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International audience; Nowadays, raw earth construction is an area of growing interest, both for its eco-friendly characteristics and very interesting thermo-hygroscopic properties. Nevertheless, this type of construction exhibits a weakness related to cracking due to the shrinkage strains caused by desiccation. In this context, this paper presents an experimental study of restrained drying-shrinkage, carried out on a fine clayey soil. Several amounts of soil reinforcement with orderly layout patterns using vegetal flax fibers have been investigated in order to enhance soil properties. The new feature of this work is the analyzing of crack initiation and propagation by coupling the Digital Image Correlation (DIC) method with the Clay-Ring-Test (CRT) technique, using an innovative device called DIC-CRT. Suction measurements in clay samples are performed during desiccation using tensiometers. A good agreement is noticed between suction and strain evolution until cracking revealing the direct influence of suction on clay shrinkage. Through the two techniques, DIC and CRT, a relevant parameter to quantify crack intensity in materials is proposed. A significant decrease of crack ratio, by a factor of about 8, highlights the impact of soil reinforcement on the level of crack opening. Likewise, a significant decrease, by a factor of about 20, is observed in the analysis of DIC and CRT slopes, highlighting the impact of reinforcement on the kinetic of crack opening.

In the context of valorizing local materials at Saharan region for road constructions, a mixture composed of 65% tuff and 35% dune sand (named 65T35DS) was previously studied. The 65T35DS was shown to have the optimum geotechnical and mechanical properties. As an extension, this study consists in investigating the behavior of the 65T35DS mixture under coupled hydro-mechanical loadings. Suction-controlled drying-wetting tests were performed on the 65T35DS statically compacted at the modified Proctor optimum (MPO) state. A series of small-strain cyclic triaxial tests under constant water content condition was then followed. Key findings of this paper include i) the 65T35DS prepared at MPO state is able to resist severe drought condition without inducing significant shrinkage. However, it swells during wetting and the swelling indices are quantified by correlations; ii) the elastic modulus under small-strains is governed by suction and the applied confining stress. The effect of confining stress becomes dominantat lower suction level and negligible when suction increases; iii) at failure, the apparent cohesion drops quickly on the dry side of the MPO, on wet side, it decreases a little. The apparent friction angle decreases for the specimens with water content larger than 5.5%, i.e. wMPO - 5. The studied mixture satisfies the design standards of Saharan pavements and seems to be a good compromise for the valorization of local materials.

International audience; This article presents a new osmotic oedometer that is able to measure changes in the degree of saturation (Sr) during suction-controlled drying-wetting and oedometric tests. A circular four-electrode cell made of polyvinyl chloride was developed. The geometric factor of the cell was determined by numerical simulation and validated by calibration tests. A total of 29 samples was statically compacted in the oedometric cell at different moisture contents and dry densities. Based on these measurements, the normalized electrical resistivity was defined and correlated with the Sr. After that, three suction-controlled drying-wetting and oedometric tests were performed on the samples statically compacted at the water content of 21 % and dry density of 1.62 g/cm3, which corresponds to the standard Proctor optimum conditions. The results show (i) the potential of the new oedometer for the study of the hydromechanical behavior of unsaturated soils, (ii) the ability of the electrical resistivity technique to estimate the variation of the Sr in unsaturated oedometric tests, with a relative error smaller than 5 %, and (iii) the coupled effect of vertical stress and suction on the change in void ratio (e) and Sr shown in the (e - suction pressure [s] - vertical total stress [σv]) and (Sr - s - σv) state surfaces.

Building construction technology by raw earth materials is already known and used since ancient times. The raw earth material is abundant, low cost, requires very low energy to manufacture and does not generate waste. Ductility is required for earth building materials in the areas of seismic risks where the earth buildings are particularly vulnerable to earthquakes. Hence, a raw earth treatment by binders and vegetal fibers is one of the techniques applied to improve its strength and ductility. This paper presents the use of mixture design as a tool to evaluate and analyze the plastic behavior of the raw earth material. The ductility is quantified through two ductility indices. The results indicate that an alternative ductility index based on the post-peak behavior of the material could be used to define a ductility criterion to meet specific requirements of the seismic regions.

