bluuebunny/crossref_metadata_2025 huggingface dataset:
Some anisotropic stiffness characteristics of a silt under general stress conditions
Authors: Zdravkovic L. , Jardine R. J.
Published: October 2009

Practical geotechnical problems invariably involve rotations of the principal stress axis direction and changes in the relative magnitude of the intermediate principal stress. To assess stiffness characteristics under such conditions requires a hollow cylinder apparatus (HCA) with independent controls and accurate measurements of the component stresses (σz, σr, σθ and τ2θ) and strains (ɛz, ɛr, ɛθ and γzθ). This paper describes how the anisotropy of a dense quartzitic silt was explored over the non-linear range by conducting tests on 254 mm diameter HCA samples, and on smaller triaxial specimens. It is shown that the stiffness characteristics depend strongly on the stress path direction and major principal stress axis inclination. K0 consolidated samples show a particularly stiff response to torsional shear straining and the silt's compliance matrix is non-symmetrical and non-unique, even at small strains. The cross-coupling terms are different from those expected conventionally. For example, τzθ stress changes can affect ɛz, ɛr and ɛθ strongly and the soil tends to compress vertically when subjected to either torsional shear straining or uniaxial lateral loading. The patterns of anisotropy are altered by overconsolidation.

Dans la pratique, les problèmes géotechniques font invariablement intervenir la rotation de l'orientation des axes des contraintes principales et la variation de l'importance relative de la contrainte principale intermédiate. L'évaluation des caractéristiques de rigidité dans de telles conditions exige l'emploi d'un appareil à cylindre creux à commandes indépendantes et la mesure précise des composantes de la contrainte (σz, σr, σθ et τzθ) et de la déformation (ɛz, ɛr, ɛθ et γzθ). L'article décrit l'étude de l'anisotropie d'un limon quartzeux dense dans la gamme non linéaire à l'aide d'essais effectués sur des cylindres creux d'un diamètre de 254mm et sur de plus petites éprouvettes de compression triaxiale. Les résultats montrent que les caractéristiques de rigidité sont fortement influencées par la direction des parcours de contrainte et par l'inclinaison prédominate des axes des contraintes principales. Les éprouvettes de sol consolidé K0 manifestent une réponse particulierèment rigide à la déformation de cisaillement en torsion, et la matrice d'élasticité du limon est asymétrique et non unique, même à de petites contraintes. Les couplages réciproques différent de ceux auxquels on pourrait normalement s'attendre. A titre d'exemple, des changements de la contrainte τzθ peuvent fortement influencer ɛz, ɛr et ɛθ, et le sol tend à se comprimer verticalement quand il est soumis à une déformation de cisaillement en torsion ou à une charge latérale uniaxiale. Les modes d'anisotropie sont modifiés par la préconsolidation.
Vertical vibration of a circular footing on a linear-wave-velocity half-space
Authors: Guzina B. B. , Pak R. Y. S.
Published: October 2009

An exact treatment is presented for the problem of a rigid surface foundation vibrating vertically on an elastic half-space with a linear wave velocity profile. By means of a displacement-potential representation and integral transforms, the dynamic problem is formulated as a set of dual integral equations which are reducible to a Fredholm integral equation of the second kind. Numerical results are presented to illustrate the effects of the in situ inhomogeneity on the static and dynamic foundation responses. Characteristic features of the inhomogeneous half-space problem, such as the presence of local maxima in the dynamic foundation compliance functions and the existence of cut-off frequencies, are demonstrated.

Les auteurs abordent le problème de la vibration verticale de fondations à surface rigide surune masse é1astique semi-infinie à vitesse de propagation d'onde linéaire. A l'aide d'une représentation du potentiel de déplacement et de transformations intégrales, ils formulent le problème dynamique sous la forme d'un ensemble de doubles équations intégrales que l'on pent réduire à une équation intégrale de Fredholm du deuxième ordre. Les résultats numériques présentés illustrent les effets de l'inhomogénéité en place sur les réactions statiques et dynamiques des fondations. Les auteurs démontrent les caractéristiques du problème des masses inhomo-gènes semi-infinies comme la présence de maxima locales dans les fonctions de conformitéde fondations dynamiques et l'existence de fréquences de transition.
Earthquake-related deformation beneath gently inclined ground
Authors: Pilgrim N. K.
Published: October 2009

The experimental data from an investigation of the response of sand slopes to centrifuge model earthquakes are presented. In each test a condition of steady state seepage was established parallel to the base of the model slope before triggering a single earthquake. Discrete slip planes are not observed; the predominant form of instability beneath both steeper and more gentle slopes is shear strain deformation. The deformation is continuous, though not linear, with depth. The data recorded by acceleration and pore pressure transducers are used to establish time histories of effective stress beneath slopes of different gradient. The mechanisms of deformation are then identified through the concept of characteristic state theory (phase transformation). It is shown that inertial loading is predominant in mechanisms associated with the deformation of slopes of moderate inclination, while transient pore pressure increase (with loss of shear strength and subsequent gravity effects) predominates in mechanisms associated with the deformation of more gentle slopes.

