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Lateritic clay is widely distributed in tropical and subtropic regions, with distinct engineering properties from other clays. Its stiffness properties, which are often anisotropic and crucial for analysing the serviceability limit state of earthen structures, have not been well understood. This study investigated the cross-anisotropic stiffness of compacted lateritic clay through comprehensive isotropic compression and consolidated drained and undrained shear tests. Both vertically and horizontally cut specimens were tested using triaxial apparatus equipped with bender elements and local strain measurements. The results show that compared with other clays, the lateritic clay shows a weaker dependency of shear modulus to confining pressure, a higher shear modulus at the same confining pressure, and a higher degradation rate of stiffness with strain. The lateritic clay behaves like granular material due to its large-size aggregated microstructure and 42% sand content. The widely used correlations between stiffness parameters and plasticity index seem unsuitable for it. Furthermore, the elastic shear modulus in the vertical direction is slightly higher than that in the horizontal direction, and the anisotropy evolves during shearing. A complete set of cross-anisotropic stiffness parameters for both effective and total stress analysis were determined. They are useful for developing constitutive models and analysing earth structures' serviceability involving lateritic soils. Key words: anisotropy, constitutive relations, lateritic soil, small strain stiffness, Introduction Lateritic soils are chemically weathered materials widely distributed in tropical and subtropical areas like South America (Brazil), West Africa (Nigeria), and Asia (India and China) (Gidigasu 1976; Ng et [...]

The effect of silt content on the mechanical behavior of silt-clay transition soils under 3D stress conditions is presented. Undrained true triaxial tests with constant b values were performed on normally consolidated specimens of silt-clay transition soils created from the same base clay and nonplastic silt, however, with systematically varying gradations. With increasing amount of nonplastic silt, the cohesive soils exhibit less contractive tendencies, stiffer stress-strain response, and larger shear strength. The magnitude of intermediate principal stress, as indicated by the b value, also strongly influences the stress-strain relations, pore pressure behavior, and both total and effective failure surfaces. Although the transition soils exhibit overall clay-like behavior, more pronounced frictional characteristics, as indicated by the shapes of the failure and plastic potential surfaces, were exhibited with increasing silt content. Key words: silt-clay soil, stress-strain, shear strength, silt content, true triaxial test, Introduction Large deposits of fine-grained cohesive soils are present in several metropolitan areas around the world. These urban areas, which include Bangkok, San Francisco, London, and Shanghai among others, are [...]

This paper presents a unified critical state parameter model for evaluating sand and overconsolidated clay, which is named as CASM-S. The model is formulated in terms of the modification of the clay and sand model, i.e., CASM, by incorporating the subloading surface theory with an overconsolidation state parameter R. Although the standard CASM proves to be useful in modelling overconsolidated clay and sand, the model (1) requires the rate of overconsolidated ratio to be constant which is in contrast to the observed behaviour of soils and (2) only allows elastic deformation to develop at the overconsolidated state that may underestimate the deformation corresponding to the peak stress or be unable to predict the actual stress path. By introducing a new material parameter u to those material properties of the standard CASM, the rate relationship of stressstrain for the CASM-S model is developed. The standard CASM can be either recovered or approximated as a special case of the overconsolidation state assumed in the CASM-S. The numerical integration of the newly proposed model is performed by the modified forward Euler method. Validation with undrained and drained overconsolidated clay and sand have demonstrated the capability of the CASM-S model to well predict the observed soil behaviours. Key words: overconsolidated clay, sand, subloading surface theory, clay and sand model, stress-strain relation, 1. Introduction The concept of critical states was initially developed based on limited triaxial test data obtained on reconstituted clay. In 1970s, Cambridge University performed numbers of triaxial tests and [...]

In this study, a unified p-y curve model is developed for clays in undrained conditions using the results of 3D finite element (FE) modeling. The p-y curves are primarily used in the analysis of laterally loaded piles. Formulas for the ultimate lateral bearing capacity factor ([N.sub.p]), and the reference deflection in the p-y curve ([y.sub.50]), were obtained using the results of parametric studies and regression analysis. The tangent hyperbolic function was used to model the p-y curve shape. In the FE models, the clay soil material was modeled as elastic-perfectly plastic material using Mohr-Coulomb criteria, and the pile material was modeled as elastic only. The parametric study results show that [N.sub.p] varies nonlinearly with depth. The proposed model for [N.sub.p] is composed of two regions: a nonlinear zone and a linear zone. The model for [N.sub.p] used the undrained shear strength ([s.sub.u]), effective unit weight of soil ([gamma]'), and pile width (D) as parameters. Further, the proposed model for [y.sub.50] was found to be dependent on the soil stiffness (Es), D, and [N.sub.p]. The dependency of [y.sub.50] on [N.sub.p] was often overlooked in previous studies. Finally, the proposed model was imported in LPILE program and the results from previous case studies were compared with the proposed model predictions. Key words: p-y curve, lateral resistance, single pile, static loading, finite element, parametric study, 1. Introduction The p-y curve is a subgrade reaction technique that describes the nonlinear relationship between the mobilized soil resistance, p, and the lateral deflection of the pile, y, in [...]

The p-y method as a simplified analysis tool has been widely used to analyze the behavior of laterally loaded piles. This paper develops a novel cyclic p-y elastoplastic model within the framework of the single-surface bounding surface theory. The model can capture the soil stiffness degradation during cyclic loading by incorporating the cumulative plastic displacement to an interpolation function of the elastoplastic resistance coefficient. The model is relatively simple with only four parameters that can be determined from standard soil properties and stress-strain responses measured in direct simple shear tests. The performance of developed model is validated by predicting the cyclic lateral response of piles installed in soft clay during field and centrifuge tests published in the literature. The model can reliably simulate monotonic and cyclic responses of piles under different lateral loading patterns, and capture main characteristics of the pile-head load-displacement curve, such as nonlinearity, hysteresis, displacement accumulation, and stiffness degradation. It can also predict the evolution of the lateral deflection and sectional bending moment along the pile during cyclic loading. Key words: p-y curve, pile, lateral loading, bounding surface model, cyclic loading, 1. Introduction In harsh offshore environmental conditions, offshore platforms and wind turbines supported by pile foundations are subjected to cyclic lateral loads due to wind, sea waves, and currents. Consequently, [...]

