Behavior Of Saturated Clays Research Articles

Energy piles: current state of knowledge and design challenges

Energy piles offer a promising and eco-friendly technique to heat or cool buildings. Energy piles can be exploited as ground heat exchangers of a ground source heat pump system. In such application, the energy pile and its surrounding soil are subjected to temperature changes that could significantly affect the pile–soil interaction behaviour. The aim of this paper is to review the current state of knowledge on the design of energy piles in terms of the geostructural and heat exchanger functions. Furthermore, a conceptual understanding of the potential temperature effects on the mechanical behaviour of piles is proposed in this paper. Based on this conceptual understanding as well as the reported thermo-hydro-mechanical behaviour of saturated clays in the literature, the challenging geotechnical aspects facing the energy pile design are highlighted, and further research efforts to refine them are recommended.

On some advanced thermo‐mechanical models for saturated clays

SUMMARYThis paper aims to evaluate the performance of several recent constitutive models in simulating the thermo‐mechanical behaviour of saturated clays. A classic thermo‐mechanical test on natural Boom Clay, commonly used in constitutive modelling, was first clarified. Different methods commonly used to measure volumetric strain in drained heating tests were then discussed. Model evaluation was performed in terms of thermodynamic and elasto‐plastic requirements. The capability of the models to capture the observed behaviour was assessed on the basis of the experimental evidence. It was shown that all the models provide reasonable predictions of the thermo‐mechanical behaviour of saturated clays. However, each constitutive model has its own limitations or unclear points from the theoretical point of view. Copyright © 2013 John Wiley & Sons, Ltd.

Undrained strength of clays derived from pressuremeter tests

The behaviour of saturated clays under undrained conditions around pressuremeter path is studied by means of a theoretical and a numerical analysis based on the generalised elastoplastic Prager’s model with the Von Mises Criterion which is suitable for these cases of soils and gives a realistic response when unloading is considered. The soil constitutive model is described depending only on three parameters. The model response on pressuremeter path and its identification from experimental data lead to the determination of the undrained cohesion and the initial Young modulus of clays. Comparisons between the undrained cohesions determined with the proposed method and those obtained by other means illustrate the applicability of the method. An application to predict the bearing capacity and the settlement of bored piles using parameters derived from the proposed approach is also presented with a comparison to the measured data. Le comportement des argiles saturées en conditions non drainées sur un chemin pressiométrique est étudié au moyen d’une analyse théorique et numérique basée sur le modèle élastoplastique du Prager généralisé avec prise compte du critère Von Mises. Ce critère est bien adapté aux sols considérés et donne une réponse réaliste en déchargement. Le modèle constitutif de sol proposé est défini seulement par trois paramètres. Cette approche permet la détermination de la cohésion non drainée et le module de Young initial des argiles saturées à partir d’essais pressiométriques. La comparaison entre les cohésions non drainées déterminées avec la méthode proposée et celles obtenues par d’autres moyens illustrent son applicabilité. Une application de l’approche proposée pour prévoir la capacité portante et le tassement d’un pieu foré soumis à une charge axiale centrée est également présentée avec une comparaison avec les mesures expérimentales.

Cyclic shearing deformation behavior of saturated clays

The apparatus for static and dynamic universal triaxial and torsional shear soil testing is employed to perform stress-controlled cyclic single-direction torsional shear tests and two-direction coupled shear tests under unconsolidated-undrained conditions. Through a series of tests on saturated clay, the effects of initial shear stress and stress reversal on the clay’s strain-stress behavior are examined, and the behavior of pore water pressure is studied. The experimental results indicate that the patterns of stress-strain relations are distinctly influenced by the initial shear stress in the cyclic single-direction shear tests. When the initial shear stress is large and no stress reversal occurs, the predominant deformation behavior is characterized by an accumulative effect. When the initial shear stress is zero and symmetrical cyclic stress occurs, the predominant deformation behavior is characterized by a cyclic effect. The pore water pressure fluctuates around the confining pressure with the increase of cycle number. It seems that the fluctuating amplitude increases with the increase of the cyclic stress. But a buildup of pore water pressure does not occur. The deformations of clay samples under the complex initial and the cyclic coupled stress conditions include the normal deviatoric deformation and horizontal shear deformation, the average deformation and cyclic deformation. A general strain failure criterion taking into account these deformations is recommended and is proved more stable and suitable compared to the strain failure criteria currently used.

