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Extreme rainfall occurred in July 1996 over the Saguenay Region, some 200 km north of Quebec City. With about 1000 landslides, seven damaged dams, one dike failure, washed out road sections, tens of bridges damaged or destroyed, 1700 properties destroyed or damaged and several casualties, this event was one of the most important natural disasters in Canada. Detailed geotechnical investigations permitted better understanding of the soils involved, mainly sensitive clays and their superficial crust, including their behaviour in landslides, the erosion processes, impacts on infrastructure and sediment deposition. [ABSTRACT FROM AUTHOR]

A new three-dimensional cone-cap limit-state surface (LSS) model is proposed for cross-anisotropic, saturated, cohesionless, or cohesive remolded soils in consideration of anisotropic yielding and kinematic hardening. Matsuoka-Nakai failure criterion equations are adopted as the cone yield functions, and a new ellipse cap associated with Matsuoka-Nakai cone is developed. The anisotropic vertical and horizontal yield stresses (σ′aL -σ′rLare used as hardening variables to describe evolution of the fabric anisotropy. A smart kinematic hardening law is suggested without any addition of material parameters. With a nonassociated flow rule and because of the cone-cap connection on a constant p0 critical state plane, a smooth transition of a plastic strain increment vector at the cone-cap intersection points is ensured for the convenience of numerical calculation. There are very few parameters involved in the proposed model, and they are the same as those in the Cam-clay model, except one parameter for cross-anisotropy [slope of the anisotropic line (AL) KAL or horizontal yield stress s σ′rt]. They can be simply determined from conventional laboratory odometer and undrained triaxial compression experiments. The soil sample is simplified as a stress element, and the element numerical analysis results validate the test data very well. The model-predicted results well illustrate the size and shape modification of the cone-cap LSS of isotropic and cross-anisotropic soils as well as the kinematic hardening effect on the stress-strain behavior. Based on this model, other important features of natural soils, such as viscosity, microstructure, and partial saturation, can be further incorporated by extending the vertical and horizontal yield stresses σ′aL and (σ′aL -σ′rL) in consideration of the effect of viscosity, microstructure, and partial saturation, respectively. [ABSTRACT FROM AUTHOR]

The goal of this article is to revise several aspects of the well-known classification of landslides, developed by Varnes (). The primary recommendation is to modify the definition of landslide-forming materials, to provide compatibility with accepted geotechnical and geological terminology of rocks and soils. Other, less important modifications of the classification system are suggested, resulting from recent developments of the landslide science. The modified Varnes classification of landslides has 32 landslide types, each of which is backed by a formal definition. The definitions should facilitate backward compatibility of the system as well as possible translation to other languages. Complex landslides are not included as a separate category type, but composite types can be constructed by the user of the classification by combining two or more type names, if advantageous. [ABSTRACT FROM AUTHOR]

Recent investigations have shown that under adverse cyclic triaxial loading, the upper part of soil specimens can turn into a fluid-like state with increased water content (i.e., fluidization), whereas the lower layers can maintain a relatively high stiffness. This paper aims to gain further insight into this behaviour by monitoring the development in excess pore water pressure (EPWP) at the top and bottom of the test specimens, followed by post-analysis of water content distribution along the specimen. The results show that the EPWP at the uppermost part of the specimen develops rapidly and approaches the zero-effective stress level, whereas the EPWP at the bottom part of the specimen tends to stabilize while undergoing densification. Accompanied with this process is a redistribution of the water content along the specimen height where the water content at the upper soil layer increases to approach the liquid limit while increasing the void ratio. [ABSTRACT FROM AUTHOR]

Observations from past events are used to show that the concept of progressive failure may explain translational progressive landslides and spreads - large landslides occurring in sensitive clays. During progressive failure, the strain-softening behaviour of the soil causes unstable forces to propagate a failure surface further in the slope. Translational progressive landslides generally take place in long, gently inclined slopes. Instability in a steeper upslope area is followed by redistribution of stress, which increases earth pressure further downslope. Passive failure may therefore occur in less-inclined ground, heaving the soil. Spreads are usually trigged by erosion of a deposit having a higher angle near the toe. Instability starts near the toe of the slope and propagates into the deposit, reducing earth pressure. This may lead to the formation of an active failure with dislocation of the deposit into horsts and grabens. The failure mechanism of both types of landslides is controlled by the stresses in the slope and the stress-strain behaviour of the soil. The mechanism presented explains the sensitivity of a slope to minor disturbances and the resulting high retrogressions observed for such landslides in Scandinavia and eastern Canada. [ABSTRACT FROM AUTHOR]

