Suffusion is a particular internal erosion process that can lead to important disorders in water ... more Suffusion is a particular internal erosion process that can lead to important disorders in water retaining structures such as embankment dams and levees. It causes modifications in the soil micro-structure and may modify the mechanical behaviour of the soil leading to deformations at the macroscopic scale. Therefore, the aim of this study is to investigate the consequences of internal erosion on the mechanical properties of the soil. We present such an investigation through numerical and experimental approaches. For the experimental approach, a newly developed suffusion test apparatus is used while for the numerical approach, a model is established based on the discrete element method (DEM) with a one-way fluid-solid coupling.
Shrinkage of expansive soils may cause serious problems to geotechnical and geo-environmental str... more Shrinkage of expansive soils may cause serious problems to geotechnical and geo-environmental structures. In this study, the shrinkage behaviour of compacted clay treated with 4% lime was investigated. The samples of compacted clay without lime treatment were also tested for comparison. Besides, changes in the microstructure were analysed by mercury intrusion porosimetry tests on both treated and untreated samples. The results showed that the shrinkage curve of untreated sample is close and almost parallel to the saturation line, prior to approaching the compacted shrinkage limit (shrinkage limit for compacted soils). By contrast, the shrinkage curve of lime-treated soil is located leftwards and exhibits a higher compacted shrinkage limit, evidencing a clear microstructure effect. Further analysis showed that large aggregates with large pores are formed by lime treatment and these large pores play an important role in the shrinkage behaviour of soils. In addition, the curing time ef...
L'érosion interne est un mécanisme qui apparait dans les ouvrages hydrauliques en terre. Elle... more L'érosion interne est un mécanisme qui apparait dans les ouvrages hydrauliques en terre. Elle est définie comme l'arrachement et le transport de particules sous l'action d'un écoulement hydraulique souterrain au sein d'un massif de sol. C'est un processus interne au sol et invisible de l'extérieur jusqu'à ce que les dégradations deviennent suffisantes pour générer des signes discernables en surface comme des tassements ou une augmentation du débit des fuites dans le cas d'une digue. Cette érosion interne est alors susceptible de s'accélérer et de mener l'ouvrage à la rupture. Le phénomène spécifique d'une érosion par suffusion correspond au cas où seules les particules fines sont arrachées et transportées à travers le squelette formé majoritairement par les grains les plus grossiers. L'apparition de la suffusion entraine souvent une modification de la microstructure initiale, et par conséquent, des caractéristiques physiques et hyd...
Several experimental methods have been developed for simulating the internal erosion process expe... more Several experimental methods have been developed for simulating the internal erosion process experimentally, and various types of equipment have been developed for performing hole erosion tests. However, few attempts have been made to model these tests. The aim of this study was to draw up a useful model for interpreting hole erosion tests.
In this study, the drying-induced microstructure evolution of compacted silt with different salin... more In this study, the drying-induced microstructure evolution of compacted silt with different salinities is investigated using mercury intrusion porosimetry and environmental scanning electron microscope. The pore size distribution (PSD) of specimens compacted near optimum (w = 17%) exhibited bimodal characteristics. Upon drying (w = 8%), the PSD changed to a trimodal pattern with the appearance of a new nano-pore population. This suggested the development of nano-fissures, which could occur in the clay fraction and at the interface between clay particles and silt/sand grains due to the clay shrinkage. With further drying (w = 3%), the nano-pores disappeared and the PSD recovered to bimodal characteristics, suggesting that the nano-fissures created were enlarged until they became micro-fissures. The salinity seemed to decrease the frequency of the drying-induced micro-pores due to the enhanced mechanical strength of salted soil by the soil aggregation resulting from the compression of...
Lime treatment is a common technique of improving the workability and geotechnical properties of ... more Lime treatment is a common technique of improving the workability and geotechnical properties of soils. In this study, the aggregate size effects on the water retention capacity and microstructure of lime-treated soil were investigated. Two soil powders with different maximum aggregate sizes (Dmax = 0·4 and 5 mm) were prepared and stabilised by 2% lime (by weight of dry soil). Soil samples were prepared by compaction at dry side of optimum water content (w = 17%) with a dry density of 1·65 Mg/m3. Suction and pore size distribution were determined after different curing periods. The results obtained show that: (a) the treated soil with smaller Dmax presents relatively smaller modal sizes and lower frequency of macropores (10–330 μm); (b) lime addition effectively improves the soil water retention capacity and decreases both the modal sizes of macro- and micropores gradually over time. Moreover, a higher air entry value and larger water retention capacity were also observed for a smal...