Managed aquifer recharge is an efficient approach using surface water for groundwater recharge. However, soil clogging in the infiltration systems represents a critical problem that reduces the efficiency of recharge systems. In recent years, much research has been conducted to investigate clogging in subsurface and surface soil (cake). Cake prevents infiltration into the water table and can drastically reduce the recharge rate. In arid and semi-arid areas, alternation of humid and dry seasons has an effect on cake cracking. In the present research, the propagation of desiccation cracking and self-healing of unconsolidated soil (cake), placed in Plexiglas columns, was investigated using X-ray computed tomography (CT) during drying–wetting (D W) paths. The results showed that during the drying path, cracks initiated at the base of the soil by friction with the bottom of the column and then propagated to the top surface of the cake. As the drying time increased, evaporation at the top surface led to more cracks growing from the surface than from the bottom of the cake. However, the cracks at the bottom tended to stabilize because the water content was greater than at the top surface. The initiation, propagation, and expansion of the cracks developed in the saturated condition of the cake. During the wetting path, some cracks were closed while others appeared. The cracks tended to close progressively with wetting time, highlighting the self-healing phenomenon, probably due to the high plasticity index of cake soil. The results showed that cake swelling is mainly related to an increase of the void ratio due to a decrease in suction between particles. The results demonstrate the capacity of the X-ray CT technique to investigate the evolution of cracks during D W paths.

International audience; The main goal of this research was to try, experimentally, to identify the cause of initiation and propagation of cracks network related to desiccation. The work may provide a better understanding of the drying behavior in clayey soils. Kaolin, which is a little swelling “nearly pure” kaolinite, was studied in this context. The experimental method is based on the determination of the local two-dimensional strains and displacements fields using the softwares Vic-2D and Vic-3D on thin layers of the initially saturated clay. Using digital image correlation technique at the macroscopic level, the analyses of strain fields during drying allow to clearly identify and characterize different phenomena such as: shrinkage, stress concentration, initiation, and propagation of cracks.

International audience; Clay fine soils are characterised by an ability to change volume when subjected to suction. Soil cracking due to desiccation is a phenomenon of great importance in the environmental geotechnical engineering domain. Aiming to understand shrinkage mechanism, and conditions that lead to appearance of drying cracks, a new experimental testing coupled device digital image correlation- clay ring test (DIC-CRT) was developed to investigate fine soils shrinkage and cracking. The new feature of this paper is to link both measurement techniques, based on 2D/3D-DIC and an innovative CRT, in order to assess stress and strain in soils during desiccation. Tests were carried out on a kaolinite having a liquid limit of wL = 40%, and prepared as a slurry with w = 1.5 wL of water content. The results highlight the relevance in combining these two techniques, particularly to assess internal stresses developed in the material using CRT and link them to strains leading to cracking measured by DIC method.

This paper aims to study the behaviour of dense RF Hostun sand subjected to dynamic loading in the triaxial cell. The wet tamping method was used to prepare the samples with the same initial conditions including water content and void ratio. The samples were firstly saturated to dissolve the remaining air bubbles inside the samples. After that, all the samples were consolidated isotropically then the cyclic deviator stress was applied to study liquefaction. All tests show that, saturation affects significantly to the cyclic stress ratio needed to liquefy the sample. The samples having an equal degree of saturation were liquefied by the same level of deviator stress; however, there is a great difference in the load cycles causing liquefaction. This consequence suggests that besides the void ratio and the saturation degree, the different soil fabrics (caused by sample preparation technique) can effect on the sand liquefaction susceptibility and as well the triggering time of liquefaction in situ or in the laboratory.

This work is part of a program for the development of a Compressed Earth Block (CEB) from a material that is readily available, and in large quantities, in the region of Beni-Saf, a town in northwestern Algeria. In this paper, an experimental study has been carried out on the influence of lime treatment on the mechanical behaviour of a compressed earth block. The first step has consisted of carrying out a complete identification process to check the eligibility criteria of the material for earth construction. The next step has intended to examine the influence of 4% and 6% lime treatment on the compaction characteristics (optimum moisture content and maximum dry density). Besides, the drying process of the material, which is characterized by variations in the moisture content and suction values, has been examined. Finally, the influence of these variations on the unconfined compressive strength and elastic modulus has been studied as well.

The paper presents an experimental study of the hydromechanical behavior of a compacted clay used in the design of the core of the Boughrara dam (western Algeria). The influence of compaction energy level (CEL) is explored using three different energies: Standard Proctor energy (SP), reduced Proctor energy (SP-20 blows) and enhanced Proctor energy (SP+ 20 blows). The resulting compaction curves are supplemented by measurements of suction, which is a very important parameter in the behavior of compacted unsaturated soils. In addition to the compaction curves, elastic modulus and immediate bearing capacity ratio (IBCR) are measured, and related to suction and compaction energy level (CEL). Mechanical compaction paths following the SP curve and drying-wetting paths starting from SPO are compared. Mechanical properties such as E-modulus and IBCR are related to the two independent major parameters γd and Sr. Measuring these mechanical properties in the field allows to evaluate the compaction state regardless of the CEL. The results are compared with those of the literature.