The rate-dependent rheological behaviour of soils of different origins and characteristics was studied and the applicability of the power law model was examined. The studied soils were divided into three groups: (i) low-activity soils, (ii) high-activity soils, and (iii) silt-rich soils. The results show that the power law applies to all these soils and is representative of soil behaviour in a strain rate range corresponding to debris flows, which is generally not the case with the Bingham model. For low-activity clays, the power law index, n, is typically equal to 0.12 and seems to increase with the plasticity index; it is larger (i.e., in the range of 0.2–0.6) for silt-rich soils. Comparison of n values for tests performed on intact and remoulded low-activity clay specimens indicates that the power law index is possibly strain-rate dependent. [ABSTRACT FROM AUTHOR]

The surfaces of real sands are often rough and a discrete element modeling of rough granulates is very important to understand the behavior of real sands. This paper presents a two-dimensional discrete element method (DEM) to capture the roughness of particles. The model consists of two parts: equations governing the motion of rough particles and mechanical contact models controlling rough-contact behavior. The key point of the theory is that the assumption in the original DEM proposed by Cundell and Strack in 1979 that a pair of particles are in single-point contact, is here replaced by that the particles are in rough contact over a width. By making the idealization that the contact width is homogeneously distributed with a finite-number of the normal/tangential basic elements (BEs) (each BE is composed of spring, dashpot, slider, or divider), we relate the governing equations to local equilibrium and also establish a rolling contact model together with normal/tangential contact models. The three main features of the theory are that: two physical parameters need to be introduced in the theory to represent particle roughness in comparison to the original DEM; rolling stiffness, rolling viscous-damping parameter, and rolling strength due to roughness are all linked with their respective counterparts in the normal direction in a simple and complete formula through these two parameters; the equations governing motion of rough particles satisfy the local equilibrium condition. The present theory was incorporated into a DEM code to investigate the mechanical response of the material of different roughness, particularly the angle of internal friction [lowercase_phi_synonym]. Twenty-four DEM simulations showed that [lowercase_phi_synonym] predicted by the theory was significantly increased in comparison to the standard DEM prediction. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to present macro- and micro-study on the yielding of microstructured geomaterials by numerical experiments. This target is achieved by carrying out 63 one-dimensional and biaxial compressions tests on an idealized bonded geomaterial with an extension of distinct element method, into which bond contact models proposed were implemented. Numerical results indicate that: (a) preconsolidated pressure appears to attribute to bond and looseness in the geomaterials, and an increase in void ratio leads to a decrease in yielding stress in one-dimensional tests; (b) an increase in bonding strength at interparticle contacts results in an increase in yielding stress and cohesion, and an internal friction angle that is smaller than the critical state value; (c) the observed first-yielding (initiation of bond breakage) is stress path dependent, and gross-yield (defined with respect to volumetric strain) of microstructured geomaterials is evidently related to bond breakage. [ABSTRACT FROM AUTHOR]

This paper describes the viscous behaviour of St-Roch-de-l'Achigan clay, a Champlain Sea clay from Quebec, Canada. The general geotechnical profile of the soil deposit was first established with static cone penetration tests, vane tests, and some laboratory tests performed at different depths. For the study of the viscous behaviour of the clay, a special laboratory test program was established for specimens taken at depths from 4.8 to 5.8 m. This program included special incremental loading oedometer tests, constant rate of strain (CRS) oedometer tests performed at different strain rates, isotropic and anisotropic triaxial compression tests, and undrained shear tests. All these tests were performed under a constant temperature, varying from 10 to 50 °C. The test results show that the vertical yield stresses and the entire limit state curve depend on strain rate and temperature. The critical state line is also temperature dependent in the void ratio (e) – log principal effective stress (p′) diagram but not in the deviator stress (q) – principal effective stress (p′) diagram. The results also show that microstructuring may develop when the temperature is high or the strain rate small. [ABSTRACT FROM AUTHOR]