This study investigated a new predictive model of the shear modulus reduction (G/[G.sub.max] - Log([[gamma].sub.c])) and damping ratio ([epsilon] - Log ([[gamma].sub.c])) curves for sensitive eastern Canada clays. The model was established based on experimental measurements of G/[G.sub.max] and [epsilon] performed on 69 sensitive clay specimens from eastern Canada. The compiled database was first analyzed to qualitatively assess the influences of different soil parameters on the measurements. Next, statistical analyses using regression analysis and the modified hyperbolic model were performed. It was found that the G/[G.sub.max] and [epsilon] values of sensitive eastern Canada clays were influenced mainly by the plasticity index ([I.sub.p]), mean effective stress ([[sigma]'.sub.m]), and structure, which was quantified by the liquidity index ([I.sub.L]). Based on the statistical analysis performed, new equations for G/[G.sub.max] and [epsilon] were proposed. The newly proposed model was compared with previously published models. The comparison clearly showed that the proposed model was more representative of sensitive eastern Canada clays. Consequently, it is suggested that the proposed model is more appropriate for use in the dynamic analysis of sensitive eastern Canada clay deposits as well as other similar soils. Key words: shear modulus, damping ratio, sensitive clay, quick clay, eastern Canada, soil dynamic, 1. Introduction The assessment of the dynamic response of soil deposits has attracted considerable attention in Canada in recent years, especially after several major modifications were incorporated in the National [...]

As a result of the growing population in Switzerland, new infrastructure is increasingly founded in areas of extremely soft clays, which are challenging to build on. Reliable characterization of such sediments is, therefore, essential to facilitate efficient and economical designs. For various reasons, it is often beneficial to measure soil properties in situ, using probes like the piezocone or self-boring pressuremeter. The main objective of this study was to explore the key differences of these two site investigation techniques in terms of measuring undrained strength and consolidation characteristics in varved lacustrine clay. Experimental data from a field-testing campaign carried out in Switzerland demonstrate that both probes yield comparable results. The quality of the predictions was further assessed by comparing the field measurements to results from laboratory tests and existing empirical relationships. Additionally, a new method based on Monte Carlo simulations was presented, to provide context to the disparity between the consolidation coefficients estimated in the field ([c.sub.h]) and laboratory ([c.sub.v]), and to aid prediction of field values of [c.sub.h] from laboratory measurements. Key words: piezocone, pressuremeter, undrained strength, consolidation, lacustrine clay En raison de l'augmentation de la population en Suisse, les nouvelles infrastructures sont de plus en plus souvent construites dans des zones d'argile extremement molle, sur lesquelles il est difficile de construire. Une caracterisation fiable de ces sediments est donc essentielle pour faciliter des conceptions efficaces et economiques. Pour diverses raisons, il est souvent avantageux de mesurer les proprietes du sol in situ, a l'aide de sondes telles que le piezocone ou le pressiometre auto-foreur. L'objectif principal de cette etude est d'explorer les differences cles de ces deux techniques d'investigation de site en termes de mesure de la resistance non drainee et des caracteristiques de consolidation dans l'argile lacustre varvee. Les donnees experimentales d'une campagne de tests sur le terrain menee en Suisse demontrent que les deux sondes donnent des resultats comparables. La qualite des predictions est ensuite evaluee en comparant les mesures sur le terrain aux resultats des essais en laboratoire et aux relations empiriques existantes. En outre, une nouvelle methode basee sur les simulations de Monte Carlo est presentee, pour fournir un contexte a la disparite entre les coefficients de consolidation estimes sur le terrain ([c.sub.h]) et en laboratoire ([c.sub.v]), et pour faciliter la prediction des valeurs de [c.sub.h] sur le terrain a partir des mesures en laboratoire. [Traduit par la Redaction] Mots-cles : piezocone, pressiometre, resistance non drainee, consolidation, argile lacustre, Introduction Detailed information about the extremely soft lacustrine clay conditions is best attained from a combination of laboratory and field experiments. Site investigation tools like the piezocone (CPTu) or self-boring [...]

The loading frequencies in cyclic tests and the rate of strain or stress in monotonic tests have a significant effect on the soil behaviour, particularly of clayey soil. This study aimed to determine the common characteristics of the behaviour of clay under cyclic loading at different frequencies and the relationship between cyclic and monotonic behaviours. Monotonic triaxial tests and cyclic triaxial tests at frequencies of 0.1 and 0.001 Hz were conducted on undrained saturated reconstituted soft clay. The results showed that the frequency of 0.001 Hz is sufficiently low to make the soil response comparable to that in monotonic tests. Second, there exists a unique 'feature line' for cyclic tests in the plot of allowable stress versus strain, independent of the frequency. Third, the feature lines for the cyclic and monotonic tests are close and parallel to each other. Therefore, although the cyclic and monotonic loadings are quite different from each other, there are connections between these different loadings in terms of the relationship between the allowable stress and strain. Key words: soft clay, cyclic tests, monotonic tests, relationship, low frequency Les frequences de chargement dans les essais cycliques et le taux de deformation ou de contrainte dans les essais monotones ont un effet significatif sur le comportement du sol, en particulier des sols argileux. Cette etude vise a determiner les caracteristiques communes du comportement de l'argile sous chargement cyclique a differentes frequences et la relation entre les comportements cyclique et monotone. Des essais triaxiaux monotones et des essais triaxiaux cycliques a des frequences de 0,1 et 0,001 Hz ont ete realises sur de l'argile molle reconstituee saturee non drainee. Les resultats montrent que la frequence de 0,001 Hz est suffisamment basse pour rendre la reponse du sol comparable a celle des essais monotones. Deuxiemement, il existe une 'ligne caracteristique' unique pour les essais cycliques dans le trace de la contrainte admissible en fonction de la deformation, independamment de la frequence. Troisiemement, les lignes caracteristiques des tests cycliques et monotones sont proches et paralleles les unes aux autres. Par consequent, meme si les charges cycliques et monotones sont tres differentes les unes des autres, il existe des liens entre ces differentes charges en termes de relation entre les contraintes et les deformations admissibles. [Traduit par la Redaction] Mots-cles : argile molle, essais cycliques, essais monotones, relation, basse frequence, 1. Introduction The cyclic deformation of soils in the field caused by, for example, traffic loading and wave loading is a major concern in practical engineering and has attracted significant [...]

