bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and performance of an equivalent-shear-beam container for earthquake centrifuge modelling
Authors: Zeng X. , Schofield A. N.
Published: October 2009

A model container used on a shaking table should cause stress and strain in the model similar to that in a soil layer of infinite lateral extent and finite depth. This paper reports the design and results of preliminary tests of a new type of centrifuge model container for earthquake tests–an equivalent-shear-beam container. The model is made of rectangular frames of aluminium alloy spaced by rubber layers so as to achieve the same dynamic stiffness as the soil it contains. To sustain the complementary shear stresses induced by base shaking at each end wall, a flexible and inextensible frictional sheet is introduced. Data of centrifuge tests indicate that this model container satisfies certain requirements for an ideal model confinement for centrifuge modelling of earthquake design conditions.

Une table vibrante pourrait induire sur un boiler-prototype les mêmes contraintes et déformations que sur une couche de sol d'épaisseur fine et d'extension latérale infinie. L'article décrit le nouveau prototype (equivalent-shearbeam container) mis en oeuvre pour des essais sismiques en centrifugeuse et les résultats des essais préliminaires réalisés. Ce prototype est constitué de plusieurs structures rectangulaires en alliage aluminium séparées par des couches de caoutchouc, de fa¸on à ce qu'il ait la m&circme raideur dynamique que le sol qu'il contient. Une feuille de friction flexible et inextensible a été introduite pour absorber les contraintes de cisaillement supplémentaires issues du vibrage de la base des parois. Les essais de centrifugation réalisés montrent que ce prototype satisfait à certaines conditions requises par le modèle idéal de confinement qui permettrait de modéliser les séismes en centrifugeuse.
Observation of Biot compressional wave of the second kind in granular soils
Authors: Nakagawa K. , Soga K. , Mitchell J. K.
Published: October 2009

The compressional wave of the second kind which was predicted theoretically by Biot (1956a) was observed in granular soils using very sensitive transducers. The Biot theory models both the individual and coupled behaviour of soil skeleton and pore fluid using the permeability, porosity, viscosity, densities and appropriate elastic constants of the solid, pore fluid and solid skeleton. The measured Biotwave velocities agree well with the theoretical values computed using properties and parameters which were obtained primarily from laboratory tests. The good agreement demonstrates that the Biot theory is valid for granular soils. The propagation of the P- and S-waves in granular materials was measured under different confining pressures and in both dry and saturated conditions. An empirical relationship between shear modulus G (in kPa) and confining pressure σc (in kPa) for Monterey sand and crystal silica sand samples was found to be given by G = 1·10(σc)0·42 1·64(σ)0·46. The measured Poisson's ratio of the soil skeleton is in the range 0·323–0·418, and it decreases as the confining pressure increases. The results of theoretical studies of the effect of frequency on wave velocities and the influences of other parameters are also presented.

Ĺonde de compression du deuxiéme type prédite en théorie par Biot (1956a) a été observée dans des sols granulaires à ľaide de capteurs très sensibles. La théorie de Blot modélise le comportement individuel et le comportement couplé du squelette du sol et de ľeau interstitielle en utilisant la permébilit*eacute;, la viscosité, les densités et les constantes élastiques voulues du solide, de ľeau interstitielle et du squelette solide. Les vitesses mesurées de ľonde de Blot concordent bien avec les valeurs théoriques calculées à ľaide de propriètès et de paramétres obtenus principalement partir ďessais en laboratoire. Cette bonne concordance montre que la théorie de Biot śapplique aux sole granulaires. On a mesuré la propagation des ondes P et S dans des matériaux granulaires secs et saturés á diverses pressions de confinement. On a constaté qúil existait un rapport empirique entre le module de cisaillement G (en kPa,/sub>) et la pression de confinement σc' (en kPa) pour les échantillons de sable de Monterey et de sable siliceux cristallin: G = 1,07(σc')0·42 1,54(σc')0·42. Le coefficient de Poisson mesuré du squelette du sol se situe dans la bretelle de 0,323 ´ 0,418 et diminue á mesure qúaugmente la pression de confinement. Ĺexposé présente également les résultats des études théoriques de ĺeffet des fréquences sur la vitesse de propagation des ondes, ainsi que de ĺinfluence dautres paramétres.
The effect of reservoir drawdown and long-term consolidation on the deformation of old embankment dams
Authors: Tedd P. , Charles C. J. A. , Holton I. R. , Robertshaw A. C.
Published: October 2009

The uncertainties surrounding the composition and behaviour of most old embankment dams are so great that a purely analytical approach to dam safety evaluation is unlikely to be adequate and an observational approach is needed. The monitoring of the deformations of embankment dams has an important role in assessing longterm behaviour and in evaluating safety. This paper describes field studies at five old embankment dams all constructed in the Pennines, Yorkshire. It has been confirmed that where there is a central core, significant crest settlement can be expected on reservoir drawdown, but this is not the case where there is an upstream watertight element. The field studies should aid the interpretation of observations associated with reservoir drawdown and assist both in identifying anomalous behaviour associated with deleterious processes and in preventing behaviour associated with steady-state loading and reservoir fluctuations giving unnecessary cause for concern.