Bender elements technique has become a popular tool for determining shear wave velocity, Vs, henc... more Bender elements technique has become a popular tool for determining shear wave velocity, Vs, hence the small-strain shear modulus of soils, Gmax, thanks to its simplicity and nondestructive character among other advantages. Several methods were proposed to determine the first arrival of Vs. However, none of them can be widely adopted as a standard and there is still an uncertainty on the detection of the first arrival. In this study, bender elements tests were performed on lime-treated soil and both shear wave and compression wave velocities at various frequencies were measured. In-depth analysis showed that the S-wave received signal presents an identical travel time and opposite polarity compared with that of the S-wave components in P-wave received signal, especially at high frequency. From this observation, a novel interpretation method based on the comparison between the S-wave and P-wave received signals at high frequency is proposed. This method enables the determination of t...
The elementary mechanisms driving the ubiquitous surface erosion of cohesive geomaterials can be ... more The elementary mechanisms driving the ubiquitous surface erosion of cohesive geomaterials can be analysed from a micromechanical perspective combining well-known numerical techniques. Here, a coupled model combining the Discrete Element and Lattice Boltzmann methods (DEM-LBM) provides an insight into the solid-fluid interaction during the transient erosion caused by a vertical fluid jet impinging on the surface of a granular assembly. The brittle cementation providing cohesion between the solid grains is described here by means of a simple bond model with a single-parameter yield surface. The initial topology of the surface erosion tends to mimic the profile of fluid velocity directly above the soil surface. We find that both the rate of erosion and the magnitude of eroded mass depend directly on the micromechanical strength of the single solid bonds.
The influence of initial sand structure on the liquefaction properties of a reference French sand... more The influence of initial sand structure on the liquefaction properties of a reference French sand is studied based on the use of two modes of reconstitution of specimens, namely dry pluviation and wet tamping. Undrained compression tests carried out in the triaxial apparatus for the same initial void ratio of specimens show well-differentiated behaviors as a function of the mode of reconstitution used. Wet tamping favors the initiation of a static liquefaction type of phenomenon (unstable behavior), whereas dry pluviation favors a dilating type of response characterized by a strain-hardening type of behavior (stable behavior). Electron microscope observations have allowed to identify two different sand structures corresponding to the two types of reconstitution methods: an aggregates and macropores type of structure is observed for specimens prepared using wet tamping method whereas a more regular single-grained arrangement is observed for specimens prepared using dry pluviation. Th...
Le risque de rupture des ouvrages hydrauliques en remblai est un souci reel auquel sont confronte... more Le risque de rupture des ouvrages hydrauliques en remblai est un souci reel auquel sont confrontes les gestionnaires. Ce type d'ouvrages souvent anciens et alors construit a partir de materiaux heterogenes, le plus souvent mal compactes et aux fondations insuffisamment traitees est affecte par plusieurs mecanismes de rupture. Parmi eux, nous distinguons la rupture par liquefaction sous sollicitations sismiques liee notamment, s'il existe dans ces ouvrages et/ou dans leur fondation, des couches de sols susceptibles de se liquefier tels que des sables lâches. Cette communication, vise a proposer une premiere caracterisation du risque de liquefaction des sols sous sollicitation sismique des ouvrages hydrauliques en remblai de la basse vallee du Rhone, soit essentiellement des digues. Les objectifs principaux de l'etude ont ete, d'une part, d'effectuer un etat de l'art sur les differentes methodes d'evaluation du risque de liquefaction sismique et sur leur do...
This paper focus on three types of erosion: the suffusion, the backward erosion, and the piping e... more This paper focus on three types of erosion: the suffusion, the backward erosion, and the piping erosion processes. A new triaxial device to quantifying suffusion and backward erosion, and a new model for interpreting the Hole Erosion Test, are presented. lt is recommended to use these erosion tests in order to evaluate the erosion parameters on any sample of cohesive soil from a site.
