Letteratura scientifica selezionata sul tema "Oedometer loading path"

This paper presents the results of a laboratory study on the lateral stress in a vibrated sand. No. 3 Ottawa sand was tested on a snaking table providing vertical vibration, and at-rest lateral stress was measured using a modified oedometer ring. The test results show that the lateral stress in normally consolidated sand increases with vibration time. The magnitude of the increase in lateral stress is related to the density of sand and the intensity of vibration. For overconsolidated sand with a high coefficient of earth pressure at rest, the lateral stress decreases with vibration time. Stress paths of a tested specimen are also presented in this paper. Key words : sand, coefficient of earth pressure at rest, lateral stress, vibration, overconsolidation ratio, stress path.

The mechanical behavior of a compacted unsaturated clay soil was experimentally investigated. Volume changes were investigated using a conventional odometer cell under a series of constant confining pressures, following a wetting path. The special loading paths were utilized to reflect field conditions associated with the compacted earth structure in earth filled embankment. The soils used in the experiments were taken from an earth dam. The compacted specimens were consolidated under k0-oedometer conditions. The volume change and the water content variation were measured during the tests. The influence of the confining pressure and the initial water saturation were taking into considerations. The experimental results show that the volumetric deformation properties of the remolded unsaturated soil could be expansive and/or contractive, depending on the confining pressure and the initial water saturation. It is also observed that for the mediate confining stress, there volumetric deformation of specimen applied to wetting loads has a transition from dilation to contraction.

An experimental study regarding the hydro-mechanical behaviour of a Malaysian Kaolin is presented. Strain rate-controlled oedometer tests have been conducted on compacted samples. The influence of initial water content on the pore-size distribution (PSD) of compacted samples was investigated by Mercury Intrusion Porosimetry (MIP) tests. The drying path of the soil-water characteristic curve was experimentally determined for initially compacted samples and slurry samples. The preconsolidation stress was found to increase with increase in initial dry density and with decrease in initial water content. The compression curves merge into a single line, as soon as they have reached full saturation during loading. Samples at the dry side of Proctor water content showed a bi-modal PSD, whereas a mono-modal PSD was found for Proctor water content and at the wet side. The different initial compaction states of the samples were getting reflected in the drying SWCC until a suction of about 2 MPa, beyond which the drying paths were found to be identical.

This study centred on the performance of the screw plate test (SPLT) to determine the deformability and consolidation characteristics of soft Bangkok clay. For comparison, a series of stress-path-controlled triaxial consolidation tests (tri) were carried out on good quality samples of Bangkok clay taken from the same testing sites and imposed with the same loading conditions as the screw plate tests. Undrained and drained moduli and coefficients of consolidation were obtained from the stress-path-controlled triaxial consolidation tests and were compared with the corresponding values of the screw plate test. In addition, the ultimate bearing capacity was derived from the pressure–deformation relationships of the screw plate test results. A graphical method was used to compute the coefficient of consolidation from the screw plate tests and from stress-path-controlled triaxial consolidation test results. The compressibility data were also obtained from conventional oedometer tests (oed). Both cv (SPLT)/cv (tri) and cv (SPLT)/cv(oed) ratios compared favorably with the cv (field)/cv (laboratory) ratio obtained from past investigations. The data from pressure–settlement–time relationships of the screw plate tests were used to successfully predict values that compared favorably with the measured values at each stress level. The pressure–deformation–time relationship from stress-path-controlled triaxial consolidation tests were also evaluated, and they indicated behaviour similar to that of the screw plate test results. Soil parameters obtained from screw plate tests were subsequently used to predict the settlement of two test embankments, giving fairly close agreement with the observed values. Key words: soft clay, settlement, deformation, consolidation, screw plate test, triaxial test, embankment, prediction, stress path.

The risk of geohazards associated with frozen subgrades is well recognized, but a comprehensive framework to evaluate frost susceptibility from microstructural characteristics to macroscopic thermo-hydro-mechanical (THM) behaviors has not been established. This study aims to propose a simple framework for quantitatively assessing frost susceptibility and compressibility in frozen soils. A systematic THM model was devised to predict heat transfer, soil freezing characteristics, and stress states in frozen soils. Constant freezing experiments and oedometer compression tests were performed on bentonite clays under varying temperatures (−5°C, −10°C, and −20°C) and stress levels to validate the proposed model. Additionally, soil electrical conductivity measurements were employed to assess the temperature- and stress-dependent volumetric and mechanical properties of frozen soils. The model used Fourier’s law to compute the transient soil temperature profile and estimated the volume change and stress states based on the soil freezing characteristic curve. Experimental results showed that frost heave of bentonite reached between 9.0% and 26.6% of axial strain, which was largely predicted by the proposed model. It also demonstrated that the frost heave was mainly attributed to the fusion of the porewater. Additionally, the preconsolidation pressure of frozen soils exhibited a rapid increasing trend with decreasing temperature, which was explained by the temperature-dependent ice morphology in the soil interpore. Furthermore, the findings also demonstrated a remarkable sensitivity in the electrical conductivity in response to the soil temperature during the frost heave process and the stress state under the loading or unloading path.

