bluuebunny/crossref_metadata_2025 huggingface dataset:
Development and applications of a synthetic material to simulate soft sedimentary rocks
Authors: Indraratna B.
Published: October 2009

Due to the fact that a model material can be made homogeneous, the influence of different variables on behavioural mechanisms can be investigated independently. Consequently, large experimental scatter attributed to inherent variables (generally unknown) of a natural material can be avoided. This Paper presents the development of an artificial material which can effectively simulate the behaviour of an array of weak, sedimentary rocks. This synthetic soft rock was constituted with gypsum cement, fine sand and water, and characterized with homogeneous and isotropic properties with insignificant variability from one batch to another. It can be easily manufactured in the laboratory and can be cast either in large or small volumes to occupy any predetermined shape of given physical dimensions. An experimental application to study the behaviour of reinforced composites (simulated bolted rock) is also described in this Paper.

Puis qu'une matière-modèle peut être rendue homogène, il est possible d'étudier de façon indépendante l'influence exercée par de diverses variables sur les mécanismes de comportement. On peut par conséquent éviter la dispersion considérable expérimentale attribuée aux variabilités inhérentes, généralement inconnues, à une matière naturelle. L'article décrit le développement d'une matière artificielle qui peut simuler effectivement le comportement d'un groupe de roches tendres Sédimentaires. Cette rocbe tendre synthétique comprenait du ciment de gypse, du sable fin et de l'eau et possédait des propriétés homogènes et isotropes qui ne variaient que très peu d'un lot à l'autre. Cette matière peut se produire très facilement dans le laboratoire et être coulée dans de petits ou grands volumes pour prendre n'importe quelle forme prédeterminée de dimensions données. L'article présente aussi une application expérimentale pour étudier le comportement des matières composites renforcées (simulation de rocbes boulonnées).
The undrained behaviour of clayey sands in triaxial compression and extension
Authors: Georgiannou V. N. , Burland J. B. , Hight D. W.
Published: October 2009

The Paper describes an experimental investigation of the stress-strain behaviour of anisotropically consolidated clayey sands, carried out using instrumented and computer-controlled triaxial cells. The specimens were prepared by sedimenting Ham river sand into a kaolin suspension. For a given granular void ratio, as the clay content of the sedi-mented clayey sands increases from 4-6 to 10%, the undrained brittleness and strains to phase transformation also increase, when the specimens are sheared in compression. When sheared in extension, liquefaction takes place for clay contents up to 7-5%. Increases in granular void ratio give rise to increased brittleness and potential to liquefaction. The effects of overconsolidation on strength and stiffness characteristics have been examined. The effective stress paths for undrained shear of the normally consolidated soil form a boundary for the effective stress paths for the lightly overconsolidated soil.

L'article décrit une étude expérimentale, effectuée a l'aide de cellules triaxiales instrumentées et con-trôlées par des ordinateurs, du comportement de sables argileux consolidés de façon anisotrope. Les échantillons ont été préparés par sédimentation du sable fluviatile (Ham) dans une suspension de kaolin. Pour un indice des vides entre les grains d'une valeur donnée, à mesure que le contenu d'argile dans les sables argileux sédimentés s'accroît de 4,6 a 10% la fragilité non-drainée et la transformation des déformations en phases s'augmentent aussi lorsque les échantillons sont soumis au cisaillement sous compression. Dans le cas du cisaillement sous extension la liquéfaction a lieu pour des teneurs en argile jusqu'à 7,5%. Des augmentations de l'indice des vides entre les grains provoquent un accroissement de la fragilité et de la liquéfaction potentielle. Les effets de la sur-consolidation sur les caractérisques de résistance et de raideur ont été examines. Les chemins effectifs de contrainte pour le cisaillement non-drainé du sol normalement consolide constituent une limite pour les chemins effectifs de contrainte dans le sol lé-gèrement surconsolidé.
Use of the observational method in the remedial investigation and clean-up of contaminated land
Authors: Dean A. , Bravenik M.
Published: October 2009

The observational method of peck Has been accepted by the geotecbnical profession for over 20 years as a cost-effective approach for addressing the uncertainties associated with subsurface engin- eering. It offers an effective means of accounting for subsurface variability without extensive upfront study. The method is even more appropriate for the inherently more complex set of uncertainties associated with the investigation and clean-up of contaminated land. The Paper describes the method as applied to achieving cost-effective designs for remediating contaminated sites so that they can be developed to their greatest potential. A case history exemplifies its use and highlights its effectiveness. Recent impediments to using the method in the USA under the existing scope of environmental regulations for the clean-up of con- taminated sites are discussed.

