Weak Layers: Their Definition and Classification from a Geotechnical Perspective

Locat, Jacques; Leroueil, Serge; Locat, Ariane; Lee, Homa

doi:10.1007/978-3-319-00972-8_1

Cited by 93 publications

(63 citation statements)

References 25 publications

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“…Does the slip plane jump to a weaker layer as it unravels? Weak layers are understood to be an important aspect of slope failures but are elusive to find (Locat et al 2013;Masson et al 2010).…”

Section: Introductionmentioning

confidence: 99%

Tiny Fossils, Big Impact: The Role of Foraminifera-Enriched Condensed Section in Arresting the Movement of a Large Retrogressive Submarine Landslide in the Gulf of Mexico

Sawyer

Hodelka

2016

Submarine Mass Movements and Their Consequences

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A 3.4-m thick condensed section enriched in foraminifera formed the final detachment horizon of a retrogressive submarine landslide, in the Ursa Basin, northern Gulf of Mexico. The high concentration of foraminifera produces a high porosity (up to five porosity units) layer distinct from the background clay. Integrated Ocean Drilling Program Expedition 308 Site U1324 cored and logged this layer. We conducted a sedimentological analysis on 31 samples across this zone and the overlying and underlying background clay. CT images show that foraminifera are individuals dispersed within the clay, unbroken, and have retained a significant amount of intraskeletal void space. The assemblage is expected for this time interval in the Late Pleistocene (~24 kya). We interpret the layer is a result of a pause in terrigenous sedimentation. The condensed section was a preferred detachment horizon but only minimal sliding occurred before further movement ceased. One possible mechanism to explain this is the presence of foraminifera results in a dilational shear strengthening behavior, which arrested movement. Further work will be required to test this, however. On a broader scale, condensed sections with abundant microfossils, may play a key role in landslide mechanics because they can alter the shearing properties of the background material.

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Section: Introductionmentioning

confidence: 99%

Tiny Fossils, Big Impact: The Role of Foraminifera-Enriched Condensed Section in Arresting the Movement of a Large Retrogressive Submarine Landslide in the Gulf of Mexico

Sawyer

Hodelka

2016

Submarine Mass Movements and Their Consequences

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“…Over the last decades the focus on mapping and characterization of weak layers has increased significantly Kvalstad et al 2005a;L'Heureux et al 2010L'Heureux et al , 2012Locat et al 2014). Locat et al (2014) discussed the formation and role of weak layers on submarine landslides and highlighted that the strain-softening behaviour of a weak layer could be the cause of many large-scale progressive failures in mild submarine slopes. Many studies also reported that the failure initiates locally in a section of the weak zone and then propagates.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, the role of a weak layer in triggering a landslide is twofold. The shear strength of a section of the weak layer might be decreased due to various reasons, such as geological activities, pore pressure generation, earthquakes, and plastic shear deformation Locat et al 2014), which could create a "fully weakened zone" (termed as "discontinuity" in Puzrin and Germanovich (2005)). If the shear stress along the fully weakened zone is greater than the reduced shear strength, the stress will be transferred to the surrounding soil elements through which shear band propagation might occur if the soil has strain-softening behaviour.…”

Section: Introductionmentioning

confidence: 99%

Modeling of large-deformation behaviour of marine sensitive clays and its application to submarine slope stability analysis