The role of the degree of microstructure on the behaviour of clayey soils has been the focus of many studies. However, none so far have quantified the evolution of the shear strength parameters for a given soil for degrees of microstructure going from an intact condition to complete remoulding. In the present study, a series of compression triaxial tests have been performed on specimens of the naturally highly structured Saint-Jean-Vianney clay under the following conditions: intact, destructured by straining outside the limit state curve, and reconstituted and reconsolidated after complete remoulding. The results show that the limit state curve is influenced by the level of destructuration reached before testing, and moreover, that the shear strength parameters at large deformation are influenced by the level of destructuration at the beginning of the test. The compression tests infer that the soil seems to retain the memory of its initial microstructure, at least for consolidation volumetric strains up to 14%. The observed behaviour has implications for the understanding and modelling of natural clays; it also explains to some extent the difference in strength parameters used in stability analyses of embankments on soft clays and natural slopes in clay.Key words: clay, microstructure, destructuration, shear strength, large deformation shear strength, triaxial test.Le rôle de la microstructure dans le comportement d'un sol argileux a fait l'objet de nombreuses études. Cependant, aucune d'entre elles jusqu'à maintenant n'a quantifié l'évolution des paramètres de résistance au cisaillement pour un sol donné avec un niveau de déstructuration variant de l'état intact au remaniement complet. Dans la présente étude, une série d'essais de compression triaxiale ont été réalisés sur des échantillons de l'argile de Saint-Jean-Vianney, reconnue comme étant fortement structurée, dans les différents états suivants : intact, déstructuré par compression volumétrique en dehors de la courbe d'état limite, et reconstitué et reconsolidé après remaniement complet. Les résultats montrent, comme l'on pouvait s'y attendre, que la courbe d'état limite est affectée par le niveau de déstructuration avant l'essai, et que de plus, les paramètres de résistance au cisaillement à grande déformation sont influencés par le niveau de déstructuration au début de l'essai. Les essais de compression indiquent que le sol semble conserver la mémoire de sa microstructure intiale après déstructuration par compression volumétrique jusqu'à 14 % de déformation. Le comportement observé a des implications sur la compréhension et la modélisation des argiles naturelles ; il explique aussi, d'une certaine manière, la différence entre les paramètres de résistance utilisés dans les analyses de stabilité des remblais sur argiles molles et des pentes naturelles dans les dépôts argileux.Mots clés : argile, microstructure, déstructuration, résistance au cisaillement, résistance à grande déformation, essai triaxial. [ABSTRACT FROM AUTHOR]

The hydraulic conductivity of six compacted tills from northern Quebec with different grain-size distributions has been studied in saturated conditions in the laboratory. The results show that compaction conditions play an important role in hydraulic conductivity. When considering the hydraulic conductivities of specimens compacted at degrees of saturation greater than the optimum, there is a good correlation with the content of clay-size particles. This paper provides a good practical tool for evaluating preliminary hydraulic conductivity values of compacted tills from northern Quebec on the basis of their grain-size distribution and compaction conditions.Key words: till, hydraulic conductivity, grain-size distribution, compaction conditions.La conductivité hydraulique de six tills du nord québécois présentant des granulométries différentes a été étudiée en conditions saturées, en laboratoire. Les résultats montrent que les conditions de compactage jouent un rôle important dans la conductivité hydraulique qui en résulte. Lorsque l'on considère les conductivités hydrauliques mesurées sur des échantillons compactés à des degrés de saturation plus élevés que celui à l'optimum, on obtient une bonne corrélation avec le pourcentage de particules de dimensions argileuses. Cet article fournit donc un bon outil pratique pour une évaluation préliminaire de la conductivité hydraulique des tills du nord québécois sur la base de leur granulométrie et des conditions de compactage.Mots clés : till, conductivité hydraulique, granulométrie, conditions de compactage. [ABSTRACT FROM AUTHOR]

The preconsolidation pressure and overconsolidation ratio profiles are the most important factors related to the mechanical behaviour of clay deposits. They are interpreted on the basis of a limited number of laboratory tests, but the near-continuous information provided by the piezocone can allow local data to be extrapolated to an entire site. Numerous methods have been proposed for relating piezocone data to preconsolidation pressure and the overconsolidation ratio, but their validity is still uncertain. In this paper, nine methods are compared on the basis of data collected on 31 sensitive clay sites in Quebec whose preconsolidation pressure profiles are well known. Each method is briefly presented and the most promising are identified. The simplest method, which directly relates preconsolidation pressure to net tip resistance, also appears to be the most effective.Key words: clay, preconsolidation pressure, overconsolidation ratio, piezocone, correlations.Les profils de pression de préconsolidation et du rapport de surconsolidation constituent les éléments les plus importants en ce qui concerne le comportement mécanique des dépôts argileux. Leur évaluation se fait par un nombre limité d'essais de laboratoire, mais les données fournies par le piézocône de manière presque continue peuvent permettre une extrapolation à l'ensemble du site de ces données locales. De nombreuses méthodes ont été proposées pour corréler les données du piézocône et la pression de préconsolidation ou le rapport de surconsolidation mais leur validité est encore incertaine. Dans le présent article, neuf méthodes sont examinées à partir de données provenant de 31 sites d'argile sensible de la province du Québec pour lesquels les profils de pression de préconsolidation sont bien connus. Chaque méthode est brièvement présentée et les méthodes les plus intéressantes sont identifiées. Il semble que la relation entre la pression de préconsolidation et la résistance en pointe nette, qui est la plus simple, est aussi la plus efficace.Mots clés : argile, pression de préconsolidation, rapport de surconsolidation, piézocône, corrélations. [ABSTRACT FROM AUTHOR]