Depuis plus de vingt ans la profession géotecbnique accepte la métbode d'observation de Peck comme maniére économique de réoudre les incertitudes de la construction souterraine. Cette métbode fournit un moyen efiicace pour tenir compte de l'hétérogtnéité souterraine sans avoir recours aux études en place. La mébode est encore plus satisfaisante pour les incertitudes essentiellement plus complexes liées à l'éude et au nettoyage de terrains contaminés. L'article décrit la métbode dans son application aux éoncepts kconomiques pour assainir les emplacements contaminés afin qu'ils puissent être développb au maximum. L'bistorique d'un cas illustre et souligne l'efflcacité de la métbode. Finalement, l'article discute des éhcecs récents dans l'emploi de la métbode aux Etats Unis réultant de la portée présente des réglements environnementaux relatifs au nettoyage des emplacements contaminés.
Coupled fluid, electrical and chemical flows in soil
Authors: Yeung A. T. , Mitchell J. K.
Published: October 2009

Renewed study of coupled flows in soils has been stimulated by the potential uses of electrokinetics for remedying waste sites. Most suggested uses involve the movements of fluid, electricity and contaminants in soil induced by the combined influence of hydraulic, electrical and chemical gradients imposed simultaneously. A general coupled flow theory describing these phenomena in soils under isothermal conditions is developed on the basis of the formalism of non-equilibrium thermodynamics to aid in the proper understanding and theoretical analysis of the physics involved in these complex transport processes. The results of experimental evaluation on the validity of the proposed theory applied to compacted clay are presented.

L'étude des écoulements couplés dans les sols a été simulée par l'utilisation potentielle de Pélectro-cinétique dans les sites de stockage de déchets. La plupart des scientifiques pensent qu'une telle utilisation implique des mouvements de fluide, d'éléments électriques et de contaminants des ces sols qui sont induits par une action combinée des gradients hydrauliques, électriques et chimiques imposés simultanément. L'article développe une théorie générale des écoulements couplés qui décrit ces phénomènes d'écoulement dans des sols sous conditions isothermes. Cette théorie est basée sur le formalisme de non-équilibre thermodynamique et permet une bonne compréhension, ainsi qu'une analyse théorique, de la physique mise en jeu dans ces processus complexes de transport. On présente les résultats, obtenus sur une argile compactée, permettant une évaluation expérimentale de la validité de la théorie proposée.
The mechanics of cemented carbonate sands
Authors: Coop M. R. , Atkinson J. H.
Published: October 2009

The behaviour of artificially cemented carbonate sand was investigated in triaxial tests at confining pressures of up to 9 MPa. The results show that an important effect of cementing is a reduction in specific volume resulting from the increase in fines content This influences both the stress-strain behaviour and the peak strength at strains beyond those required to fracture the cement bonding. Comparisons between the behaviour of cemented and uncemented soils should, therefore, be carried out on samples with the same gradings. For cemented samples it is possible to identify a yield curve outside the state boundary surface of the uncemented soil. A framework for the behaviour has been defined which depends on the relative magnitudes of the confining pressure and cement bond strength. The behaviour of a natural cal-carenite agreed well with this framework which is also likely to be applicable to other cemented soils.

Le comportement d'un sable carbonate artificiellement cimenté a été étudié à l'aide d'essais tri-axiaux à pression de confinement pouvant atteindre 9 MPa. Les résultats obtenus montrent que la cimentation se traduit par une diminution du volume spécifique due à une augmentation du nombre de particules fines. Ceci modifie le comportement contrainte-déformation ainsi que la résistance ultime pour des déformations supérieures à celles provoquant la rupture des liaisons du ciment. L'étude comparative du comportement de sols cimentés et de sols non-cimentés a donc dû être réalisée sur des échantillons de mâme granulo-métrie. Pour des échantillons cimentés, une courbe de rupture située en dehors de l'enveloppe limite d'un sol non-cimenté a été mise en évidence. Une classification de comportement a été élaborée en fonction des amplitudes relatives de la pression de confinement et de la résistance des liaisons du ciment. Le comportement d'une calcarénite naturelle est tout à fait en accord avec cette classification qui apparaît applicable à d'autres sols cimentés.
Hydraulic fracturing of soil during laboratory experiments Part 2. Propagation
Authors: Murdoch L. C.
Published: October 2009

The propagation of hydraulic fractures in soil was studied in the laboratory by glycerine injected at a constant rate into rectangular samples of silty clay confined in a triaxial cell. During propagation, the trace of a hydraulic fracture appeared on the side of the cell as a nearly straight, narrow line that tapered from 0-05 mm to negligible aperture at the tip. Pressure of the glycerine was recorded as a function of time and is characterized by a period of nearly linear increase, a break in slope followed by a period of increasing pressure but decreasing slope, a maximum, and then a period of decreasing pressure. Tests terminated early in that sequence of events indicated that the break in slope marks the onset of hydraulic fracturing. The pressure at the onset of fracturing was predicted from a determination of the fracture toughness of the silty clay. The forms of the pressure records were markedly affected by the water content of the soil: increasing water content decreased the pressure required to initiate a hydraulic fracture (and decreased fracture toughness) and flattened the pressure record during propagation.

