Numerical modeling of progressive failure and its application to spreads in sensitive clays

Les étalements sont de grands glissements de terrain survenant dans les argiles sensibles. Les méthodes d’analyse de la stabilité utilisant la méthode à l’équilibre limite donnent des coefficients de sécurité élevés et ne peuvent s’appliquer à ces glissements. Le mécanisme de rupture progressive expliquerait l’initiation et la propagation de la surface de rupture et la dislocation du sol en horst et en grabens, typiques aux étalements. Une méthode numérique est présentée afin d’identifier les paramètres influençant la rupture progressive et de valider son application aux étalements. Cette méthode évalue les contraintes présentes initialement dans le talus et modélise l’initiation et la propagation de la rupture progressive. Il est démontré que les hautes pentes, fortement inclinées ayant un coefficient de pression des terres au repos élevé sont susceptibles à la rupture progressive et que la surface de rupture se propage sur une grande distance. La rupture est favorisée par un sol ayant une grande fragilité lors du cisaillement. Une faible résistance à grande-déformation du sol favorise une grande distance de propagation. Les argiles de l’est du Canada, pouvant présenter une forte sensibilité et une grande fragilité lors du cisaillement, sont donc susceptibles à la rupture progressive et celle-ci explique l’occurrence d’étalements dans ces sols.Spreads are a type of large landslide occurring in sensitive clays. Stability analyses using the limit equilibrium method give factors of safety that are too large and are therefore not applicable to this type of landslide. The progressive failure mechanism is believed to explain the initiation and propagation of the failure surface and the dislocation of the soil mass in horsts and grabens, typical of spreads. A numerical method is presented to identify the parameters influencing progressive failure and to validate the application of this mechanism to spreads. The method evaluates the stresses acting in the slope before failure and models the initiation and propagation of the progressive failure. It is demonstrated that high, steep slopes, with a large earth pressure ratio at rest, are more susceptible to progressive failure and the failure surface propagates over a large distance. Failure is more likely to occur when soil with high brittleness is involved. Soil with low strength at large deformation induces failure propagation over a larger distance. Eastern Canadian clays can exhibit high sensitivity and large brittleness during shear and are susceptible to progressive failure, which explains the occurrence of spreads in these soils

Numerical Implementation of a Critical State Model for Soft Rocks

This paper details the basic tasks for the numerical implementation of a simple elasto-plastic critical state model for bonded materials (i.e. soft rocks-hard soils) into the finite element program SNAC developed at the University of Newcastle in Australia. The first task described focusses on the derivation of the incremental constitutive relationships used to represent the mechanical response of a bonded/cemented material under saturated conditions. The second task presents how these stress-strain relations can be numerically integrated using an explicit substepping scheme with automatic error control. The third task concentrates on the verification of the substepping algorithm proposed. The model used to represent the saturated mechanical response of a bonded material combines the modified Cam clay with the constitutive relationships for cemented materials proposed in Gens & Nova (1993), but incorporates some flexibility on the degradation law adopted. The role of suction and other relevant aspects of unsaturated behaviour are also discussed at the end of the paper

The 1994 landslide at Sainte-Monique, Quebec : geotechnical investigation and application of progressive failure analysis

In 1994, a landslide occurred in the municipality of Sainte-Monique, Quebec. The debris of the landslide had graben and host shapes, typical of spreads in sensitive clays. The geotechnical investigation shows that the soil involved is a firm to stiff, sensitive, nearly normally consolidated grey silty clay of high plasticity. This soil exhibits a high sensitivity and a high brittleness during shear and is therefore susceptible to progressive failure. Traditional stability analysis cannot explain this landslide. This gives the opportunity to examine the applicability of progressive failure analysis to this spread. Using the finite elements method, it is demonstrated that the initiation and observed extent of the failure surface are explained by a soil having high brittleness during shear and a large-deformation shear strength close to the remoulded shear strength of the soil. The dislocation of the soil mass can also be explained by the active failure occurring in the soil mass above the failure surface during or shortly after failure propagation. It is therefore numerically demonstrated that progressive failure explains the initiation and the extent of the failure surface of this spread.Un glissement de terrain est survenu en 1994 dans la municipalité de Sainte-Monique, Québec. Les débris présentaient des formes de horsts et grabens typiques des étalements dans les argiles sensibles. L’investigation géotechnique démontre que le sol impliqué dans ce glissement est une argile silteuse grise normalement consolidée, sensible, de forte plasticité et ayant une consistance ferme à raide. Ce sol présente une sensibilité et une fragilité lors du cisaillement élevées et peut donc être susceptible à la rupture progressive. Les analyses de stabilité traditionnelles n’arrivent pas à expliquer ce glissement. Ceci offre donc l’opportunité d’examiner l’application du concept de la rupture progressive sur cet étalement. À l’aide de programmes d’éléments finis, il est démontré que l’initiation et l’étendue de la surface de rupture observée peuvent être expliquées par un sol ayant une grande fragilité lors du cisaillement et une résistance à grandes déformations près de la résistance du sol remanié. La dislocation de la masse de sol en horsts et grabens est expliquée par la rupture active survenant dans la masse de sol au-dessus de la surface de rupture pendant ou peu après la propagation de la rupture. Il est donc démontré numériquement que la rupture progressive explique l’initiation et l’étendue de la surface de rupture d’un étalement

