Stress-strain Behaviour Of Clays Research Articles

A Simple Pneumatic Loading System Controlling Stress and Strain Rates for One-Dimensional Compression of Clay

A simple but automated pneumatic loading system that can control the stress and strain rates for one-dimensional (1D) compression of clay was developed. The rate-dependency of stress-strain behaviour due to the viscous property of clay was investigated by 1D compression tests on standard-size specimens by various loading methods: 1) Standard Consolidation Tests (SCTs), stepwise increasing the axial stress two times every one day; 2) ordinary Constant-Rate-of-Strain (CRS) tests at different strain rates; 3) special CRS tests including unloading and reloading cycles with different stress amplitudes at strain rates of which the absolute value was either kept constant throughout respective tests or changed at the start of reloading; and 4) special CRS tests including a number of sustained loading (SL) during otherwise primary loading or unloading or reloading at constant strain rate. Sufficiently low strain rates were employed to ensure essentially fully drained condition. The followings were found. Despite that the newly developed pneumatic loading system is rather simple, 1D compression tests following such various loading histories as above can be performed on four types of clay rather accurately. The stress-strain behaviour of clay is significantly rate-dependent, exhibiting significant creep strains at SL stages. The creep strain rate is significantly different whether SL starts during otherwise primary loading or unloading or reloading, controlled by the magnitude and sign of the initial strain rate at the start of SL. The whole observed trends of rate-dependent stress-strain behaviour can be qualitatively explained by the non-linear three-component elasto-viscoplastic model extended to cyclic loading conditions.

Cryogenic properties of soils and rocks 2. The influence of water types on the uniaxial mechanical behaviour of clays

The characteristic changes in mechanical behaviour occurring in clays as the temperature is reduced to 77 K have been compared with the molecular mobility and freezing behaviour of the contained water: conventional techniques are used, together with the novel application to clays of dynamic mechanical-thermo analysis (DMA). There is now substantial evidence linking the low-temperature dilation of clays primarily with the loosely bound freezable water component as defined by differential scanning calorimetry; however, dilation is a complex process, and before an acceptable engineering model can be derived which will predict the performance of soils under conditions appropriate to cryogenic storage of liquefied gases, it will be necessary to develop a sound understanding of this phenomenon. A transition in the stress-strain behaviour of clays from ductile to brittle behaviour occurs at approximately 173 K; this transition has been shown to coincide with the loss in mobility of water observed by nuclear magnetic resonance techniques. It is clear that non-freezable water in clays contains sufficient mobility above 173 K to act as a lubricant between the laminae and allow some ductility. It is only below 173 K that clays become fracture-sensitive. Les changements caractéristiques dans le comportement mécanique des argiles au fur et à mesure que la température s'abaisse jusqu'à 77 K sont comparés avec la mobilité moléculaire et le comportement à la congélation de l'eau contenue. Des techniques classiques ont été employées en combinaison avec l'analyse thermomécanique dynamique, qui est nouvelle pour l'étude des argiles. Il existe maintenant beaucoup d'indications qui montrent la corrélation entre la dilation des argiles à basse température au constituant d'eau congelable défini par analyse différentielle calorimétrique. La dilation est cependant un événement complexe, et il faudra acquérir une bonne compréhension de ce phénomène avant d'obtenir un modèle de construction acceptable capable de prédire le comportement des sols dans des conditions adaptées au stockage cryogénique des gaz liquéfiés. Une transition entre la ductilité et la fragilité a lieu dans le comportement tension-déformation des argiles à environ 173 K ; il a été démontré que cette transition coïncide avec la perte de mobilité de l'eau observée par des techniques de résonance magnétique nucléaire. Il est clair que l'eau non-congelable dans les argiles a assez de mobilité audessus de 173 K pour agir comme lubrifiant entre les lamelles et pour permettre quelque ductilité. Les argiles ne deviennent sensibles à la rupture qu'audessous de 173 K.

MODELLING FOR THE STRESS-STRAIN BEHAVIOR OF ANISOTROPICALLY LIGHTLY OVERCONSOLIDATED CLAY

A series of drained stress probe test on saturated remoulded clay specimens consolidated and rebounded under anisotropic stress condition was performed to investigate the influence of anisotropic stress history and stress path on the stress-strain behavior of clay. Based on the test results, a new constitutive model was proposed which could successfully describe the stress-strain behavior of anisotropically lightly overconsolidated clay.

