bluuebunny/crossref_metadata_2025 huggingface dataset:
Design of driven piles in sand
Authors: Randolph M. F. , Dolwin R. , Beck R.
Published: October 2009

Estimation of the axial capacity of piles driven into sand involves considerable uncertainty, and design rules are generally not consistent with the physical processes involved. This Paper reviews current understanding of the factors that determine the axial capacity of piles driven into sand, and outlines a new framework for design which takes account of the physical processes, is consistent with the existing database of load test results, and is sufficiently flexible to permit refinement as new data become available. It allows for the effects of confining stress on the frictional and compressibility characteristics of sand, and hence on end-bearing capacity. In keeping with field observations, shaft friction is assumed to degrade with driving of the pile past a particular location, from an initial maximum value linked to the local end-bearing capacity. The resulting design approach is compared with field data, and effects of factors such as the direction of loading are discussed.

L'estimation de la résistance axiale de pieux battus dans du sable présente une grande incertitude et les lois de conception ne sont généralement pas en accord avec les processus physiques impliqués. L'article passe en revue les connaissances usuelles permettant de déterminer la résistance axiale de pieux battus dans du sable et présente une nouvelle méthode de conception qui intègre les processus physiques, est en accord avec les bases de données d'essais de chargement disponibles et est suffisamment flexible pour permettre leur mise à jour lorsque de nouvelles données sont disponibles. Elle tient également compte de l'influence de la contrainte de confinement sur les caractéristiques de frottement et de compressibilité du sable et donc sur la résistance à la pointe. Lorsque le pieu dépasse au cours du battage une position particulière, le frottement latéral est supposé, pour rester en accord avec les observations in-situ, diminuer depuis une valeur maximale initiale fonction de la résistance à la pointe locale. Les résultats obtenus à l'aide de cette approche sont comparés aux données in-situ et l'influence de certains facteurs, tels que la direction de chargement ou la vitesse de déplacement du pieu, est étudiée.
Experiments on piping in sandy gravels
Authors: Skempton A. W. , Brogan J. M.
Published: October 2009

Tests on internally unstable sandy gravels show that a significant proportion of the sand content is washed out by piping at hydraulic gradients far lower than the critical gradient given by a classical theory. The probable explanation is that a major part of the overburden load is carried on a framework of gravel particles, leaving the sand under relatively small pressures. By contrast, piping of the sand from stable sandy gravels occurs at approximately the full theoretical gradient. The tests broadly confirm Kenney's criterion for the internal stability of granular materials.

Des essais réalisés sur des graves sableuses à instabilité interne importante montrent qu'une proportion non négligeable du sable est lessivée pour des gradients hydrauliques bien inférieurs au gradient critique donné par les théories classiques. L'explication la plus probable est que la majeure partie de la surcharge des couches subjacentes est transmise au réseau des particules graveleuses, le sable n'étant alors plus soumis qu'à de relativement faibles pressions. Au contraire, l'aspiration du sable dans des graves sableuses stables se produit approximativement au gradient théorique. Dans l'ensemble, ces essais confirment le critère de Kenney sur la stabilité interne des matériaux granulaires.
Application of the observational method to hydraulic fill reclamation projects
Authors: Choa V.
Published: October 2009

This Paper describes the reclamation works at Changi Airport, Singapore, and the associated soil improvement works. Further reclamation work being carried out for future expansion of the airport is also described. Over 2000 ha is being reclaimed using about 200 x 106 m3 of sand. The observational method has been applied to control the execution of the projects. Soil instrumentation has been used to control staged construction of the hydraulic fill, the coastal protection works and soil improvement of the vertical drains. Monitoring systems and site procedures to enact contingency plans are discussed. A trial using dredged clay as a reclamation material is described and the Tianjin Port East Pier project in China is used to illustrate the observational method for the construction of a retaining structure founded on soil improved by deep cement mixing. The Paper also discusses the vacuum preloading method used in combination with vertical drains to improve the hydraulically placed silty clay reclamation in Tianjin

L'article présente les travaux d'amélioration des sols et les essais associés réalisés actuellement sur l'aéroport de Changi, Singapour. Il décrit également les travaux qui devront être menés pour une extension future de l'aéroport. Plus de 2000 ha ont été traités à l'aide d'environ 200.106 m3 de sable. Des méthodes d'observation ont été mises en oeuvre pour suivre l'exécution des projets. L'instrumentation du sol a permis à la fois de contrôler les différentes étapes de la mise en place du remblai hydraulique et des travaux de protection côtière, et de tester le drainage vertical du sol. On s'intéresse également aux systèmes d'enregistrement et aux procédures in-situ de déclenchement des plans d'urgence. Un essai utilisant de l'argile de dragage comme matériau de traitement est décrit. Le projet du port East Pier de Tianjin, Chine, permet d'illustrer les méthodes de suivi utilisées lors de la construction d'un ouvrage de soute nement fondé sur un sol injecté par un mélange de ciments. L'article décrit également la méthode de préchargement par vide utilisée en complément des drains verticaux pour étudier le comportement de l'argile silteuse, mise en place hydrauliquement, utilisée à Tianjin comme matériau de traitement.
Knowledge-based systems in geotechnical engineering
Authors: Moula M. , Toll D.G. , Vaptimas N.
Published: October 2009

The Paper reviews knowledge-based systems which have been developed for geotechnical applications and the geotechnical aspects of the systems are described. Systems have been developed for, among other topics, site characterization, foundations, earth-retaining structures, slope stability, tunnels, groundwater problems and ground improvement. An assessment has been made of the stage of the development of each system (where possible) and also the source of the knowledge incorporated in the systems.