On est tellement incertain de la composition et du comportement de la plupart des vieux barrages remblayés qu'une évaluation purement analytique de la sûreté des barrages laisse probablement à désirer et qu'une démarche basée sur l'observation s'impose. La surveillance des déformations des barrages remblayés joue un rôle important dans ľvaluation du comportement à long terme et dans 1'évaluation de la sûreté. Ľexposé décrit les études sur le terrain dont ont fait l'objet cinq vieux barrages remblayés des Pennines. Elles ont confirmé qu'il faut s'attendre à un tassement substandel du couronnement de barrages à noyau central lors de 1'évacuation du réservoir, à moins qu'il n'y ait un masque amont. Les études sur le terrain devraient alder à interpréter les observations faites lors de ľévacuation des réservoirs et à définir les comportements anormaux qu'on associe à des processus préjudiciables, ainsi qu'à prévenir les comportements associés à un niveau Wean constant ou & agrave; des fluctuations du niveau Wean, qui suscitent des inquiétudes inutiles.
Settlements of shallow foundations on sand: geometrical effects
Authors: Montrasio L. , Nova R.
Published: October 2009

The paper is an extension of a previous work concerning the behaviour of model strip shallow foundations subjected to eccentric or inclined loading. The effects on the overall behaviour of the shape and the embedment of the foundation are considered here. The structure of the mathematical model employed to describe the behaviour of the strip foundations is recalled. The results of an extensive series of tests on model foundations of rectangular shape and various degress of embedment are then presented, together with the numerical results obtained by means of the mathematical model. It is shown that experimental evidence is generally well matched by the theory. The values of the constitutive parameters of the mathematical model in the various cases considered are compared. It is shown that only two out of nine vary significantly with the shape of the foundation. Embedment has a small influence on the value of an additional two parameters; the other five remain constant. The results of a back-analysis on a full-scale embedded foundation under eccentric and inclined load are discussed.

L'article est unextension un travail précedent dont on analyze le comportement d'une semelle filante, soumise à l'action combinée des chargements inclinés et excentrés. Ici on considère les éffets de la forme et du niveau de base de la fondation sur son comportement. D'abord, on rappelle briefment la structure du modèle mathématique utilisé pour decrire le comportement des semelles filantes. On présente en suite le résultats expérimentaux obtenus dans une serie d'essais sur fondations en modèle reduit et les correspondents resultats calculés à l'aide du modèle mathématique. On montre que la théorie donne des bonnes prédictions. Le valeurs des paramétres constitutifs dans les différents cas condiderés sont comparés. On montre que, entre les neufs paramètees qui characterisent le modèle, deux seulement sont influencés par la forme de la fondation, tandis que Sept restent constants. Le niveau de fondation a influence sur quatre paramétres. On discute finalement le resultats 'un analyse á posteriori 'una fondation réelle soumise a un chargement incliné et excentré.
The concept of effective stress for soil, concrete and rock
Authors: Lade P. V. , De Boer R.
Published: October 2009

Many different expressions have been proposed for the effective stress principle for porous media, but none has clearly been acknowledged as being the correct one. It should be possible to determine the correct expression, because this is fundamental principle of mechanics. Following review of the candidate expressions proposed for soil, concrete and rock, a comprehensive expression is derived involving the factors observed in experiments on 'artificial rock'. In this new expression a distinction is made between the compressibilities of grains and skeleton due to total stresses and pore pressures. This general and more comprehensive expression is then tested against the experimental evidence. The expression may be specialized for (a) granular materials with separate grains with contact points and (b) solid rock with interconnected pores. The new expression for the effective stress contains most of the previously proposed expressions as special cases. Based on results of compression tests on quartz (with hard grains) and on gypsum (with soft grains) it is shown that Terzaghi's effective stress principle works well for most geotechnical applications, but significant deviations occur at very high stresses.

Un grand nombre d'expressions différentes du principe de la tension efficace ont été proposées pour les matériaux poreux, mais aucune n'a vraiment été acceptée comme parfaite. II devrait Être possible de déterminer la bonne expression, vu qu'il s'agit là d'un principe fondamental de mécanique. Après avoir examiné les expressions proposées pour le sol, le béton et la roche, les auteurs ont dérivé une expression globale qui met en jeu les facteurs observés lors d'essais sur de la « roche artificielle» Cette nouvelle expression fait la distinction entre les compressibilités des grains et du squelette dues aux contraintes totales et aux pressions interstitielles. Les ré sultats d'études expérimentales servent ensuite à véerifier la validité de cette expression générale et plus étendue. L'expression pent Être modifiée pour (1) les matériaux granulaires à grains séparés avec points de contact et (2) la roche en place à interstices interconnectés. Cette nouvelle expression de la tension efficace contient comme cas particuliers la plupart des expressions proposées antérieurement. À partir des résultats d'essais sur du quartz (à grains durs) et du gypse (à grains tendres), on montre que le principe de la tension efficace de Terzaghi s'applique à la plupart des cas géotechniques, mais qu'il se produit des écarts importants quand les contraintes sont très élevées.
Settlement of piled foundations
Authors: Mandolini A. , Viggiani C.
Published: October 2009