Strength and stress-strain behaviour of clays from the Nares abyssal plain: Zizza, M M; Silva, A J Marine GeotechnolV7, N3, 1987, P221–244

Strength and stress-strain behaviour of clays from the Nares abyssal plain: Zizza, M M; Silva, A J Marine GeotechnolV7, N3, 1987, P221–244

Testing for Evaluation of Stress-Strain Behavior of Clays

Abstract A technique to predict the stress-strain behavior of clays along various stress paths is presented. The experimental results of stress-controlled triaxial pure shear and consolidation tests conducted on normally consolidated and lightly overconsolidated samples are given, and a method to evaluate the parameters required for prediction by the proposed technique is discussed. Comparison between experimental and predicted stress-strain behavior of normally consolidated and lightly overconsolidated samples along stress paths shows that the technique predicts the behavior quite well.

Closure to “Anisotropic Undrained Stress-Strain Behavior of Clays”

Closure to “Anisotropic Undrained Stress-Strain Behavior of Clays”

Discussion of “Anisotropic Undrained Stress-Strain Behavior of Clays”

Discussion of “Anisotropic Undrained Stress-Strain Behavior of Clays”

Experimental study of clay deformability in terms of initial fabric and soil-water potential

Included in this paper are the results of an experimental study directed toward improving our understanding of the complex relationship between the stress-strain behavior of clay and its initial fabric and soil-water potential. Three blocks of a kaolinite clay were consolidated from a slurry under controlled conditions of pore fluid chemistry and stress path, and the fabrics of these samples were evaluated by use of scanning electron microscopy, optical microscopy, andX-ray diffraction. Upon completion of consolidation, test specimens trimmed from these samples were placed under air pressure in an extractor and brought to equilibrium at soil-water potentials up to 15 bars. Fabric changes during this phase are expressed in terms of changes in dry density. Then, these specimens were subjected to a constant strain rate uniaxial compression test, and empirical relationships among the undrained modulus,Poisson's ratio, strength parameter, initial fabric, and soil-water potential at the beginning of the test are presented.

In-situ Determination of Undrained Stress-strain Behavior of Sensitive Clays with the Pressuremeter

A theory originally proposed by Gibson and Anderson (1961) has been extended to enable a direct determination of the whole undrained stress-strain curve of the clay from the pressure-expansion curve obtained in a conventional pressuremeter test.When applied to some pressuremeter tests carried out in Leda clay in the Ottawa area, the method enabled us to determine the undrained stress-strain behavior of the clay up to axial strains of about 20%. It is thought that, when properly performed, the test is able to furnish the data on the undrained stress-strain and strength properties of sensitive clays comparable to the laboratory test results obtained on block samples. Its particular feature is that it also furnishes a true picture of the post-peak strength decrease in terms of shear strain which is usually difficult to obtain by any other type of test.

Discussion: Some Factors Controlling the Predictability of Stress-Strain Behaviour of Clay

Discussion: Some Factors Controlling the Predictability of Stress-Strain Behaviour of Clay

Some Factors Controlling the Predictability of Stress-Strain Behaviour of Clay

A graphical interpolation method which had previously been used for predicting the behaviour of sand in triaxial test conditions has been modified to become applicable to a remoulded saturated clay.The method consists in covering a given region of the principal stress plane by the results of a number of drained compression tests whose stress paths are related to a common consolidation line and are sufficiently close to each other so as to enable intermediate values of different parameters to be found by simple interpolation.The method was applied to a remoulded saturated clay both in normally consolidated and overconsolidated state, and an attempt was made to predict by interpolation the behaviour of the clay in undrained shear and K0-consolidation test respectively.By comparing the predicted behaviour of the clay with that observed in actual tests, a fair agreement was found for undrained tests, whereas for the K0-consolidation test the agreement was poor.It is suggested that the predicting of the behaviour of the clay in a given type of test on the basis of a general picture obtained from a series of tests of a different type is possible provided that in both types of tests the type of consolidation, the sign of the isotropic and deviatoric components of the strain tensor, and the rate of strain are respectively the same.