La propagation de fractures hydrauliques dans un sol a été étudiée en laboratoire par injection de glycérine à vitesse constante dans des échantillons rectangulaires d'argile silteuse confinés dans une cellule triaxiale. Lors de la propagation, la trace laissée par la fracture hydraulique apparaît sur le côté de la cellule comme une ligne étroite presque droite variant de 0*05 mm à une ouverture presque négligeable aux extrémités. La pression de la glycérine a été enregistrée en fonction du temps et est caractérisée par une période d'accroissement presque linéaire, un changement de pente suivi d'une période d'accroissement de pression à pente décroissante, un maximum et une période de décroissance de la pression. Les essais terminés prématurément lors de cette séquence indiquent que le changement de pente marque le début de la fracturaron hydraulique. La pression à l'initiation de la fracturation est déduite de la résistance de la fracture dans une argile silteuse. La forme des courbes de pression dépend beaucoup de la teneur en eau du sol: une augmentation de teneur en eau entraîne une diminution de la pression nécessaire à l'initiation de la fracturation hydraulique (et diminue la résistance de la fracture). Elle aplanit également les courbes de pression lors de la propagation.
The landslide of Cortes de Pallas, Spain
Authors: Alonso E. E. , Gens A. , Lloret A.
Published: October 2009

A large landslide in Cretaceous limestone and marl formations, reactivated by quarry excavations, has been stabilized by weight-transfer procedures designed by using a conventional limit-equilibrium analysis. The analysis was based on strength parameters derived from a back-analysis of the conditions leading to instability. Slide reactivation, excavation and Ailing have also been modelled by a finite element analysis in which the sliding surface has been represented by elastoplastic joint elements. This has provided important information regarding the sliding mechanisms and the effects of the remedial measures. Shear strength parameters determined in the laboratory are compared with those obtained from back-analysis. A significant discrepancy was reconciled when it was found that the sliding surface was located in a very thin and continuous clay layer of uncertain origin; possible mechanisms explaining the presence of the clay layer are suggested. The case demonstrated the importance of knowing in detail the geometry of the sliding surface, proves the value of field instrumentation and shows the fundamental role that geological details play in landslide problems.

Un grand glissement de terrain, affectant des formations crétacées marno-calcaires et réactivé par des excavations de carrière, a été stabilisé à l'aide d'un procédé de transfert de mass conçu à partir d'une analyse conventionnelle d'équilibre-limite. Cette analyse est fondée sur des paramètres de résistance eux-même issus d'une rétro-analyse des conditions d'instabilité. La réactivation du glissement, l'excavation et le remblai ont également été modélisés à l'aide d'une analyse par éléments finis, dans laquelle la surface de glissement a été représentée par des éléments jointifs élasto-plastiques. D'importantes informations ont été obtenues sur les mécanismes du glissement et sur les effets des mesures curatives. Les paramètres de résistance au cisaillement mesurés au laboratoire ont été comparés à ceux calculés à partir de la rétro-analyse. La dispersion, initialement importante, est réduite pour une surface de glissement située dans une couche d'argile très fine et continue, d'origine incertaine. Des mécanismes permettant d'expliquer la présence de la couche argileuse sont proposés. Ce cas-type démontre l'importance d'une parfaite connaissance de la géométrie de la surface de glissement, témoigne de la validité de l'instrumentation in-situ et montre le rôle fondamental joué par les détails géologiques dans les problèmes de glissements de terrain.
Geotechnical behaviour of saline sabkha soils
Authors: Abduljauwad S.N. , Al-Amoudi O.S.B.
Published: October 2009

The behaviour of salt-cemented sabkha soil was investigated by considering the effect of brine and distilled water on its properties. Laboratory and field testing programmes were conducted to examine the effect of soaking and leaching on the structure, compressibility, collapse, permeability, load-carrying capacity and settlement of sabkha soil. Results indicate that the percolation of distilled water through the sabkha causes destruction of the natural cementation, leading to collapse, increase in permeability, reduction in strength and increase in settlement. Dissolution and leaching of halite, gypsiferous and calcarenite cements occur, leaving the quartz particles covered by a thin loose mat of illitic clay with large voids. The collapse deformation of sabkha is inclusively linked to the ambient salt complex, which determines the structural properties of the soil and promotes the development of collapse on wetting. The soaking of sabkha produces practically negligible collapse; leaching causes a significant collapse due to the softening, dissolution and effusion of salts from the soil skeleton.