A numerical code for the prediction of the settlement of pile groups and piled rafts is presented. The code is based on the interaction factors method; the non-linearity is simulated as suggested by Caputo and Viggiani, that is, concentrating it at the pile—soil interface. In the linear range, the accuracy is checked against known benchmark solutions. A standard procedure, based on the results of load tests on single piles, is suggested for the evaluation of soil properties and for the implementation of the analysis in real cases. Nineteen well-documented case histories are then analysed, calculating for each of them a linear elastic, an equivalent linear elastic and a non-linear solution. Five out of the 19 cases are illustrated in some detail, to allow a deeper insight into the procedure. In all but one of the analysed cases the predicted values of the average settlement are within ±20% of the observed values. The maximum differential settlement is predicted with slightly lesser accuracy. For foundations characterized by a relatively high safety factor, linear and non-linear analyses are essentially equivalent. Some evidence suggests that the low-strain shear modulus, obtained by in situ shear wave velocity measurements, can be successfully employed in the prediction of the settlement. When the safety factor is low, the consideration of non-linearity becomes mandatory.
Three-dimensional back-analysis of saturated rock slopes in discontinuous rock—a case study
Authors: Hatzor Y. H. , Goodman R. E.
Published: October 2009

Two historic block failures on the left abutment of Pacoima Dam, California, are back-analysed using three-dimensional limit equilibrium analysis. Water pressures within the boundary joints are introduced by parametric addition of vectors using enhanced stereographic projection. The magnitude and orientation of the resultant necessary to cause failure are established, as a function of the available friction angle. The influence of joint friction on the joint water pressure required to initiate block sliding and on the failure mode is discussed. It is shown that with increasing joint water pressure the orientation of the resultant dictates a changing failure mode, in the cases studied, from double plane to single plane sliding. The actual failure mode depends on the available friction angle of the joints. The influence of increasing joint water pressure on the factor of safety is also discussed. It is shown that the rotation of the resultant force by the addition of joint water forces rapidly reduces the factor of safety. The rate of change of the factor of safety with respect to joint water pressure in the base joints is shown to be higher for double plane sliding and lower for single plane sliding for the same block, when both failure modes are investigated. Block theory analysis is used to assess the stability of the right abutment of Pacoima Dam, presently concealed by a thick layer of gunite, and the critical blocks in the abutment are found using the procedure of Hatzor. It is demonstrated that in contrast to the unstable left abutment, the right abutment is perfectly safe, by virtue of kinematics alone. This theoretical result is strongly validated by the field performance of the right abutment, which experienced several episodes of strong ground motions in the past.
Passive earth pressures in the presence of hydraulic gradients
Authors: Soubra A.-H , Kastner R. , Benmansour A.
Published: October 2009

The paper describes a variational approach applied to the limit equilibrium method for calculating the effective passive pressures of a cohesionless soil, taking into consideration the seepage flow. It is shown that in the general case of non-homogeneous and non-isotropic hydraulic properties of the soil medium, the shape of the slip surface which verifies the three limiting equilibrium equations of the soil mass at failure is a log-spiral. It is also shown that the passive earth pressure calculation is independent of the normal stress distribution along this surface. The variational limit equilibrium method is equivalent to the upper bound method in limit analysis for a rotational log-spiral mechanism. Numerical results of the coefficients of passive earth pressures in the presence of seepage flow are presented and discussed.

Cet article présente une approche variationnelle appliquée à la méthode du prisme de rupture permettant le calcul de la pression passive effective des terres en présence d'écoulement dans le cas d'un sol purement pulvérulent. On montre que dans le cas général d'un sol aux propriétés hydrauliques non homogénes et non isotropes, la forme de la surface de rupture qui vérifie les trois équations d'équilibre est une spirale logarithmique. Nous montrons aussi que le calcul de la pression passive ne dépend pas de la distribution des contraintes normales agissant le long de cette surface. La méthode du prisme de rupture variationnelle est équivalente à la méthode de la borne supérieure en analyse limite pour un mécanisme rotationnel en spirale logarithmique. Des valeurs numériques du coeﬃcient de butée en présence ďécoulement sont présentées et discutées.
Slope stability analysis by finite elements
Authors: Griffiths D. V. , Lane P. A.
Published: October 2009

The majority of slope stability analyses performed in practice still use traditional limit equilibrium approaches involving methods of slices that have remained essentially unchanged for decades. This was not the outcome envisaged when Whitman & Bailey (1967) set criteria for the then emerging methods to become readily accessible to all engineers. The finite element method represents a powerful alternative approach for slope stability analysis which is accurate, versatile and requires fewer a priori assumptions, especially, regarding the failure mechanism. Slope failure in the finite element model occurs 'naturally' through the zones in which the shear strength of the soil is insufficient to resist the shear stresses. The paper describes several examples of finite element slope stability analysis with comparison against other solution methods, including the influence of a free surface on slope and dam stability. Graphical output is included to illustrate deformations and mechanisms of failure. It is argued that the finite element method of slope stability analysis is a more powerful alternative to traditional limit equilibrium methods and its widespread use should now be standard in geotechnical practice.

