
The Finite Element Analysis ◽  
Yellow Clay

The mechanism of progressive failure is well understood as one which involves nonuniform straining of a strain-weakening material. Traditional limit equilibrium analysis cannot be used alone to obtain a rational solution for progressive failure problems because the deformation of the structure must be taken into account in the analysis. The failure of the Carsington Dam during construction in 1984 has been attributed to progressive failure of the underlying yellow clay and the dam core materials. The dam was monitored extensively prior to failure, and an elaborate geotechnical investigation was undertaken after failure. The limit equilibrium analysis indicated that the factors of safety were over 1.4 using peak strength of intact clay material or 1.2 based on reduced strength accounting for preshearing of the yellow clay layer. Factors of safety were found to be less than unity if residual strengths were used. The actual factor of safety at failure was, of course, equal to one. By using the finite element analysis with strain-weakening models, the extent and degree of weakening along the potential slip surface were calculated. The calculated shear strength was then used in the limit equilibrium analysis, and the factor of safety was found to be 1.05, which is very close to the actual value of 1.0. More importantly, the mechanism of failure and the initiation and propagation of the shear zones were captured in the finite element analysis. It was also found that accounting explicitly for pore-water pressure effects using the effective stress approach in the finite element and limit equilibrium analyses provides more realistic simulations of the failure process of the structure than analyses based on total stresses. Key words : progressive failure, strain softening, finite element analysis, dams.

Numerical Simulation Method Ascertaining Slope Stabilization Anti-Slippery Pile's Basic Parameters

2012 ◽  
Vol 594-597 ◽  
pp. 222-225
Author(s):  
Wen Juan Feng ◽  
Xiao Dong Ju ◽  
Zheng Sheng Zou
Keyword(s):  
Numerical Simulation ◽  
Safety Factor ◽  
Limit Equilibrium ◽  
Simulation Method ◽  
Simulation Software ◽  
Strength Reduction ◽  
Slope Stabilization ◽  
Limit Equilibrium Methods ◽  
Basic Parameters ◽  
Shear Strength Reduction

Although anti-slide pile take a key position in slope-treating measures, the method of designing is far from perfect. The methods used in actual projects are based on the rigid body limit equilibrium methods. There is a tendency to using numerical methods in the progress of pile-designing. The safety factor of landslide is calculated according to shear strength reduction theory in the numerical simulation software. Using the shearing forces on pile and the safety factor can ascertain the position of anti-slide piles, the area and distance of piles. For numerical simulation can well perform the simulation slope moving and the load on piles and can give a more reasonable designing.

Pre- and Post-Tsunami Depth Changes of Submarine Topography for the Analysis of Submarine Landslide-Induced Tsunami: Proposal of Digitization Method and Application to the Case of the 1923 Great Kanto Earthquake Tsunamis

2021 ◽  
Author(s):  
Kazuki Murata ◽  
Shinji Sassa ◽  
Tomohiro Takagawa ◽  
Toshikazu Ebisuzaki ◽  
Shigenori Maruyama
Keyword(s):  
Large Scale ◽  
Interpolation Method ◽  
Weighted Average ◽  
Tokyo Bay ◽  
Submarine Landslides ◽  
Sagami Bay ◽  
Seabed Topography ◽  
Kanto Earthquake ◽  
Before And After ◽  
Tsunami Event

Abstract We first propose and examine a method for digitizing analog data of submarine topography by focusing on the seafloor survey records available in the literature to facilitate a detailed analysis of submarine landslides and landslide-induced tsunamis. Second, we apply this digitization method to the seafloor topographic changes recorded before and after the 1923 Great Kanto earthquake tsunami event and evaluate its effectiveness. Third, we discuss the coseismic large-scale seafloor deformation at the Sagami Bay and the mouth of the Tokyo Bay, Japan. The results confirmed that the latitude / longitude and water depth values recorded by the lead sounding measurement method can be approximately extracted from the sea depth coordinates by triangulation survey through the overlaying of the currently available GIS map data without geometric correction such as affine transformation. Further, this proposed method allows us to obtain mesh data of depth changes in the sea area by using the interpolation method based on the IDW (Inverse Distance Weighted) average method through its application to the case of the 1923 Great Kanto Earthquake. Finally, we analyzed and compared the submarine topography before and after the 1923 tsunami event and the current seabed topography. Consequently, we found that these large-scale depth changes correspond to the valley lines that flow down as the topography of the Sagami Bay and the Tokyo Bay mouth.

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