Plane Strain Apparatus Research Articles

Shear bands in plane strain compression of loose sand

Experimental results are presented which characterize the behaviour of a loose, fine-grained, water-saturated sand tested under globally undrained and drained conditions in a plane strain apparatus. The objective of this investigation is to provide insight into the phenomenon of shear banding in loose sand. Together with local measurements of boundary forces and deformations, stereophotogrammetry is used to investigate the progression of strain localization in plane strain compression. Typical results and findings concerning the evolution of non-homogeneous deformation are presented in detail. Shear banding occurred in both undrained and drained experiments on loose masonry sand. In general, temporary modes of strain localization, observed during macroscopically ‘uniform’ deformations of a specimen, gave way to a single, persistent shear band. A clear pattern of onset of the formation of the persistent shear band, mobilization of the maximum effective friction and complete formation of the band was observed in all tests. The stress state when the localization begins is very close to, yet precedes that corresponding to the maximum mobilized friction. The persistent shear bands evolve with changing width and orientation. L'exposé présente les résultats d'essais de compression plane visant à caractériser le comportement de sable meuble, à grains fins et saturé d'ean dans des conditions générales non drainées et drainées. L'objectif de cette étude est de mieux faire comprendre la formation de bandes de cisaillement dans le sable meuble. En plus de mesurer les forces limites et les déformations, on a eu recours à la stéréophotogrammétrie pour étudier la progression de la localisation des tensions sous l'effect d'une compression plane. L'exposé présente en détail les résultats et constatations types concernant l'évolution de déformations non homogénes. Lors d'essais non drainés et drainés, des bandes de cisaillement se sont formées dans du sable de construction meuble. En règlegénérale, la formation d'une seule bande de cisaillement persistante s'est substituée aux modes temporaires de localisation des contraintes, observés pendant des déformations macroscopiquement «uniformes« d'une éprouvette. Dans tous les essais, le début de la formation d'une bande de cisaillement persistante, la mobillsation du frottement efficace maximal et la formation complète de la bande ont suivi un schéma bien défini. L'état de contrainte où commence la localisation est très proche de celui qui correspond au frottement mobilisé maximal, mais le précède. Les bandes de cisaillement persistantes évoluent en fonction de la largeur et de l'orientation

Plane-strain compression of rock-like materials

A new apparatus for determining the constitutive response of rock and concrete, named the University of Minnesota Plane-Strain Apparatus, was designed and built on a passive stiff-frame concept. The biaxial device, with U.S. Patent number 5,063,785, is unique, because it allows the failure plane to develop and propagate in an unrestricted manner, as opposed to conventional systems where the material is constrained by the testing apparatus. By placing the upper platen on a low friction linear bearing, the prismatic specimen, subjected to confining pressure and compressed axially, has the freedom to translate in the lateral direction once the deformation has localized across the entire specimen. In addition, homogeneous deformation is prompted by the use of a stearic-acid based lubricant, which is placed on the four surfaces of the specimen contacting hardened-steel platens. Thus, the apparatus combines the positive features of a conventional triaxial compression test and a direct shear test. Some 30 experiments on sandstone and mortar indicated that even though localization of deformation was detected by locations of acoustic emission prior to peak load, the failure plane was not fully formed at the peak. For the mortar, one more or less planar shear band, the orientation of which is well predicted by plasticity theories, was observed. A kinked rupture zone with two main portions, one steep and one less inclined, appeared in the sandstone; the steep portion may be a result of fracture phenomena. The dilatancy characteristics of rock-like materials may dictate the type of failure mode, either shear banding for ductile behavior or crack propagation for brittle behavior.

Strain Localization and Undrained Steady State of Sand

Experimental results are presented that characterize the behavior of a loose, fine-grained, water-saturated sand tested under globally undrained conditions is a plane strain apparatus. Together with local measurements of boundary forces and deformations, stereophotogrammetry is used to track the progressive localization of strain. The constitutive behaviors in the tests prior to localization can be characterized as either undrained local softening or undrained load softening and subsequent rehardening. In both cases, a consistent pattern of onset of the formation of the persistent shear band, mobilization of the maximum effective friction, and the complete formation of the band was observed. Conditions approximating steady state only were observed in the shear bands. The effect of strain localization on the conventionally derived steady state line was found to be minimal when undrained load softening behavior was observed, but significantly different steady-state lines were found from results of plane strain and axisymmetric tests. The differences between tests conducted under these two stress conditions assessed to evaluate the practical implications of the observed differences.