En grande majorité, les analyses de stabilité de pente menées dans la pratique continuent à utiliser les méthodes traditionnelles d'équilibre limite et des systèmes de tranches qui n'ont pratiquement pas changé depuis des dizaines d'années. Ce n'était pas le résultat envisagé quand Whitman et Bailey (1967) ont établi des critères pour que ces méthodes alors émergeantes puissent devenir facilement accessibles à tous les ingénieurs. La méthode d'éléments finis qui représente une alternative puissante pour les analyses de stabilité de pente, est exacte, polyvalente et demande moins d'hypothèses ‘a priori’, surtout en ce qui concerne les mécanismes de rupture. La rupture de pente dans le modèle à éléments finis se produit ‘naturellement’ à travers des zones dans lesquelles la résistance au cisaillement du sol est insuffisante pour résister aux contraintes tangentielles. Cet exposé décrit plusieurs exemples d'analyses de stabilité de pente utilisant les éléments finis et établit des comparaisons avec d'autres méthodes, comme l'influence d'une surface libre sur la stabilité d'une pente et d'une digue. Nous joignons une représentation graphique pour illustrer les déformations et mécanismes de rupture. Nous avançons que la méthode d'éléments finis pour analyser la stabilité des pentes constitue une alternative plus puissante aux méthodes traditionnelles d'équilibre limite et que son utilisation devrait maintenant devenir une pratique standard en géotechnique.
Severn–Trent sand: a kinematic-hardening constitutive model: the q–p formulation
Authors: Gajo A. , Wood Muir
Published: October 2009

A simple model is described which is able to represent the mechanical behaviour of granular soils over a wide range of void ratios and mean stresses (neglecting grain crushing). The model combines Mohr–Coulomb failure, critical states, dependence of strength and stiffness on the state parameter, a hyperbolic law for plastic stiffness degradation and a flow rule similar to that of Cam Clay. The model is formulated within the framework of kinematic hardening and bounding-surface plasticity. The model requires two elastic and eight plastic parameters which are linked to clear physical features of the mechanical response. The formulation and numerical implementation are eased by making use of a 'normalized' stress space in which the stress– strain response shows no strain softening. The model is validated by comparison with experimental results obtained from triaxial tests on Hostun sand covering a wide range of density and stress level. Some proposals are made for possible future developments of the model within the same underlying framework.

Nous décrivons ici un modèle simple capable de représenter le comportement mécanique des sols granuleux sur une vaste gamme de taux de pores et de contraintes moyennes (sans tenir compte de l'écrasement des grains). Ce modèle combine la défaillance Mohr-Coulomb, les états critiques, l'assujettissement de la force et de la rigidité au paramàtre d'état, une loi hyberbolique pour la dégradation de rigidité plastique et une règle ďécoulement similaire à celle de Cam-Clay. Le modèle est formulé dans le cadre du durcissement cinématique et de la plasdcité de surface limite. Le modèle demande deux paramètees èlastiques et huit paramètees plastiques qui sont liés à des caractérisdques physiques claires de la réponse mécanique. La formulation et la mise en oeuvre numérique àsont facilitées par ľutilisation ďun espace de contrainte 'normalise' dans lequel la réponse contrainte-dé;formation ne montre aucun amollissement dû à la déformation.

Le modèle est validé par une comparaison avec les résultats expérimentaux obtenus àla suite ďessais sur trois axes sur du sable de Hostun couvrant une vaste gamme de densités et de niveaux de contrainte. Nous proposons certaines possibilités de développement du modèle à ľintérieur du même cadre de travail.
On the measurement of the undrained strength of discontinuities in the direct shear box
Authors: Chandler R. J. , Hamilton P. S
Published: October 2009

A series of unconsolidated, undrained shear box tests on a tectonic shear discontinuity in the London Clay Formation yielded unexpectedly high values of undrained strength. Measurement of the effective stress in the block samples prior to shear leads to the suggestion that the measured undrained strength on the discontinuity is controlled by the post-sampling mean effective stress, rather than the original in situ effective stress acting across the discontinuity. This observation has the result that in any soil where K0 ≠ 1·0, a rigid-boundary test apparatus (such as the shear box) that does not re-establish the in situ stresses cannot measure the correct undrained strength on a discontinuity.

Keywords: clays; failure; laboratory tests; shear strength.