We performed a field investigation into the effective stress, the shaft friction at the pile-soil interface, and the pile-end base resistance of a 29.5 m long prestressed concrete pipe pile in soft clay under static and cyclic loadings (50 000 cycles). Our results indicate that under low-level cyclic loading (CLR [less than or equal to] 0.2, where CLR is the ratio of cyclic load amplitude to the ultimate capacity), the pore water pressure at the pile-soil interface initially accumulates with the number of cycles, followed by gradual dissipation after reaching its maximum value. The effective stress also initially decreases and then increases. The shaft friction increases after cyclic loading. Owing to axial load redistribution, the base resistance decreases with the number of cycles. When the pile is subjected to high-level cyclic loading (CLR [greater than or equal to] 0.5), the pore water pressure at the pile-soil interface keeps accumulating while the effective stress continues to decrease, leading to the degradation of shaft friction. The base resistance increases as a result of axial load redistribution. In particular, we analyzed the effects of the static load level and the cyclic load level on the changes shaft friction. Key words: pore water pressure, effective stress, shaft friction, base resistance, cyclic loading, soft clay. Cette recherche presente une etude de terrain sur l'evolution de la contrainte effective, du frottement de l'arbre a l'interface pieu-sol et de la resistance de la base de l'extremite du pieu d'un pieu tubulaire en beton precontraint de 29,5 m de long dans de l'argile molle sous des charges statiques et cycliques (50 000 cycles). Les resultats revelent que sous une charge cyclique de faible niveau (CLR [less than or equal to] 0,2; CLR designe le rapport entre l'amplitude de la charge cyclique et la capacite ultime), la pression de l'eau interstitielle a l'interface pieu-sol s'accumule initialement avec le nombre de cycles, puis se dissipe progressivement apres avoir atteint sa valeur maximale. La contrainte effective diminue d'abord, puis augmente a nouveau. On observe que le frottement de l'arbre augmente apres un chargement cyclique. La resistance de base diminue avec le nombre de cycles en raison de la redistribution de la charge axiale. Lorsque le pieu est soumis a une charge cyclique elevee (CLR [greater than or equal to] 0,5), la pression d'eau interstitielle a l'interface pieu-sol continue de s'accumuler tandis que la contrainte effective continue de diminuer en consequence, entrainant la degradation du frottement de l'arbre. La resistance de base augmente en raison de la redistribution de la charge axiale. En particulier, les effets du niveau de charge statique et du niveau de charge cyclique sur les variations du frottement de l'arbre sont analyses. [Traduit par la Redaction] Mots-cles : pression d'eau interstitielle, contrainte effective, frottement de l'arbre, resistance de la base, chargement cyclique, argile molle., Introduction Piled embankments have been widely used in high-speed railways, especially in the coastal areas of southeast China where extensive deposits of soft clay are constantly encountered (Chen et al. [...]

Fine-grained marine sediments often contain gas bubbles that can cause many geotechnical problems. This soil has a composite structure with gas bubbles fitting within the saturated soil matrix. The gas cavity has a detrimental effect on the soil stiffness and strength when they are filled with undissolved gas only. The gas cavity can be filled with gas and pore water due to 'bubble flooding'. Bubble flooding has a beneficial effect on the soil stiffness and undrained shear strength because it makes the saturated soil matrix partially drained under a globally undrained condition. A critical state constitutive model for gassy clay is presented that accounts for the composite structure of the soil and bubble flooding. The gas cavity is assumed to have a detrimental effect on the plastic hardening of the saturated soil matrix. Some of the bubbles can be flooded by pore water from the saturated soil matrix, which leads to higher mean effective stress of the saturated soil matrix. Consequently, both soil stiffness and strength increase. Only one new parameter is introduced to model the detrimental effect of gas bubbles on plastic hardening. The model has been validated by the results of three gassy clays. Key words: gassy clay, critical state, constitutive model, undrained shear strength, pore pressure. Les sediments marins a grain fin contiennent souvent des bulles de gaz qui peuvent causer de nombreux problemes geotechniques. Ce sol a une structure composite avec des bulles de gaz s'inserant dans la matrice du sol sature. La cavite gazeuse a un effet nefaste sur la rigidite et la resistance du sol lorsqu'elle est remplie uniquement de gaz non dissous. La cavite gazeuse peut etre remplie de gaz et d'eau interstitielle en raison de l'inondation des bulles. L'inondation par bulles a un effet benefique sur la rigidite du sol et la resistance au cisaillement sans drainage, car elle permet a la matrice de sol saturee d'etre partiellement drainee dans une condition globalement non drainee. Un modele constitutif d'etat critique pour l'argile gazeuse est presente, qui tient compte de la structure composite du sol et de l'inondation des bulles. La cavite gazeuse est supposee avoir un effet nefaste sur le durcissement plastique de la matrice du sol sature. Certaines des bulles peuvent etre inondees par l'eau interstitielle de la matrice du sol sature, ce qui entraine une augmentation de la contrainte effective moyenne de la matrice du sol sature. Par consequent, la rigidite et la resistance du sol augmentent. Un seul nouveau parametre est introduit pour modeliser l'effet nefaste des bulles de gaz sur le durcissement plastique. Le modele a ete valide par les resultats de trois argiles gazeuses. [Traduit par la Redaction] Mots-cles : argile gazeuse, etat critique, modele constitutif, resistance au cisaillement sans drainage, pression interstitielle., 1. Introduction Submarine soils with free gas bubbles are widely seen in the seabed throughout the world (Hong et al. 2017; Gao et al. 2020; Sultan and Garziglia 2014). Gas [...]