L'article passe en revue les différents systèmes empiriques qui ont été développés en vue d'applications géotechniques et décrit les aspects géotechniques de ces systémes. De nombreux sujets sont concernés, par exemple: la caractérisation des sites, les fondations, les souténements, la stabilité des pentes, les tunnels, les eaux souterraines et l'amélioration des sols. Une estimation a été réalisée, dans la mesure du possible, du développement de chacun des systémes ainsi que de son origine.
Geotechnical materials and the critical state
Authors: Novello E.A. , Johnston L.W.
Published: October 2009

Comparison is made between the triaxial compres-sion behaviour of soil, soft rock and hard rock. On the basis of the evidence, it is argued that the brittle and ductile fields of rock behaviour can be interpreted with reference to the critical state framework originally developed for soils. Within this framework, the brittle—ductile transition in rock is the equivalent to the change in overconsolidated to normally consolidated behaviour found in soils. The critical states for soils and soft rocks represent the frictional plasticity of porous materials, whereas the equivalent critical state for hard rocks is heavily influenced by the cohesive plasticity present in mineral solids. A view of geotechnical materials emerges to emphasize the simiarity of soil and rock behaviour. This suggests that the critical state concept has application to all geotechnical materials.

L'article établit une comparaison entre le comportement en compression triaxiale d'un sol, d'une roche tendre et d'une roche duve. Au vu des résul;tats, it semble que le comportement d'une roche dans le domaine ductile et dans le domaine fragile peut s'interpréter en faisant reférence aux modéles à l'état critique développés a l'origine uniquement pour les sols. Dans ces modéles, la transition ductilefragile des roches devient équivalente a la transition surconsolidénormalement consolidé des sols. L'état critique d'un sol ou d'une roche tendre peut étre assimilé à la plasticité de frottement des matériaux poreux alors que l'état critique d'une roche duve dépend fortement de la plasticité de cohésion des minéraux. L'étude de difrerents materiaux géotechniques apporte confirmation de la similitude de comportement existant entre un sol et une roche. Ceci laisse à supposer que le concept d'état critique peut s'appliquer é tous les matériaux géotechniques.
Interpretation of a footing load test on a saprolitic soil from granite
Authors: Da Fonseca A. Viana , Fernandes M. Matos , Cardoso A. Silva
Published: October 2009

In the north-western region of Portugal residual soils from granite are dominant. Their porous cemented structure leads to a complex geotechnical behaviour, quite distinct from that of transported soils with a similar grain size distribution. The paper describes some of the studies carried out at an experimental site on which a fairly homogeneous saprolitic soil 6m thick was encountered. These studies included: (i) a full-scale load test of a circular concrete footing (1·20m diameter), under carefully controlled conditions and with extensive monitoring; (ii) in situ testing techniques (SPT, CPT, SBPT, CH) and (iii) laboratory testing on high-quality block samples, including triaxial tests with local strain measurement. The discussion is concentrated on the interpretation of the pressure—settlement curve from the footing load test, for a range of pressures typical of working conditions, by means of linear and non-linear elastic analyses based on stiffnesses from the laboratory and in situ tests. Some practical conclusions are extracted regarding the use of in situ and laboratory test results in analytical and empirical or semi-empirical methods for settlement estimation on these residual soils.

Les sols résiduels du granit dominent le littoral de la région nord du Portugal. Les fabrique et structure de ces sols et particullièrement leur matrice cémentée et poreuse conduissent à des comportements géotechniques complexes, trés diff6rents des sols transportés avec granulomé trie similaire. Varticle décrit une partie des études réalisé sur un terrain expérimental où apparaissent des niveaux superficiels typiques des sols saprolitiques du granit de la région. Les études réalis6s comprennent: (i) un essai de charge d'une semelle circulaire de béton armé (avec 1·20 m de diamètre), soigneuse et extensivement instrumentée; (ii) diverses essais in situ (SPT, CPT, SBPT, CH); (iii) essais en laboratoire sur des échantillons de haute qualité retirés des blocks taillés en pmts, comprennant des essais triaxiaux avec instrumentation interne des déformations. La discussion est concentrée dans l'interpr6tation de la courbe de chargement-tassement obtenu de Pessai de charge de la semelle en utilisant des résultats des essais in situ et en laboratoire, considérant les niveaux de charge typiques des conditions de service. On extrait des conclusions sur ľapplication des résultats des essais in situ et en laboratoire aux méthodes empiriques et semi-empiriques pour ľvaluation des tassements des fondations en sols résiduels du granit.
Finite element analysis of the Nerlerk underwater berm failures
Authors: Hicks M. A. , Boughrarou R.
Published: October 2009