The main objective of this paper is to examine how different engineering soils react to environmental variations and to provide correlations to characterize their behaviour under null external mechanical stress. Two French and two Algerian soils with liquid limits ranging from 36 to 112 were prepared under both slurry and Proctor compaction conditions, and then subjected to drying–wetting paths with suction controlled from several kPa to several hundreds of MPa. Experimental results are presented in five diagrams to show globally and simultaneously the shrinkage–swelling, saturation–desaturation and water retention characteristics. A reasonable consistency was observed between the oedometric and drying curves of slurry, confirming the equivalence between hydraulic loading (suction) and mechanical loading (consolidation stress) on the volume change behaviour of different soils. As an intrinsic parameter of soil nature, liquid limit was found to have a significant influence on the shrinkage limit, air-entry suction and compressibility of both slurry and compacted samples. For that reason, correlations between these characteristics and liquid limit were set up, providing a good basis for a first estimation of the drying–wetting curves. At the micro-scale, new experimental results were obtained: either on drying or wetting path, the micro-pores were almost unaffected, whereas, when matrix suction increased from 0.1 to 8 MPa, the volume of macro-pores decreased to quasi-closure. At last, the analogy between the compaction and drying–wetting curves, and the comparison of different methods to determine the water retention curve were addressed. Such analogies and comparisons contribute to a better understanding of the mechanisms of mechanical stress and suction.

This paper presents an experimental investigation of the hydro-mechanical behaviour of two compacted non-standard soils with respect to the French standards GTR 92 in the framework of embankment construction (a low plasticity silt and a high plasticity marl). The aim is to establish relationships between the mechanical parameters (small-strain stiffness, bearing capacity index IBCR …) and hydraulic parameters (water and air permeabilities, and suction). Results show that, for water content lower than the optimum water content, the small-strain stiffness, IBCR index, air permeability and suction change little with water content, whereas for water content larger than the optimum, there is a sharp drop of all the parameters.

The study investigates shrinkage behaviour of a new earth concrete amended with various volume percentages of recycled concrete aggregates (RCA). Two preparations techniques, in situ (industrial) and laboratory (manual), were used. Shrinkage was evaluated using a one-dimensional method and a 2D image analysis. Shrinkage decreases with RCA percentages. Industrial vibration has also an impact on shrinkage. Adding superplasticizer reduces crack appearance without affecting the global shrinkage. Mechanical tests were performed to evaluate the impact of RCA. Compressive strength increases with the addition of RCA, and the bending tensile strength remains quasi constant. Keywords: Recycled concrete aggregates, Earth concrete, Superplasticizer, Shrinkage, Cracks, Image analysis

International audience; Reinforcement feasibility of a new ecological earth concrete was examined. Steel rebar corrosion, when in contact with three different types of clayey soil, was investigated using electrochemical methods, potentiodynamic voltammetry and impedance spectroscopy (EIS). Results have shown that the voltammetry method overestimates the corrosion rate while EIS supplies the most reliable results. Corrosion rate decreased and a steady state was reached after four months of contact. The type of clay does not have a significant influence on the corrosion rate of the steel rebar, and the average value of 3 µm/year was considered acceptable for the lifetime of the structure.

This article presents the results of the volumetric behaviour of an Algiers clayey soil. An experimental work was carried out both in situ (core drilling; pressuremeter testing) and in the laboratory (drying–wetting and oedometric tests). Drying–wetting paths of soil samples were obtained using vapour equilibrium method and osmotic technique. These suction-controlled methods have gained widespread acceptance as reliable methods for imposing suction on soil specimens. They allowed for tests to be performed in the range of suction comprised between 0 and 300 MPa. The ability to impose suction on soil specimens allows for drying and wetting stress paths to be imposed to evaluate resulting changes in void ratio, degree of saturation and water content. These paths were explored at different initial states of clay. Slurries of soil were used to characterise the reference behaviour, whereas undisturbed soil samples allow characterising the material under in situ conditions.