The Interaction of Targeted and Non-Targeted Nanoparticles with Cells and Model Membranes.

The first component of the thesis examines the binding of a multivalent, folic acid (FA) receptor targeted, generation 5 (G5) PAMAM dendrimer using force pulling spectroscopy. This targeted nanoparticle, when conjugated to the therapeutic methotrexate and then acetylated to form a neutral complex, has been shown to be effective at reducing FA-receptor expressing KB cell tumors. Surface plasmon resonance (SPR) showed a 100,000-fold decrease in the dissociation rate of the G5-FAn from a model FA receptor surface, folate binding protein (FBP), as the number of FAs (n) increased from 1-12. Force pulling spectroscopy was then used to compare the force required to rupture the interaction between the FBP and a single G5-FAn taken from a solution of G5-FAn where n = 0, 4.7, 2.7, and 7.2. A difference in rupture force was measured but due to the heterogeneity of the number of FAs per G5-FAn within a given solution, it was not possible to assign the measured forces to a specific number of FA-FBP interactions. The second component of this thesis examines the interaction of a variety of non-targeted, charged nanoparticles with cells and model membranes. Five polycationic polymers (G5 and G7 PAMAM dendrimer, branched polyethylenimine (PEI), poly-L-lysine (PLL) and diethylaminoethyl-dextran (DEAE-DEX)) were shown to induce nanoscale hole formation in cells as measured by enzyme and dye diffusion assays, as well as in dimyristoylphosphatidylcholine (DMPC) supported lipid bilayers (SLB) as measured by atomic force microscopy (AFM). In contrast, neutral polymers polyethylene glycol and polyvinyl alcohol did not induce nanoscale hole formation in cells or DMPC SLBs. This suggests that a possible mechanism for polycationic polymer internalization and/or nanoparticle-induced cytotoxicity of cells is through nanoscale hole formation. The interaction between SLBs and a variety of other charged nanoparticles (MSI-78, Au-NH2, G3-NH2 PAMAM dendron, and silica-NH2 were also investigated using the AFM-SLB assay. The general trend taken from the AFM-SLB studies is that surface area of the polycationic nanoparticles is the largest contributing factor to membrane disruption. In addition, micelles of charged detergents cetyl trimethylammonium bromide bromide (CTAB) and sodium dodecyl sulfate (SDS) were also shown to induce hole formation in SLBs.Ph.D.ChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/58463/1/lerouepr_1.pd

A constitutive model for unsaturated cemented soils under cyclic loading

On the basis of plastic bounding surface model, the damage theory for structured soils and unsaturated soil mechanics, an elastoplastic model for unsaturated loessic soils under cyclic loading has been elaborated. Firstly, the description of bond degradation in a damage framework is given, linking the damage of soil's structure to the accumulated strain. The Barcelona Basic Model (BBM) was considered for the suction effects. The elastoplastic model is then integrated into a bounding surface plasticity framework in order to model strain accumulation along cyclic loading, even under small stress levels. The validation of the proposed model is conducted by comparing its predictions with the experimental results from multi-level cyclic triaxial tests performed on a natural loess sampled beside the Northern French railway for high speed train and about 140 km far from Paris. The comparisons show the capabilities of the model to describe the behaviour of unsaturated cemented soils under cyclic loading

The Saint-Jude landslide of May 10th, 2010, Quebec, Canada : investigation and characterisation of the landslide and its failure mechanism