Le comportement d'un sol de Sabkha cimenté par du set a été étudié au travers de l'effet de la circulation d'une saumure ou d'une eau distillée sur ses propriétés. Des programmes d'essais réalisés en laboratoire et in-situ ont permis d'examiner l'influence d'une immersion et d'un lessivage sur la texture, l'effondrement dû à la compressibilité des minéraux, la perméabilité, la charge admissible et le tassement du sol. Les résultats montrent qu'une percolation d'eau distillée dans la Sabkha induit une destruction de la cimentation naturelle qui se traduit par un effondrement du sol, une augmentation de la perméabilité, une diminution de la résistance et un accroissement du tassement. La dissolution et le lessivage des minéraux halitiques, gypseux et calcaires constitutifs du ciment font que les particules de quartz ne sont plus recouvertes que par une couche d'illites mince, peu dense et a larges vides. La déformation par effondrement de la Sabkha est à relier au complexe salin présent qui, parce qu'il régit les propriétés texturales du sol, favorise le développement d'effondrements lors de l'humidification. Si l'effondrement résultant d'une immersion est quasiment négligeable, it ne l'est plus lors d'un lessivage et devient même important en raison du ramollissement, de la dissolution et de l'effusion des sels du squelette solide.
The depth of influnce of loaded areas
Authors: Charles J. A.
Published: October 2009

The depth of influence of a foundation load has to be evaluated so that the settlement which will be caused by the loading can be calculated. It also needs to be assessed for the design of schemes of ground improvement by preloading with a surcharge of fill. It is usually assumed that the variation of vertical stress with depth below a loaded area can be predicted with sufficient accuracy using linear, homogeneous, isotropic elastic theory. However, although such theory adequately predicts the depth of influence of typical foundation loads it overpredicts the depth of influence of more extensive surcharge loads. A simplified model of soil behaviour, based on the Marston analysis of stress conditions in trenches, has been used to investigate the effect of an increase in shear strength with increase in effective stress on the depth of influence of a surface loaded area. Although the effect is not significant for typical relatively small foundation loads, it is likely to be significant for much more extensive surcharge loads. Comparisons with the monitored depths of influence of surcharges on uncompacted fills confirm the behaviour predicted by the nalysis.

La profondeur d'influence due à la mise en charge d'une fondation doit être évaluée afin de calculer le tassement résultant de ce chargement et d’élaborer des programmes permettant de tester le sol par préchargement à I'aide de remblais. Généralement on suppose qu'en des-sous d'une zone chargée, la variation de la contrainte verticale avec la profondeur pent être calculée avec suffisamment de précision en appliquant une théorie isotrope, homogène et linéaire. Cependant, même si de telles théories donnent une bonne estimation de la profondeur d'influence générée par des chargements typiques, elles tendent à surestimer celle occasionnée par des charges plus importantes. Un modèle simplifié de comportement, fondé sur une analyse de Marston des conditions de contraintes règnant dans une tranchée, a été utilisé afin d'étudier Pinfluence d'un accroissement de la résistance au cisaillement, dû à une augmentation de la contrainte effective, sur la profondeur d'influence dune surface chargée. Bien que les résultats ne soient pas très significatifs pour une charge typique relativement faible, ils le deviennent pour des charges beaucoup plus importantes. Les essais de mesure de profondeurs d'influence, réalisés sur des remblais non compactés et mis en charge, confirment les comportements prévus par L'analyse.
Dimensional analysis for geotechnical engineers
Authors: Butterfield R.
Published: October 2009

Dimensional analysis is an important tool for engineers, aiding the design of experiments and concise expression of the results generated by them. The dimensionless groups, which are the output of a successful dimensional analysis, are usually developed via Buckingham's ‘Pi’ theorem. Because this alone is a necessary, but not sufficient, condition for a solution, difficulties are frequently encountered. This paper presents a general, dimensional analysis algorithm which imposes both necessary and sufficient conditions. Illustrative problems are included, together with a Mathematica program which generates all possible sets of admissible dimensionless groups for a specific problem.

L'analyse dimensionnelle est un outil important pour les ingénieurs car elle les aide à concevoir des expériences et à exprimer de manière concise les résultats qui en découlent. Les groups non dénommés, qui sont le résultat d'une analyse dimensionnelle réussie, sont normalement développés au moyen du théorème ‘pi’ de Buckingham. Comme ce théorème seul est une condition nécessaire mais pas suffisante pour amener à la solution, des difficultés surviennent souvent. Cet exposé présente un algorithme général d'analyse dimensionnelle imposant des conditions nécessaires et suffisantes. Pour illustrer, nous joignons des problèmes avec un programme Mathematica qui produit tous les ensembles de groupes non dénommés admissibles pour un problème spécifique.
Explosive compaction: design, implementation and effectiveness
Authors: Gohl W. B. , Jefferies M. G. , Howies J. A. , Diggle D.
Published: October 2009

Although used for over 70 years, Explosive Compaction (EC) has not attained widespread acceptance despite the attraction of low cost and ease of treating large depths. Lack of familiarity with the method, and an empirical design approach unrelated to theory, appear the primary cause for reticence in adopting EC. To alleviate these concerns, practical design considerations for EC based on detailed experience from nine applications and trials are presented here to illustrate the predictable and repeatable effectiveness of EC. Design is based on cavity expansion theory. EC readily gives volume changes 2–3 times larger than might occur under large earthquake motions, with final average relative densities often greater than 70%. Further, environmental and vibration control issues do not constrain the use of EC provided that appropriate explosives and delayed detonation sequences are used. As pronounced post-blast time effects are evident in penetration testing, evaluation of the effectiveness of EC should be based on a combination of pre- and post-blast penetration testing and volume change measurements.
Evaluation of axial shear test using plane strain simulations
Authors: Molenkamp F.
Published: October 2009