Summary Granular materials like sand are widely used in civil engineering. They are composed of different sizes of grains, which generate a complex behaviour, difficult to assess experimentally. Internal instability of a granular material is its inability to prevent the loss of its fine particles under flow effect. It is geometrically possible if the fine particles can migrate through the pores of the coarse soil matrix and results in a change in its mechanical properties. This paper uses the three-dimensional Particle Flow Code (PFC3D/DEM) to study the stability/instability of granular materials and their mechanical behaviour after suffusion. Stability properties of widely graded materials are analysed by simulating the transport of smaller particles through the constrictions formed by the coarse particles under the effect of a downward flow with uniform pressure gradient. A sample made by an initially stable material according to the Kenney & Lau geometrical criterion was divided into five equal layers. The classification of these layers by this criterion before and after the test shows that even stable granular materials can lose fine particles and present local instability. The failure criterion of eroded samples, in which erosion is simulated by progressive removal of fine particles, evolves in an unexpected way. Internal friction angle increases with the initial porosity, the rate of lost fine particles and the average diameter D50. Copyright © 2016 John Wiley & Sons, Ltd.

International audience; Series of drying tests are carried out on natural silt intended for the preparation of new raw earth concrete. This technique is different from rammed earth. The study treats the drying of various formulations of the natural silt with and without reinforcement. No binders were added to highlight the impact of reinforcement. Global and local deformation around a single crack are analysed using image processing. Adding reinforcements to natural silt reduces the percentage of cracking by a factor around 10. The suction is derived from water content corresponding to crack appearance and correlated to the ultimate resistance of the material. (C) 2015 Elsevier Ltd. All rights reserved.

A study was undertaken to characterise the evolution of the clogging of various porous media during filtration experiments. Long-term tracer tests were carried out at various flow velocities. To highlight the effects of intraporosity on transport and retention mechanisms, both single porosity and double porosity media (DPM) were used. The presence of matrix porosity in the two investigated DPM provided additional sites, promoting retention of suspended particles (SP). The particle size distribution (PSD) of the recovered particles increased with time. However, and due to the additional retention sites in intraporosity, the changes in PSD with time were slower for tests on DPM. Ultrasonic transmission was used to detect modifications to the properties of the porous media induced by particle retention. The results demonstrate the capacity of ultrasound for detecting the evolution of physical clogging as a consequence of particle deposition.

The present study focuses on a theoretical model for unsaturated soils based on elastic spherical particle arrangement, which can be considered to be a simplified Discrete Element Method. As a first step, a uniform model is introduced with a single soil particle diameter. This approach follows a new research methodology so that the physical relations between soil particles, interstitial water and air are used. With such a model, the number of experimental parameters needed will be limited. The theoretical model takes into account the different arrangement of soil particles so that the entire voids ratio scale is covered. The wetting and drying paths are modelled. A comparison with previous theoretical model and the proposed new theory is achieved on experimental results with two uniform glass samples. It shows that this new theory improves the precision of the prediction, using only simple physical parameters.

Granular soil in construction of earth works can be solicited by hydrodynamic and mechanical forces. Fine particles constituting these soils may be eroded by the flow leading to a modificat...

The present study is focused on a theoretical model of unsaturated soil based on elastic spherical particle arrangement, which can be considered to be a simplified DEM method. The model is presented with a large graded soil. This approach follows a new research method so that the physical phenomena are explained and the number of experimental parameters is limited. The theoretical model takes into account the different arrangements of soil particles so that the entire void ratio scale is covered. The wetting and drying paths are modelled. A comparison with the Brooks and Corey (1962) theory and the new theory is achieved on experimental results with a sample of glass micro-sphere and two natural soils, the Livet-Gavet sandy-loam and the Livet-Gavet loam. It shows that this new theory improves precision of the prediction using only simple physical parameters.

International audience; The study of the temperature effects on the behaviour of saturated and unsaturated soils on triaxial paths requires the development of a new triaxial experimental device of 3.5 MPa of confining pressure and equipped with a heating collar-controlled temperature. In addition to this case of the unsaturated soils, a special pedestal is developed, so as to impose suctions up to 9 MPa using an osmotic solution of polyethylene glycol (PEG) 6000 through a permeable semi-membrane. Measurements of the degree of saturation and the variation of volume during tests induce various problems, primarily related to the thermal dilation of the osmotic solution and the cell-water system. These problems have been solved by carrying out a preliminary calibration. The applicability of this new apparatus concerns environmental geotechnics and geological engineering such as the design and behaviour of engineered barriers as well as the behaviour of the receiving layers of storage sites like radioactive waste.