The paper proposes equations describing the transport of gases through the initially unsaturated core of a dam by dissolution and diffusion in water and examines different numerical simulations based on these equations. The simulation results provide pore-water pressure distributions similar to those observed in several earth dams, with higher pore-water pressures than expected in the downstream part of the core. Practical considerations to estimate the implications of the phenomenon are then discussed.Key words: dam, unsaturated soil, pore pressure, dissolution of gas, diffusion of gas, hydraulic conductivity.L'article propose des équations décrivant le transport des gaz par dissolution et diffusion dans l'eau à travers le noyau initialement non saturé d'un barrage et examine différentes simulations numériques basées sur ces équations. Les résultats des simulations fournissent des distributions de pressions interstitielles semblables à celles observées dans plusieurs barrages en terre, avec des pressions interstitielles plus élevées qu'escomptées dans la partie aval du noyau. On discute alors de considérations pratiques pour évaluer les implications du phénomène.Mots clés : barrages, sol non saturé, pression interstitielle, dissolution des gaz, diffusion des gaz, conductivité hydraulique.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

The method of soil stabilization is well known and has been used throughout the world for many decades to improve some soil properties. Although many researchers have studied the effect of adding a cementing agent to a soil, not many of these researchers have explored the effect of treatment on the resulting properties of high water content soils like dredged material. Also, there has been little work concerning the prediction of the mechanical changes to the soil. Therefore, this paper summarizes the results of a research project conducted to define the general mechanical behavior of high water content clayey soils from eastern Canada treated with lime or cement, in terms of compressibility. In the light of this research, the general compressibility behavior has been obtained, defined by relationships between initial void ratio, additive content, and vertical yield stress for a given inorganic or organic soil. These relationships have been normalized on the basis of the one-dimensional compression curve of the remolded and reconstituted untreated soil to give a simple method for predicting the vertical yield stress of a treated soil for any initial void ratio and its resistance to compression.Key words: stabilization, compressibility, yield stress, clayey soils, lime, cement.La méthode de stabilisation des sols est bien connue et a été utilisée depuis plusieurs décades à travers le monde pour améliorer certaines propriétés des sols. Quoique plusieurs chercheurs aient étudié l'effet de l'addition d'un agent de cimentation au sol, peu d'entre eux ont exploré l'effet du traitement sur les propriétés résultantes des sols à teneur en eau élevée tels que les matériaux dragués. Également, il y a eu peu d'études portant sur la prédiction des changements mécaniques apportés au sol. En conséquence, cet article résume les résultats d'un projet de recherche réalisé pour définir un comportement mécanique général en terme de compressibilité de sols argileux à hautes teneurs en eau de l'est du Canada avec de la chaux ou du ciment. À la lumière de cette recherche, on a obtenu le comportement général en compressibilité défini par la relation entre l'indice des vides initial, la teneur en additif, et la contrainte de préconsolidation apparente verticale pour un sol donné organique ou inorganique. Finalement, ces relations ont été normalisées sur la base de la courbe de compression unidimensionnelle du sol non traité remanié et reconstitué pour donner un méthode simple pour prédire la contrainte de préconsolidation apparente verticale d'un sol traité pour n'importe quel indice de vide initial, et sa résistance à la compression.Mots clés : stabilisation, compressibilité, contrainte de préconsolidation apparente, sols argileux, chaux, ciment.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

The Saint-Fabien landslide occurred in December 1976, 270 km northeast of Quebec City, Canada. The landslide took place in a valley filled with glaciomarine sensitive clay covered by peat bog deposits and presenting an upwards hydraulic gradient. Unique features of this event are the ground surface and the failure surface that are both close to the horizontal. In addition, passive and active failure zones were observed in the debris after the landslide, indicating a possible downward progressive failure mechanism, rarely observed in Eastern Canadian clays. Possible triggers of the event are: the continuous exploitation of the peat downslope and (or) the roadworks going on along Road 132 at the time of the event, which is crossing the landslide area upslope. Conventional stability analysis for the site gives a factor of safety of 1.43, indicating that limit equilibrium analysis cannot explain the formation of the failure surface observed at Saint-Fabien. The initiation and the propagation of the failure were analysed through 1D numerical modelling using the concept of progressive failure. The methodology consists of two steps: first the calculation of the initial stresses in the slope with the finite element software PLAXIS 2D; and second, the modelling of initiation and propagation of the progressive failure along the potential failure surface with the finite element code BIFURC, developed at the Norwegian Geotechnical Institute. Results from the modelling with BIFURC show that the concept of progressive failure is able to explain the extent of the landslide observed at Saint-Fabien with parameter values based on what was measured in situ. [ABSTRACT FROM AUTHOR]