Finite element analyses have been carried out to investigate the possible causes of failure, during construction, of the Nerlerk underwater berm– a hydraulically placed sand slope, designed to form part of a bottom-founded offshore oil exploration platform at Nerlerk in the Canadian Beaufort Sea. The double-hardening Monot constitutive law has been used for modelling the fill materials, while an elastic–perfectly plastic von Mises idealization has been used for modelling the weak underlying clay layer, on which the structure was founded. The computed results demonstrate that, for conditions of rapid loading, there are three possible failure mechanisms, depending on the shear strength of the clay. All mechanisms result in liquefaction of the Nerlerk fill and are hence consistent with the flat post-failure slopes observed on site. However, the most likely cause of failure seems to be that of limited movements in the clay layer triggering liquefaction in the Nerlerk fill near to the berm crest. This investigation represents a major step forward over previously published back-analyses, in that no prior assumptions regarding failure mechanism have been involved. It is also a significant improvement over conventional slope stability calculations, which, for liquefiable soils, tend to greatly overestimate on-site factors of safety.

Des analyses des éléments finis ont étéeffectuées pour examiner les causes possibles de la rupture, en cours de construction, de la berme submergée Nerlerk–un talus en sable remblayé hydrauliquement, qui devait faire partie ďune plate-forme de prospecdon pétroliére sous-marine á Nerlerk, dans la mer de Beaufort, au Canada. La loi constitutive du double durcissement Monot a servi á modéliser les matériaux de remblai, tandis qu’une idéalisation élastique parfaitement plastique de von Mises a servi á mod6liser la couche sous-jacente &coron;argile faible sur laquelle reposait &coron;ouvrage. Les résultats calculés montrent que, dans des conditions de charge rapide, il existe trois mécanismes possibles de rupture, en fonction de la résistance au cisaillement de &coron;argile. Tous ces mécanismes aboutissent á la liquéfaction du remblai de Nerlerk et sont donc compatibles avec les talus plats observés sur place aprés la rupture. Toutefois, la cause la plus probable de la rupture semble Être celle des mouvements limités dans la couche &coron;argile, qui ont provoqué la liquéfaction du remblai prés du sommet de la berme. Cette étude constitue un grand pas en avant par rapport aux rétroanalyses déjá publiées, en ce sens qu’lle ne part &coron;aucune hypothése quant au mécanisme de rupture. Par ailleurs, elle offre bien plus que les calculs classiques de la stabilité des talus, qui, dans le cas des sols liquéfiables, tendent á surestimer considérablement les coefficients de sécurité sur le terrain.
An experimental study of the behaviour of embedded lengths of cantilever walls
Authors: Bica A. V. D. , Clayton C. R. I.
Published: October 2009

Laboratory-based 1–g experiments are described which model the embedded length of cantilever walls in sand, and in which the shear and normal stresses between the soil and the wall were measured, together with wall displacements, as the load on the wall was progressively increased to failure. The results show that comparatively large earth pressures, associated with high effective angles of wall friction, are mobilized just below the soil surface in front of the wall. Earth pressures on the retained side, below the centre of rotation of the wall, were smaller than Rankine passive values, confirming Krey's original views on the downwards direction of wall friction at this location. The results fit well within the relatively small available data set for free embedded cantilever walls, and show the trend of increasing bending moment with depth of embedment, given a constant effective angle of friction.
Ground deformations and stress redistribution due to a reduction in volume of zones of soil at depth
Authors: Skinner H. D. , Charles J. A. , Watts K. S.
Published: October 2009

The ground deformations and stress redistribution resulting from collapse compression in discrete zones of highly collapsible fill located at different depths within fill with little or no collapse potential has been investigated in the 4-m-deep BRE large test pit facility. The moisture contents and densities of the colliery spoil fill which was used in the test were selected to ensure that, as well as high collapse potential, the zones of dry fill had lower compressibility than the surrounding wetter fill. During fill placement, significant stress transfer occurred, resulting in the measured vertical stresses in the zones being much higher than the stresses in the bulk of the fill. As the fill was inundated by a rising water level, collapse compression occurred in the dry zones and the stress transfer was reversed, with stresses in the zones reducing to very low values. The collapse compression in all the zones was of similar magnitude but the measured surface settlements were dependent on the depth of the zone. The test was modelled using the Sage–Crisp finite element package together with a simple procedure for simulating collapse compression. The observed behaviour was replicated with sufficient accuracy for the numerical procedure to form a means of estimating behaviour with zones of fill of different geometries and located at different depths.

