Behaviour Of Natural Clays Research Articles

Effects of soil structure and anisotropy on undrained shear behavior of natural clays

Effects of soil structure and anisotropy on undrained shear behavior of natural clays

Influence of fissure inclination and confining pressure on the local behaviour of natural clays

In this experimental study the influence of fissuring orientation and confinement pressure on the mechanical behaviour of natural clays is investigated. The tested material, the scaly clay from Santa Croce di Magliano (south of Italy), is characterised by an intense network of pre-existing fissures of single orientation. Several plane strain compression tests have been conducted, under different confinement pressures (i.e., from 50 to 600 kPa), on specimens having fissures with vertical, medium and horizontal inclination. Digital Image Correlation has been used to follow the deformation processes of the specimens throughout the tests by measuring incremental shear and volumetric strain maps. The results showed a strong coupling between the total confinement and the fissure inclination, that is controlling both the onset and the development of the patterns of the localisation processes. The new results have been compared with previous ones carried out on the same material without confinement. The comparison shed light on the role of total confinement that becomes particularly relevant from certain levels of pressures and fissuring inclination.

An Oedometer-Based Method for Preparing Reconstituted Clay Samples

It is well known that the mechanical behavior of the natural intact soft clay is usually quite different from that of the reconstituted counterpart. Hence, how to predict the influences of soil structure on the mechanical behavior of natural clays is an important issue in geotechnical engineering.The mechanical behavior of structured soils can usually be quantitatively assessed based on the mechanical behavior obtained from corresponding reconstituted clays. The preparing method for reconstituted soils will affect the quality of reconstituted samples greatly, and therefore, affect their mechanical parameter. To guarantee the quality of reconstituted soil samples, a large diameter oedometer apparatus is developed. Also, an oedomer-based method for preparing reconstituted clay samples is proposed. Typical soft Lianyungang city clay from China is chosen to testify the methods and corresponding procedures. The feasibility of the improved method is confirmed by comparing its results with those of the normal oedometer test.

Influence of Sintering Behavior of Natural Clay Sand on Surface Quality of Iron Castings

The surface quality of iron castings is influenced by the sintering behavior of natural clay sand.The components of natural clay sand are allocated and controlled according to the different thickness of castings with the purpose of achieving the appropriate sintering behavior and smooth-surface products.A series of sintering experiments are carried out with different weight ratios of clay 1#,2# and slag.Furthermore,the ferrite oxide is selected as an additive in the experiments.As a result,the sintering process is influenced a lot by the slag amount.The sintering speed of 1# is faster than that of 2#.On the basis of experiments,the molding sand composed of 2#,1# and slag with mixing ratios of 4:2:4 and 3:3:4 can be implemented in the production of inertia wheel,and the adherent sand defect at the spoke of the inertia wheel is solved by these molding sand.

Reply to the discussion by Mesri on "Viscous behaviour of St-Roch-de-l'Achigan clay, Quebec"

The authors thank Professor Mesri for his discussion of their paper on the combined effects of strain rate and temperature on the behaviour of St-Roch-de-l’Achigan clay. Two aspects were discussed: the method of analysis and the value of m ′. These two aspects will be considered in the following paragraphs. The discusser presents eq. [D1] showing the variation of σ p′ with strain rate. It is equivalent to the linear relationship between the logarithm of preconsolidation pressure and the logarithm of strain rate, as described by eq. [2] in our paper, with m ′ = Cc /Cα. The discusser indicates that eq. [D1] would be valid only after primary consolidation, which corresponds to the discusser’s own view that viscosity applies only after dissipation of excess pore pressures. Previous studies (Leroueil 1988, 1996, among others) have shown that this is not the case and, in this sense, eq. [2] is more general than eq. [D1]. The discusser questions the analysis of the test results, alleging that the evaluation of the preconsolidation pressure could be erroneous if u b ′ /σv is larger than 15%. In fact, in all the CRS tests performed, the ratio u b ′ /σv remained smaller that 10% at the passage of the preconsolidation pressure. The evaluation of σ p′ values and of m ′ have thus not been influenced by the method of analysis. As indicated in the paper, the obtained value of m ′ = 16 for St-Roch-de-l’Achigan clay is lower than expected for inorganic clays and indicates a strain-rate effect larger than that usually observed. The authors agree on this point with the discusser. It is however not clear why this m ′ value is low — possibly soil variability and the small number of CRS tests carried out; or possibly the limited range of strain rate that was considered. However, as previously explained, it is not due to excessive pore pressures. In any case, as the m ′ value does not change, all of the conclusions in the paper concerning the combined effects of strain rate and temperature on the mechanical behaviour of natural clays remain valid.