The topic of soil anisotropy is still rather unfamiliar to the majority of geotechnical engineers. To clarify the effects that anisotropy can have on the response of soil specimens under plane unconfined vertical compression, the response of a simple anisotropic elastic specimen with inclined bedding plane and rough end platens is investigated numerically. In these simulations various lower platen boundary conditions, including axial shear control are applied. The results demonstrate that the response of the specimen depends on both the anisotropy of the material and the applied boundary conditions. For axial shear control the stress is shown to be homogeneous and coaxial with the sheared shape of the specimen in the central part. Also, the potential capabilities and limitations of axial shear control are investigated in an abstract way, giving support to the expectations of a novel elegant practical tool that could form the vital link in a chain of measures facilitating the incorporation of soil anisotropy in geotechnical engineering practice.
A model for rockfill compressibility
Authors: Oldecop L. A. , Alonso E. E.
Published: October 2009

The paper presents a macroscopic constitutive model for rockfill that includes the effect of water on compressibility and collapse phenomena. Breakage of rock particles and fracture propagation are basic underlying mechanisms controlled by the relative humidity of the air filling the rockfill voids. A conceptual deformation model based on these mechanisms is first proposed and discussed. The results of oedometer tests on a quartzitic slate rockfill, in which the air relative humidity was controlled, are then presented. A significant finding is that bringing the relative humidity within the specimen to its maximum (100% RH) leads to a collapse strain equal to that observed in flooded specimens. An elastoplastic constitutive model, consistent with the basic deformation framework, is developed. Its parameters have a clear physical meaning. Guidelines for parameter determination are given. Model performance is finally compared with the results of the experimental programme.
Undrained cavity expansion in modified Cam clay II: Application to the interpretation of the piezocone test
Authors: Chang M. F. , Teh C. I. , Cao L. F.
Published: October 2009

This paper presents an interpretation of the piezocone test in clay based on a simplified theoretical solution of cavity expansion in modified Cam clay. The cone resistance and the pore pressures measured on the cone tip and just behind the cone tip are interpreted using the framework of cavity expansion theories with due consideration of the effect of strain rate and the initial stress state. Methods for estimating the overconsolidation ratio, the undrained shear strength and the rigidity index of clay are proposed. A comparison of results obtained from the proposed methods with published data and limited field data collected in the Singapore marine clay indicates the validity of the proposed analysis methods.
Bearing capacity of spatially random soil: the undrained clay Prandtl problem revisited
Authors: Griffiths D. V. , Fenton G. A.
Published: October 2009

By merging elasto-plastic finite element analysis with random field theory, an investigation has been performed into the bearing capacity of undrained clays with spatially varying shear strength. The object of the investigation is to determine the extent to which variance and spatial correlation of the soil's undrained shear strength impact on the statistics of the bearing capacity. Throughout this study, bearing capacity results are expressed in terms of the bearing capacity factor, Nc, in relation to the mean undrained strength. For low coefficients of variation of shear strength, the expected value of the bearing capacity factor tends to the Prandtl solution of Nc = 5·14. For higher values of the coefficient of variation, however, the expected value of the bearing capacity factor falls quite steeply. The spatial correlation length is also shown to be an important parameter that cannot be ignored. The results of Monte Carlo simulations on this non-linear problem are presented in the form of histograms, which enable the interpretation to be expressed in a probabilistic context. Results obtained in this study help to explain the well-known requirement that bearing capacity calculations require relatively high factors of safety compared with other branches of geotechnical design.
Deformation of landfill from measurements of shear wave velocity and damping
Authors: Abbiss C. P.
Published: October 2009

A method is developed for finding the non-linear deformation properties of a material from its shear wave velocity and damping. A way of calculating a parameter called the characteristic strain that defines a non-linear term in the equation for strain as a function of stress is given. It is shown that this parameter may be found from a measurement of damping at known strain. The method is tested on a highly deformable landfill. Initially two loaded skip tests were carried out to measure the deformation of the landfill. Shear wave velocities were obtained by a surface wave technique and seismic refraction to find the low-strain elastic properties. Damping and the corresponding strain were then found from an impact on the surface of the material. An analysis of the stress–strain behaviour, in terms of a quadratic function of strain, leads to an expression for the damping as a function of strain that depends upon the characteristic strain. Thus this parameter can be obtained from the damping and strain measurement. The immediate settlement in the fill, under the skips, was calculated from these measured properties using a non-linear finite element program. Close agreement with observation was obtained when a scaling factor was used to take stiffness anisotropy into account.
Macro–micro measurement of particle arrangement in sheared kaolinitic matrices
Authors: Dudoignon P. , Pantet A. , Carrara L. , Velde B.
Published: October 2009