Une série dessais utilisant une boîte de cisaillement non drané et non consolidé sur une discontinuité de cisaillement tectonique dans la formation dargile de Londres a donné des valeurs étonnamment élevées de résistance non drainée. Les mesures de la contrainte effective dans les échantillons blocs avant cisaillement laissent penser que la résistance non drainée mesurée sur la discontinuité est tributaire de la contrainte effective moyenne après échantillonnage plutôt que de la contrainte effectivein situ ´origine agissant à travers la discontinuité. Cette observation montre que dans tout sol où K0 ≠ 1.0, un appareil ´essai à limite rigide (comme la boîte de cisaillement) qui ne reproduit pas les contraintes in situ ne pent mesurer correctement la résistance non drainée sur une discontinuité.
Depth-dependent permeability in London Clay measured using standpipe piezometer equilibration data
Authors: Dixon N. , Bromhead E. N.
Published: October 2009

An investigation into the pore water pressure regimes in the actively eroding London Clay coastal slopes at Warden Point, Isle of Sheppey, Kent included the installation of 56 standpipe piezometers at a range of depths down to 60 m below original ground level. As expected, given the active coastal environment, a significant number of the instruments were destroyed before final equilibration water levels had been obtained. Using initial equilibration data from the fully equilibrated instruments, it is demonstrated that Hvorslev's theory for the response of a piezometer located in incompressible soil is valid for standpipe piezometers installed in unweathered London Clay. Using this theory a simple method is proposed for predicting the final equilibration water level of partially equilibrated instruments. The initial equilibration data from 13 of the piezometers were of sufficient quality to enable calculations of in situ, permeability. These demonstrate a relationship of decreasing permeability with depth for London Clay, conforming to and greatly extending the small number of existing results.

Les pentes côdères de Warden Point, dans l'lle de Sheppey, dans le Kent, sont constituées d'argile de Londres qui subit une érosion active. Dans le cadre d'une étude des régimes de pression d'eau interstitielle, on a installé 56 piézomètres sur des tuyaux verticaux enfoncés agrave; diverses profondeurs, jusqu'à 60 m en dessous du niveau original du sol. Comme l'on s'y attendait, étant donné l'activité de l'environnement c&cric;tier, un nombre significatif d'instruments a été détruit avant que les niveaux définitifs d'eau équilibrante n'aient été obtenus. En utilisant des données d'équilibre initiales produites par les instruments entièrement équilibrés, nous avons démontré que la théorie de Hvorslev pour la réponse d'un piézomètre situé dans un sol incompressible est valable pour des piézomètres installés sur des tuyaux verticaux dans de l'argile de Londres non altérée. En utilisant cette théorie, nous proposons une méthode simple pour prédire le niveau final de l'eau d'équilibre des instruments parrtiellement équilibrés. Les données d'équilibre initiales produites par 13 des piézométres étaient de qualité suffisante pour permettre les calculs de perméabilitéin-situ. Ceux-ci montrent une relation de perméabilité décroissante avec la profondeur pour l'argile de Londres, ce qui confirme le petit nombre de résultats existants et permet d'aller au-delà.
Building response and ground movements induced by a deep excavation
Authors: Ou C.-Y. , Liao J.-T. , Cheng W.-L.
Published: October 2009

This paper presents building responses and ground movements induced by an excavation using the top-down construction method. The ground surface settlement and lateral wall displacement for each excavation stage were observed. The displacement performances of the soil were further studied by examining the strain field and displacement vector developing in a soil mass behind the wall. The centre of the vertical-strain concentration area was found to be consistent with the location of the maximum ground surface settlement. For a given distance from the wall, the maximum vertical soil movement occurred at a certain depth below the ground surface. The soil behind the wall had a non-zero volume change during excavation. Both consolidation and soil creep behaviour might contribute towards the volume change of the soil. Factors such as the type of foundation, the size of foundation, the length of the side of the excavation and the shape of the settlement profile may affect the building performance during excavation. Information regarding a building's location relative to the settlement influence zone is helpful in planning building protection measures during excavation.
Etude en centrifugeuse de l'élargissement de remblais sur argile molle
Authors: Akou Y. , Magnan J.-P. , Dubreucq T. , Rault G.
Published: October 2009

This paper presents the results of tests performed on small-scale models of embankments on soft clay foundation. The clay models were prepared from ‘Speswhite’ kaolin powder, which was given an undrained cohesion of 14–18 kPa by consolidation under natural gravity (1g). The main and widening embankments were built in flight inside the centrifuge by using a specifically designed hopper. Seven tests were completed at 70g, with two types of embankment widening. The clay models were equipped with surface settlement, pore water pressure and horizontal displacement gauges. Each test lasted for about 10 h.

The geometry of the embankments and the test procedure (preparation of the clay model, instrumentation, loading and measurements) are described in the paper. The results are then analysed and compared with classical analyses for embankments on soft soils.