Experimental and numerical study of sand–steel interfaces

AbstractExperimental and numerical studies on and sand–steel interfaces are presented. Emphasis is laid on the effect of boundary conditions of the whole system and of localized deformation. The experiments with different roughness of steel surface, sand density, normal stress and grain size are carried out in a plane strain apparatus, a parallely guided direct shear apparatus and in a planar silo model with a movable bottom and parallel steel walls. During the test in the plane strain apparatus the localized zone is observed with the help of X‐rays. The results indicate a significant effect of wall roughness and boundary conditions of the whole system on the wall friction angle and the thickness of the localized zone along the steel surface.An elastoplastic constitutive model established within the framework of a Cosserat continuum, capable of describing isotropic hardening, softening and dilatancy, is implemented in a finite element code. The model differs from the conventional theory of plasticity due to the presence of Cosserat rotation and couple stress using the mean grain diameter as the characteristic length. Finite element simulations of simple shear tests are presented. The additional boundary condition along the steel plate, characteristic of the Cosserat continuum, allows for modelling the different roughness of the steel plate with consideration of grain rotations. A comparison between the numerical calculations and the experimental results shows acceptable agreement.

Model Prediction of Anisotropic Behavior of Boston Blue Clay

This paper investigates predictive capabilities of the effective stress soil model MIT‐E3 (described in a companion paper) through detailed comparisons with laboratory test data for Boston blue clay (BBC). The main focus of these evaluations is predictions of anisotropic stress‐strain behavior using data from two special laboratory shear devices: the directional shear cell (DSC), and the multi‐directional direct simple shear apparatus (MDSS). Input parameters are first estimated from standard types of laboratory data, including one‐dimensional (K0) compression and undrained triaxial shear tests. The DSC is a plane strain apparatus with the additional capability of controlling principal stress directions during shear. Measurements in this device include undrained shear tests with principal stress rotations at OCR=1, and with fixed stress direction but different principal stress orientation at OCR=4. The MIT‐E3 model describes accurately the observed variations in undrained shear strength and stress‐strain ...

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.

886047 To overcome frictional effects in a large scale plane strain apparatus. Technical note : Matthews, R S; Boot, J C GeotechniqueV38, N2, June 1988, P311–315

886047 To overcome frictional effects in a large scale plane strain apparatus. Technical note : Matthews, R S; Boot, J C GeotechniqueV38, N2, June 1988, P311–315

To overcome frictional effects in a large scale plane strain apparatus

An economical low friction layer has been developed which is capable of maintaining the coefficient of friction for soil/container interfaces in large-scale laboratory tests at 3%-10% for a wide range of stresses. The claimed level of performance is supported by the results of two monitoring methods in a large-scale laboratory model. A comparison of the results for extensive plane strain simulation using both physical and numerical techniques (Matthews, 1985) yields further quantitative evidence.

A deep retaining structure in till and sand. Part II: Performance and analysis

The problem of magnitude and distribution of lateral pressure acting on a deep retaining structure supporting an excavation in till and sand is studied by an approach integrating field measurements from a case history with a finite element analysis. Also studied are ground movements associated with the excavation. The finite element analysis is based on stress path dependent testing of the soils involved.The case history is the behaviour of a deep supported wall of the underground Churchill Square Station of the recently built line of the Light Rail Transit System in Edmonton. A tangent pile wall, 17 m deep, has been placed through glacial till to underlying sands. The site has been instrumented to record displacements of the wall and of the surrounding ground as well as the loads carried by the lateral supports.A finite element analysis employing several stress–strain models was used to simulate the excavation and its sequence, the placement of lateral support, and the differential stiffness of the structural components and of the surrounding soil. Special attention has been given to the effect of different stress–strain models of soils, with a particular focus on the influence of stress paths typical for the studied structure.Agreement between the field and analytical results for displacements is accepted as a criterion of validity of the analytical results of stresses, where direct in situ stress measurements are difficult to obtain and interpret. Of special importance is the calculated lateral pressure against the wall and its relation to the stiffness of the wall and to the magnitude of associated ground movements. The calculated lateral pressure has been found to differ significantly from the semiempirical design pressure diagrams used in practice.The soil stress–strain model found to describe the field behaviour most closely has been derived from test results obtained using a plane strain apparatus. Keywords: deep supported excavation, displacement, lateral pressure, field measurement, finite element analysis.