Ĺauteur présente les données expérimentales de recherches sur la réaction de talus de sable &garve; des modélisations de tremblement de terre en centrifugeuse. Dans chaque essai, on a établi un régime permanent de suintement parallèlement à la base du talus modé1isé avant de déclencher un tremblement de terre. On ńobserve aucun plan de glissement distinct, et le cisaillement est la forme prédominante ´instabilité sous les pentes abruptes comme sous les pentes plus douces. La déformation est continue, mais pas linéaire, en profondeur. Les données enregistrées par les capteurs d'accé1ération et de pression ´ean interstitielle servent à établir les diagrammes ´évolution des contraintes intergranulaires sous des talus de pente variée. Les m6canismes de déformation sont alors identifiés à ĺaide du concept de la Worie de ĺétat caractéristique (transition de phase). On montre que le chargement inertiel est prédominant dans les mécanismes associés à la déformation des talus de pente modérée, tandis que ĺaugmentation transitoire de la pression ´ean interstitielle (avec perte de r6sistance au cisaillement et effets de gravité subséquents) prédomine dans les mé- canismes associés à la déformation de talus à pente plus modérée.
Tectonic shear zones in the London Clay Formation
Authors: Chandler R. J. , Willis M. R. , Hamilton P. S. , Andreou I.
Published: October 2009

Subhorizontal shear zones observed in the London Clay Formation are described. The physical properties of the shear zones are examined, and it is demonstrated both that they are of tectonic origin, the result of bedding plane slip during minor folding, and that they were probably formed before there had been any significant erosion of the London Clay or later overlying formations. The occurrence of the shear zones is reviewed, and it is shown that similar features have been recorded in other areas to the west of London, and it seems likely that they will be encountered elsewhere in the London basin, wherever minor folding occurs. The shape of the London Clay Formation—Reading Formation interface appears to give an indication of the degree of folding, and hence of the possible occurrence of shear zones. The displacements of the shear zones examined are believed to be small, perhaps only a few centimetres, and consequently the strength along the shear zones is probably slightly above the true large-displacement residual, although it is suggested that the drained strength of the shear zone should be assumed to be close to the field residual strength.

L'article décrit les zones de cisaillement subhorizontales observées dans la formation argileuse de Londres. Les auteurs examinent les pro-priétés physiques des zones de cisaillement et montrent qu'elles sont d'origine tectonique, étant le résultat d'un glissement intercouche survenu pendant un plissotement, et qu'elles se sont probablement formées avant toute érosion sensible de Pargile londonienne on de formations sus-jacentes ultérieures. Les auteurs examinent la venue des zones de cisaillement et montrent que des caracteristiques semblables ont été relevées dans d'autres régions à 1'ouest de Londres et qu'il est probable qu'on en trouvera d'autres dans toute autre zone de plissotement du bassin de Londres. La configuration de 1'interface entre la formation argileuse de Londres et la formation de Reading semble donner une indication du degré de plissement et, par conséquent, de la venue possible de zones de cisaillement. On pense que les déplacements des zones de cisaillement examinées sont faibles, pas plus de quelques centimétres peut-être. En conséquence, it et probable que la résistance le long des zones de cisaillement est légérement supérieure au véritable résidu des grands déplacements, bien que certaines indications permettent de supposer que la résistance drainée de la zone de cisaillement se rapproche de la résistance de champ résiduelle.
Model testing of closely spaced tunnels in clay
Authors: Kim S. H. , Burd H. J. , Milligan G. W. E.
Published: October 2009

This paper describes the use of reduced-scale model testing to study the effect of shield tunnel construction on the structural liners of existing nearby tunnels. The research considered the influence of tunnel proximity and alignment, liner stiffness and soil overconsolidation ratio on the nature of short-term interactions between closely spaced tunnels in clay. Seven sets of carefully controlled tests were performed in two main series: (a) parallel tunnels; and (b) perpendicular tunnels. Two different test tanks were developed and used to produce clay samples of Speswhite kaolin: a plane strain tank for the parallel tunnels; and a cylindrical tank for the perpendicular tunnels. Three model tunnels were installed in each clay sample in order to conduct two separate interaction experiments. The tunnel liners were installed using a model tunnelling machine that was designed to simulate the construction of a full scale shield tunnel. The first tunnel liner to be installed in any test was instrumented. Measurements of interaction effects were then made during and after the installation of new adjacent tunnels. The interaction mechanisms observed in the physical model tests are discussed and interpreted.