A landslide occurred on May 10, 2010, along the Salvail River, in the municipality of Saint- Jude, Quebec. Debris of the landslide was formed of blocks clay having horst and graben shapes, typical of spreads in sensitive clays. A detailed investigation was carried out by the Ministère des Transports, de la Mobilité durable et de l’électrification des transports du Québec in collaboration with Université Laval, with the objective of characterizing this landslide, determining the causes and learning about its failure mechanism. The soil involved is a firm, grey, sensitive lightly overconsolidated clay with some silt. Data from piezometers installed near the landslide indicated artesian conditions underneath the Salvail River. Cone penetration tests allowed to location of two failure surface levels. The first one starting 2.5 m below the initial river bed and extending horizontally up to 125 m and a second one 10 m higher reaching the backscarp. Investigation of the debris with onsite measurements, light detector and ranging surveys, cone penetration tests, and boreholes allowed a detailed geotechnical and morphological analysis of the debris and reconstitution of the dislocation mechanism of this complex spread.Un glissement est survenu le 10 mai 2010 le long de la rivière Salvail, dans la municipalité de Saint-Jude au Québec. Les débris de ce glissement étaient formés de blocs d’argile ayant la forme de horst et de grabens, typique des étalements dans les argiles sensibles. Le Ministère des Transports, de la Mobilité durable et de l’électrification des transports du Québec et l’Université Laval ont réalisé l’investigation détaillée de ce glissement de terrain, dans le but de le caractériser, d’en déterminer les causes et d’en apprendre d’avantage sur le mécanisme de rupture. Le sol impliqué est une argile sensible grise avec un peu de silt, de consistance ferme, légèrement surconsolidée. Les piézomètres installés à proximité du glissement indiquent des conditions artésiennes sous la rivière Salvail. L’utilisation du piézocône a permis de localiser deux niveaux de surfaces de ruptures. L’un à 2,5 m sous la position initiale de la rivière, s’entendant horizontalement sur 125 m, et l’autre 10 m plus haut, allant jusqu’à l’escarpement arrière. L’investigation des débris par mesures prises sur le terrain, levées de télédétection par laser, piézocônes et forages a permis une analyse géotechnique et morphologique détaillée de ces derniers et la reconstitution du mécanisme de dislocation de ce glissement complexe

A novel consolidation-based representative volume element for granular materials and its application for the characterization of the mechanical response of sand during impact loading

Open Access funded by European Structural Integrity Society Defense Threat Reduction Agency (DTRA), Grant No: HDTRA1-12-1-004

Identification of novel proteins affected by rotenone in mitochondria of dopaminergic cells

Background: Many studies have shown that mitochondrial dysfunction, complex I inhibition in particular, is involved in the pathogenesis of Parkinson's disease (PD). Rotenone, a specific inhibitor of mitochondrial complex I, has been shown to produce neurodegeneration in rats as well as in many cellular models that closely resemble PD. However, the mechanisms through which complex I dysfunction might produce neurotoxicity are as yet unknown. A comprehensive analysis of the mitochondrial protein expression profile affected by rotenone can provide important insight into the role of mitochondrial dysfunction in PD. Results: Here, we present our findings using a recently developed proteomic technology called SILAC (stable isotope labeling by amino acids in cell culture) combined with polyacrylamide gel electrophoresis and liquid chromatography-tandem mass spectrometry to compare the mitochondrial protein profiles of MES cells (a dopaminergic cell line) exposed to rotenone versus control. We identified 1722 proteins, 950 of which are already designated as mitochondrial proteins based on database search. Among these 950 mitochondrial proteins, 110 displayed significant changes in relative abundance after rotenone treatment. Five of these selected proteins were further validated for their cellular location and/or treatment effect of rotenone. Among them, two were confirmed by confocal microscopy for mitochondrial localization and three were confirmed by Western blotting (WB) for their regulation by rotenone. Conclusion: Our findings represent the first report of these mitochondrial proteins affected by rotenone; further characterization of these proteins may shed more light on PD pathogenesis.The study is supported by NIH grants to JZ (R01AG025327 and R01ES012703)

Development of a long term monitoring network of sensitive clay slopes in Québec in the context of climate change

The Government of Québec recently initiated the deployment of a vast groundwater pressures monitoring network in postglacial marine clays to document their variations in time and improve our understanding of the relationship between failure initiation and climate in clay slopes. This project aims at evaluating the impacts of climate change on clay-slope stability and how it can be integrated in landslide risk management to improve public safety. Hydrogeological data will be acquired at sites located throughout the Québec Province’s post-glacial clay deposits to create a public georeferenced index of typical hydrogeological conditions. The project goes beyond the characterization of groundwater pressures and their variations in clay slopes. Indeed, slope deformation will be measured at several sites. Also, two sites in flat terrain will be instrumented in order to evaluate mechanical properties of clay layers in simple 1-D conditions and groundwater recharge. The unsaturated clay crust in slopes susceptible to superficial landslides will be characterized and instrumented. The current lifetime of the monitoring project has been set to a period of 25 years.