Shear wave velocity, [V.sub.s], is an important mechanical-dynamic parameter allowing the characterization of a soil in the elastic range ([gamma] < [10.sup.-3]%). Thirty-five existing [G.sub.max] or [V.sub.s] laboratory correlations were examined in this study and are grouped into different general forms based on their geotechnical properties. A database of 11 eastern Canadian clay deposits was selected and used for the critical insights. The effect of the coefficient of earth pressure at rest, [K.sub.0], was also examined. A range of variation for each general form of correlation was determined to take the plasticity index and void ratio values of investigated sites into account. The analysis shows a significant scatter in [V.sub.s1] values predicted by existing correlations and raises questions on the applicability of these correlations, especially for eastern Canadian clays. New correlations are proposed for Champlain clays based on laboratory measurement of [V.sub.s] using the piezoelectric ring-actuator technique, P-RAT, incorporated in consolidation cells. An analysis of P-RAT results reveals the sample disturbance effect and suggests an approach to correct the effect of disturbance on laboratory [V.sub.s] measurements. The applicability of the proposed correlations, including the disturbance correction, is validated by comparison with in situ measurements using multi-modal analysis of surface waves (MMASW). Key words: shear wave velocity ([V.sub.s]), [K.sub.0] coefficient, correlations, eastern Canadian clays, Champlain clays, piezoelectric ring-actuator technique (P-RAT),multi-modal analysis of surface waves (MMASW). La vitesse des ondes de cisaillement, [V.sub.s], est un parametre mecanique-dynamique important pour caracteriser un sol dans le domaine elastique ([gamma] < [10.sup.-3]%). Parmi les correlations de laboratoire [G.sub.max] ou [V.sub.s] existantes, 35 ont ete examinees dans cette etude et sont regroupees sous differentes formes generales en fonction de leurs proprietes geotechniques. On a selectionne et utilise une base de donnees de 11 depots d'argile de l'est du Canada pour l'examen critique. L'influence de la pression des terres au repos, [K.sub.0], a ete egalement examinee. Une plage de variation pour chaque forme generale de correlation a ete determinee afin de prendre en compte la plasticite et les valeurs de l'indice de vide des sites etudies. Les resultats de l'analyse montrent la dispersion entre les valeurs de [V.sub.s1] predites par les correlations existantes et soulevent des questions sur l'applicabilite de ces correlations pour les argiles de l'est du Canada. De nouvelles correlations sont proposees pour les argiles de Champlain, basees sur la mesure en laboratoire de [V.sub.s] a l'aide de la technique des anneaux piezoelectriques, P-RAT, incorporee dans des cellules de consolidation. Une analyse des resultats du P-RAT revele l'effet du remaniement de l'echantillon et suggere une approche pour corriger l'effet du remaniement sur les mesures de [V.sub.s] en laboratoire. La possibilite d'appliquer les correlations proposees, y compris la correction du remaniement, est validee au moyen d'une comparaison des mesures in situ en utilisant l'analyse multimodale des ondes de surface (MMASW). Mots-cles : vitesse de l'onde de cisaillement ([V.sub.s]), coefficient [K.sub.0], correlations, argiles de l'est du Canada, argiles de Champlain, technique des anneaux piezoelectriques (P-RAT), analyse multimodale des ondes de surface (MMASW)., 1. Introduction Since the 1985 Mexico earthquake, a lot of effort has been invested by researchers into better assessing the dynamic response of soil deposits. The low strains shear modulus [...]

Fully softened shear strength mobilized in first-time slope failures, introduced by Skempton in 1970, corresponds to a random edge-face arrangement and interaction of clay particles in an entirely destructured fabric of stiff clays and clay shales. A series of triaxial compression tests was conducted on reconstituted normally consolidated specimens of 15 stiff clay and clay shale compositions. Based on the laboratory results an empirical correlation for secant fully softened friction angle, [Please download the PDF to view the mathematical expression], was developed for clay compositions with plasticity index in the range of 10%-250%, in effective normal stress range of 10-700 kPa. The laboratory measurements confirm an empirical equation for fully softened shear strength in terms of parameters [[[[phi]'.sub.fs].sup.100.sub.s] and [m.sub.fs]. The field application of secant fully softened friction angle was examined by stability analyses of 63 first-time slope failures in 38 geologic materials. These include 45 slope failures with a segment of observed slip surface at residual condition and the back-scarp mobilizing fully softened shear strength, and 18 slope failures with entire observed slip surface at fully softened condition. The back-calculated fully softened secant friction angles for first-time slope failures are in good agreement with [Please download the PDF to view the mathematical expression] correlation based on laboratory tests. Key words: fully softened shear strength, stiff clays, clay shales, first-time slope failures. La resistance au cisaillement entierement ramollie mobilisee dans les ruptures de pente initiales, mise en evidence par Skempton en 1970, repond a une disposition aleatoire des bords et a une interaction des particules d'argile au sein d'un assemblage completement destructure d'argiles rigides et de schistes argileux. On a realise un ensemble d'essais de compression triaxiale de 15 compositions d'argiles rigides et de schistes argileux sur des echantillons reconstitues et normalement consolides. Les resultats de laboratoire ont permis d'etablir une correlation empirique pour l'angle de frottement secant entierement ramolli, [Please download the PDF to view the mathematical expression] pour des compositions d'argile presentant un indice de plasticite de 10-250 %, dans une plage de contraintes normales effectives de 10-700 kPa. La recherche en laboratoire confirme une equation empirique pour la resistance au cisaillement entierement ramollie en termes de parametres [[[[phi]'.sub.fs]].sup.100.sub.s] et [m.sub.fs]. On a examine comment l'angle de frottement secant entierement ramolli peut etre applique sur le terrain en effectuant des analyses de stabilite de 63 ruptures de pente initiales dans 38 materiaux geologiques. Parmi celles-ci, 45 ruptures de pente avec un segment de la surface de glissement observee a l'etat residuel et l'escarpement arriere mobilisant la resistance au cisaillement entierement ramollie, et 18 ruptures de pente avec toute la surface de glissement observee a l'etat entierement ramolli. Les valeurs retro-calculees des angles de friction secants entierement ramollis pour les ruptures de pente initiales sont en bon accord avec la correlation [Please download the PDF to view the mathematical expression] basee sur des essais en laboratoire. [Traduit par la Redaction] Mots-cles : resistance au cisaillement entierement ramollie, argiles rigides, schistes argileux, ruptures de pente initiales., Introduction The urgent need for the introduction of fully softened shear strength (Skempton 1970) followed the Skempton (1964) recommendation of residual shear strength for the long-term stability of stiff fissured [...]