On 9 November 2016, a landslide in sensitive glaciomarine sediments occurred on a terrace of the Champlain River near the municipality of Saint-Luc-de-Vincennes, Quebec. The particularity of this event is that there are evidences that the movement started as a flowslide and then finished as a spread. The landslide morphology comprises horsts and grabens typical of spreads and also a large quantity of remolded material that flowed out of a pear-shaped crater with a narrow bottleneck, typical of flowslides. The geotechnical investigation of this landslide was performed by the Ministère des Transports du Québec (MTQ) in collaboration with Université Laval, and consisted of light detection and ranging (LiDAR) surveys, drone photography, several boreholes, piezocone tests with pore pressure measurements (CPTUs), field vane tests, and piezometric monitoring. They were used to characterize the landslide, to determine the location of the failure surface, and also to acquire information on the properties of the clay deposit. A combined analysis of the debris and volume calculations was done to reconstruct the different phases of flowing and spreading and their relative chronologies. [ABSTRACT FROM AUTHOR]

Presents a reply to professor Gholamreza Mesri's discussion of a paper on the combined effects of strain rate and temperature on the behaviour of St-Roch-de-l'Achigan clay. Aspects that were discussed in the paper; Question on the analysis of the test results on preconsolidation pressure; Description of the linear relationship between the logarithm of preconsolidation pressure and the logarithm of strain rate.

This paper examines the geotechnical and rheological characteristics in terms of the transition from slide to flow in submarine landslides. This paper contains the results of a series of laboratory tests on the Saguenay Fjord fine-grained sediments. There are two types of tests: (1) vane shear tests in which intact and remolded samples are sheared and exposed to ambient water and (2) rheological tests performed on remolded sediment (with variable liquidity index) using a viscometer. The results explain the effect of water infiltration into soil. The sudden reduction in shear strength varied between about 300 and 800 Pa (Δw = 2–20%). The viscosity obtained from normalized flow curves (i.e., the logarithmic plot of shear stress versus the shear rate) were employed to characterize the rheology of soil. The mean value of viscosity (strength parameter in this case) as a function of shear rate from the results of fine-grained sediments varied between about 0.1 and 0.4. The values of yield stress and viscosity that were associated with the passage from the remolded to the fluidized state were in the range of 200 to 300 for Saguenay Fjord sediments. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The thick sequences of marine clayey deposits that blanket the St. Lawrence Lowlands in south-eastern Canada are highly susceptible to landslides. With 89% of the population of the province of Quebec living in this region, improving our understanding of the mechanisms causing landslides in these sediments is a matter of public security. To accomplish this goal, instruments were deployed at a field site in Sainte-Anne-de-la-Pérade, Quebec, Canada to monitor atmospheric, soil, and groundwater conditions. Field and laboratory measurements of soil geotechnical and hydraulic properties were also performed. Results indicate that the groundwater and pore pressure dynamics at the site cannot be explained using simplified site conceptual models. Further analysis indicates that groundwater dynamics and pore pressures in the massive clay deposits on site are determined by (i) the highly heterogeneous nature of the local geological materials, (ii) the contrasting hydraulic and geotechnical properties of these materials, (iii) the presence of two unconfined aquifers at the site, one surficial and one at depth, and (iv) the presence of the Sainte-Anne River. These results were used to create a new conceptual model that illustrates the complex groundwater flow system present on site and shows the importance of including hydrogeologic context in slope stability analysis. [ABSTRACT FROM AUTHOR]

Fluidization processes in submarine landslides were studied by physical and numerical means. To examine soil-water interactions in the fluidization process, the computer axial tomography (CAT)-scan imaging techniques and laboratory vanes were utilized with a focus on the transition from failure to post-failure. Based on the results that were obtained from the scanning images and laboratory vane tests after the process of water infiltration into the soil sample, it appears that a gradual decrease in shear strength is unavoidable with increasing water content in a shear zone. From the numerical results, which were based on the dam-break problem using the transport equation coupled with the Navier-Stokes equation, if the slide is assumed to be initially unstable, a possible transition of fluidization processes that are dependent upon a change in density occurs. The density of the mud decreases with time during the flow at the interface between mud and water. The upper part of the mud pushes the lower part of the mud and then induces a rotation of mud that moves substantial distances. These results emphasize the importance of the soil-water interaction, the need for sediment rheology and the influence of the water circulation on the motion of the landslide. [ABSTRACT FROM AUTHOR]