Experimental folding in ice and the resultant c-axis fabrics

FOLDS are commonly observed features of naturally deformed rocks1 and glaciers2,3. Many different materials4 have been used to model naturally occurring fold patterns. The deformation experiment described here used ice as an analogue for quartz in quartz-rich rocks by deforming a sample with an initially planar layering or anisotropy. This deformation is compared with samples of unlayered isotropic polycrystalline ice (Fig. 1a). Ice is convenient to use in the laboratory because of its relative ease of deformation at readily controlled temperatures. When used to model the behaviour of quartz-rich rocks, ice is a realistic analogue because both ice and quartz have: (1) hexagonal crystal structures; (2) exhibit similar optical properties; (3) form polycrystalline aggregates; and (4) deform using common crystallographic slip planes, particularly the (0001) basal planes5,6. In our experiments, a sample of multilayered ice consisting of plates of fine-grained ice sandwiched between layers of coarser ice (Fig. 1c) was deformed in a plane strain apparatus. The c-axis orientations of the grains were initially random and therefore the composite sample resembled the structure of many naturally occurring quartzites7. The experimental technique described here makes it possible to explore the relationship between initial anisotropy on folding and fabric development.

The defect structure in molybdenum single crystals deformed in plane strain

Single crystals of molybdenum deformed in plane strain have been examined in conventional 100 kV and 800 kV transmission electron microscopy. Specimens compressed along <110> and free to extend along <001> work-harden more slowly at strains above ∼0.09 than crystals free to extend along <110>, but initially they work-harden more rapidly. The work-hardening behaviour at strains >0.09 can be understood in terms of the different dislocation densities and arrangements observed at 800 kV. The behaviour at low strains cannot be assessed accurately with the present plane-strain apparatus but some latent hardening tests have been carried out (which in fact show latent softening is observed) and these observations appear to throw some light on the work-hardening rate at low strains.

ELASTIC AND SLIP COMPONENTS OF THEDEFORMATION OF SAND

The significance of a separation into elastic and slip components is considered for the case of particulate material. Tests on sand, including a variety of stress paths in a triaxial and a plane strain apparatus, indicate that for a majority of first-loading paths the total strains are closely given by the slip strains alone. The stress dilatancy theory is seen to provide a simple and accurate flow rule for predicting the slip strains.

Some Experiments on the Influence of Strain conditions on the Strength of Sand

Synopsis The Paper describes briefly the plane strain apparatus developed at Imperial College, London, and the techniques employed to prepare and test specimens of sand. The characteristics of Brasted sand sheared under plane strain conditions are described and it is noted that the value of the intermediate principal stress in plane strain is considerably less than one-half the sum of the other two principal stresses. The drained strengths of Brasted sand in plane strain compression tests are compared with strengths measured in triaxial tests at the same placement density. The strength-density curves have the same general shape but the plane strain strengths are always higher, the differences in strength increasing progressively from about ½° in loose sand to more than 4° in the densest specimens tested. On the other hand, triaxial compression and extension tests agree approximately to a common strength-density curve. The ultimate strengths measured in plane strain compression tests are constant, irrespective of placement density, and have approximately the same value as those measured in triaxial compression tests. The development of strength in an intergranular structure is discussed and it is concluded that the strain condition is a major factor influencing the strength of sands. L'article décrit brièvement l'appareil de déformation de plan développé au Collège Impérial de Londres et les techniques employées pour préparer et essayer les échantillons de sable. Les caractéristiques du sable de Brasted cisaillé dans des conditions de déformation de plan y sont décrites et on remarque que la valeur de tension intermédiaire principale est beaucoup moindre que la demi-somme des deux autres tensions principales. On compare les résistances drainées de sable de Brasted dans les essais de compression de déformation de plan avec les résistances mesurées dans les essais triaxiaux à la même densité lors de la mise en oeuvre. Les courbes résistance-densité ont la même forme générale mais les résistance de déformation de plan sont toujours plus hautes, les différences de résistance augmentant progressivement d'environ ½° dans le sable meuble à plus de 4° dans les échantillons essayés les plus denses. D'autre part, la compression triaxiale et les essais d'extension s'accordent approximativement avec la courbe commune résistance-densité. Les résistances finales mesurées dans les essais de compression de déformation de plan sont constantes, irrespectivement de la densité lors de la mise en oeuvre, et elles ont approximativement la même valeur que celles mesurées dans des essais de compression triaxiales. On discute le développement de la résistance dans une structure granulaire par gradations et on conclut que la condition de déformation est un facteur primordial influençant résistance des sables.