Accurate prediction of soil deformations is important in unloading as well as loading. Historically, however, the loading scenario has been the most common and thus the most extensively studied phenomenon, leaving unloading less well described. Overconsolidated high-plasticity clays are particularly challenging in this regard due to their complex deformation behaviour that has previously shown two conceptually different unloading behaviours. Based on a series of incremental loading and constant rate of strain compression and swelling tests on folded Rosnaes Clay, these unloading behaviours are unified in a framework as different swell modes, and an additional swell mode is identified. These different modes represent a variation in swell-inhibiting structure, seemingly unrelated to the structure in compression. The use of constant rate of strain tests greatly enhanced the detailed description of stiffness development in each mode, which may be characterised by up to three swell phases. The parameters governing the occurrence of the swell modes are identified along with the variables that define the transition between the swell phases and their detailed development. Key words: high-plasticity clay, constant rate of strain, incremental loading, one-dimensional unloading, swell modes. Il est important de predire avec precision les deformations du sol, que ce soit en charge ou en decharge. Auparavant, le scenario de chargement etait le plus courant et donc le phenomene le plus etudie, alors que le dechargement etait moins bien decrit. A cet egard, les argiles surconsolidees a haute plasticite representent un defi particulier en raison de leur comportement de deformation complexe qui a precedemment montre deux comportements de dechargement conceptuellement differents. Apres avoir realise une serie d'essais de compression et de gonflement a charge incrementielle et a taux de deformation constant sur de l'argile de Rosnaes pliee, ces comportements de dechargement sont unifies dans un cadre en tant que differents modes de gonflement, et un mode de gonflement supplementaire est identifie. Les deux methodes representent une variation de la structure inhibant le gonflement, apparemment sans rapport avec la structure en compression. L'utilisation d'essais a taux de deformation constant a considerablement ameliore la description detaillee du developpement de la rigidite dans chaque mode, qui peut etre caracterise par jusqu'a trois phases de gonflement. Nous identifions les parametres qui regissent l'apparition des modes de gonflement ainsi que les variables qui definissent la transition entre les phases de gonflement et leur developpement detaille. [Traduit par la Redaction] Mots-cles : argile a haute plasticite, taux de deformation constant, chargement progressif, dechargement unidimensionnel, modes de gonflement., Introduction Efficient performance of large infrastructure projects requires accurate prediction of deformations during the project lifetime. With an increasing demand for high-speed railway connections worldwide, this challenge is emphasised by [...]

The low-strain dynamic behavior of Leda clays is investigated using resonant column (RC) and bender element (BE) tests. Four undisturbed, lightly overconsolidated Leda clay samples, collected from two sites near the St. Lawrence River valley, are tested at different strains, confining stresses, and frequencies. To evaluate the effect of excitation frequency, simultaneous measurements of shear wave velocity using RC and BE tests are performed. The results show that the samples from the different sites behave differently. The high sensitivity of the Leda clays does not have a significant effect on the modulus degradation curves. However, the measured degradation curves are similar to those of soft clays with high plasticity, which is contrary to the expected behavior of these low plasticity ([I.sub.p] = 6.2-20) specimens. Likewise, the measured damping ratios are on the lower end of the typical values reported for soils of high plasticity. Low values of damping ratio make the amplification of small seismic events more likely in Leda clay deposits. The difference in the shear wave velocity measurements from RC and BE tests ranges from 17% to 26% depending on the confinement, likely because of the strong influence of P-waves observed in the BE tests for these soils. Key words: shear modulus, damping ratio, shear wave velocity, seismic characterization, dynamic properties, soil testing. Le comportement dynamique a faible deformation des argiles Leda est etudie a l'aide d'essais de colonne resonante (RC) et d'elements plies (BE). Quatre echantillons d'argile Leda non perturbes et legerement surconsolides, preleves sur deux sites pres de la vallee du fleuve Saint-Laurent, sont testes a differentes contraintes, contraintes de confinement et frequences. Pour evaluer l'effet de la frequence d'excitation, des mesures simultanees de la vitesse de l'onde de cisaillement sont effectuees au moyen d'essais RC et BE. Les resultats montrent que les echantillons provenant des differents sites se comportent differemment. La sensibilite elevee des argiles Leda n'a pas d'effet significatif sur les courbes de degradation du module. Cependant, les courbes de degradation mesurees sont similaires a celles des argiles molles a plasticite elevee, ce qui est contraire au comportement attendu de ces eprouvettes a faible plasticite ([I.sub.p] = 6,2-20). De meme, les rapports d'amortissement mesures se situent dans la partie inferieure des valeurs typiques rapportees pour les sols ayant une plasticite elevee. Les faibles valeurs du rapport d'amortissement rendent l'amplification des petits evenements sismiques plus probable dans les depots d'argile a Leda. La difference entre les mesures de vitesse des ondes de cisaillement des essais RC et BE varie de 17 a 26 % selon le confinement, probablement en raison de la forte influence des ondes P observee dans les essais BE pour ces sols. [Traduit par la Redaction] Mots-cles : module de cisaillement, rapport d'amortissement, vitesse des ondes de cisaillement, caracterisation sismique, proprietes dynamiques, essais de sol., Introduction The Canadian Highway Bridge Design Code (CSA Group 2019) and National Building Code of Canada (NRCC 2015) have recently standardized the provisions of seismic design of infrastructures in which [...]

The authors would like to thank the discussers for their interest in our paper (Ng et al. 2021). They questioned the reliability of the measured damping ratio (D) and shear [...]

