Slope Stability Analysis using a Large Deformation Finite Element Modeling Technique

Biswajit Saha, Bipul Hawlader, Rajib Dey, Rodney McAffee

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Landslides and Geohazards

ABSTRACT: bility Analysis using a Large Deformation Finite Element Modeling Technique Biswajit Saha, Bipul Hawlader and Rajib Dey Memorial University of Newfoundland, St. John's, Canada Rodney McAffee C-CORE, St. John's, Canada A1B 3X5 ABSTRACT The limit equilibrium (LE) methods are generally used by geotechnical engineers for stability analysis of slopes. It is also widely accepted that the finite element (FE) methods provide more accurate and refined solutions than the LE methods. Significantly large deformation occurs around the failure plane if the slope is brought to the verge of global failure. Large deformation FE analyses are performed in this study. The shear strength reduction technique is used to bring the slope to the state of failure. Analyses are performed for undrained condition. Based on FE simulation, the formation of shear bands and their propagation leading to failure are presented. It is shown that the shear strength does not mobilize at the same time along the entire length of the potential failure plane during its formation. Depending upon the undrained shear strength of the layered soil, other shear zones might develop in addition to the failure plane through which global failure occurs. RÉSUMÉ La limite d'équilibre (LE) méthodes sont largement utilisées par les ingénieurs géotechniques pour l'analyse de la stabilité des pentes. Il est également largement admis que l'élément fini (FE) des méthodes de fournir des solutions plus précises et plus raffinés que les méthodes LE. Significativement grande déformation se produit dans le plan de rupture si la pente est amené au bord de l'échec global. Analyses grande déformation FE sont effectuées dans cette étude. La technique de réduction de la résistance au cisaillement est utilisée pour amener la pente de l'état de défaillance. Les analyses sont effectuées pour connaître l'état non drainé. Sur la base de la simulation FE, la formation de bandes de cisaillement et leur propagation conduisant à une défaillance sont présentés. Il est montré que la résistance au cisaillement ne mobilise pas en même temps sur toute la longueur du plan de rupture potentielle lors de sa formation. En fonction de la résistance au cisaillement non drainée de sol stratifié, une autre des zones de cisaillement peuvent être développées en plus du plan de rupture à travers laquelle se produit l'échec global. 1 INTRODUCTION The analysis of the stability of slopes is an important aspect of geotechnical engineering. Traditionally, the limit equilibrium (LE) method is widely used and accepted by engineers and researchers for slope stability analysis because of its simplicity and availability of computer program such as SLOPE/W or analytical tools and charts. However, the finite element analysis (FE) has gained popularity in recent years in slope stability analysis as it could handle more complex problems with better modeling of deformation behaviour. Duncan (1996) reviewed the available LE and FE methods and discussed the advantages and limitations of FE methods for slope stability analysis. The main advantages of FE method over LE method are that in FE analysis: (i) no need to define the shape and location of the failure plane as LE method, (ii) no need to define the interslice forces based on some assumptions, (iii) realistic stress-strain behaviour can be incorporated, and (iv) the initiation of local shear failure leading to global failure could be simulated. A number of previous studies used the FE methods (e.g. Griffiths 1989; Potts et al. 1990; Matsui and San 1992; Kovacevic et al. 2013), and showed that FE modeling could be a better approach for slope stability analysis. The comparison between LE and FE analysis has also been performed in the past for various loading conditions, geometry and soil properties (e.g. Tan and Sharma 2008, Loukidis et al. 2003, Griffiths and Lane 1999). Two techniques are generally used to bring the slope to failure condition: (i) the gravity induced method (e.g. Li et al. 2009; Khosravi et al. 2013) and (ii) shear strength reduction technique (e.g. Cheng et al. 2007; Griffiths and Lane 1999; Griffiths and Marquez 2007). These studies show that many aspects involved in slope stability could be simulated using FE methods. However, one of the major issues in FE modeling is the mesh distortion around the failure plane. It is recognized that large inelastic shear strains concentrate in critical locations and form shear bands, which propagate further with loading and/or reduction of shear strength that might lead to formation of a complete failure plane for global failure of the slope. Significant deformation occurs around this area and therefore convergence of the solution becomes a major issue in numerical analysis. Some authors (e.g. Griffiths and Land 1999) considered the non-convergence of the solution as an indicator of failure. In the present study, large deformation FE modeling is performed for slope stability analysis. The FE analyses are performed using the Coupled Eulerian Lagrangian (CEL) approach available in Abaqus FE software. The soil flows though the fixed mesh and therefore a very large deformation could be simulated without any numerical issues related to mesh distortion.

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Biswajit Saha; Bipul Hawlader; Rajib Dey; Rodney McAffee (2014) Slope Stability Analysis using a Large Deformation Finite Element Modeling Technique in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper417,author = Biswajit Saha; Bipul Hawlader; Rajib Dey; Rodney McAffee,title = Slope Stability Analysis using a Large Deformation Finite Element Modeling Technique,year = 2014}