Cet article décrit l’utilisation d’essais de maquette à déchelle rdéduite pour détudier l’effet de la construction d’un tunnel de protection sur les doublures structurales des tunnels avoisinants. Cette recherche a pris en compte l’influence de la proximitdé et de l’alignement des tunnels, de la rigiditdé' de la doublure et du taux de surconsolidation du sol sur la nature des interactions à court terme entre les tunnels rapprochdés dans l’argile. Sept lots d’essais soigneusement controldés ont détdé re'alisdés sur deux groupes principaux: (a) tunnels paralldéles; (b)tunnels perpendiculaires. Deux bassins d’essai diffdérents one détdé développdés et utilisdés pour produire des déchantillons d’argile de kaolin Speswhite; un bassin d’efforts plan pour les tunnels parallèles et un bassin cylindrique pour les tunnels perpendiculaires. Trois maquettes de tunnels ont détdé installdées dans chaque déchantillon d’argile afin de permettre deux expdériences d’interaction sdépardées. Les doublures ont détdé installdées en utilisant une maquette de tunnelier concue pour simuler la construction d’un tunnel de protection grandeur nature. La premidére doublure installdée dans chaque essai a détdé munie d’instruments. Des mesures des effets d’interaction ont alors détdé prises pendant et aprdés l’installation de nouveaux tunnels adjacents. Nous ddécrivons et interprdétons ici les mdécanismes d’interaction observdés dans les essais de maquette physique.
Mechanical behaviour of a natural soft clay
Authors: Callisto L. , Calabresi G.
Published: October 2009

The results of an experimental study on the mechanical behaviour of the natural soft clay found at Pisa are discussed. Triaxial and true triaxial stress path—controlled tests were carried out, in which the soil was subjected to a variety of drained stress paths, each starting from the in situ stresses. The stress—strain behaviour was observed to be substantially non—linear from the very beginning of the loading process. The observed results are interpreted using concepts of hardening plasticity. The influence of the damage produced in the clay microstructure during loading is evaluated through a normalization technique. A comparison between the behaviour of the natural and the reconstituted clay is also presented. The results of the true triaxial tests show strength anisotropy. In both the triaxial and the true triaxial tests, the observed stiffness was found to depend strongly on the direction of the stress path.

Dans cet exposé, nous présentons les résultats d'une étude expérimentale sur le comportement mécanique de ľargile tendre naturelle trouvée dans la région de Pise. Nous avons effectué des essais de contrainte triaxiale et de contrainte triaxiale réelle á trajectoire conrô1ée, essais au cours desquels le sol a été soumis á une variété de trajectoires de contrainte drainées, chacune commençant á partir des contraintes in situ. Nous avons observé que le comportement contrainte—déformation était substantiellement non linéaire depuis le commencement du processus de charge. Nous appliquons des concepts de plasticité durcissante pour interpréter les résultats observés. Nous évaluons ľinfluence des dé gâts infligés â la microstructure de ľargile pendant la charge grâce á une technique de normalisation. Nous comparons aussi le comportement de ľargile naturelle et de ľargile reconstituée. Les résultats des essais triaxiaux réels ont mis en évidence une anisotropie de résistance. Dans les essais triaxiaux tout comme dans les essais triaxiaux réels, il est apparu que la rigidité observée dépendait fortement de la direction de la trajectoire de la contrainte.
Deformation of granular materials due to rotation of principal axes
Authors: Joer H. A. , Lanier J. , Fahey M.
Published: October 2009

The behaviour of granular materials when subjected to rotation of their principal axes of stress or strain is not fully understood. In the late 1980s a new apparatus was developed to allow general plane strain conditions to be applied to an analogue soil (Schneebeli cylinders). This paper presents a short description of this apparatus and its capabilities. Experimental results from different types of cyclic tests involving the continuous rotation of principal axes are given, mainly in terms of volume change and the co-axiality of stress and strain increment tensors. The results show that cyclic rotation induces a general tendency to compaction, and that the principal axes of stress and strain increment are not coincident as it is generally assumed in isotropic elastoplastic modelling.

Le comportement des matériaux granulaires soumis à une rotation des axes principaux de contrainte ou de dèformation ňest pas parfaitement compris. Vers la fin des années 1980, un nouvel appareil a éwé mis au point pour appliquer les conditions générales de contrainte plane ˇ un sol analogique ('rouleaux de Schneebeli'). Cet article présente une brève description de cet appareil et de ses capacités. Les résultats expérimentaux concernant divers types `essais cycliques avec rotation continuelle des axes principaux sont present6s surtout en termes de changement de volume et de coaxialité des tenseurs ďincréments de contrainte et de d6formation. Les résultats montrent que la rotation cyclique provoque une tendance générale ď la compaction et que les axes principaux ďincré ments de contrainte et de dèformation ne sont pas coincidents, contrairement ˇ ce qui est généralement admis pour les modéles élastoplastiques isotropes.
Combined loading of skirted foundations
Authors: Bransby M. F. , Randolph M. F.
Published: October 2009

>The response of skirted offshore foundations to combined vertical (V), moment (M) and horizontal (H) loading has been studied using two-dimensional finite-element analysis and upper-bound plasticity analysis assuming the soil to be undrained. New information has been gained about the shape of the yield locus and the soil deformation mechanisms occurring at yield from the finite-element analysis. The shape of the yield locus was found to be similar to that predicted by previous workers in V—M and V— H space but differed significantly in M—H space. This behaviour is explained using upper-bound plasticity mechanisms suggested by the soil deformation mechanisms calculated in the finite element analysis. This procedure is then used to give a good approximation to the shape of the yield locus and thus may form the basis for future design methods. Additionally, a simplifying transformation is suggested for the yield locus in H—M space based on plasticity analysis, which allows use of simple mathematical expressions to form a design envelope.