Suffusion is a particular internal erosion process that can lead to important disorders in water ... more Suffusion is a particular internal erosion process that can lead to important disorders in water retaining structures such as embankment dams and levees. It causes modifications in the soil micro-structure and may modify the mechanical behaviour of the soil leading to deformations at the macroscopic scale. Therefore, the aim of this study is to investigate the consequences of internal erosion on the mechanical properties of the soil. We present such an investigation through numerical and experimental approaches. For the experimental approach, a newly developed suffusion test apparatus is used while for the numerical approach, a model is established based on the discrete element method (DEM) with a one-way fluid-solid coupling.
Shrinkage of expansive soils may cause serious problems to geotechnical and geo-environmental str... more Shrinkage of expansive soils may cause serious problems to geotechnical and geo-environmental structures. In this study, the shrinkage behaviour of compacted clay treated with 4% lime was investigated. The samples of compacted clay without lime treatment were also tested for comparison. Besides, changes in the microstructure were analysed by mercury intrusion porosimetry tests on both treated and untreated samples. The results showed that the shrinkage curve of untreated sample is close and almost parallel to the saturation line, prior to approaching the compacted shrinkage limit (shrinkage limit for compacted soils). By contrast, the shrinkage curve of lime-treated soil is located leftwards and exhibits a higher compacted shrinkage limit, evidencing a clear microstructure effect. Further analysis showed that large aggregates with large pores are formed by lime treatment and these large pores play an important role in the shrinkage behaviour of soils. In addition, the curing time ef...
L'érosion interne est un mécanisme qui apparait dans les ouvrages hydrauliques en terre. Elle... more L'érosion interne est un mécanisme qui apparait dans les ouvrages hydrauliques en terre. Elle est définie comme l'arrachement et le transport de particules sous l'action d'un écoulement hydraulique souterrain au sein d'un massif de sol. C'est un processus interne au sol et invisible de l'extérieur jusqu'à ce que les dégradations deviennent suffisantes pour générer des signes discernables en surface comme des tassements ou une augmentation du débit des fuites dans le cas d'une digue. Cette érosion interne est alors susceptible de s'accélérer et de mener l'ouvrage à la rupture. Le phénomène spécifique d'une érosion par suffusion correspond au cas où seules les particules fines sont arrachées et transportées à travers le squelette formé majoritairement par les grains les plus grossiers. L'apparition de la suffusion entraine souvent une modification de la microstructure initiale, et par conséquent, des caractéristiques physiques et hyd...
Several experimental methods have been developed for simulating the internal erosion process expe... more Several experimental methods have been developed for simulating the internal erosion process experimentally, and various types of equipment have been developed for performing hole erosion tests. However, few attempts have been made to model these tests. The aim of this study was to draw up a useful model for interpreting hole erosion tests.
In this study, the drying-induced microstructure evolution of compacted silt with different salin... more In this study, the drying-induced microstructure evolution of compacted silt with different salinities is investigated using mercury intrusion porosimetry and environmental scanning electron microscope. The pore size distribution (PSD) of specimens compacted near optimum (w = 17%) exhibited bimodal characteristics. Upon drying (w = 8%), the PSD changed to a trimodal pattern with the appearance of a new nano-pore population. This suggested the development of nano-fissures, which could occur in the clay fraction and at the interface between clay particles and silt/sand grains due to the clay shrinkage. With further drying (w = 3%), the nano-pores disappeared and the PSD recovered to bimodal characteristics, suggesting that the nano-fissures created were enlarged until they became micro-fissures. The salinity seemed to decrease the frequency of the drying-induced micro-pores due to the enhanced mechanical strength of salted soil by the soil aggregation resulting from the compression of...
Lime treatment is a common technique of improving the workability and geotechnical properties of ... more Lime treatment is a common technique of improving the workability and geotechnical properties of soils. In this study, the aggregate size effects on the water retention capacity and microstructure of lime-treated soil were investigated. Two soil powders with different maximum aggregate sizes (Dmax = 0·4 and 5 mm) were prepared and stabilised by 2% lime (by weight of dry soil). Soil samples were prepared by compaction at dry side of optimum water content (w = 17%) with a dry density of 1·65 Mg/m3. Suction and pore size distribution were determined after different curing periods. The results obtained show that: (a) the treated soil with smaller Dmax presents relatively smaller modal sizes and lower frequency of macropores (10–330 μm); (b) lime addition effectively improves the soil water retention capacity and decreases both the modal sizes of macro- and micropores gradually over time. Moreover, a higher air entry value and larger water retention capacity were also observed for a smal...