Nous étudions les déformations de sol et la redistribution des contraintes provoquées par la compression d'affaissement dans certaines zones d'une décharge extrêmement sujette aux effondrements, situées à différentes profondeurs avec pen on pas de potentiel d'effondrement dans une fosse d'essai BRE de 4 m de profondeur. Le contenu humide et les densiés des déchets miners qui ont été utilisés dans cet essai ont été choisis de fagon à ce que, en même temps que le fort potentiel d'affaissement, les zones de décharge sèches aient une compressibilité inférieure à celle des zones environnantes plus humides. Pendant la mise en place des déchets, un transfert de contraintes significatif s'est pro-duit, rendant les contraintes verticales mesurées dans ces zones bien plus hautes que les contraintes dans le reste de la décharge. Comme la décharge a été inondée en raison de la monée du niveau des eaux, la compression d'affaissement s'est produite dans les zones séches et le transfert de contraintes s'est inversé, les contraintes dans ces zones devenant triès faibles. IL est apparu que la compression d'affaissement était de magnitude similaire dans toutes les zones mais les dépôts de surface dépendaient de la profondeur de la zone. L'essai a été mis en maquette en utilisant le logiciel d'é1éments finis Sage–Crisp avec une procédure simple pour simuler la compression d'affaissement. Le comportement observé a été reproduit avec suffisamment d'exacdtude pour que la procédure numérique forme un moyen d'évaluer le comportement dans des zones de décharge de géométries et de profondeurs différentes.
Net pressure analysis of cantilever sheet pile walls
Authors: Day R. A.
Published: October 2009

There are many methods for the analysis and design of embedded cantilever retaining walls. They involve various different simplifications of the net pressure distribution to allow calculation of the critical retained height. In the UK, it is commonly assumed that net pressure consists of the sum of the active and passive limiting pressure values. In the USA, the net pressure is commonly simplified by a three-line rectilinear pressure distribution. Recently, centrifuge tests have led to a proposed semi-empirical rectilinear method in which an empirical constant defines the point of zero net pressure. Finite element analyses presented in this paper examine the net pressure distribution at limiting equilibrium. The study shows that the point of zero net pressure for a best-fit rectilinear approximation is dependent on the ratio between the passive and active earth pressure distributions at limiting conditions. A simple empirical equation is proposed which defines the point of zero pressure. The predictions for the critical retained height and bending moment distribution using this empirical equation are in excellent agreement with the finite element results and centrifuge data. They are in better agreement than the predictions of the commonly used analysis methods.
A conceptual model for the yielding and consolidation of clays
Authors: Houlsby G. T. , Sharma R. S.
Published: October 2009

A simple micromechanical model is used to derive the shapes of yield surfaces for clays. The simplest version of the model contains features that are similar to the behaviour of clays, and in particular it is able to predict the shape of anisotropic yield surfaces due to K0 consolidation, and their evolution with subsequent straining. The model predicts, however, unrealistic values of certain parameters. A more sophisticated model is derived using similar concepts, so that the derived parameters are realistic, and also so that the model is compatible with the concept of critical state.

Un simple modèle micromécanique est utilisé pour déduire les formes des surfaces d'écoulement des argiles. La version la plus simple du modèle contient des caractérisdques qui sont similaires au comportement des argiles, et notamment, elle est capable de prédire la forme des surfaces d'écoulement anisotropes dues à une consolidation K0 et leur évolution à l'effort ult´rieur. Cependant, le modèle prévoit des valeurs non réalistes pour certains paramètres. Un modèle plus sophistiqué est dérivé en utilisant des concepts similaires afin que les paramètres dérivés soient réalistes et que le modèle soit compatible avec le concept d'état critique.
Clay–interface shear resistance
Authors: Lemos L. J. L. , Vaughan P. R.
Published: October 2009

The shear of clays of varying plasticity against interfaces of different materials and varying roughness has been studied in the ring shear apparatus. Results are compared with the shearing resistance of clay-on-clay. Particular attention has been paid to shearing resistance with large displacements, and the influence of the interface in changing the shearing mode. The effect of corrosion of steel interfaces has been examined, as has the effect of fast shearing.
Theory and practice of the fall cone test
Authors: Koumoto T. , Houlsby G. T.
Published: October 2009

The fall cone is considered as a more reliable method for determining the liquid limit than the Casagrande method, and is standardised in many countries as the preferred liquid limit test method. In this paper the theory and practice of the fall cone test are described. First the penetration mechanism of a fall cone into clay is analysed, introducing the concept of dynamic strength to the static results. Next the applicability of dynamic analysis to the fall cone test is examined with regard to Hansbo's cone factor, K, for various cone angles. The theoretical K value for the 60° cone with a semi-rough surface is found to agree better with experimental results than is the case for the 30° cone. It is proposed that the liquid limit be redefined internationally as the water content at which a 60°, 60g fall cone penetrates 10 mm. Finally the applicability of the fall cone test as a device to relate the strength of a clay with the index properties is examined.
Monitoring sedimentation of a clay slurry
Authors: Blewett J. , McCarter W. J. , Chrisp T. M. , Starrs G.
Published: October 2009