Viscous effects on deformation of kaolin clay in drained 1D compression with cyclic loading

Viscous effects on the drained stress-strain behaviour of kaolin (D50=0.001 3 mm; plasticity index(PI) is 41.6, liquid limit (LL) is 79.6%) were evaluated by performing a series one-dimensional(1D) compression tests on saturated specimens. Cyclic loading with a large stress amplitude was applied during otherwise monotonic loading at a constant strain rate. In the tests, one observation consistent with the previous research is that, significant loading rate effects on the stress-strain behaviour of saturated clay due to the material viscosity, not due to the delayed dissipation of excess pore water pressure, were observed during not only primary monotonic loading but also unloading and reloading. The results in cyclic loading show that creep deformation characteristics change significantly by preloading history, which is simulated by incorporating the viscous property into a non-linear three-component rheology model having isotach type viscosity with hysteretic inviscid stress-strain property.

BEHAVIOR OF SATURATED CLAY RECONSOLIDATED AT HIGH TEMPERATUE IN CYCLIC TRIAXIAL CONSOLIDATION TESTS

BEHAVIOR OF SATURATED CLAY RECONSOLIDATED AT HIGH TEMPERATUE IN CYCLIC TRIAXIAL CONSOLIDATION TESTS

A Study of the Stress-Strain-Time Behavior of Saturated Clays Based on a Theory of Nonlinear Viscoelasticity

In order to analyse the time-dependence of the stress-strain behavior of saturated clays, a nonlinear theory with the single integral representation has been proposed and compared with the experimental results. It is revealed that the relative deformation-dependent response function in the theory can be reduced to a simple form easy to treat by introducing the relaxation spectra and making use of stress relaxation characteristics. Thus, it is shown that the proposed theory successfully predicts several time-dependent behaviors such as stress relaxation after the stoppage of steady shear, steady shearing and steady state creep. Furthermore, the equilibrium properties are discussed in relation to consolidation and dilatancy characteristics.

Analysis of Strain Rate Influence on Shear Strength by Rate Processes

A hypothetical rheological model of the nonlinear Maxell type has been proposed to study the stress-strain characteristics of a saturated clay, assuming the soil structure resistance to be viscoelastic. The various elements in the proposed model consider both the elastic and viscous character of clays. The viscous character is considered in the form of structural viscosity derived from the considerations of the theory of rate processes. Experimental verification is done by strength tests on saturated kaolinitic clay whose initial structural state is mainly controlled by system chemistry. The existence of postulated initial structural difference has been amply substantiated by indirect and direct methods of identification of soil structure. An attempt has been made to explain the relationship between the flow parameters and the mechanism of the clay behaviour in relation to initial soil structure. The experimental evidence regarding the prediction of the model has been examined and the limitations highlighted. It is believed that this analysis would ultimately help in developing a more comprehensive constitutive relationship. Prediction of the general stress-strain behaviour of clays has been the object of numerous investigators in recent times. A general picture of this behaviour would be of immense help not only in understanding the stress-strain relations but also in forming a basis of solving many field problems with given stress or strain paths. It is postulated that the shearing stresses developed in a saturated clay subjected to a constant rate of strain are due to the resistance offered by the forces developed at interparticle contacts. Further deformation of a soil mass involves microscale movements of particles and proceeds at a rate commensurate with the initial structural state of clay-water-electrolyte system and the rate of strain (Mitchell 1964). The theory of rate processes is being used in the analysis of stress-strain-time behaviour of saturated clay since it postulates that an activation energy is required for loosening of particles from their equilibrium positions and displacement to new positions. Much of the pioneering work on the deformation behaviour of clays is done by Murayama and Shibata (Murayama and Shibata 1958, 1959, 1961) by applying the theory of rate processes. Analysis of shearing resistance (Mitchell 1964) and consolidation behaviour (Wu; Resendiz and Neukirchner 1966) have also been attempted by the application of theory of rate processes.