Identification of Weak Layers and Their Role for the Stability of Slopes at Finneidfjord, Northern Norway

L’Heureux, Jean-Sébastien; Longva, Oddvar; Steiner, André; Hansen, L.F.; Vardy, Mark E.; Vanneste, Maarten; Haflidason, Haflidi; Brendryen, Jo; Kvalstad, Tore J.; Forsberg, Carl Fredrik; Chand, Shyam; Kopf, Achim J

doi:10.1007/978-94-007-2162-3_29

Cited by 62 publications

(63 citation statements)

References 10 publications

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“…Several terrestrial landslides have been triggered in these marine sensitive clays in historic and prehistoric times (e.g., Fig. 1, Olsen et al 2006;L'Heureux et al 2012). Some of the largest events resulted in deposition of distinct event beds in the fjord Vardy et al 2012).…”

Section: Regional Settingmentioning

confidence: 96%

“…This sequence, which was deposited following a turbidity current at the mouth of the river, correlates to the slide plane of the 1996 landslide. It has therefore been interpreted as a weak layer (see L'Heureux et al 2012;Steiner et al 2012 for details). In such a weak layer, pore pressure or artesian groundwater pressure can build up resulting in a decrease of the effective stresses and reduction of the slope stability.…”

Section: Soil Properties Valuesmentioning

confidence: 99%

“…Consequently, the investigated differences between dynamic CPTU, static CPTU, and laboratory datasets can potentially be the result of: (i) effects related to the comparison of different equipment, (ii) the strain-rate effect, (iii) the spatial variability in the natural geological settings, and (iv) time between the different surveys (i.e., from 1997 to 2010). However, all tests were carried out at nearly the same location (i.e., distance less than 10 m), and the integrated datasets of highresolution seismics, cores, and CPTUs have shown that the spatial variability in the natural soils within given areas in the fjord is minimal (see L'Heureux et al 2012;Steiner et al 2012;Vardy et al 2012). Moreover, as no major sedimentary event (e.g., landslide) has occurred in the study area after 1996, the soil conditions in 1997 were most likely similar to those in 2010.…”

Section: Strain-rate Correctionmentioning

confidence: 99%

“…In situ dynamic CPTU tests in overconsolidated clays (OC) were conducted on samples found under erosion surfaces or within transported blocks, as shown in Fig. 1 (see also Longva et al 2003;L'Heureux et al 2012). The maximum z depth is empirically described by…”

Section: Initial Penetration Rate and Maximum Depthmentioning

confidence: 99%

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In situ dynamic piezocone penetrometer tests in natural clayey soils — a reappraisal of strain-rate corrections

SteinerAlois

KopfAchim

L’HeureuxJean-Sebastien

et al. 2014

Can. Geotech. J.