The authors conducted an experimental study to investigate the influence of sesquioxide composition of unsaturated compacted lateritic soils on the shear modulus (G) and damping ratio (D) using a Drnevich [...]

The cyclic response of subgrade clays under traffic loadings is likely to be partly drained rather than undrained, and the traffic-induced dynamic stress field is three-dimensional rather than axisymmetric. To compare the three-dimensional deformation behaviors of saturated clays between partly drained and undrained conditions, a large number of cyclic true triaxial tests were conducted. Experimental results show that a partly drained condition leads to a remarkable increase of permanent major principal strain ([[epsilon].sup.p.sub.1]) compared to an undrained condition, and the differences of [[epsilon].sup.p.sub.1] between the two drainage conditions are affected greatly by the factors of cyclic stress ratio (CSR), overconsolidation ratio (OCR), and coefficient of cyclic intermediate principal stress ([b.sub.cyc]). The increase of [b.sub.cyc] induces a linear reduction of [[epsilon].sup.p.sub.1] in an undrained condition, while it causes an increase first followed by a decrease of [[epsilon].sup.p.sub.1] in a partly drained condition. The clays undergo stiffness softening and hardening in partly drained and undrained conditions, respectively, and the effects of [b.sub.cyc] and CSR on the stiffness evolution are very different between the two drainage conditions. The mechanism of the complex [[epsilon].sup.p.sub.1] and resilient modulus behaviors in a three-dimensional state and partly drained condition is further discussed. In addition, two different empirical models are employed to predict [[epsilon].sup.p.sub.1] in partly drained and undrained conditions. Key words: true triaxial test, clays, three-dimensional deformation, drainage condition, empirical models. La reponse cyclique des argiles de fondation sous les charges du trafic est susceptible d'etre partiellement drainee plutot que non drainee, et le champ de contrainte dynamique induit par le trafic est tridimensionnel plutot qu'axisymetrique. Pour comparer les comportements de deformation tridimensionnelle des argiles saturees entre les conditions partiellement drainees et non drainees, un grand nombre d'essais cycliques triaxiaux reels ont ete realises. Les resultats experimentaux montrent que l'etat partiellement draine conduit a une augmentation remarquable de la souche principale permanente ([[epsilon].sup.p.sub.1]) par rapport a l'etat non draine, et les differences de [[epsilon].sup.p.sub.1] entre les deux etats de drainage sont fortement affectes par les facteurs de rapport de stress cyclique (CSR), de rapport de surconsolidation (OCR) et de coefficient de stress principal intermediaire cyclique ([b.sub.cyc]). L'augmentation de [b.sub.cyc] induit une reduction lineaire de [[epsilon].sup.p.sub.1] dans un etat non draine, alors qu'il provoque une premiere augmentation puis une diminution de [[epsilon].sup.p.sub.1] a l'etat partiellement draine. Les argiles subissent un assouplissement et un durcissement de la rigidite respectivement dans des conditions partiellement drainees et non drainees, et les effets de [b.sub.cyc] et de CSR sur l'evolution de la rigidite sont tres differents entre les deux conditions de drainage. Le mecanisme du complexe [[epsilon].sup.p.sub.1] et les comportements du module de resilience dans un etat tridimensionnel et dans un etat partiellement draine est examine plus en detail. En outre, deux modeles empiriques differents sont utilises pour faire des previsions [[epsilon].sup.p.sub.1] dans des conditions partiellement drainees et non drainees. [Traduit par la Redaction] Mots-cles: essai triaxial veritable, argiles, deformation tridimensionnelle, etat de drainage, modeles empiriques., Introduction Road design, construction, as well as many road defects (e.g., rutting, cracking) are highly related to the traffic-induced permanent and resilient deformations in subgrade soils, which have been studied [...]

This paper presents an interpretation technique to quantify the effects of compaction state and matric suction on the undrained shear strength of compacted clay under confined undrained triaxial compression. This novel technique is based on the mathematical frameworks of the 'stress history and normalized soil engineering property' (SHANSEP) method for saturated soil and the 'Barcelona basic model' (BBM) for unsaturated soil. Test data of compacted Calgary till were analyzed and interpreted using the proposed technique. The interpretation technique is very useful in delineating the relative impacts of the factors on the behavioural trends in measured undrained shear strength. It was found that in addition to the initial compacted void ratio and suction, soil structure and failure mode exert significant influence on the undrained shear strength of compacted clay. This technique is attractive to engineering practitioners because the confined undrained compression tests (with no pore-air and pore-water pressure measurement) are much simpler and less time-consuming compared to rigorous laboratory tests on unsaturated soil. Key words: compacted clay, undrained shear strength, suction, soil structure, tensile rupture, strain softening, ductile yielding. Cet article presente une technique d'interpretation permettant de quantifier les effets de l'etat de compactage et de la succion matricielle sur la resistance au cisaillement non drainee de l'argile compactee sous compression triaxiale confinee non drainee. Cette nouvelle technique est basee sur les cadres mathematiques de la methode SHANSEP ([musch less than] stress history and normalized soil engineering property [much greater than]) pour les sols satures et BBM ([musch less than] Barcelona basic model[much greater than]) pour les sols non satures. Les donnees d'essai du till compacte de Calgary ont ete analysees et interpretees a l'aide de la technique proposee. La technique d'interpretation est tres utile pour delimiter les impacts relatifs des facteurs sur les tendances comportementales de la resistance au cisaillement mesuree sans contrainte. Il a ete constate qu'en plus de l'indice des vides initial et de la succion initiale de l'argile compactee, la structure du sol et le mode de defaillance exercent une influence significative sur la resistance au cisaillement non drainee de l'argile compactee. Cette technique est attrayante pour les ingenieurs car les tests de compression confinee non drainee (sans mesure de la pression de l'air interstitiel et de l'eau interstitielle) sont beaucoup plus simples et moins longs que les tests rigoureux en laboratoire sur des sols non satures. [Traduit par la Redaction] Mots-cles : argile compactee, resistance au cisaillement non drainee, succion, structure du sol, rupture a la traction, ramollissement par contrainte, deformation ductile., Introduction The undrained shear strength, [s.sub.u], of saturated soil is one of the key input parameters in total stress analysis for short-term stability and capacity of geotechnical structures (e.g., shallow [...]