Two series of shear tests on normally consolidated drained and over-consolidated drained kaolinitic test specimens were performed in a triaxial cell coupled with petrographic investigations. The axial deformation, the volumetric deformation and the void ratio changes were measured during each shear test in order to represent the macroscopic behaviour of the material in the Cam Clay diagram. The macroscopic-to-microscopic relation was treated through microscopical analysis of thin sections under polarised light coupled with image analysis and grey-level diagram analysis in particular. The image analysis quantifies the percentage increase of the parallel orientated particles from the sub-isotropic matrix of the initial consolidated sample to the quite anisotropic matrix of the normally consolidated sheared samples. The SEM observations indicate particle movements that allow the measurement of the void ratio differences between the matrix and the shear planes by microprobe analysis.
Upper-bound load estimates on square and rectangular footings
Authors: Michalowski R. L.
Published: October 2009

Limit analysis of square and rectangular rough footings is presented in this paper. All mechanisms of failure considered in the analysis consist of four regions, each characterised by plane deformation. However, the geometry of the mechanisms is three-dimensional. Both continuous deformation and multi-block patterns are considered. A common feature in all mechanisms is truncation of the blocks with conical surfaces. Standard calculations of the work dissipation rate are complex because of the elaborate three-dimensional geometry. However, a theoretical development is shown indicating that the tedious calculations of work dissipation on curved velocity discontinuity surfaces and within the deforming regions of cohesive-frictional soils can be substituted with an integral over the surface of the mechanism. While this method cannot be used easily for soils with an arbitrary distribution of properties, its application is straightforward for homogeneous soils, and it can also be used for layered soils. Calculations of bearing capacity are performed for both square and rectangular footings. It was surprising to find that the least upper-bound estimates of loads on square footings occur for mechanisms with no symmetry with respect to diagonal planes. The results are given in terms of the bearing capacity coefficients, and shape factors applicable as modifiers in the bearing capacity solution for strip footings. As expected, these factors approach unity with an increase in the footing aspect ratio L/B. The factors calculated are typically larger than earlier empirical proposals in the literature.
Simulation of triaxial and true triaxial tests on natural and reconstituted Pisa clay
Authors: Callisto L. , Gajo A. , Muir Wood D.
Published: October 2009

A kinematic hardening/bounding surface plasticity model is used to reproduce the experimental behaviour of the natural soft clay found at Pisa. The model accounts for progressive loss of structure with plastic strains, and can be made to degenerate into a structureless state. Model parameters are calibrated on drained triaxial probing tests on natural Pisa clay, and are subsequently used for predicting behaviour of the soil in one-dimensional loading, in triaxial undrained deformation and under true triaxial shearing. Model predictions for the destructured clay are compared with experimental results from triaxial tests on reconstituted Pisa clay. Comparison with experimental results provides information on the quality of the proposed modelling approach.
Two large-scale injection experiments, and assessment of the advection–dispersion–filtration model
Authors: Bouchelaghem F.
Published: October 2009

An assessment is presented of the validity of a theoretical model for miscible grout injection in a deformable porous medium. The mathematical formulation couples analysis of the fluid flow and the grout mass transport with a study of the solid skeleton's displacements and the porous medium stucture evolution. In particular, hydromechanical coupling, grout dispersion and filtration were considered in order to produce a realistic model of injection within a saturated deformable soil. The results of the theoretical formulation were compared with those obtained from two original large-scale injection tests performed in the laboratory. Controlled laboratory tests permitted study of the basic characteristics of fluid flow and grout propagation for a micro-cement grout, and an examination of the performance of the complete injection model was made possible. A numerical solution of the formulation was performed using the finite element method, and good agreement was obtained between the experimental and numerical results. The measured pore fluid pressures, soil displacements, grout front positions, porosities and hardened bulb dimensions were compared with their numerical counterparts. While the first large-scale injection experiment confirmed the fundamental assumptions made during writing of the model, the second injection test offered a complete phenomenological validation procedure, thus illustrating the capacity of the model to reproduce the behaviour of the porous medium during the injection, for a situation similar to a real injection operation.
Uplift resistance of buried submarine pipelines: comparison between centrifuge modelling and full-scale tests
Authors: Palmer A. C. , White D. J. , Baumgard A. J. , Bolton M. D. , Barefoot A. J. , Finch M. , Powell T. , Faranski A. S. , Baldry J. A. S.
Published: October 2009