Abstract: At least three major landslide events formed the submarine and subaerial Betsiamites (Québec, Canada) landslide complex and mobilized an estimated total volume of 2000million m3 (2km3). Linkage between offshore and onshore geophysical investigations with borehole data and in situ testing allows reconstruction of the architecture of the Betsiamites River delta area and leads to the identification of the main failure events. The submarine scar of the Betsiamites landslide complex may have resulted from a first failure, dated at about 9250cal BP, which mobilized a minimum volume of 200million m3. A second landslide dated at 7250cal BP mobilized a volume of 1300million m3 over an area of 54km2. The Betsiamites submarine landslide event dated at 7250cal BP left the largest scar yet identified on the St. Lawrence estuary seafloor. Furthermore, this paper demonstrates that the subaerial scar of the Betsiamites landslide complex is a result of the Colombier landslide event, which was initiated by the 1663 earthquake and involved four successive failure phases: one submarine and three subaerial. The February 5th 1663 earthquake triggered a submarine landslide event, which reached the shoreline, and led in a short period of time successively to two subaerial flowslides in sensitive clayey material and a subaerial lateral spread. The four failure phases mobilized a possible total volume of about 530million m3 over an area of 20km2. The Colombier landslide event is among the largest documented historic landslides in Canada. The presence of submarine scars left by the early Holocene events acted as predisposition factors for the development of the failure while the earthquake of 1663 was the main triggering factor of the first submarine failure. [Copyright &y& Elsevier]

Rheological properties of fine-grained sediments depending on index properties and salinity were examined. To characterize flow behaviors as a function of soil type, groups were made for convenience: (i) low-activity clays (group 1), (ii) high-activity clays (group 2), and (iii) silt-rich soils (especially for iron tailings; group 3). Low-activity and high-activity clays have characteristics of pseudoplastic (shear thinning) fluids, and exhibit a decrease in viscosity with increasing shear rate. However, in terms of the change in soil structure due to particle-particle interactions, illitic and montmorillonitic clays have opposite responses to salinity. As most of our data were obtained on low-activity clays - mostly illitic mixtures - we implemented a test program to ascertain the influence of montmorillonite on flow behavior. Using the Bingham model, a simple relationship is presented in terms of the possible critical limits of rheological transitions from clay- to silt- to sand-rich soils. [ABSTRACT FROM AUTHOR]

Fragmentation is one of the mechanisms involved in rock avalanches. Quantifying the associated energy during a rock avalanche can help to assess the influence of fragmentation on post-failure mass movements. In this paper, in situ block size distributions of the intact rock mass and the debris deposits are presented and analyzed for nine rock avalanches, five in the Canadian Rocky Mountains and four in the European Alps. Degrees of fragmentation are estimated from these data. Two methods are examined to assess fragmentation energy, one based on the comminution theory, and one on the blasting energy used in the mining industry. The results show that, for the studied rock avalanches, there is a relationship between the reduction in diameter ratio, Rr = D50/d50 (where D50 and d50 are the mean diameter of the intact rock mass and the mean diameter of the debris, respectively), and the potential energy per unit volume normalized with respect to the point load strength of rock (γHG/σc), where γ is the unit weight of the material, HG is the vertical distance between the centres of gravity of the mass at the start and end positions, and σc is the point load strength). For the cases studied, fragmentation energy calculations average 20% of the potential energy. An empirical relationship between Rr and γHG/σc has been established and is used in the definition of a disintegration index (ID). This index seems to reflect the physics of the disintegration process, since it accounts for the fact that the reduction in diameter ratio is a function of the dissipated energy and the strength of the rock. These factors have long been known to affect fragmentation but have never been presented in a coherent manner for rock avalanches. [ABSTRACT FROM AUTHOR]

Using some new and previously published sedimentation rate data the relationship between sedimentation rate and distance from sediment source was statistically modelled for the Saguenay Fjord, Canada. Sedimentation rates obtained from these models can be used to reasonably predict the range of ages for submarine mass movements in the Saguenay Fjord. Error in the prediction is mostly associated with the natural variability of sedimentation rate. Ranges of dates were predicted for several submarine mass movements in the Upper Saguenay Fjord. In many cases the predicted date range did not correspond to the 1663 earthquake which had been previously assumed to have triggered these mass movements. [ABSTRACT FROM AUTHOR]