Compacted fills in earthworks are in an unsaturated state, with suctions (negative pore-water pressures) usually ranging from several kPa to several MPa. Characterizing the variation of pore-water pressure is a major concern in the estimation of embankment stability and, at the same time, a big challenge when its value falls below –80 kPa. This technical note presents an improved triaxial system based on the standard triaxial cell, equipped with a tensiometer, a thermocouple psychrometer, and local strain gauges. The main objective of these improvements is to measure the pore-water pressure and local volume changes during isotropic loading. In this study, three compacted specimens were tested under undrained conditions. Pore-water pressure was continuously measured by means of the psychrometric probe in the range of –3,000 to –100 kPa and by the tensiometer in the range of –80 to 1,100 kPa. Volume change was measured by the local strain gauges. Analysis and development of the results from both this study and the literature lead to the conclusions that i) specimens with occluded air bubbles (e.g., at the standard Proctor optimum) behave like a saturated soil, as Bw is close to unity when pore-water pressure becomes positive, and ii) a pore-water pressure coefficient Bw close to 1 is not necessarily a sign of saturation, as soil in an unsaturated state may also have a pore-pressure coefficient close to unity, especially at the beginning of the mechanical loading.

The use of electro-osmosis in geotechnical engineering has been considered since 1930. Its application has been tested in several sectors like the fight against rising damp in porous materials, the consolidation of soils as well as the remediation of the soils contaminated by oil and heavy metals, etc. The paper presents an experimental study of the electrokinetic phenomena resulting from the application of an electric field to argillaceous sandstones. The electroosmotic tests required the development of a completely new experimental device composed of a confining cell, of a system of measurement and control of the pH of the electrolyte near the electrodes, of a system of control and measurement of the voltage and current at the edges of the sample, and of a system of measurement of inlet (anodic) and outlet (cathodic) flows. Various boundary conditions are considered with and without control of pH. In addition, a micro structural modelling of the electrokinetic phenomena makes it possible to quantify the electro osmotic conductivity with a good agreement with experiments.

International audience; In granular soils, suffusion may occur only if three conditions are met: (i) the hydraulic gradient is high enough; (ii) the fine particles are not blocked by the constrictions of the larger ones; and (iii) the fine particles are free to move, i.e. they are not prevented to move by a steric condition. The aim of the paper is to determine the maximum diameter of the particles for the third condition, which are called the free fines. Three methods are examined: (i) the direct measurement of the bulk volume of binary mixtures of fine and coarse grains, (ii) the method proposed by Ghafghazi and Azhari in 2012 and (iii) a new method based on the calculation of the fine content for which the fines fill the voids between the coarse grains. Some methods, proved difficult to apply in practice, whereas the new method appeared consistent with the available experimental results. In particular, the method permitted to predict the results of flow tests carried out on binary mixtures of glass balls as well as gap-graded granular materials or materials with continuous grain size distributions.

This paper presents an experimental study carried out on some clayey soils of Tlemcen region situated in the North West of Algeria. The characterization of the volumetric behavior under the effect of suction is studied on drying–wetting paths which highlight the correspondence between void ratio, degree of saturation, and water content versus suction. The initial conditions of studied material are in slurry form and compacted at different initial water contents. For the slurry form, correlations are derived to predict parameters characterizing the drying path. Arabian Journal of Geosciences, Online ISSN 1866-7538; Springer-Verlag.doi 10.1007/s12517-012-0777-1.

A simple thermohydromechanical (THM) constitutive model for unsaturated soils is described. The effective stress concept is extended to unsaturated soils with the introduction of a capillary stress. This capillary stress is based on a microstructural model and calculated from attraction forces due to water menisci. The effect of desaturation and the thermal softening phenomenon are modelled with a minimal number of material parameters and based on existing models. THM process is qualitatively and quantitatively modelled by using experimental data and previous work to show the application of the model, including a drying path under mechanical stress with transition between saturated and unsaturated states, a heating path under constant suction and a deviatoric path with imposed suction and temperature. The results show that the present model can simulate the THM behaviour in unsaturated soils in a satisfactory way. Comptes Rendus Geoscience, ISSN : 1631-0713, DOI: 10.1016/j.crte.2010.09.006, Issue : 12, Volume : 342, pp. 892-900, December 2010.