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Cone penetration testing with pore pressure measurement (CPTU) is a cost-and time-efficient way of collecting in situ geotechnical parameters of near-surface marine soils for cable and pipeline tracks, offshore foundations, and geohazard identification. The measured dynamic CPTU parameters (cone penetration resistance, sleeve friction, pore pressure) are higher than the measured static CPTU parameters. This mismatch is caused by the different penetration rates used for dynamic and static CPTU tests (dynamic tests have up to 500 times higher penetration rates than the static tests; i.e., with the commonly used 2 cm/s penetration rate). This study presents comprehensive Calypso piston and gravity core as well as dynamic and static CPTU datasets acquired in the landslide-prone Sørfjorden area (Finneidfjord, northern Norway). The fjord-marine sediments at the study site are characterized as normally consolidated to slightly over consolidated clay-dominated soils with embedded layers of sandy silt to sand. The dynamic CPTU results were corrected to match the nearby static CPTU (i.e., distance less than 10 m) using strain-rate factors (SF) derived from three known correction methods. Based on a statistical test and visual comparison of dynamic and static CPTU profiles, the modified inverse sin-hyperbolic correction method is found to be best suited for the strain-rate correction of dynamic CPTU tests, and results in SF less than 1.35 for the corrected cone penetration resistance and up to 2.4 for the sleeve friction. Our data illustrate a positive correlation between penetration rate and penetration depth, which is governed by the consolidation state of the clays. The good agreement between SF-corrected dynamic CPTU data from 34 deployments (acquired within less than 36 h shiptime) with data obtained from static CPTU and laboratory experiments on sediment cores further demonstrates that the MARUM dynamic CPTU device is a powerful tool for characterizing the properties of surficial seafloor sediments in shallow-water environments.Key words: dynamic cone penetration testing with pore pressure measurement (CPTU), static CPTU, clayey soils, in situ comparison, Finneidfjord, weak layer, strain-rate effect, soil-specific rate coefficient.Résumé : L'essai de pénétration du cône avec la mesure des pressions interstitielle (CPTU) est une façon efficace d'un point de vue temps et coûts pour récolter des paramètres géotechniques in situ de sols marins près de la surface pour des applications comme le placement de câbles et pipelines, les fondations en mer et l'identification des risques géotechniques. Les paramètres dynamiques CPTU mesurés (résistance à la pénétration du cône, friction de l'enveloppe, pression interstitielle) sont supérieurs aux paramètres statiques CPTU mesurés. Cette différence est due aux taux de pénétration différents qui sont utilisés pour les essais dynamiques et statiques de CPTU (les essais dynamiques ont des taux de pénétration jusqu'à 500 fois plus élevés que les essais statiques, par exemple un taux de...

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Section: Regional Settingmentioning

confidence: 96%

Section: Soil Properties Valuesmentioning

confidence: 99%

Section: Strain-rate Correctionmentioning

confidence: 99%

Section: Initial Penetration Rate and Maximum Depthmentioning

confidence: 99%

See 2 more Smart Citations

In situ dynamic piezocone penetrometer tests in natural clayey soils — a reappraisal of strain-rate corrections

SteinerAlois

KopfAchim

L’HeureuxJean-Sebastien

et al. 2014

Can. Geotech. J.

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“…The failure occurred through the marine-glacimarine sensitive clay layers. 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.…”

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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Origin of shallow submarine mass movements and their glide planes—Sedimentological and geotechnical analyses from the continental slope off northern Norway

et al. 2014

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Submarine landslides are often characterized by a basal surface of rupture parallel to the stratigraphy, in which downslope movement is initiated. However, little is known about the sedimentology and physical properties of the sediments within these surfaces. In this study, we present a multiproxy analysis of the sediments collected from a giant piston core penetrating a shallow submarine mass transport deposit, in combination with high-resolution seismoacoustic data to identify and characterize the basal glide plane and the weaker sediments in which movement was initiated. The initial phase of instability consists of a single fracture that formed due to the downslope movement of a mostly intact slab of sediments. The 16 m long core, comprising mostly undisturbed massive and laminated ice-rafted debris-rich clay penetrated this slab. The base of the slab is characterized by a high-amplitude semicontinuous reflection visible on the subbottom profiler data at about 12.5 m depth, interpreted to originate from the glide plane on top of a plumite deposit. This plumite has dilative behavior with pore pressure decrease with increasing shear strain and high undrained shear strength. Movement probably started within contouritic sediments immediately above the glide plane, characterized by higher sensitivities and higher water contents. The occurrence of the mass movements documented in this study are likely affected by the presence of a submarine landslide complex directly downslope. The slide scar of this landslide complex promoted retrogressive movement farther upslope and progressive spreading of strain softening along the slide base and in the slide mass. Numerical models (infinite slope, BING, and retrogressive slope models) illustrate that the present-day continental slope is essentially stable and allow reconstruction of the failure processes when initiated by an external trigger.

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Identification of Weak Layers and Their Role for the Stability of Slopes at Finneidfjord, Northern Norway

Cited by 62 publications

References 10 publications

In situ dynamic piezocone penetrometer tests in natural clayey soils — a reappraisal of strain-rate corrections

In situ dynamic piezocone penetrometer tests in natural clayey soils — a reappraisal of strain-rate corrections

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

Origin of shallow submarine mass movements and their glide planes—Sedimentological and geotechnical analyses from the continental slope off northern Norway

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