Bender elements technique has become a popular tool for determining shear wave velocity, Vs, henc... more Bender elements technique has become a popular tool for determining shear wave velocity, Vs, hence the small-strain shear modulus of soils, Gmax, thanks to its simplicity and nondestructive character among other advantages. Several methods were proposed to determine the first arrival of Vs. However, none of them can be widely adopted as a standard and there is still an uncertainty on the detection of the first arrival. In this study, bender elements tests were performed on lime-treated soil and both shear wave and compression wave velocities at various frequencies were measured. In-depth analysis showed that the S-wave received signal presents an identical travel time and opposite polarity compared with that of the S-wave components in P-wave received signal, especially at high frequency. From this observation, a novel interpretation method based on the comparison between the S-wave and P-wave received signals at high frequency is proposed. This method enables the determination of t...
The elementary mechanisms driving the ubiquitous surface erosion of cohesive geomaterials can be ... more The elementary mechanisms driving the ubiquitous surface erosion of cohesive geomaterials can be analysed from a micromechanical perspective combining well-known numerical techniques. Here, a coupled model combining the Discrete Element and Lattice Boltzmann methods (DEM-LBM) provides an insight into the solid-fluid interaction during the transient erosion caused by a vertical fluid jet impinging on the surface of a granular assembly. The brittle cementation providing cohesion between the solid grains is described here by means of a simple bond model with a single-parameter yield surface. The initial topology of the surface erosion tends to mimic the profile of fluid velocity directly above the soil surface. We find that both the rate of erosion and the magnitude of eroded mass depend directly on the micromechanical strength of the single solid bonds.
The influence of initial sand structure on the liquefaction properties of a reference French sand... more The influence of initial sand structure on the liquefaction properties of a reference French sand is studied based on the use of two modes of reconstitution of specimens, namely dry pluviation and wet tamping. Undrained compression tests carried out in the triaxial apparatus for the same initial void ratio of specimens show well-differentiated behaviors as a function of the mode of reconstitution used. Wet tamping favors the initiation of a static liquefaction type of phenomenon (unstable behavior), whereas dry pluviation favors a dilating type of response characterized by a strain-hardening type of behavior (stable behavior). Electron microscope observations have allowed to identify two different sand structures corresponding to the two types of reconstitution methods: an aggregates and macropores type of structure is observed for specimens prepared using wet tamping method whereas a more regular single-grained arrangement is observed for specimens prepared using dry pluviation. Th...
Le risque de rupture des ouvrages hydrauliques en remblai est un souci reel auquel sont confronte... more Le risque de rupture des ouvrages hydrauliques en remblai est un souci reel auquel sont confrontes les gestionnaires. Ce type d'ouvrages souvent anciens et alors construit a partir de materiaux heterogenes, le plus souvent mal compactes et aux fondations insuffisamment traitees est affecte par plusieurs mecanismes de rupture. Parmi eux, nous distinguons la rupture par liquefaction sous sollicitations sismiques liee notamment, s'il existe dans ces ouvrages et/ou dans leur fondation, des couches de sols susceptibles de se liquefier tels que des sables lâches. Cette communication, vise a proposer une premiere caracterisation du risque de liquefaction des sols sous sollicitation sismique des ouvrages hydrauliques en remblai de la basse vallee du Rhone, soit essentiellement des digues. Les objectifs principaux de l'etude ont ete, d'une part, d'effectuer un etat de l'art sur les differentes methodes d'evaluation du risque de liquefaction sismique et sur leur do...
This paper focus on three types of erosion: the suffusion, the backward erosion, and the piping e... more This paper focus on three types of erosion: the suffusion, the backward erosion, and the piping erosion processes. A new triaxial device to quantifying suffusion and backward erosion, and a new model for interpreting the Hole Erosion Test, are presented. lt is recommended to use these erosion tests in order to evaluate the erosion parameters on any sample of cohesive soil from a site.
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