Transparent Amorphous Silica to Model Clay

The fundamental premise of this research is that transparent synthetic materials with geotechnical properties similar to natural soils can be used in model tests to study three-dimensional deformation and flow problems using nonintrusive optical visualization techniques. The transparent “clays” discussed in this paper were made by consolidating suspensions of amorphous silica in a pore fluid with a matching refractive index. Conventional triaxial compression, consolidation, and permeability tests were performed to study the behavior of the material under normally consolidated and overconsolidated conditions. This paper demonstrates the feasibility of producing a family of transparent materials, which can be customized to exhibit shear-strength, pore-pressure, volume-change, and permeability characteristics that are consistent with the behavior of natural clays.

An elasto-viscoplastic constitutive model for clay using a transformed stress tensor

It is well-known that the behavior of natural clay is anisotropic. One of the reasons is that the behavior is strongly affected by the history of stress, strain, temperature and chemical reactions. This type of anisotropy is called ‘stress induced anisotropy’ or ‘structural anisotropy’. On the other hand, the behavior of clay also strongly depends on the current stress state. The current stress sensitivity is one of the salient features of granular materials. An anisotropic stress state causes results in anisotropic and pseudo-anisotropic deformation behavior. The objective of the present paper is to propose a constitutive model for clay to describe the rate-dependent anisotropic and/or the current stress induced pseudo-anisotropic behavior of clay based on a transformed stress tensor. It is shown that the proposed constitutive model is noncoaxial and applicable to explain the current stress induced pseudo-anisotropy, the effect of the intermediate stress dependency of the soil behavior and the deviatoric flow rule. In addition, an objective formulation of the constitutive model for large deforamations is discussed.

Observed stress–strain behaviour of remoulded saturated clay under plane strain conditions

The stress-strain behaviour of saturated, remoulded clay has been investigated in a cuboidal plane strain apparatus. The tests covered a variety of strain paths ranging from proportional paths starting from a slurry state to complex paths with up to two sharp bends. Both normally consolidated and overconsolidated samples were investigated. As a result of these observations, a list of material properties has been formulated. The most important properties refer to: the dependence of the stress response on the stress level, the asymptotic property of clay, the influence of the history of straining on the stress response, and the ohservation that the stress paths reaching the state boundary surface may move along this surface. The list of material properties is thought to be a guideline for development of constitutive theories. It provides also a useful framework within which the behaviour of natural clays may be qualitatively described. Le comportement contrainte/déformation de l'argile saturée remanisé a été étudiée à l'aide d'un appareil à déformation plane cuhoide. Les essais comprenaient plusieurs chemins de déformation, y compris des chemins proportionnels en commençant par un état de coulis et aussi des chemins complexes avec jusqu'à deux coudes aigus. Des échantillons normalement consolideś et sur-consolidés furent examinés. Comme résultat de ces études une liste de propriétés de la matière fut formulée. Les propriétés les plus importantes sont les suivantes: le rapport entre la réponse à la déformation et le niveau de déformation, la propriété asymptotique de l'argile et l'influence de l'histoire de déformation sur la réponse à la deformation. Les chemins de déformation qui atteignent la surface limite de l'état peuvent suivre celle-ci. Il parait que la liste des propriétés de la matière peutservir comme base pour le déloppement des théories contituantes et fournir un cadre convenable pour la description qualitative du comportement des argiles naturelles.

Behavior of Destructured Natural Clays

Natural clays possess a structure as a result of the deposition environment, consolidation, aging, thixotropy, and cementation. To gain understanding on the relation between this structure and the behavior of natural clays, samples of three undisturbed clays have been tested in both the intact and the destructured states. The destructuration resulted in all cases in a modification of the shape of the limit state surface of the clay, in a reduction of its strength in the overconsolidated state, and in strong reductions of shear and bulk moduli.