A new experimental series on the highly plastic (plasticity index, IP = 34%) Lower Rhine clay (LRC) is presented. The study comprises tests on normally as well as overconsolidated samples under monotonic and cyclic loading. The loading velocity has been varied to evaluate the strain rate dependency of the LRC behaviour, testifying the well-known reduction of undrained shear strength with decreasing displacement rate. Isotropic consolidation followed by a cyclic loading with constant deviatoric stress amplitude leads to a failure due to large strain amplitudes with eight-shaped effective stress paths in the final phase of the tests. The inherent anisotropy has been additionally evaluated using samples cut out in either the vertical or the horizontal direction. Furthermore, the behaviour of LRC is compared with the behaviour of low plastic kaolin silt (IP = 12.2%). A new visco-hypoplastic-type constitutive model with a historiotropic yield surface has been used to simulate some of the experiments with cyclic loading. Even the eight-shaped stress loops at cyclic mobility are reproduced well with this model. The data of this paper can be also used by other researchers for the examination, calibration, improvement, or development of constitutive models dedicated to fine-grained soils under monotonic and cyclic loading. Key words: fine-grained soils, high-plasticity clay, Lower Rhine clay (LRC), viscosity, time dependency. Une nouvelle etude experimentale sur les argiles du Bas Rhin (ABR) hautement plastiques (indice de plasticite, IP = 34 %) est presentee. L'etude comprend des tests sur des echantillons normaux ainsi que sur des echantillons consolides sous charge monotone et cyclique. La vitesse de chargement a ete modifiee afin d'evaluer la dependance du comportement de l'ABR par rapport a la vitesse de deformation, ce qui temoigne notamment de la reduction bien connue de la resistance au cisaillement non deformee lorsque la vitesse de deplacement diminue. Une consolidation isotrope suivie d'une charge cyclique avec une amplitude de contrainte deviatrice constante conduit a une defaillance due a de grandes amplitudes de deformation avec des chemins de contrainte efficaces en forme de huit dans la phase finale des essais. L'anisotropie inherente a en outre ete evaluee a l'aide d'echantillons decoupes dans le sens vertical ou horizontal. En ce qui concerne le comportement de l'ABR, il est compare au comportement du limon de kaolin a faible teneur en plastique (IP = 12,2 %). Un nouveau modele constitutif de type visco- hypoplastique avec une surface d'elasticite historiotrope a ete utilise pour simuler certaines des experiences de charge cyclique. Meme les boucles de contrainte en forme de huit a la mobilite cyclique sont bien reproduites avec ce modele. Les donnees de cet article peuvent egalement etre utilisees par d'autres chercheurs pour l'examen, l'etalonnage, l'amelioration ou le developpement de modeles constitutifs dedies aux sols a grain fin sous charge monotone et cyclique. [Traduit par la Redaction] Mots-cles: sols a grains fins, argile a haute plasticite, argile du Bas Rhin (ABR), viscosite, dependance temporelle., 1. Introduction Worldwide, more and more areas with soils of low bearing capacity and low stiffness, as in the case of fine-grained soils, have to be assessed. Reasons for this [...]

The shear modulus and hysteretic damping of three sensitive clays from the sediments of Champlain Sea were investigated using a combined triaxial simple shear apparatus. The tests were conducted on undisturbed samples and were carried out on a wide range of shear strains from about 0.001% to 1%. The values of the small-strain shear modulus of the tested clays were further confirmed through a series of piezoelectric ring actuator tests. Although the shear modulus and damping ratio of the sensitive eastern Canadian clays follow some classic literature models, the results show that the examined clays exhibited more linear behaviour. Such behaviour may be attributed to their highly structured nature compared to other clays. The compilation of available data on the shear modulus and damping ratio of several sensitive eastern Canadian clays confirmed this trend and showed that some literature models might not be representative. Key words: shear modulus, damping ratio, sensitive Champlain Sea clays, triaxial simple shear ([T.sub.x]SS), dynamic, earthquake. Le module de cisaillement et l'amortissement hysteretique de trois argiles sensibles provenant des sediments de la mer de Champlain ont ete etudies a l'aide d'un appareil de cisaillement simple triaxial combine. Les essais ont ete effectues sur des echantillons non perturbes et ont ete realises sur une large gamme de deformations de cisaillement allant d'environ 0,001 a 1 %. Les valeurs du module de cisaillement a faible deformation des argiles mises a l'essai ont ete confirmees par une serie d'essais de l'anneau piezoelectrique (<>). Bien que le module de cisaillement et le rapport d'amortissement des argiles sensibles de l'est du Canada suivent certains modeles classiques de la litterature, les resultats montrent que les argiles examinees presentent un comportement plus lineaire. Ce comportement peut etre attribue a leur nature hautement structuree par rapport a d'autres argiles. La compilation des donnees disponibles sur le module de cisaillement et le rapport d'amortissement de plusieurs argiles sensibles de l'est du Canada a confirme cette tendance et a montre que certains modeles de la litterature pourraient ne pas etre representatifs. [Traduit par la Redaction] Mots-cles : module de cisaillement, rapport d'amortissement, argiles sensibles de la mer de Champlain, cisaillement simple triaxial ([T.sub.x]SS), dynamique, seisme., 1. Introduction Each year, approximately 450 earthquake events are recorded in eastern Canada (Natural Resources Canada 2018). Although the majority of these earthquakes are of a low magnitude, some can [...]