Electrical impedance measurements are monitored during the sedimentation of a clay slurry and provide an in-situ, non-invasive technique to study the sedimentation process. The term normalised resistivity is introduced and data are interpreted in terms of the development of a density profile and the influence of pore fluid concentration on this process. Particle alignment mechanisms are also inferred from the electrical properties of the slurry.
Arminou Dam, Cyprus, and construction joints in diaphragm cut-off walls
Authors: Brown A. J. , Bruggemann D. A.
Published: October 2009

This paper is in two parts. The first part describes the foundation seepage cut-off to a new 42 m high gravel fill dam with central clay core. A single 0·8 m wide plastic concrete diaphragm wall, together with adjacent bentonite cement alluvial grouting, provides a seepage cut-off through the 15 m depth of underlying granular alluvium. The discovery of bentonite infill in construction joints in trial panels for the diaphragm wall led to the introduction of alluvial grouting, to inhibit erosion of this bentonite infill into coarse zones in the alluvium. The second part of the paper discusses the main factors governing the effectiveness of diaphragm walls as seepage cut-offs and related dam safety issues, including construction joints, hydraulic gradients and hydraulic fracture. There are a number of issues relating to the use of diaphragm walls as seepage cut-offs that are not well understood, which should be considered in design, construction and monitoring of such walls and where further research is needed.
The performance of pressure cells for sprayed concrete tunnel linings
Authors: Clayton C. R. I. , Van Der Berg J. P. , Heymann G. , Bica A. V. D. , Hope V. S.
Published: October 2009

The paper examines the factors that affect the performance of tangential cells embedded in shotcrete tunnel linings. New data, derived from field monitoring, numerical modelling, and calibration tests carried out to simulate the embedment and crimping processes, are presented. These suggest that although well-designed embedded total pressure cells will have cell action factors close to unity, they cannot be assumed to provide reasonable estimates of the stresses within sprayed concrete linings, unless the influences of installation effects, temperature changes, shrinkage and subsequent crimping can be taken into account.
Numerical modelling of group effects on the distribution of dragloads in pile foundations
Authors: Lee C. J. , Bolton M. D. , Al-Tabbaa A.
Published: October 2009

Negative skin friction on pile foundations, predicted from the results of numerical analyses, is presented. Soil slip at the pile–soil interface has been found to be the most important factor in governing pile behaviour in consolidating ground. Reduction in dragload is predicted for piles in a group owing to interaction between soil and pile. It has been demonstrated that the group effect depends not only on the configuration of the pile group, but also on soil slip along the pile–soil interface, governed mainly by the interface friction coefficient and the soil settlement. Various factors should be included in an evaluation of the group effect, including the pile spacing, the number of piles in a group, the relative location of piles in a group, the pile type, the pile installation method, the surface loading and the stiffness of the soil. Existing design approaches result in overprediction of dragload for a single pile and of group effect for a pile group. Back-analysed dragloads and group effects considering soil slip are compared with a number of case histories.
Porosity of fluid-saturated porous media from measured seismic wave velocities
Authors: Foti S. , Lai C. G. , Lancellotta R.
Published: October 2009

This paper presents a novel procedure for determining porosity in fluid-saturated porous media from measured shear and dilatational wave velocities. The method is developed using the theory of linear poroelasticity in the low-frequency limit, which is equivalent to considering the fluid-saturated porous medium as a closed (un-drained) system with the pore fluid moving in phase with the soil skeleton. The new procedure for the in-situ measurement of porosity has been applied at two sites in Italy using cross-hole seismic data. The results obtained are in excellent agreement with independent laboratory data gathered from undisturbed soil specimens.
Piled rafts in overconsolidated clay: comparison of in situ measurements and numerical analyses
Authors: Reul O. , Randolph M. F.
Published: October 2009

This paper presents the results of detailed back-analysis, using three-dimensional finite-element analysis, of three piled raft foundations on overconsolidated clay. Comparisons of overall settlement, differential settlements and the load carried by the piles show reasonably good agreement, although the finite-element analyses generally show a higher proportion of the overall load being carried by the piles than estimated from the field measurements. Three main performance indicators of the piled raft are proposed: the proportion of load carried by the piles, and the maximum settlement and maximum differential settlement, both as a proportion of the corresponding quantity for an unpiled raft foundation. The last indicator, in particular, suggests that improved layout of the pile support can lead to a reduction both in the maximum differential settlement and in the overall quantity of piles. This is illustrated for one of the case histories.
On the relationship between stress–dilatancy, anisotropy, and plastic dissipation for granular materials
Authors: Collins I. F. , Muhunthan B.
Published: October 2009