Nous 6tudions la réponse de fondations offshore à jupe à une combinaison de charge verticale (V), instantanée (M) et horizontale (H) en utilisant des analyses d'é1éments finis en deux dimensions et une analyse de plasticité de limite supérieure en supposant un sol non drainé. Nous drons de Panalyse d'é1éments finis de nouveaux renseignements sur la forme du lieu d'é1asticité limite et sur les mécanismes de déformation du sol qui se produisent à la limite é1astique. La forme du lieu se révèle comme similaire à celle présagée par les travaux précédents dans les espaces Vmdash;M et V—H mais considérablement différente dans Pespace M—H. Nous expliquons cc comportement en utilisant les mécanismes de plasticité de limite supérieure qui sont suggérés par les mécanismes de déformation du sol calcu1és dans 1'analyse d'é1éments finis. Cette procédure est alors utilisée pour donner une bonne approximation de la forme du lieu qui pourra ainsi former la base des futures méthodes de design. De plus, nous suggérons une transformation simplificatrice pour le lieu d'é1asticité limite dans Pespace H—M sur la base de 1'analyse de plasticité qui permet Putilisation d'expressions mathématiques simples pour former une enveloppe de design.
Analysis of a sample containing a shear surface from a recent landslip, south Cotswolds, UK
Authors: Anson R. W. W. , Hawkins A. B.
Published: October 2009

The paper reports analysis of a block sample taken from a trial pit, hand dug across the shear surface of an active landslide in the south Cotswolds. The slide is located on the Upper Fuller's Earth, some 50m downslope of the overlying Great Oolite limestone, the weathering of which has produced ooliths and gravel-sized fragments which are incorporated within the slipped mass. Sampling at 5 mm intervals confirmed the inverse relationship between the natural moisture content and calcite content. In order to assess the significance of changes in moisture content in the fine fraction, the influence of the non-sorptive calcite was removed and a normalized moisture content profile established. Examination of the lower shear surface using scanning electron microscopy confirmed the parallel orientation of the clay minerals for a thickness of some 1 μm. This thin veneer extended over areas of granular material, highlighting the importance of obtaining representative samples when shear strength assessment is undertaken.

Le papier rend compte de 1'analyse d'un échantillon de bloc prélevé dans un pmts d'exploration creusée à la main à travers la surface de cisaillement d'un glissement de terrain actif dans le sud des Cotswolds. Le glissement est situé sur la terre à foulon supérieure, é quelque 50 m en contrebas du calcaire oolithique (Great Oolite) sus-jacent; dont l'altération a produit des oolithes et des fragments de la taille de gravillons incorporés dans la masse glissée. Les prélèvements d'échantillons, à intervalles de 5 mm, ont confirmé la relation inversement pro-portionelle entre la teneur en eau naturelle et la teneur en calcite. Pour pouvoir évaluer l'importance des changements de la teneur en eau dans la fraction fine, on a éliminé l'influence de la calcite non adsorbante et établi un profil de teneur en eau normalisé. L'examen de la surface de cisaillement inférieure par microscopie électronique à balayage, a confirmé l'orientation paralléle des minéraux d'argile sur une épaisseur de quelque 1 μm. Cette fine couche s'étendait sur les zones de matériaux granulaires, soulignant ainsi l'importance de l'obtention d'échantillons représentatifs lorsqu'on étudie la résistance au cisaillement.
The influence of soil structure and stress history on the soil–water characteristics of a compacted till
Authors: Vanapalli S. K. , Fredlund D. G. , Pufahl D. E.
Published: October 2009

The soil–water characteristic defines the relationship between the soil suction and gravimetric water content, w, or the volumetric water content, θ, or the degree of saturation, S. Theoretical and empirical relationships are available to model the unsaturated soil properties such as the coefficient of permeability and shear strength using the soil–water characteristic and the conventional saturated soil properties. These procedures are attractive to engineering practitioners because rigorous laboratory tests on unsaturated soil are difficult and time-consuming and, therefore, costly. Various investigators generally have used the soil–water characteristic over a limited suction range (usually 0 to about 1500 kPa) to model the unsaturated soil behaviour. Soils, however, change from a saturated to a dry condition over a range of suctions from 0 to 1000 000 kPa. A rationale for extending the soil–water characteristic up to 1000 000 kPa is provided in this paper, and a method for estimating the residual state of saturation is presented. Soil–water characteristics were developed for the entire range of suctions from 0 to 1000 000 kPa on statically compacted clayey till specimens prepared at three different initial water contents. The influence of initial water content, soil structure and stress history, as it relates to the soil–water characteristic, has been studied and is reported in this paper. The initial water contents selected for this study represent the dry of optimum, optimum and wet of optimum conditions with corresponding densities determined from the standard AASHTO test. The results indicate that initial moulding water content has considerable influence on the resulting structure (and aggregation), which in turn influences the soil–water characteristics. In the low suction range (i.e. 0–1500 kPa), macrostructure governs the soil–water characteristics for specimens compacted with dry of optimum initial water contents and they exhibit a steeper slope. However, for the specimens compacted at wet of optimum, microstructure governs the soil–water characteristic behaviour. The soil–water characteristic of the specimens compacted at dry of optimum are influenced by the stress history; however, stress history appears to have no significant influence on the soil–water characteristics of the specimens compacted with wet of optimum conditions. The soil–water characteristic behaviour of specimens compacted with optimum initial water contents lies in between those of specimens compacted with water contents that are dry and wet of optimum. It appears that soil–water characteristics are not significantly influenced either by the soil structure (aggregation) or the stress history for the high suction ranges (i.e. 20 000–1 000 000 kPa).
Variational solution for vertically loaded pile groups in an elastic half-space
Authors: Shen W. Y. , Chow Y. K. , Yong K. Y.
Published: October 2009