This paper presents hydraulic conductivity measurements carried out on unsaturated Mers El Kebir clay, from Algeria, using the vapour equilibrium technique. The principle is to measure the water exchanges between the sample and the environment under a relative humidity imposed by saturated salt solutions, to establish the relationships between hydraulic conductivity, water content (w), degree of saturation (Sr) and suction (uc). Samples are initially compacted to the standard Proctor optimum water content and maximum density and used as such and after saturation or drying. Drying-wetting paths were also performed in order to compare the direct hydraulic conductivity measurements to the values derived from Fredlund et al. (1994) and Mualem (1976)-van Genuchten (1980) models.

A simple thermo-hydro-mechanical (THM) constitutive model for unsaturated soils is described. The effective stress concept is extended to unsaturated soils with the introduction of a capillary stress. This capillary stress is based on a microstructural model and calculated from attraction forces due to water menisci. The effect of desaturation and the thermal softening phenomenon are modelled with a minimal number of material parameters and based on existing models. THM process is qualitatively and quantitatively modelled by using experimental data and previous work to show the application of the model, including a drying path under mechanical stress with transition between saturated and unsaturated states, a heating path under constant suction and a deviatoric path with imposed suction and temperature. The results show that the present model can simulate the THM behaviour in unsaturated soils in a satisfactory way. Copyright © 2010 John Wiley & Sons, Ltd.

The aim of this paper is to study the effect of suction on the hydro-mechanical behaviour of a partially saturated soft rock (a porous chalk) under low confining stress. Such conditions correspond to those of the vertical chalk cliffs of the English Channel, which are subjected to spatial and temporal variations of the water table under climatic variations. We apply to this material a method usually used in soils, whose hydro-mechanical behaviour is strongly modified by changes in matric suction (or capillary suction), according to the degree of water saturation. Under controlled matric suction conditions, wet chalk undergoes volume changes due to pore infilling and drainage. Relationships between matric suction and the mechanical behaviour of the chalk are analysed on the basis of drying–wetting cycles, variations of maximum strength, secant modulus during uniaxial unconfined compression and confined triaxial tests. Mechanical and drying–wetting tests were carried out on dry, saturated and moist natural chalk samples. Drying–wetting cycles result in two types of behaviours according to the range of imposed matric suction, with irreversible paths in the [ s , S r ] plane for high gravimetric water contents (i.e. matric suction values between 0.1 and 6 MPa) and reversible paths for low water contents (i.e. high values of matric suction, larger than 6 MPa). For chalk samples initially at their natural water content, the behaviour is intermediate between those of the dry and saturated chalk samples. Comparison of the behaviour of the two chalk formations highlights differences on wetting, which could be linked to the different pore size distributions from one chalk formation to the other. The results of uniaxial and triaxial compressive strength tests at various water contents show elastic–brittle behaviour. Brittle failure occurs at very low water contents. The secant modulus reaches 600 MPa for dry chalk samples and decreases to 250 MPa for quasi-saturated samples. Concerning triaxial tests, the envelopes of maximum strength (failure criteria) show a noticeable shift, with an apparent cohesion varying by a factor of 2 to 3 from dry to saturated chalk. The effect of matric suction is interpreted using an effective stress approach, based on a simple model for granular soils, by considering the expression of the intergranular forces between two particles in an idealised medium at the microscopic scale. It makes it possible to describe the behaviour of chalk in relation to the variations of suction. The capillary effect is well marked at very low values of water saturation, whereas it disappears at high water content values.

Water unsaturated hydraulic conductivity (kw) functions of two remolded fine-grained materials were measured over a wide range of degrees of saturation (Sr) with two methods. The instantaneous profile method (IPM) was used for Sr>50%. An original vapor equilibration method (also known as the vapor equilibrium technique, VET) was used for Sr

The goal in this research was to analyze the effects of decompression and suction on the formation of cracks in a clay rock from the Andra (French National Radioactive Waste Management Agency) site at Bure (Meuse–Haute-Marne, France). The article investigates the relationship between the changes in the hydromechanical properties and the changes in microstructure and porosity. Concerning the effect of decompression, at the macroscopic scale, the study highlighted an important effect on the elastic modulus and permeability, but little effect at the microscopic scale except an evolution of mineralogy related to the oxidation of pyrite often present in layers where cracks develop. Concerning the effect of suction, at the macroscopic level, the results showed that, on drying path, the change in the properties of the material was very small, whereas, on wetting path, a large decrease in tensile strength and gas permeability was observed. At the microscopic level, observations with SEM and ESEM, and measurements with MIP, highlighted the evolution of microstructural organization as a function of suction, and the propagation and enlargement of cracks on wetting path, rather than on drying path.