These analyses pointed out the importance of a precise knowledge of the detailed history of the soil models, starting from their preparation in the container under natural gravity. The clay behaviour in the centrifuge depends on a combination of consolidation and creep, which in turn depends on the initial overconsolidation state of the clay. This makes the interpretation of the experimental results more difficult.
Rocking response of rigid blocks under near-source ground motions
Authors: Makris N. , Roussos Y. S.
Published: October 2009

In this paper the transient rocking response of a rigid block subjected to trigonometric pulses and near-source ground motions is investigated in detail. First, the rocking response to a half-sine pulse motion is revisited. It is shown that the solution presented by Housner for the minimum acceleration amplitude of a half-sine pulse that is needed to overturn a rigid block is incorrect. In reality, under a half-sine pulse, a block overturns during its free vibration regime and not at the instant that the pulse expires, as was assumed by Housner. Within the limits of the linear approximation, the correct conditions for a block to overturn are established and the correct expression that yields the minimum acceleration required to overturn a block is derived. Subsequently, physically realizable cycloidal pulses are introduced and their resemblance to recorded near-source ground motions is illustrated. The study uncovers the coherent component of some near-source acceleration records, and the overturning potential of these motions is examined. It is found that the toppling of smaller blocks is more sensitive to the peak ground acceleration, whereas the toppling of larger blocks depends mostly on the incremental ground velocity. The kinematic characteristics of recorded near-source ground motions are examined in detail, and it is found that the high-frequency fluctuations that occasionally override the long-duration pulse will overturn a smaller block, whereas a larger block will overturn due to the long-duration pulse. A simple, yet dependable, method to determine the level of a recorded ground motion that is needed to overturn a given block is developed and illustrated through examples. The method examines the acceleration amplitude, and the duration and the type of distinct local pulses that are identifiable within the record, including the pulse that contains the peak ground acceleration. According to the type of each pulse identified, the method estimates the minimum acceleration amplitude needed to overturn a given block, and this value is compared with the recorded acceleration amplitude of each pulse identified within the record. In this light, the rocking response of rigid blocks subjected to strong near-source ground motions is shown to be quite ordered and predictable.
An experimental investigation on the independent isotropic stress variables for unsaturated soils
Authors: Tarantino A. , Mongiovì L. , Bosco G.
Published: October 2009

The isotropic stress state in an unsaturated soil is generally described by three measurable stress variables: the mean total stress, the pore air pressure and the pore water pressure. Constitutive models of unsaturated soils presented so far have been developed on the basic assumption that only two of these variables are actually independent. As a consequence, the experimental data based on the axis translation technique have been extrapolated to real conditions, where the pore air pressure is atmospheric and the pore water pressure is negative. However, experimental evidence to support this assumption is still limited. In an attempt to provide a better understanding of the response of unsaturated soils, a specific experimental programme has been planned and completed. To this aim a new apparatus to test unsaturated soils in a broad range of degree of saturation and negative pore water pressures was designed and constructed. Using this apparatus a total of eight tests was performed on saturated and unsaturated kaolin samples consolidated from slurry and air dried to degrees of saturation ranging from 0·5 to 0·8 with corresponding negative pore water pressures in the range –1400 to –1100 kPa. In this paper the apparatus used in the experimental programme is described and the results obtained so far are presented and discussed.
Consolidation of a very soft clay with vertical drains
Authors: Almeida M. S. S. , Santa Maria P. E. L. , Martins I. S. M. , Spotti A. P. , Coelho L. B. M.
Published: October 2009

The paper analyses the performance of an embankment built on a very soft and extremely compressible organic clay where prefabricated vertical drains have been installed. Coefficients of horizontal consolidation, ch, obtained from settlement analyses took into account the smear resulting from the installation of the drains and also the vertical drainage. These values of ch are compared with the measurements obtained from special laboratory tests with drains installed in the sample, and from in-situ tests using the piezocone. The three sets of figures showed good agreement with each other, which suggests that the secondary consolidation was negligible compared with the primary consolidation in the case herein, in which vertical drains were used.
Group effects in stone column foundations: model tests
Authors: Muir Wood D. , Hu W. , Nash D. F. T.
Published: October 2009

Model tests have been performed to determine the mechanisms of response for beds of clay reinforced with stone columns subjected to surface footing loads. An exhumation technique has been used to discover the deformed shapes of the model stone columns and thence to deduce the way in which the columns have transferred load to the surrounding clay. Tests have explored the effect of varying the diameter, length and spacing of the model stone columns. These parameters control whether the columns act as somewhat rigid inclusions transferring load to their tips and eventually deforming either by bulging or by the formation of a failure plane, or whether they are able to compress axially or even, if sufficiently slender, to ‘bend’ and undergo significant lateral deformation. Miniature pressure transducers have been used to reveal the distribution of contact pressure between columns and clay at various stages during the loading of the footings. It appears that the columns at mid-radius of the footing are typically the most heavily loaded. Results from numerical analysis are used to provide qualitative support for some of the findings from the physical model tests.
The densification of granular soils using vibro methods
Authors: Slocombe B. C. , Bell A. L. , Baez J. I.
Published: October 2009