This paper presents a variational approach that can be used to analyse vertically loaded pile groups in soil modelled by an elastic half-space. With use of a variational approach, both the displacements and shear stresses of group piles are each represented by a finite series. The principle of minimum potential energy is used to determine the response of pile groups. Good agreement between the present analytical method and other numerical methods is observed for the behaviour of pile groups. The theoretical predictions compare reasonably well with field measurements.
Assessing a soft soil tunnelling numerical model using field data
Authors: Bernat S. , Cambou B. , Dubois P.
Published: October 2009

The aim of this paper is to assess a numerical soft soil tunnelling model, using field data. The lining of the tunnel to be studied was a fairly thick, very rigid structure. Given the low level of applied stresses, lining deformation was slight, and the deformation around the tunnel essentially concerned the annular space created between the soil and the lining during tunnelling. This void was partially filled with injected grout. The primary purpose of this paper is to examine models that demonstrate soil–tunnelling interactions. An empirical ‘deconfinement factor λ’ is then used to represent stress reduction around tunnels during construction. In the first model it is simply assumed that soil stresses around the tunnel reduce linearly by a factor λ. The second analysis refines this notion and considers a temporary 'reconfinement' stage in order to represent both the grouting behind the lining once it is installed, and the hydrostatic pressure that acts on the impervious tunnel (pushing the lining up into the grout). Comparisons between these models and field data measurements obtained in three fully instrumented areas of the Lyons-Vaise metro site will be discussed.

Cet article a pour but d'évaluer un modèle numérique pour la construction d'un tunnel dans un sol meuble, en utilisant des données de terrain. Le revêtement du tunnel à étudier était une structure assez épaisse et très rigide. Étant donné que les contraintes appliquées étaient faibles, la déformation du revêtement était 1égère et la déformation autour du tunnel était liée essentiellement a l;espace annulaire créé entre le sol et la paroi pendant la construction. Ce vide était partiellement rempli de coulis injecté. Cet article a pour objet, principalement, d'examiner les modèles qui montrent les interactions entre le sol et l;action de creusement du tunnel. Nous utilisons ensuite un ‘facteur de d6confinement λ, obtenu de mamère empirique, pour représenter la baisse de contrainte autour des tunnels pendant la construction. Dans le premier modèle, nous présumons simplement que les contraintes dans le sol autour du tunnel baissent de fa¸on linéaire d'un facteur λ. La seconde analyse raffine cette notion et considère une étape de ‘re-confinement’ temporaire afin de représenter à la fois l'injection de coulis derrière la paroi une fois que celle-ci est installée et la pression hydrostatique qui agit sur le tunnel étanche (déplacement vertical du revetement à l'intéreur du coulis). Nous ommentons la comparaison entre ces modèles et les mesures obtenues sur le terrain dans trois zones entièrement instrumentées sur le site du métro de Lyon-Vaise.
Rigorous plasticity solutions for the bearing capacity of two-layered clays
Authors: Merifield R. S. , Sloan S. W. , Yu H. S.
Published: October 2009

This paper applies numerical limit analysis to evaluate the undrained bearing capacity of a rigid surface footing resting on a two-layer clay deposit. Rigorous bounds on the ultimate bearing capacity are obtained by employing finite elements in conjunction with the upper and lower bound limit theorems of classical plasticity. Both methods assume a perfectly plastic soil model with a Tresca yield criterion and generate large linear programming problems. The solution to the lower bound linear programming problem is obtained by modelling a statically admissible stress field, whereas the upper bound problem is solved through modelling a kinematically admissible velocity field. Results from the limit theorems typically bracket the true collapse load to within approximately 12%, and have been presented in the form of bearing capacity factors based on various layer properties and geometries. A comparison is made between existing limit analysis, empirical and semi-empirical solutions. This indicates that the latter can overestimate or underestimate the bearing capacity by as much as 20% for certain problem geometries.