A long-term issue that has hampered the efficient operation of heavy-haul tracks is the migration of fluidized fines from the shallow soft subgrade to the overlying ballast, i.e., mud pumping. This paper presents a series of undrained cyclic triaxial tests where realistic cyclic loading conditions were simulated at low confining pressure that is typical of shallow subgrade beneath a ballast track. Subgrade soil specimens with a low-plasticity index collected from a field site with recent history of mud pumping were tested at frequencies from 1.0 to 5.0 Hz and a cyclic stress ratio (CSR) from 0.1 to 1.0. The experimental results indicate that under adverse loading conditions of critical cyclic stress ratio (CSRc) and frequency, there is upward migration of moisture and the finest particles towards the specimen top and this causes the uppermost part of the soil specimen to soften and fluidize. Conversely, a smaller value of CSR tends to maintain stability of the specimen despite the increasing number of loading cycles. It is noteworthy that for any given combination of CSR and frequency, the relative compaction has a significant influence on the cyclic behaviour of the soil and its potential for fluidization. [ABSTRACT FROM AUTHOR]

Sensitive clays, mostly found in Eastern Canada and Scandinavia, are prone to various types of landslides; among them are flowslides that may affect hectares of land. Debris from those slides has high mobility, with runout distances that may extend over hundreds of meters in relatively flat and non-channelized terrain. Most studies on the mobility use apparent rheological properties to back-calculate the runout behavior of these landslides. This works well for back-analyses of landslides but is of little help in a context of hazard mapping, where prospective analysis of future landslides is necessary. In this study, a new factor, using the destructuration index concept, is introduced to estimate the remaining energy available as kinetic energy for runout after the remolding of the sensitive clay: the energy reduction factor (FER). Using the FER allows the use of real rheological data acquired with a rheometer to analyze the post-failure behavior of a flowslide in sensitive clays. This method is applied on a sensitive clay landslide which took place in Quebec and where rheological and geotechnical data are available. [ABSTRACT FROM AUTHOR]

A landslide occurred on 10 May 2010, along the Salvail River, in the municipality of Saint-Jude, Quebec. Debris of the landslide was formed of 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 was 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 the location of two failure surface levels: the first one starting 2.5 m below the initial river bed, 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. [ABSTRACT FROM AUTHOR]

When vacuum preloading is applied with vertical drains, the rate of consolidation can be increased, and the stability of an embankment is enhanced due to the inward lateral movement. The aim of this study is to develop an analytical solution for vacuum preloading that accurately captures the more realistic variations in compressibility and permeability in actual ground conditions as a result of drain installation. The soil samples were obtained from various locations after drain installation to determine the characteristics of soil surrounding the vertical drain in terms of compressibility and permeability. The main differences between the proposed and conventional models are described by considering the stress history and preloading pressure. The effect of pre-consolidation pressure and the magnitude of applied preloading are examined through the dissipation of average excess pore pressure and associated settlement. The analysis of a selected case history employing the writers' solution indicates improved accuracy of the predictions in comparison to the field measurements. [ABSTRACT FROM AUTHOR]

This Note presents a laboratory study using a Rowe cell to compare the consolidation responses upon vacuum pressure and fill load application and removal. The influences of the duration of application and removal of fill load and vacuum pressures on radial consolidation were investigated using excess pore-water pressure, axial strain, and overconsolidation ratio. It is shown that the appropriate removal time for vacuum pressure can be determined based on excess pore pressure responses. [ABSTRACT FROM AUTHOR]

Time-dependent yield stress fluids display hysteresis with respect to reversible and irreversible structural changes. We report an experimental study of the rheological behavior of clay-rich soils (i.e., Mediterranean Sea and bentonite clays) and clay-poor material (i.e., iron mine tailings) that includes steady state, dynamic response, and hysteresis measurement. The Mediterranean Sea and bentonite clays are low- and high-activity clays, respectively. For the materials examined, different thixotropic behaviors are observed as a function of the time of shearing. These materials typically exhibit strong thixotropic behavior for a given shear rate in the limited time of shearing. In general, larger grain sizes produce larger hysteresis loop areas. However, the bentonite clay experiences an increase in viscosity with shear time, regardless of the salinity effect, for sufficiently long shearing times under continuous shear conditions at the shear rate of 1200 s − 1 (the maximum value in the present study). As a result, the flow behavior of clayey soils is strongly influenced by the imposed shearing time. [ABSTRACT FROM AUTHOR]

Rates of settlement and excess pore pressure dissipation will be slightly faster when vertical drainage is considered at the shallow depth, if the drains are relatively short. Although the settlement predictions are similar, the current model can simulate the retarded pore pressure dissipation much better, which has often been a trend observed in the field, yet not captured in many of the past studies adopting ideal drain conditions. For the SBIA and Muar clay embankment, although the differences in terms of excess pore pressure predictions among the three models are relatively small (less than 4 kPa), the current model still provides a significantly better agreement with the field measurements. [Extracted from the article]