et al. 2016

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Post-slide investigations suggest that many large-scale submarine landslides occur through marine sensitive clay layers. A nonlinear mathematical model for post-peak degradation of undrained shear strength of sensitive clay is proposed based on experimental results. A method for estimation of model parameters is presented. Incorporating the model, an analytical solution is developed to examine possible mechanisms of large-scale submarine landslides. Analyses are performed for mild infinite slopes where the failure initiates from a "fully weakened zone" of soil having undrained shear strength lower than the shear stress acting parallel to the slope. The driving force, in excess of resistance, generated from the fully weakened zone is then transferred to the surrounding soil elements resulting in shear band formation due to strain-softening behaviour of sensitive clays. When the length of the fully weakened zone is greater than a critical length, catastrophic shear band propagation (self-driven without any additional external force) occurs, which could result in large-scale offshore landslides. A simple design chart is developed to calculate the critical length. Compared with a 2005 study by Puzrin and Germanovich based on a linear post-peak shear strength degradation model, the present study gives a conservative estimation of critical length for catastrophic shear band propagation.Key words: sensitive clay, large deformation, submarine landslides, shear band, undrained shear strength.Résumé : Les enquêtes post-glissement de terrain suggèrent que de nombreux glissements de terrain sous-marin à grande échelle se produisent à travers les couches d'argiles marines sensibles. Un modèle mathématique non linéaire de la dégradation post-pic de la résistance au cisaillement non drainée de l'argile sensible est proposé sur la base de résultats expérimentaux. Une méthode d'estimation de paramètres du modèle est présentée. Incorporant le modèle, une solution analytique est développée pour examiner les mécanismes possibles de glissements de terrain sous-marin à grande échelle. Les analyses sont effectuées pour des pentes infinies douces où l'échec est entamé à partir d'une « zone totalement affaiblie » du sol ayant une résistance au cisaillement non drainé inférieure à la contrainte de cisaillement agissant parallèlement à la pente. La force d'entraînement, au-delà de la résistance, générée à partir de la zone entièrement affaiblie est transférée aux éléments de sol environnant aboutissant en la formation de bandes de cisaillement en raison du comportement d'adoucissement à la déformation des argiles sensibles. Lorsque la longueur de la zone entièrement affaiblie est supérieure à une longueur critique, une propagation d'une bande de cisaillement catastrophique (auto-conduit sans aucune force externe supplémentaire) se produit qui pourrait entraîner des glissements de terrain en mer à grande échelle. Un graphique de conception simple est développé pour calculer la longueur critique. Par rapport à une étude réalisée e...

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“…Harders et al 2010;Expedition 340 Scientists 2012;Sassa et al 2012;Strasser et al 2012;Laberg et al 2014;Wiemer et al 2015), where earthquaketriggered liquefaction (Castro 1975) was argued to be the most likely sediment failure mechanism. The submarine landslide community currently debates on whether fresh volcanic fallout ash may act as 'induced weak layer' as defined in Locat et al (2014).…”

Section: Introductionmentioning

confidence: 99%

Altered marine tephra deposits as potential slope failure planes?

Wiemer¹,

Kopf²

2015

Geo-Mar Lett

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Weathering of tephra results in increasing proportions of mechanically weak, authigenic clay minerals (smectite). This suggests that altered tephra represent inherent weak layers in slope sediment sequences, and these may facilitate slope failure in submarine and other aquatic environments. In drained direct shear experiments, tephra in different alteration stages were compared to common sand-clay mixtures for geotechnical reference. Attention is drawn to the influence of particle shape on shear strength. The results revealed volcanic ash to have (1) a high strength end-member at low alteration stages due to particle roughness and angularity and (2) a low strength end-member after complete diagenetic alteration, both under static conditions. This would suggest that strongly altered volcanic ash layers could potentially be responsible for slope failures. However, a review of ODP and IODP Expedition reports shows that advanced ash alteration mostly occurs at depths below (>800 mbsf) those commonly observed for slope failure initiation (<400 mbsf). This, in turn, suggests that volcanic ash alteration does not play an important role in the initiation of slope failure.

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Weak Layers: Their Definition and Classification from a Geotechnical Perspective

Cited by 93 publications

References 25 publications

Tiny Fossils, Big Impact: The Role of Foraminifera-Enriched Condensed Section in Arresting the Movement of a Large Retrogressive Submarine Landslide in the Gulf of Mexico

Tiny Fossils, Big Impact: The Role of Foraminifera-Enriched Condensed Section in Arresting the Movement of a Large Retrogressive Submarine Landslide in the Gulf of Mexico

Modeling of large-deformation behaviour of marine sensitive clays and its application to submarine slope stability analysis

Altered marine tephra deposits as potential slope failure planes?

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