The method of densifying in-situ sandy soils using deep vibration (vibro) was first developed in Germany over 60 years ago. Since then the technique has been extended to improve a wide range of soil types for structures of up to 30 storeys in height. A major development in the vibro market worldwide over the last 25 years has been the treatment of soils to resist the effects of liquefaction during seismic events. It is well known that the presence of silt and clay fines inhibits the physical in-situ densification of sandy soils. Experience has shown that a maximum fines content of about 15% would normally permit the performance of vibro compaction methods without the addition of stone aggregate. However, the development of new vibrators and modified construction techniques has enabled sands with significantly higher fines content to be treated. The paper describes how densification of granular soils has progressed with the development of new equipment, the greater appreciation in the manner in which soils respond to both vibration and displacement, and the importance of workmanship during treatment. A number of case histories including in-situ test results, long-term monitoring of ageing effects and references to treated sites already subjected to earthquakes are presented.
Vibro-replacement for industrial plant on reclaimed land, Bahrain
Authors: Renton-Rose D. G. , Bunce G. C. , Finlay D. W.
Published: October 2009

This paper describes the improvement by means of vibro-replacement of hydraulically placed fill, recently constructed to form a reclaimed platform for a coke calcining plant in Bahrain. The improved fill will directly support some of the principal structures constructed with shallow foundations. The alternative would be to support these structures by means of bored piles extending into the bedrock, some 15–20 m below. The initial density/stiffness properties of the as-placed calcareous sand fill are presented, together with observed improvement with time after placement, prior to treatment. The pre-tender design method is described, from which confidence to proceed with the approach was derived. Relevant construction details are presented and, in particular, the validation testing regime, which included pre- and post-construction cone penetration tests and five large zone load tests (up to 11·5 m2 loaded area). The improvement achieved by the treatment works is compared with the initial improvement predictions as well as with recalculated predictions using the tender design approach, but employing observed stone column and treated fill properties. This review indicates that the design approach adopted was acceptable, slightly underestimating the improvement achieved by a factor of around 1·3.
Analysis of single-fluid jet grouting
Authors: Croce P. , Flora A.
Published: October 2009

An overall analysis of single-fluid jet grouting is presented. Current concepts and design rules are first reviewed and compared. Alternative approaches to the analysis of single-fluid jet grouting are proposed and implemented with experimental data and observations taken from recent and well-documented case histories. In-situ observations and measurements as well as laboratory tests are presented, indicating the influence of both treatment parameters and original soil properties on treatment effects. On the basis of the experimental evidence, the mechanical phenomena induced by jet grouting are discussed.
Consolidation equation valid for both Darcian and non-Darcian flow
Authors: Hansbo S.
Published: October 2009

In an earlier paper, a comparison was made between the consolidation process experienced in practice and the theoretical consolidation process both determined according to the classical consolidation theory based upon the validity of Darcy's law and obtained on the assumption of an exponential correlation between hydraulic gradient and flow velocity (non-Darcian flow). The results obtained, based on back-analysis of field data, showed a better agreement between theory and practice if non-Darcian rather than Darcian flow was assumed. In this paper new equations are demonstrated covering the exponential as well as the linear correlation between hydraulic gradient and flow velocity, including the effect of smear and well resistance. A comparison is made between the results obtained by the solution based merely on Darcian flow and the new solution based on exponential flow. It is shown that the new, more general solution can replace the solution based on Darcian flow.
A parametric study of the pull-out capacity of bucket foundations in soft clay
Authors: Zdravkovic L. , Potts D. M. , Jardine R. J.
Published: October 2009

This paper investigates the effect of several parameters on the pull-out capacity of bucket foundations in soft clay. These parameters are load inclination, skirt length, foundation diameter, soil adhesion and soil anisotropy. Initially the soil is assumed to be isotropic soft clay, and is represented using a form of the modified Cam clay model. Some recent laboratory experiments performed in a hollow cylinder apparatus, which were designed to investigate strength anisotropy of a particular silt soil, are then used to represent the behaviour of an anisotropic soft clay. The anisotropic behaviour is simulated using anisotropic soil model MIT-E3. Both models are then used in finite element analyses to predict the behaviour of bucket foundations on pull-out. All analyses were performed using the three-dimensional Fourier series aided finite element method (FSAFEM).
The effect on anisotropy of rotating the principal stress axes during consolidation
Authors: Zdravković L. , Jardine R. J.
Published: October 2009