Techniques of modern thermomechanics are used to analyse the stress–dilatancy relation for shear deformations of frictional, granular materials. Central to this approach is the recognition that in general, deformations of granular materials can involve stored plastic work. It is recognised that in shear deformations, where the shape of the grains induces the dilatancy, the confining pressure is a constraint and dissipates no energy. Nevertheless it is shown that, in such a shear deformation, the total plastic work rate is equal to the rate of energy dissipation, and that this is given by Thurairajah's classical observations. It is further shown that anisotropy is necessarily induced, and that the stress–dilatancy relation is given by Taylor's well-known formula. It is also demonstrated that the extant procedure for deducing yield conditions and flow rules from specified dissipation functions is invalid.
Random field characterisation of stress-nomalised cone penetration testing parameters
Authors: Uzielli M. , Vannucchi G. , Phoon K. K.
Published: October 2009

Random field modelling of soil variability allows significant statistical results to be inferred from field data; moreover, it provides a consistent framework for incorporating such variability in reliability-based design. Cone penetration testing (CPT) is increasingly appreciated because of its near-continuity and repeatability. Stress-normalised CPT parameters are included in widely used engineering procedures. Nonetheless, the results of variability analyses for these parameters are surprisingly limited. This paper attempts to characterise normalised cone tip resistance (qc1N) and friction ratio (FR) rigorously using a finite-scale weakly stationary random field model. It must be emphasised that inherent soil variability so determined strictly refers to the variability of the mechanical response of soils to cone penetration. The variability of soil response potentially depends on the failure mode (shear for sleeve friction or bearing for tip resistance) and most probably on the volume of soil inﬂuenced (averaging effect). To investigate spatial variability, 70 physically homogeneous CPT profiles were first identified from 304 soundings (subdivided into five regional sites) and subsequently assessed for weak stationarity using the modified Bartlett test. Only 40 qc1N profiles and 25 FR profiles were deemed sufficiently homogeneous from both physical and statistical considerations for the scales of ﬂuctuations to be valid and for estimation of the coefficient of variation of inherent soil variability. The majority of the acceptable profiles were found in sandy soils. The remaining profiles are in fine-grained soils, with a few in intermediate soils. Trends in the estimated random field parameters indicate that qc1N is more strongly autocorrelated than FR, probably because qc1N is influenced by a larger volume of soil around the cone tip, and that the mechanical response of cohesionless soils to cone penetration is significantly more variable and erratic than that of cohesive soils. Comparison with literature data indicates that normalisation leads to a decrease in the scale of fluctuation for cone tip resistance and a reduction in the coefficient of variation. A tentative explanation is that normalisation tends to minimise systematic in situ effects that are explainable by physical causes.
Realistic assessment of slope reliability for effective landslide hazard mangement
Authors: Cheung R. W. M. , Tang W. H.
Published: October 2009

Probabilistic methods have been employed as a practical aid for slope management in respect of the stochastic nature of landsliding. The effect of deterioration on the reliability of slopes of various periods of service, however, has seldom been considered explicitly in the current reliability evaluation. The first part of this paper will present an empirical procedure, using past performance of an extensive set of cut slopes in Hong Kong as an example, to model probabilistically the deteriorating effect on the failure probability with age for a population of slopes. The procedure extends further to predict the failure probability of slopes over different future service periods. Although this probability would serve as an estimate of average slope reliability to assist landslide hazard management by planners, a more accurate site-specific failure probability would be preferred for individual projects. The second part of this paper will adopt a Bayesian procedure to map the calculated probability of a given slope to a more realistic estimate of failure probability. The procedure enables performance records, the effect of system deterioration and other unaccountedfor factors to be systematically incorporated for the estimation. Finally, a procedure is developed to assess the uncertainty associated with the updated probability, resulting from limited observed performance data available for the probability mapping process.
Generalised scaling relations for dynamic centrifuge tests
Authors: Iai S. , Tobita T. , Nakahara T.
Published: October 2009

The trend toward physical modelling of larger prototypes triggers a move towards expansion of the current capability of dynamic centrifuge tests. In this paper a method based on the concept of two-stage scaling is proposed that allows expanded use of the currently available facilities. In the first stage a prototype is scaled down into an intermediate virtual model based on the scaling relations in a 1g field with a scaling factor of μ (prototype/virtual model). In the second stage this model is scaled down into a physical model using the conventional scaling relations in the centrifugal field with a scaling factor of η (virtual model/physical model). In this manner, a large scaling factor λ = μη (prototype/physical model) can be broken down into the smaller scaling factors μ and η, and thus the centrifuge model tests can be performed with the smaller scaling factor η. In effect, the limits in the scaling factor for the currently available centrifuge facilities can be expanded by a factor of μ. Validation of the proposed method is provided by algebraic derivations based on the mechanics of model tests.
The concept of stored plastic work or frozen elastic energy in soil mechanics
Authors: Collins I. F.
Published: October 2009