Dans cet exposé, nous servons d'analyses limites numériques pour évaluer la capacité porteuse non drainée d'une assise à surface rigide reposant dur un dépöt argileux à deux couches. On obtient des limites rigoureuses pour la capacité porteuse ultime en employant des é1éments finis en conjonction avec les théorèmes de limite à borne supérieure et inférieure de la plasdcité classique. Les deux méthodes supposent un modéle de sol parfaitement plastique avec un critère d'élasdcité Tresca et entraïnent de gros problèmes de programmation linéaire. On obtient la solution au problème de programmation linéaire de limite inférieure en faisant la maquette d'un champ de contrainte admissible en statistique tandis que le problème de limite supérieure est résolu par la mise en maquette d'un champ de vélocité admissible en cinétique. De manière typique, les résultats de théorèmes limites cernent dans une marge d'environ 12% la vraie charge d'affaissement et sont présentés sous forme de facteurs de capacité porteuse basés sur les propriétés et géométries des diverses couches. Nous comparons les analyses limites existantes, les solutions empiriques et les solutions semiempiriques. Cette comparaison indique que ces dernières peuvent surévaluer ou sousestimer de 20% la capacité porteuse dans le cas de certaines géométries à problème.
A micromechanics-based methodology for evaluating the fabric of granular material
Authors: Pan Y. -W. , Dong J. -J.
Published: October 2009

A micromechanics approach can successfully model the stress–strain–strength relation of a granular material once the microcharacteristics of the material have been obtained. However, it is usually difficulty to determine the fabric of natural granular materials. Using a stress-dependent micromechanics model, the elastic properties can become a function of the geometric and kinetic fabric. Also, the wave velocity can be related to the elastic properties. Consequently, this paper proposes a methodology for evaluating the fabric of a granular assembly from a set of measured wave velocities. The methodology contains three elements: (a) a stress-dependent micromechanics elastic model, (b) an anisotropic elastic wave propagation theory and (c) an optimization procedure. It is verified by calibrating available wave velocity data of a glass assembly and washed mortar sand. The methodology is further applied to study the microstructural evolution of the washed mortar sand under biaxial stresses. Two aspects of fabric change can be observed: (a) concentration of contact normals in the major principal direction and (b) a residual fabric after subsequent loading/unloading.

Une approche micromécanique permet de faire une maquette de la relation tension-allongementrésistance ďun matériau granulaire une fois que ses micro caractérisdques ont W obtenues. Cependant, il est habituellement difficie de déterminer la structure des matériaux granulaires naturels. Si ľon utilise une maquette micromécanique tributaire de la tension, les propr!étés élastiques peuvent devenir fonction de la structure géométrique et cinédque. De plus, la vitesse des ondes pent Être apparentée aux propriétés é1astiques. C'est pourquoi, dans cette étude, nous proposons une méthodologie permettant ďévaluer la structure &caorn;un assemblage granulaire à partir &acorn;un lot de vitesses ďondes mesurées. La méthodologie contient trois éléments: (a) une maquette élastique micromécanique tributaire de la tension, (b) une théorie de propagation des ondes élastiques et anisotropes et (c) une procé& dure ďoptimisation. Nous vérifions en les calibrant les données disponibles sur les vitesses ďondes ďun assemblage de boule de verre et ďun sable de morder lavé La méthodologie sert ensuite à étudier ľévolution microstructurale du sable de morder lavé soumis à des tensions biaxiales. On observe alors deux genres de changements de structure: (a) une concentration des perpendiculaires de contact dans la direction majeure principale et (b) une structure résiduelle aprés des charges/décharges consécutives.
Intergranular state variables and stress–strain behaviour of silty sands
Authors: Thevanayagam S. , Mohan S.
Published: October 2009

Relative contributions by the coarser and finer grains in a silty sand to its stress–strain response are affected by the intergranular matrix structure. The nature of this contribution is illustrated using an intergranular matrix phase diagram in terms of void ratio (e), fines content (FC), and intergranular and interfine void ratios (es and ef). New intergranular state parameters (ψs, ψf) and (es, ef) are introduced as state variables to characterize silty sands; es and ef dictate the steady-state characteristics of silty sand at low and high fines contents, respectively; ψs and ψf reflect the plastic compressibility characteristics at low and high fines contents, respectively. Using these state variables, the anticipated stress–strain–strength behaviour of silty sand in comparison to that of the host sand is presented. Similar stress-strain behaviour is expected at the same es and initial confining stress σ′c, with a few exceptions.

At a constant void ratio e, es increases while ef decreases with addition of fines; a silty sand passes through different states. First, at low fines content, es (< emax,HS, the maximum void ratio of the host sand, case 1), and high ef the stress–strain behaviour is primarily governed by intergranular friction between the coarser grains. The steady-state line (SSL) is primarily dependent on es and is fairly independent of σ′c; When compared at the same es and at the same σ′c(or at the same ψ or ψs), the silty sand and the host sand show similar (not identical) stress–strain behaviour; with addition of fines, as es increases, the collapse potential increases and the stress–strain response becomes weaker. Second, with further addition of fines, when es approaches or exceeds emax,HS, the SSL is influenced by es and σ′c. When es is near emax,HS (case 2), the stress–strain curves for silty sands are similar at the same es and the same σ′c (or at the same ψ or ψs), but different from and stronger than that of the host sand. At very loose states (es > emax,HS; case 3), the stress–strain curves, normalized with respect to σ′c, are similar at the same es (or at the same ψ or ψs). Third, with further addition of fines beyond a threshold value, ef becomes sufficiently low (case 4); the fines impart a significant influence, while the role of intergranular (coarser-grain) friction diminishes; the silty sand is expected to behave similarly (not identical) to the host fines at the same ef and ψf ; at this stage, with further addition of fines, the collapse potential decreases.
A finite strain theory for gassy sludge
Authors: Wichman B. G. H. M.
Published: October 2009