It is well known that Ko-consolidated natural sediments have anisotropic strength, yielding and stiffness characteristics, particularly at low overconsolidation ratios. For example, the undrained triaxial compression shear strengths developed after Ko-consolidation far exceed those available in extension. This paper describes recent hollow cylinder apparatus research into other types of stress-induced anisotropy, reporting experiments on dense silt samples that involved rotation of the principal stress axes during consolidation. The results show strikingly different anisotropies from those developed by Ko-consolidated samples. The effective stress paths chosen for the laboratory studies were guided by the conditions expected under multi-stage embankments built on soft ground, but the results have considerable significance in other practical geotechnical problems.
Field behaviour of very soft clays at the Athlone embankments
Authors: Long M. M. , O'riordan N. J.
Published: October 2009

The approach road embankments to the new Shannon bridge rise up to 8·6 m above the marshlands of the River Shannon to the north of the town of Athlone in the Irish Midlands. These embankments are located on very soft glacial lake clay, highly compressible organic clay and calcareous marls, the geotechnical properties of which were largely unknown at the commencement of design in the early 1980s. Comparisons between compressibility, consolidation and shear strength parameters derived during the site investigation and those measured by monitoring the works are presented in this paper. It was found, for example, that the installation of vertical drains can significantly alter consolidation behaviour, that field compressibility was greater than that expected from laboratory testing, and that lateral movement monitoring was a useful indicator of embankment instability. Data from the construction of the Athlone embankments also confirm that the field vane strength underestimates the operational strength of the clays, owing to a combination of anisotropic and vane insertion disturbance effects. Good estimates of the operational strength are given by the piezocone. Details of some investigative work carried out on the soils beneath the embankments, some nine years after completion of construction, are also presented. It was shown that this testing confirms the findings of Mesri (1989) that the increase in shear strength is approximately equal to 0·22Δσ′v. Also, the piezocone is capable of defining zones of anisotropy induced by embankment loading.
Undrained cavity expansion in modified Cam clay I: Theoretical analysis
Authors: Cao L. F. , Teh C. I. , Chang M. F.
Published: October 2009

This paper presents an analysis of the undrained expansion of a cavity in modified Cam clay. The problem is formulated in small strain in the elastic zone and large strain in the plastic zone. Exact closed-form solutions of the effective stresses around the expanded cavity are presented. Closed-form expressions for the excess pore water pressure and the total stresses have also been derived based on a simplified assumption regarding the shear stress variation around the cavity. The analytical solution shows clearly the influence of the overconsolidation ratio on the excess pore water pressure induced by cavity expansion. As both the excess pore water pressure and the cavity pressure are expressed explicitly in terms of the primitive modified Cam clay parameters, the solutions may provide a theoretical basis for the interpretation of in-situ tests such as the piezocone test and the pressuremeter test.
Consolidation of soil with vertical and horizontal drainage under ramp load
Authors: Zhu G. , Yin J.-H.
Published: October 2009

This technical note presents a new analytical solution for consolidation analysis of soil with vertical drains under ramp load. The solution is described in detail. A new normalised time factor, T, is suggested. It is shown in the note that the average degree of consolidation exhibits very good normalised behaviour using this new T. Results are presented in figures and tables for practical applications.
Development of stabilisation and solidification in lime–clay mixes
Authors: Boardman D. I. , Glendinning S. , Rogers C. D. F.
Published: October 2009

Two refined clay minerals, English China Clay (predominantly kaolinite) and Wyoming Bentonite (predominantly sodium-montmorillonite), were used to assess the time-dependent effects of mineral structural chemistry on the lime–clay reaction. The two clays, representing the extremes of structural negative charge development, were treated with two lime contents. Changes in the physico-chemistry of the samples were monitored after three curing periods by performing batch leaching tests and monitoring changes in undrained shear strength and Atterberg limits. The effects of changing the batch test operating parameters and increasing the curing period were assessed by measuring changes in solution pH and conductivity, and by analysis of eight elements in solution. The solidification mechanisms due to lime addition were found to be different for the two minerals. Pozzolanic reactions involving English China Clay and Wyoming Bentonite were found to occur owing to the dissolution of aluminium and silicon from the respective mineral. Development of the batch leaching test showed that changing the operational parameters had no effect on the observed trends associated with the time-dependent modification and solidification reactions. It was also shown that successful solidification could be monitored using simple conductivity measurements without the need for extensive and complex elemental analysis.
Drained and undrained anisotropic elastic stiffness parameters
Authors: Lings M. L.
Published: October 2009

Equations that map drained to undrained elastic stiffness parameters in a cross-anisotropic material are presented. Graphs of various anisotropic stiffness ratios are used to illustrate the important trends. A new 2-D graph showing the elastic bound enables measured elastic parameters to be plotted, which all lie well within it. The 2-D graph enables uncoupled and incompressible materials to be shown, plus materials with particular initial effective stress path slopes in an undrained triaxial test. Bounds more restrictive than the elastic one are also discussed, and the likely ranges of various anisotropic stiffness ratios are presented. In general, undrained anisotropy is much less than drained: that is, closer to isotropic. In undrained plane strain conditions, vertical and horizontal moduli are found to be the same. In drained plane strain conditions, the ratios of the moduli are almost the same as the Young's moduli.