A buried pipeline can buckle upwards if there is not enough resistance to movement. Both the uplift resistance (the maximum force per unit length) and the mobilisaion distance (the distance the pipeline has move before the maximum force is reached) are important in design. Tests on pipes in several soils were carried out at 1 g at full scale and in a centrifuge at 10 g and 1/10 scale. A comparison shows that the measured uplift resistances are consistent with the conventional understanding of centrifuge tests, but that the measured mobilisation distances are not consistent with that understanding. Unscaled mobilisation distance in the centrifuge is roughly the same as at full scale. Mobilisation distance does not scale with particle size. This discrepancy is related to the formation of shear zones, and to theory and observations in other areas of the mechanics of brittle materials, among them ice, concrete and heavily overconsolidated clays. An idealised analytical model displays the same behaviour.
The mechanical behaviour of a reconstituted unsaturated silty clay
Authors: Cunningham M. R. , Ridley A. M. , Dineen K. , Burland J. B.
Published: October 2009

This paper describes a novel method of controlling suction by means of air circulation in combination with independent suction measurement. The technique has been incorporated in a standard triaxial stress path cell, and could easily be incorporated in other standard apparatus such as the direct shear box and oedometer. The application of the technique is demonstrated by means of an exploratory testing programme in which samples of a reconstituted saturated clayey silt were progressively dried to various predetermined suctions, which were then maintained constant during isotropic compression followed by shearing to failure. In this way the drying and stress history of the soil was carefully controlled in a way that could be made representative of the genesis of natural unsaturated soils. Though exploratory, the experimental investigation described in this paper has provided some interesting and thought-provoking results. Prior to desaturation the clayey silt behaves in accordance with the classical critical-state framework, even under suctions as high as 400 kPa. Once desaturation occurs, important changes in behaviour take place. In particular, the behaviour changes from being ductile to very brittle in a way that is difficult to account for within the critical-state framework. The new technique provides a ready means of carrying out detailed studies of the influence of various combinations of changes in suction and applied stress on a wide range of soil types and in a variety of apparatus.
Water infiltration into a large-scale in-situ experiment in an underground research laboratory
Authors: Thomas H. R. , Cleall P. J. , Chandler N. , Dixon D. , Mitchell H. P.
Published: October 2009

This paper describes the re-saturation behaviour of a large-scale in-situ experiment carried out at Atomic Energy of Canada's (AECL) underground research laboratory. The experiment, known as the isothermal test, examines water inflow, from the surrounding rock, into highly compacted, unsaturated buffer material. Comparisons of physical measurements and a finite element numerical simulation are presented of water uptake and distribution during the 7-year life of the test. The numerical simulations were performed using an approach developed to model the thermo/hydraulic/mechanical behaviour of the system. A comprehensive data set of the physical behaviour was available from AECL. The simulation of the experiment, using a ‘conventional’ hydraulic conductivity variation, revealed that neither the duration nor the pattern of moisture influx could be modelled accurately. Further study suggested that the expansion of the microstructure of the bentonite, as the material saturated, would tend to reduce the void spaces in the macrostructure, as the material, overall, was constrained from swelling. This in turn was likely to reduce the material's hydraulic conductivity. Incorporation of these ideas within the approach yielded significant results. Both the pattern and the rate of water uptake were now modelled with much greater accuracy. The approach adopted is different from the ‘conventional’ method, in the sense that the material's ‘effective’ hydraulic conductivity decreases as moisture content increases, as opposed to increasing, as is the ‘normal’ case. The repercussions may be significant in terms of total time for re-saturation of the buffer. The process is significantly delayed as a result of this phenomenon. Also, the pattern of moisture distribution during water influx is quite different. These general conclusions, in turn, may be significant when considering the overall performance of a disposal repository, as the total time for re-saturation would be increased. This in turn may be of interest in performance assessment considerations.
Stress and pore pressure changes due to sand compaction pile installation in soft clay
Authors: Lee F. H. , Juneja A. , Tan T. S.
Published: October 2009

This paper presents centrifuge model data and describes a semi-empirical approach to predict short-term total radial stress and pore pressure changes around sand compaction piles installed in soft marine clays. Comparison of the measured changes in radial stress and pore pressure with plane strain cavity expansion theory shows that the latter gives a reasonably good estimate at large depth for the entire installation process and for the peak stress measured during casing jack-in, but not for the residual stress after casing jack-in. However, deviation from plane strain cavity expansion theory was noted at shallow depths. To account for the effect of the ground surface, a plane stress cavity expansion theory was proposed for the shallow zones, which assumes constant vertical overburden stress. The establishment of the two limits formed by the plane strain and plane stress theories allows semi-empirical relations to be established by fitting to the data. These semi-empirical relations allow the post-installation and peak jack-in stress and pore pressure to be reasonably estimated. However, postjack-in values remain significantly overestimated. These findings imply that, in order to mobilise significant set-up of stress in the improved ground, there must be substantial further cavity expansion during the sand injection stage of SCP. Cumulative total stress increment at a given location due to the installation of multiple piles in a grid may be reasonably estimated by superimposing the increments due to the installation of each pile. On the other hand, pore pressure build-up is shown to be less readily superimposed, possibly because the shear-induced component of excess pore pressure does not increase linearly and infinitely with deviator stress.
Particle breakage during shearing of a carbonate sand
Authors: Coop M. R. , Sorensen K. K. , Bodas Freitas T. , Georgoutsos G.
Published: October 2009