L'étude de la microstructure des argiles remaniées et saturées est cruciale pour la compréhension de leur comportement mécanique et des mécanismes de déformations volumiques. Cette thèse vise à identifier en 3D les mécanismes locaux qui s'activent au niveau de la microstructure en lien avec le chargement mécanique des milieux argileux. D'abord le comportement mécanique du Kaolin K13 est étudié à l'échelle de l'éprouvette sur deux chemins de chargement : œdométrique et isotrope. Ensuite, un protocole d'observation a été mis en place pour l'acquisition des images tridimensionnelles en utilisant la microscopie électronique à balayage (MEB) couplée à la Sonde Ionique Focalisée (FIB). La reconstitution des images obtenues par FIB-MEB nous permet d'accéder à la géométrie 3D d'un sous volume de l'échantillon. La deuxième partie consiste à développer une approche d'analyse quantitative en 3D permettant d'identifier les propriétés de la microstructure sur les différents chemins de chargement étudiés. La morphologie des pores est étudiée en utilisant les paramètres : flatness, élongation et sphéricité. L'orientation des pores et des particules a été d'abord identifier sur des images 2D représentants des coupes dans l'échantillon et étendue au 3D sur l'ensemble du volume et ceci sur les deux chemins de chargement. Les résultats obtenus dans le cadre de ce travail de thèse ont permis de mettre en évidence l'apport des images 3D à la compréhension de la microstructure des argiles remaniées saturées
AbstractMicrostructure investigation is essential for a better understanding of the mechanical behaviour and volumetric deformation mechanisms of remolded and saturated clays. The goal of this thesis is to identify in 3D the local mechanisms which can be activated at the microstructural level in relation to the mechanical loading of clayey meida. The mechanical behaviour of Kaolin k13 is firstly studied at on two loading paths - oedometric and isotropic. Then, an observation protocol was established for the acquisition of three-dimensional images using Scanning Electron Microscopy (SEM) coupled with Focused Ion Beam (FIB). The reconstruction of the images obtained by FIB-SEM allows us to study the 3D geometry of a sub-volume of the sample. The second part consists of developing a quantitative analysis approach in 3D to identify the microstructure properties on different loading paths. The pore morphology is studied using parameters such as flatness, elongation, and sphericity. The orientation of the pores and particles was first identified on 2D images representing cross-sections in the sample and extended to 3D throughout the entire volume for both loading paths. The results obtained in this thesis highlight the contribution of 3D images for a better understanding of the microstructure of saturated remolded clays

We studied one dimensional compressive behaviour of gap-graded granular mixtures, using the numerical simulations of the three-dimensional Discrete Element Method (DEM). Spherical particles of different size ranges were generated inside a cubical box to numerically create granular samples with the particle size distributions of a sand-like material mixed with different proportions of a uniform silt-size material. The DEM samples were subjected to one-dimensional compression similar to the loading path of the oedometer test in soil mechanics. Micromechanical characteristics behind the compressibility of granular mixtures were investigated with an emphasis on the strong force network. Unlike monodisperse assemblies, the deviatoric stress is mainly attributed to contact forces with a magnitude greater than the mean contact force of the system, the deviatoric stress of these mixture materials is attributed to a combination of the different contact types between different particle sizes. There is a primary shear-strength related load-bearing contact network, and this depends on the relative proportion of the silt particles in the system. For systems with a very little amount of silt, mainly consisting of sand particles, the main contribution to deviatoric stress is due to the contacts between the sand particles. On the other hand, for systems that have the void space between sand particles efficiently occupied by silt particles, all contact types contribute to the deviatoric stress. If strong forces of a particulate system are those responsible for the deviatoric stress, the characteristic force - that separates strong and weak forces - depends on the contact-type, the particle size distribution and the stress level; the value of the overall characteristic force however is not far from the mean force value of the system.