In this work, the effect of the fine content on the undrained mechanical behavior of a granular material is studied. Consolidated undrained triaxial tests were carried out on sand and gravel mixtures. The intact sample contains 30% of sand. In order to simulate suffusion in the sample, degradation consisted in reducing the fines amount to 20, 10 and 5%. The undrained peak strength and the dilative phase amplitude decrease when the fine content decreases, with the highest values for the intact sample and the lowest values for the sample with 5% fines. On the other hand, the contractive phase progressively increases with the fine content. The degraded samples present a higher internal friction angles than the intact one.

International audience; In order to study the evolution of a lime-treated silty soil under in-situ conditions of mixing, laying out, compaction and environment, an experimental dike was built near Rouen, in northwest France; this dike is 25 m long, 4 m wide at the crest and 1.8 m high. While special care was taken to mix the soil and lime very thoroughly, to precisely measure the quantity of water, to compact the soil using a vibrating sheepsfoot roller, the building conditions were those usually used to construct embankments in all other respects. Samples were taken from the dike approximately 1 month, 6 months and 12 months after the completion of the work and underwent triaxial and oedometric testing. To compare the properties of treated soil with those of untreated soil, another smaller "reference" embankment was built nearby under similar conditions with silty soil.Small-strain triaxial tests were performed on unsaturated specimens of treated and untreated soil using an original strain measurement device. The change in axial secant moduli can be described by a power law E = beta sigma(m)(1), where beta is a parameter that depends on curing time and m is nearly constant (m approximate to 0.45).CU and CD large-strain triaxial tests carried out on saturated treated and untreated specimens, consolidated under confining stresses ranging from 10 to 300 kPa, showed a definite increase in cohesion as a function of Curing time, with nearly unchanged friction angles. The possibility to use a non-linear failure criterion was examined. The compressibility coefficient C-iso,C- slope of the critical state line (CSL) in the [log(p'), e] coordinate system, is significantly lower in treated than untreated specimens, but its value remains constant whatever the curing time. At the same time, the CSL of the treated specimens is above that of the untreated silt. The brittleness of the material, derived from the peak to residual deviator stress ratio q(peak)/q(res) is the same for treated and untreated specimens and is independent of curing time and confining stress. However, the axial strain corresponding to the peak of CD curves is much higher in untreated than in treated specimens. The permeability of the saturated lime-treated soil (10(-9) m/s) is the same as that of the untreated soil. The value measured one month after the embankment was constructed, does not change with time or with the confining stress. The results of the present study confirm those of previous studies on laboratory-prepared unsaturated specimens: they have demonstrated the effectiveness of lime-treatment in the much more difficult environment of a real working site and shown that lime-treated samples present a significant gain in their engineering properties, even when saturated, provided that the dosage of lime and water, mixing and compaction conditions are carefully controlled. The new material thus obtained presents lower plasticity, improved workability, increased stiffness and cohesion without any loss of performance in terms of brittleness or permeability. (C) 2015 Elsevier B.V. All rights reserved.

International audience; The paper presents a study of some macroscopic properties of a plastic clay saturated with water and lead or zinc solutions at 1M concentration, in relation to its fabric. The study shows that the zinc- and lead-saturated samples present lower liquid limit, lower free swelling strain and swelling pressure, and higher permeability. X-ray diffraction analysis shows that the presence of lead results in an increase in the anisotropy of the sample. With zinc, the fabric isotropy increases, which can be attributed to higher clay-metal interactions. Mercury intrusion porosimetry shows that the saturation of the sample with lead and zinc reduces the inter-aggregate pore volume.

An experimental study of the thermo-mechanical behaviour on isotropic paths of a sandy clay prepared in the laboratory has been carried out. The material is characterised by its liquid limit wL = 38% and plasticity index Ip = 19%. Thermal consolidation tests under constant stress followed by mechanical consolidation tests at imposed temperatures were carried out on samples preconsolidated under a vertical stress of 100 kPa. The results of heating tests with measurement of volume changes highlighted the equivalence between thermal consolidation and mechanical consolidation. Thermal compressibility modulus of a normally consolidated material derived from these tests increases with temperature. Mechanical consolidation at different given temperatures shows a decrease of the thermal compressibility modulus at high temperature (80 °C). In addition, permeability increases with temperature.