This paper is part of a series that aims to explore systematically the applications of the modern theory of thermomechanics to the constitutive modelling of soils and other geomaterials. Although the division of the applied work into recoverable elastic energy and irrecoverable plastic energy is straightforward at the level of single grains, this is not true at the continuum level. Because of the highly heterogeneous nature of the stress and deformation fields at the micro level, some of the micro-level elastic energy is ‘frozen’, and consequently some of the applied plastic work is stored and is recoverable. The concept is explained at the micro level, at the meso level of the force chains, and at the continuum level. It is also explained in terms of a schematic spring–slider model. These ideas have very important ramifications for constitutive modelling at the continuum level. In particular it is shown that there are two causes for dilation in a soil, one due to Reynolds’ dilatancy, the other due to the recovery of the frozen energy (or stored plastic work). This has significant consequences for the concept of critical states. Implications for future research are indicated.
Coefficient of consolidation by plotting velocity against displacement
Authors: MCKINLEY J.D. , SIVAKUMAR V.
Published: October 2009

A method is presented for estimating the initial compression, the final compression and the coefficient of consolidation from an observed, experimental consolidation response, using a plot of velocity versus displacement and the conventional Taylor plot of compression versus the square root of time. Goodness of fit measures indicate that the method produces good agreement between fitted and measured displacement values, at least up until the point where the impact of secondary compression on the overall displacement response becomes significant.
Creep of Concrete in Compression During Drying and Wetting
Authors: Gamble B. R. , Parrott L. J.
Published: October 2009

SYNOPSIS

The paper describes a study of concrete creep during drying-and-wetting regimes. Damp specimens were loaded at ages of 7 or 140 days and drying began at intervals thereafter. Drying creep was observed; its rate of development was linearly related to that of concurrent shrinkage. The correlation was independent of age at loading and of delay in drying, and only mildly dependent upon stress. For different concretes, drying creep can be closely predicted from water/cement ratio or 28 day strength. The creep recoveries of drying specimens were greater than those of damp specimens; drying creep was recoverable to the same extent as basic creep. No additional recovery of drying creep was observed upon rewetting unloaded specimens. Specimens rewetted under load exhibited wetting creep which was linearly related to concurrent swelling. Reference is made to the calculation in practice of strains in concrete subjected to stress and varying humidity. The nature of drying creep is discussed briefly.
Ultrasonic wave velocities in concrete
Authors: Reynolds W. N. , Wilkinson S. J. , Spooner* D. C.
Published: October 2009

SYNOPSIS

The elastic constants of wet and dry concrete specimens of known composition have been calculated from those of cement paste, water and two types of aggregate by using a theoretical model due to Boucher. The densities were also calculated and the velocities of three types of ultrasonic wave were obtained. It has been shown that the calculated velocities are in satisfactory agreement with those measured on some typical concretes. The suitability of gamma radiometry as a measure of density was also assessed by the measurement of mass absorption coefficients on all the materials involved using a 137 Cs source of energy 667 keV.
Fracture toughness measurements of polymer concretes
Authors: Cook D. J. , Crookham G. D.
Published: October 2009

SYNOPSIS

This paper describes the use of linear elastic fracture mechanics to examine the behaviour of premix and impregnated polymer concretes. Results are given for three monomers, viz. styrene, methyl methacrylate and butyl methacrylate, and two strengths of concrete, as well as for appropriate control series. The notched-beam technique is used to determine fracture parameters, together with compliance measurements to determine slow crack growth. Experimental results indicate that thermal treatment to polymerize the monomer in the premix concrete has a marked influence upon fracture toughness. Irradiation on the other hand has little influence. Polymer impregnation increases the stress-intensity factor and the strain at failure, the latter increase being influenced by the extensibility of the polymer. The results also show that the plain and the premix polymer concretes are partially notch-sensitive, whereas the impregnated polymer concrete is a notch-sensitive material.
A study of transitional thermal creep in hardened cement paste
Authors: Parrott L. J.
Published: October 2009

Synopsis

Creep measurements on hardened cement paste subject to various temperaturehistories are described. It wasfound that, when loaded prisms were gradually heated from 2O° to 60°C, creep increased substantially. This transitional thermal creep was pronounced for virgin heating, but was also present to a lesser extent during a second heating to 60°C. Delays in loading and heating generally led to smaller creep strains, and cooling did not induce any transitional thermal creep.
Developments in the variable-stiffness approach to reinforced concrete column design
Authors: Wood R. H. , Shaw M. R.
Published: October 2009

Synopsis

Exceptionally accurate results were recently obtained by Butler, by a new simplified method of design of restrained reinforced concrete columns which was basically an intuitive combination of the variable-stiffness approach developed for steel columns (by Wood) and graphical construction (due to Roik) employing ultimate moment charts. Here an attempt is made to eliminate the graphical construction and to substitute an alternative arithmetical rational procedure, which should be more amenable for development for a code of practice.
A mathematical description of the strength properties of concrete under generalized stress
Authors: Kotsovos Michael D.
Published: October 2009