In sludge, which can be considered as a soft soil, biogenic gas occurs mostly in the form of discrete gas bubbles that are much larger than the surrounding void spaces. In this article, one-dimensional finite strain consolidation theory has been extended for gassy, soft soils and has been implemented numerically in an existing finite strain consolidation program. This theory has been verified experimentally by means of specific laboratory tests. A sensitivity analysis has been performed for a typical disposal site, using different assumptions of the distribution of gas versus sludge height. Compressibility and solubility of the gas, consisting mainly of methane, have been included as well as advection of the dissolved gas with the pore water outflow. It is shown that gas causes a significant retardation of consolidation. In addition, the final degree of consolidation is less, due to the presence of the gas. Practical consequences are a loss of disposal capacity and a change in the outflow of contaminated pore water.
Energy aspects of particle breakage in drained shear of sands
Authors: Ueng Tzou-Shin , Chen Tse-Jen
Published: October 2009

The effect of particle breakage on the shear strength of sand is studied by considering the energy consumption due to particle breakage at the contacts between sand particles. A stress–dilatancy relationship for sand under a triaxial loading condition is developed, adopting Rowe's minimum energy ratio principle. Particle breakage and its relation to the shear strength of a sand can then be evaluated based on this relationship. The increment of specific surface of the sand is used as an indication of the amount of particle breakage. Results of laboratory triaxial compression tests for Fulung sand, Tamsui River sand and a decomposed granite are examined and compared with the stress–dilatancy relationship. The effect of particle breakage on the shear strength of a sand can be correlated with rate of energy consumption of particle breakage and rate of increment in particle surface area per unit volume of sand as proposed in this study. The rate of energy consumption by particle breakage increases with increasing confining pressure, but is only slightly affected by the relative density of sand. The effect of energy consumption of particle breakage on the friction angle of these sands is also evaluated.
Model study of seepage in smear zones around vertical drains in layered soil
Authors: Hird C. C. , Moseley V. J.
Published: October 2009

Physical model tests were conducted to investigate the effects of soil disturbance, commonly termed smear, around vertical drains installed to accelerate consolidation in compressible soils. A 25 mm dia. mandrel carrying a cylindrical drain was driven into 252 mm dia. models composed of alternating layers of preconsolidated kaolin and silty sand, and the effect of smear was quantified by means of radial flow permeability tests. A parametric study of the influence of sand layer thickness, clay layer thickness, mandrel driving speed and mandrel tip angle was conducted. Two tests were also conducted on clay models without sand layers. In the layered models, for which the undisturbed horizontal permeability was always much greater than the vertical permeability, the smear effect was found to be substantial. In the absence of sand layers, it was relatively modest and consistent with previous research.
A kinematic hardening constitutive model for natural clays with loss of structure
Authors: Rouainia M. , Muir wood D.
Published: October 2009

A rate-independent constitutive model for natural clays is presented, formulated within the framework of kinematic hardening with elements of bounding surface plasticity. The modelling framework is intended to include effects of damage to structure caused by irrecoverable plastic strains caused by sampling, laboratory testing, or geotechnical loading. The incorporation of a structure measure allows the size of the bounding surface to decay with plastic deformations. This model can be seen as a logical extension from the Cam-clay model. The steady fall of stiffness with strain towards the Cam-clay value is controlled by a particular interpolation function. This ensures a smooth degree of approach between a kinematically hardening bubble (which is the boundary of the elastic region) and the bounding surface during their relative translation with stress history. The model describes the essential phenomena of pre-failure behaviour of natural clays: stiffness variation with strain, volumetric change accompanying distortion, peak strength at small strains. Illustrative numerical results for common geotechnical experiments on a low-sensitivity Swedish clay demonstrate the potential of the proposed model.
Numerical modelling of full-scale tests on drystone masonry retaining walls
Authors: Harkness R. M. , Powrie W. , Zhang X. , Brady K. C. , O'Reilly M. P.
Published: October 2009

The behaviour of four drystone masonry retaining walls of different geometry has been modelled numerically using the discrete element code UDEC, and the results have been compared with the field trials carried out by Burgoyne in Ireland in 1834. By using appropriate soil and wall mass densities, strengths and stiffnesses, it was possible to reproduce in the numerical analyses the field behaviour observed by Burgoyne. Reasonably close agreement was obtained between the horizontal components of earth pressures calculated in the numerical analyses and using the earth pressure coefficients given by Caquot and Kerisel. Basal stress distributions calculated using the condition of equilibrium of the wall were also broadly consistent with those resulting from the numerical analyses. The results also confirm both the influence of the geometry of a drystone masonry retaining wall on its performance and ultimate stability, and the soundness of Burgoyne's engineering judgement in specifying his programme of field tests.
Combined loading of spudcan foundations on clay: laboratory tests
Authors: Martin C. M. , Houlsby G. T.
Published: October 2009