The book addresses the latest issues in multiscale geomechanics. Written by leading experts in the field as a tribute to Jean Biarez (1927-2006), it can be of great use and interest to researchers and engineers alike., Very small to large strain properties of a silty sand were measured at several water contents ranging from a few percentage points to saturation level by the use of three triaxial devices with different types of transducers. In the analysis of the data, attention was paid to the influence of the water content on the maximum (Young's) modulus and the effect of the confining stress, etc. Isotropic and triaxial tests, with the measurement of capillary pressure (suction), were also performed on the same material. The effective stress concept was used to interpret the results. The predictions of a rnicromechanical model were compared with the experimental data in the elastic domain and on the failure criterion. The method highlights a simple way to relate the strength and stiffness of the soil to its capillary pressure., (undefined)

The results of an experimental work on three non standard road granular materials and a standard one are presented, including small strain precision triaxial tests under cyclic loading. The non standard materials have index parameters such as attrition coefficient, plasticity index, and fines content above the allowed limits of road specifications. The role of each parameter and the influence of the water content on the macro mechanical behaviour are studied. The geomechanical behaviour is evaluated by coupling resilient modulus and resistance to permanent strains. Results show an almost unique relationship between these parameters for each geological origin of the studied materials., The authors want to thank the French Embassy in Bogota, the French Ministry for Foreign and European Affairs and GRICES in Portugal for their support of the research and international cooperation.

The concept of “effective stress extended to unsaturated soils” is one of the most discussed concepts in soil mechanics today. This concept enters in the formulation of the constitutive laws of elastic as well as elastoplastic solid phases, and controls the stress‐strain relations, the volume changes and the strength of the solid skeleton, independently of the amplitude of the pore water pressure. These last years, several researchers showed that the extended effective stress concept remains an effective tool to describe qualitatively and quantitatively the unified mechanical behavior of the soils, assuring continuity between saturated and unsaturated domains. This paper presents the effect of the air‐water surface tension and wettability of the solid particles by the liquid in the formulation of the capillary force between the particles; this force, integrated in a representative elementary volume (REV), makes it possible to define a “capillary” stress σ’cap(pc), function of the capillary pressure pc. Ta...

The results of small and large strain triaxial tests and matrix suction measurements, performed on a compacted low plasticity silt under different conditions of water content, density and confining stress, are presented. Simple models are proposed to interpret the results, one based on an empirical approach and the other one derived from micromechanics. Based on the calculation of the capillary forces between individual particles and using a single parameter, the micromechanical model yields a satisfactory interpretation of the changes in the elastic modulus and maximum strength of the soil with water content.

The paper describes experimental results on triaxial paths at high temperature concerning an unsaturated clay (w_L = 38%, I_P = 19 and C_c = 0.23). Unsaturated drained triaxial compression tests on normally consolidated samples were carried out at constant temperatures varying from 22 to 80˚ C. Desaturation of samples were carried out by the imposition of suctions using the osmotic method. This required the development of a new triaxial cell equipped with a collar heating and an osmotic pedestal which allows the circulation of an osmotic solution of Poly Ethylen Glycol (PEG) 6000, in contact with the sample via a dialysis membrane. The principal phenomena simultaneously related on the temperature and saturation were highlighted, in particular the hardening of material on isotropic path, a secant modulus which decreases with temperature and increases with suction, a light reduction in the maximum stress on deviator path at high temperature and the increase in this maximum stress when suction increases.

The paper deals with the hydraulic behaviour of a clay used in the construction of the Boughrara dam core (West of Algeria). Various methods were used, on the one hand, to characterise the drying-wetting paths, and on the other hand, to measure the hydraulic conductivity, according to the degree of saturation (osmotic method, desiccators' method with saturated salt solutions, the Fredlund & Xing model based on the exploitation of the water retention curve). The used techniques allowed scanning a wide range of suctions up to 340 MPa. Subsequently, we were able to measure very low values of unsaturated permeability (up to 10−16 m/s). In addition, mathematical models of hydraulic conductivity were calibrated on the experimental results. This allows to establish a k(Sr) function on a wide range of degree of saturation. This function is necessary for modeling hydro-mechanical behaviour of the dam core.

Wetting and oedometric loading tests have been performed on several clayey compacted soils. The results highlight the influence of compaction water content and compaction stress on wetting paths. Comparing the changes in degree of saturation induced by mechanical loading and hydraulic loading (wetting path under null stress), it may be noticed that the oedometric path has an opposite curve of that of the wetting path, due to the fact that the void ratio decreases under constant water content when the stress is increased in one case (compression) and increases with water content in the other (swelling). GEOTECHNIQUE, ISSN : 0016-8505, DOI : 10.1680/geot.SIP11.P.020, Issue : 5, Volume : 61, pp. 431–437,May 2011.

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