Synopsis

A mathematical description of the ultimate strength envelope of concrete under axisymmetric stress states has been derived by analysing experimental data obtained in previous investigations of the Concrete Materials Research Group at Imperial College. The derived equations, when combined with an proposed elsewhere for the description of the effect of the intermediate stress σ2 upon the ultimate strength level, define a surface in stress space which provides a simple mathematical representation of the ultimate strength of concrete under generalized short-term loading conditions. The resulting ultimate strength surface conforms with generally accepted shape requirements and has been found to provide a close fit for most biaxial and triaxial strength data published to date.
Effect of sulphate content of cement upon heat evolution and slump loss of concretes containing high-range water-reducers (superplasticizers)
Authors: Khalil S. M. , Ward M. A.
Published: October 2009

Synopsis

At normal temperatures (25°C), concretes containing superplasticizers lose much of their initial high workability within approximately 45 minutes from initial mixing. When the concrete is hot (40°C), the effect is more severe with significant workability (slump) loss occurring within 30 minutes. In this study, the optimum range of SO3, contents for an ordinary Portland cement, with and without superplasticizer addition, has been determined at these two temperatures by using a conduction calorimeter and Lerch's criteria for optimum SO3 content. Concretes were manufactured at both temperatures using cements with the as received and modified SO3 contents, identified in the calorimeter study. It is concluded that there is an optimum range of SO3 content for which workability loss is minimized for concretes containing the superplasticizer, both at the normal and at the elevated temperature. In addition, short- and long-term strengths are improved.
Effect of in-source variability of pulverized-fuel ash upon the strength of OPC/pfa concrete
Authors: Dhir Ravindra K. , Arun G. Aptet , Munday John G. L.
Published: October 2009

Synopsis

The paper describes an investigation into the effect upon the strength of OPC/pfa concrete of the variability of pulverized-fuel ashes from single sources over a period of time. Twenty weekly samples of four ashes were used to make OPC/pfa concretes at three nominal strengths which were then cured under five different conditions. The strength variations caused by the pulverized-fuel ashes were compared with those caused in OPC concretes by an equal number of weekly cement samples. Although variability in ash properties was observed, only one ash exhibited a significantly greater variation in concrete strength than was shown by the cement. Correlations between ash properties and OPC/pfa concrete strengths did not reveal any property which could by itself reliably give any more than a general indication of the probable effect of a batch of pulverized-fuel ash upon OPC/pfa concrete strength.
Shrinkage of oil-soaked concrete
Authors: Matti M. A. , Watson A. J.
Published: October 2009

Synopsis

This paper describes an investigation into the shrinkage of concrete in direct contact with crude oil. The shrinkage or volume change was studied by using 100 × 100 × 500 mm concrete prisms. Ordinary Portland cement, natural river aggregates, four water/cement ratios, and four curing regimes were used. Similar specimens were cast and continuously kept in water and in a constant temperature and humidity room for comparative purposes.
Testing of concrete specimens for permeability at cryogenic temperatures
Authors: Hanaor Ariel
Published: October 2009

Synopsis

The permeability of concrete to cryogenicfluids, in the context of the use of concrete for storage of liquefied gases, has received very scant attention, in comparison with mechanical properties. A series of preliminary tests on concrete specimens, employing liquid nitrogen as the permeating fluid, is presented here. The tests were carried out by means of a rig specially developed for the purpose, a major feature of which is an effective method of sealing the specimen under cryogenic conditions. Results obtained indicate that mechanismsgoverning the permeability of concrete at cryogenic temperatures differ substantially from those prevailing at ambient conditions. Aggregate and aggregate-paste interaction, in particular, play a major role.
Superplasticized high-workability concrete: some properties in the fresh and hardened states
Authors: Dhir Ravindra K. , Yap Andrew W. F.
Published: October 2009

Synopsis

The paper describes the first stage of a wide-ranging investigation into superplasticized high-workability concrete. The properties studied were, in the fresh state, flow characteristics, stability (bleeding and segregation) und air content and, in the hardened, compressive strength (both early and subsequent up to 90 days) and drying shrinkage. A ranking order of the superplasticizers used was obtained, together with proposals on the flow and segregation behaviour in response to variations in cement content and sand grading. The bleeding of the superplasticized highworkability concrete was found to be higher, and the air content generally lower, than for the corresponding normul concrete. Compressive strength was found to be generally of the same order as that of normal concrete, whilst drying shrinkage was higher for the superplasticized high-workability concrete.
Accuracy of estimating long-term strains in concrete
Authors: Brooks J. J.
Published: October 2009

Synopsis

A method developed earlier for estimating long-term creep and shrinkage from short-term measured test data is shown to be satisfactory for predicting ten-year values. For water-stored concrete, swelling at ten years is appreciable, and therefore the method is extended to predict long-term swelling. Using thirty-year strain (extrapolated from experimentally determined ten-year strain), five standard methods of prediction are compared in performance. When applied in their basic form, all methods are unsatisfactory and it is recommended that, depending on the required accuracy, the secant modulus of elasticity be determined and used with the Concrete Society/Cement and Concrete Association method to predict thirty-year strain. For improved accuracy, short-term test data are necessary for use with either the author's method or the Bažant and Panula model II method.