Recent research has shown that work-hardening plasticity theory provides a suitable framework for interpreting and predicting the load–displacement behaviour of rigid shallow foundations under combined vertical, moment and horizontal loading. Most previous work has, however, been restricted to footings on granular soils. This paper describes a series of laboratory tests conducted at unit gravity using a small circular footing and specimens of reconstituted kaolin. The results indicate that work-hardening plasticity concepts can also be applied to the modelling of shallow foundation behaviour on undrained clay. The footing shape chosen for the experiments is representative of the ‘spudcan’ foundations which support the legs of jack-up drilling platforms. A novel testing apparatus allows independent control of the vertical, rotational and horizontal footing displacements within a single vertical plane. Tests conducted at constant vertical penetration are used to investigate the shape and size of the combined load yield surface at embedments ranging from 0 to 1·6 footing diameters. Tests under vertical load control provide further information about the yield surface, and are used to assess the suitability of an associated flow rule for predicting plastic footing displacements. The yield surface shape determined experimentally is compared with that implied by the general bearing capacity formula of Brinch Hansen, and some significant discrepancies are highlighted.
A variational approach for the analysis of pile group–pile cap interaction
Authors: Shen W. Y. , Chow Y. K. , Yong K. Y.
Published: October 2009

This paper presents a variational approach for the analysis of pile groups having rigid pile caps in contact with the ground. The pile groups are assumed to be embedded in an isotropic elastic half-space. Both the deformations and shear stresses of group piles are each represented by a finite series with a set of undetermined constants, and Mindlin's solution is applied to evaluate the interaction among the piles, pile cap and soil. The response of the pile group–pile cap system is determined by the use of the principle of minimum potential energy. Comparison of the present solutions with other numerical methods has shown good agreement. The computed results are also shown to be in favourable agreement with field measurements.
Minimum undrained strength of Hostun RF sand
Authors: Doanh T. , Ibraim E.
Published: October 2009

The minimum undrained behaviour of very loose Hostun RF sand is described. The analysis is based on the results of several series of undrained triaxial compression and extension tests. The samples were consolidated isotropically or anisotropically along constant effective stress ratio paths. The initial void ratios at fabrication state and at the end of the monotonic consolidation stage of each test were also evaluated. This experimental study confirms the conceptual framework proposed by Konrad, based only on isotropically consolidated undrained triaxial tests (CIUs) to explain the undrained behaviour of very loose sands during monotonic loading. The systematic evaluation of the experimental errors and sample variabilities using probabilistic techniques assesses the existence of an upper boundary (upper flow) and a lower boundary (lower flow) of the steady state of deformation. This paper extends the scope of the previous framework for sand samples subjected to an initial monotonic consolidation history. The extended framework draws on the instability concept of Lade and the asymptotic stabilization of the effective stress ratio at peak. The minimum undrained strength of Hostun RF sand at steady state is strongly influenced by the normalized mean effective stress at peak, and by the void ratio at the end of the initial monotonic consolidation.
Mud pumping problem in tunnels on erosive soil deposits
Authors: Hayashi S. , Shahu J. T.
Published: October 2009

High-speed train travel round the world has given rise to newer geotechnical problems that require ingenious solutions. In tunnels laid on erosive soil deposits, pore water pressure build up due to traffic loading and ensuing seepage flow loosens soil particles beneath the tunnel invert, and mud slurry is pumped out from invert weep holes with a passing train load. This causes loss of tunnel support, giving rise to uneven deformation of the concrete slab track that requires costly and difficult maintenance. From tests performed on a new model experimental set-up, it is observed that there is a limiting distance such that no mud pumping occurs if the distance of an open slit (simulating weep holes) from the point of application of cyclic loading is greater than this limiting value. Relocating the invert weep holes at a suitable elevation along tunnel walls with their intake firmly secured by a geotextile overlain by a thin sand layer, acting together as a filter, appears to be the most effective way of countering the mud pumping problem. Two full-scale model tests, one in a yard containing a tunnel invert made of Portland cement concrete and the other one in a yard containing a tunnel invert made of slag concrete, are carried out to investigate the proposed solution in the field.
A general framework for the mechanical behaviour of clays
Authors: Cotecchia F. , Chandler R. J.
Published: October 2009

It is suggested that the structure of clays may be distinguished simply as either ‘sedimentation’ or ‘post-sedimentation’, depending on whether gross yield in one-dimensional compression in void ratio-vertical effective stress plane occurs on the original sedimentation compression curve or to the right of this curve. A behavioural framework is proposed for clays having either of these structures, the magnitude of the strength sensitivity St when consolidated to the gross yield state (in compression) quantifying the effects of structure. The behaviour of natural clay consolidated to stress states pre-gross yield is related to the undisturbed clay sensitivity St; the gross yield curve is generally of arch shape, its size relative to that of the reconstituted clay depending on this sensitivity. Clays having St > 1 consolidated to stresses beyond gross yield exhibit post-gross yield behaviour in which values of sensitivity reduce with increasing post-yield strain. It is found that following normalization for composition (using the stress ratio at critical state M), volume (using p*e) and structure (using the sensitivity at gross yield St ), many different clays have the same gross yield curve. A basically frictional linear flow rule is found to operate from small or medium to large strains for both natural and reconstituted clays.