Abstract: Compacted materials are fundamentally unsaturated soils whose behaviour can be expansive or collapsible depending upon changes in water content or stresses. Their behaviour is strongly dependent upon matric suction, water content, and stress history. This paper presents a methodology for investigating the stress/strain, and suction/water content paths during one dimensional compaction of unsaturated soils. It focuses on anisotropic behaviour. The testing programme was carried out in a new automated oedometer apparatus that allows measurement of axial strain, radial and axial stresses, suction, and water content during tests. The laboratory component used in this study involves kaolin compacted with different water contents. After compaction, the soil was subjected to wetting while the volumetric changes and stress paths were being examined. The results were interpreted within an anisotropic elasto-plastic framework. The proposed methodology provides new insights into the behaviour of unsaturated soils during compaction and wetting. [Copyright &y& Elsevier]

A correction to the article "Laboratory Study on Subgrade Fluidization Under Undrained Cyclic Triaxial Loading" by Buddhima Indraratna, Mandeep Singh, Thanh Trung Nguyen, Serge Leroueil, Aruni Abeywickrama, Richard Kelly and Tim Neville which appeared in a 2020 issue is presented.

The effect of soil microstructure on the compressibility of natural Singapore marine clay is studied in this paper. It was found that natural Singapore marine clay can sustain higher void ratio than reconstituted Singapore marine clay at the same effective stress in one-dimensional compression. This difference is most noticeable between yield stress and two times the yield stress. This void ratio difference is commonly attributed to soil microstructure, and the decrease in this difference at higher stresses is attributed to progressive destructuration. As a consequence of progressive destructuration, the virgin compression curve is nonlinear and the compression index along the virgin compression range is variable, which is only noticeable during the constant rate of strain consolidation test on high-quality samples. In the absence of high-quality samples and constant rate of strain consolidation tests, an empirical method is proposed to obtain a first-order estimation of a nonlinear virgin compression curve using index properties and yield stress. This paper demonstrates that the proposed method works reasonably well with natural Singapore marine clay. The error bound for the predicted compression indices is approximately ±20% of the compression indices measured with constant rate of strain test on high-quality samples. [ABSTRACT FROM AUTHOR]

It is well known that organic matter may affect the cementing process in soils, but what happens when cement is added to an organic soil? Both the organic matter content and the nature of this organic matter affect the properties of a treated soil. It appears that some organic compounds delay or even inhibit the hydration process of cement, while others do not affect the reaction at all. This paper presents some results of a laboratory study in which 13 different organic compounds were added separately to two different soils, and then treated with 10% cement. To assess the cementing process, undrained shear strength was measured on the different specimens, and some chemical analyses were performed on the pore liquid. The results indicate that the organic acids producing a pH lower than 9 in the pore solution strongly affect the development of cementing products and almost no strength gain was noted. Also, oils and hydrocarbons, which are insoluble in water, delay the cement hydration but do not affect the final strength. Finally, the pH value and the SO[sub 4] concentration in the pore solution are good indicators of the cementing effectiveness of the treated specimens.Key words: soil stabilization, organic compounds, undrained shear strength, cement, chemical analyses.Il est bien connu que la matière organique peut affecter le processus de cimentation dans les sols, mais qu'arrive-t-il lorsque le ciment est ajouté à un sol organique? Tant la matière organique que sa nature affecte les propriétés du sol traité. Il semble que certains composés organiques retardent ou même empêchent le processus d'hydratation du ciment, alors que d'autres n'affectent aucunement la réaction. Cet article présente des résultats d'une étude en laboratoire dans laquelle 13 composés organiques différents ont été ajoutés séparément à deux différents sols, et ensuite traités avec 10 % de ciment. Pour évaluer le processus de cimentation, la résistance au cisaillement non drainé a été mesurée sur différents spécimens, et des analyses chimiques ont également été réalisées sur le liquide interstitiel. Les résultats indiquent que les acides organiques qui produisent un pH inférieur à 9 dans la solution interstitielle affectent fortement le développement des produits de cimentation de sorte qu'on note presque aucun gain de résistance. Aussi, les huiles et les hydrocarbures insolubles dans l'eau retardent l'hydratation du ciment, mais n'affectent pas la résistance finale. Finalement, la valeur du pH et la concentration de SO[sub 4] dans la solution interstitielle sont de bons indicateurs de l'efficacité du traitement au ciment des spécimens.Mots clés : stabilisation du sol, composés organiques, résistance au cisaillement non drainé, ciment, analyses chimiques.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]