A series of ring shear tests was conducted to investigate the development of particle breakage with shear strain for a carbonate sand. It was found that at very large displacements the soil reached a stable grading, but that the final grading was dependent on both the applied normal stress and the initial grading. The particle breakage caused a volumetric compression, which again ceased only when the stable grading had been attained, emphasising that critical states as observed at much smaller strains in triaxial tests are not rigorously defined. Despite the severe degradation of the soil particles the mobilised angle of shearing resistance was found not to change significantly.
A shear strength model for idealised infilled joints under constant normal stiffness
Authors: Indraratna B. , Welideniya H. S. , Brown E. T.
Published: October 2009

Infill materials found in natural rock joints may cause a reduction in joint shear strength, influencing rock mass stability. This paper reports a study aimed at developing a semi-empirical methodology for predicting the shear strength of infilled joints, taking into account joint surface characteristics and the properties of the joint and infill materials. A new model for predicting the shear strength of infilled joints is presented, on the basis of a series of tests carried out on two types of model joint surface having asperity angles of 9·5° and 18·5°, with graphite and bentonite used as infill materials. All tests were carried out in a large-scale shear apparatus under constant normal stiffness (CNS) conditions. The results indicate that at low infill thickness to asperity height ratio (t/a), the combined effect of the basic friction angle (ϕb) and the joint asperity angle (i) is pronounced, but it diminishes with increasing t/a ratio so that the shear strength converges towards that of the infill alone. Summation of two algebraic functions (A and B) that represent the joint and infill characteristics correctly models the decay of normalised shear strength with increasing t/a ratio. The new model successfully describes the observed shear strengths of the graphite and clay (bentonite) filled model joints.
Computer experiments on environmentally induced stresses in unreinforced concrete pavement slabs
Authors: Illston J. M. , Tajirian A.
Published: October 2009

Synopsis

The paper is concerned with the computation of deflections and stresses in an unreinforced concrete pavement slab subjected only to the effects of tempera–ture and humidity. The basis of the computer simula–tion is presented in three stages: (a)the histories of material properties and environmental variables; (b)the computation of the distributions of imposed ther–mal and shrinkage strains through the depth of the slab, using finite difference techniques; (c) the compu–tation of the lift–off of the slab and the consequent stresses, using finite element techniques. It is shown that by far the largest tensile stresses are induced ifthere is external restraint of the longitudinal movement of the slab. Stresses significant enough to threaten tensile fail–ure of the concrete can also occur (in the absence of restraint) as a result of the early effects associated with the heat of hydration of the cement, and under the influence of the long–term shrinkage. Computer exper–iments are reported in which the injhences of a number of variables are examined, including those for slab dimensions, climatic changes and the curing of the concrete.
Recoverable and irrecoverable deformation of heat-cured cement paste
Authors: Parrott L. J.
Published: October 2009

Synopsis

Heat curing at temperatures up to 65°C reduced the creep and shrinkage of ordinary Portland cement pastes having a water/cement ratio of 0·47. Strain measured after unloading and after rewetting indicated that the reductions were primarily associated with the irrecoverable components of creep and shrinkage. The reductions did not correlate with differences between the combined water content or the capillary porosity of the cement pastes, but they were associated with differences in the extent of silicate polymerization within the cement hydrate. Elastic strains, creep-recovery strains and cube strengths of the cement pastes were not noticeably affected by the extent of silicate polymerization.
The effect of variations in the aggregate content of concrete columns upon the estimation of strength by the pulse-velocity method
Authors: Davis S. G.
Published: October 2009

Synopsis

The results are reported of a series of tests planned to place quantitative limits upon the accuracy of the ultrasonic-pulse-velocity method, when it is used to assess the variations in strength through the height of a lift of concrete. Changes in the mix proportions of the concrete resulting from the placing process have been monitored, and the effect of such changes upon the correlation between strength and pulse velocity has been investigated. The results suggest that, for a typical structural concrete mix, the error in the estimation of the variability of strength is likely to be in the range from 4·5 to 9%.
Effects of embedded steel bars upon ultrasonic testing of concrete
Authors: Chung H. W.
Published: October 2009

Synopsis

Ultrasonic testing of a reinforced concrete member by means of the Pundit apparatus is affected by the steel bars embedded in the concrete. An investigation of the effects of the reinforcement has been made, using the bar diameter and the concrete strength as the variables. It is found that the steel bar appears to act compositely with the surrounding concrete in transmitting ultrasonic pulses. The effective pulse velocity is somewhat between the pulse velocities in the two separate media, and varies with the diameter of the bar and the pulse velocity in the concrete. An empirical formula for the effective pulse velocity is proposed. On the basis of this formula and further theoretical consideration, the zone of steel influence is defined. A correction factor is derived whereby the measured pulse velocity in a concrete–steel medium is adjusted to give the pulse velocity in the plain concrete.