A modified piezocone penetration test (CPTu) analytical solution based on spherical cavity expansion and critical state soil mechanics (SCE-CSSM) is employed for assessing yield stress, undrained shear strength, and flow parameters in sensitive Leda clay at the Gloucester test site. For sensitive and structured clays, the formulation relies on the mobilized effective stress friction angle ([phi]') defined at two parts of the stress-strain curve: (i) peak stress ([[phi]'.sub.max]) and (ii) maximum obliquity ([[phi]'.sub.MO]). Input parameters for assessing the overconsolidation ratio (OCR = [[sigma]'.sub.p]/[[sigma]!.sub.vo], where [[sigma]'.sub.p] is preconsolidation stress and [[sigma]'.sub.vo] is current effective vertical stress) from CPTu results include: undrained rigidity index ([I.sub.R] = G/[s.sub.u], where G is shear modulus and [s.sub.u] is undrained shear strength), plastic volumetric strain potential ([LAMBDA] = 1 - ([C.sub.s]/[C.sub.c]), where [C.sub.s] is swelling index and [C.sub.c] is virgin compression index), and effective friction angles ([[phi]'.sub.max] and [[phi]'.sub.MO]). A direct CPTu means of assessing the undrained rigidity index in a reliable manner is also developed that gives the [N.sub.kt] cone factor and matches profiles of undrained shear strength from triaxial compression tests ([s.sub.uTC]). The modified solution is also implemented on two additional sites: a sensitive-quick clay in Norway and structured varved clay from New England. Interpretations of the coefficient of consolidation and permeability from pore-water pressure dissipation tests at Gloucester are evaluated using the SCE-CSSM formulation and shown to be comparable with independent laboratory and field tests.Key words: clays, cone penetrometer, in situ testing, overconsolidation ratio, piezocone, preconsolidation, sensitive clays, yield stresses.Une solution analytique CPTu modifiee basee sur l'expansion spherique et la mecanique des sols a l'etat critique (SCE-CSSM) est utilisee pour evaluer la limite elastique, la resistance au cisaillement non draine et les parametres d'ecoulement dans l'argile a Leda sensible au site d'essai de Gloucester. Pour les argiles sensibles et structurees, la formulation repose sur l'angle de frottement de contrainte effective mobilise ([phi]') defini a deux parties de la courbe contrainte- deformation : (i) contrainte de la crete ([[phi]'.sub.max]), et (ii) obliquite maximale ([[phi]'.sub.MO]). Parametres d'entree pour evaluer le rapport de surconsolidation (OCR = [[sigma]'.sub.p]/[[sigma]'.sub.vo] ou [[sigma]'.sub.p] est la contrainte de preconsolidation et [[sigma]'.sub.vo] est la contrainte verticale effective actuelle) des resultats CPTu comprennent : indice de rigidite non drainee ([I.sub.R] = G/[s.sub.u] ou G est le module de cisaillement et su est la resistance au cisaillement non draine) le potentiel de deformation volumetrique plastique (A = 1- [C.sub.s]/[C.sub.c] ou [C.sub.s] est l'indice de gonflement et [C.sub.c] est l'indice de compression vierge), et l'angle de frottement effectif ([[phi]'.sub.max] et [[phi]'.sub.MO]). Un moyen CPTu direct permettant d'evaluer de maniere fiable l'indice de rigidite non drainee est egalement developpe. Le meme fournit le cone [N.sub.kt] et correspond a des profils de resistance au cisaillement non draine a partir d'essais de compression triaxiale ([s.sub.uTC]). La solution modifiee est egalement mise en oeuvre sur deux sites supplementaires : une argile sensible rapide en Norvege et une argile variee structuree de la Nouvelle-Angleterre. Les interpretations du coefficient de consolidation et de la permeabilite obtenues lors des essais de dissipation de la pression interstitielle a Gloucester ont ete evaluees au moyen de la formulation SCE-CSSM et se sont averees comparables aux essais independants en laboratoire et sur le terrain. [Traduit par la Redaction]Mots-cles : argiles, penetrometre a cone, essais in situ, rapport de surconsolidation, piezocone, preconsolidation, argiles sensibles, contraintes d'elasticite., IntroductionA recent series of piezocone penetration tests (CPTu) have been conducted at Canadian test site No. 1 in Gloucester, Ontario, with one sounding providing a total 23 pore-water pressure dissipation [...]

An existing effective stress limit plasticity solution for piezocone penetration tests (CPTu) is calibrated to evaluate the effective stress friction angle ([phi]') for undrained conditions for a variety of fine-grained soils ranging from natural lean to plastic clays and clayey silts from marine, alluvial, lacustrine, deltaic, and glaciofluvial origins. Data from 105 clay sites are compiled to examine the CPTu-interpreted [phi]' values in comparison with laboratory benchmark values obtained from undrained consolidated anisotropic (CAUC) and undrained compression (CIUC) triaxial tests made on undisturbed samples. An approximate inversion of the theoretical solution is developed to allow profiles of [phi]' to be evaluated with depth. Five well-documented case studies in Illinois, Louisiana, South Carolina, Ireland, and Massachusetts are presented to illustrate the application of the solution. Lastly, results from 1g chamber tests involving kaolin and kaolinitic-silica mixtures tested by miniature piezocone probes are shown for additional verification. Key words: clay, limit plasticity solution, cone penetrometer, friction angle, piezocone, strength. Une solution de plasticite effective de limite de stress existante pour les tests de penetration au piezocone (CPTu en anglais) est calibree pour evaluer l'angle de friction de stress reel ([phi]') dans des conditions non drainees pour une variete de sols fins allant du sol ordinaire aux argiles plastiques et limons argileux d'origines marine, alluviale, lacustre, deltaique et glacio-fluviale. Les donnees de 105 sites argileux sont rassemblees pour examiner les chiffres interpretes des [phi]' CPTu par rapport aux chiffres de reference de laboratoire obtenus par les tests triaxiaux CAUC-CIUC realises sur des echantillons intacts. Une inversion approximative de la solution theorique est developpee pour permettre aux profiles de [phi]' d'etre evalues en profondeur. Cinq etudes de cas bien documentees en Illinois, Louisiane, Caroline du Sud, Irlande et Massachusetts sont presentees pour illustrer l'application de la solution. Enfin, les resultats des tests en chambre 1-g par melanges de kaolin et silice kaolinique testes par sondes piezocones miniatures sont presentes comme verification supplementaire. [Traduit par la Redaction] Mots-cles : argile, solution de plasticite limite, penetrometre A cone, angle de friction, piezocone, force., Introduction The piezocone penetration test (CPTu) is a quick in situ test that permits the delineation of soil stratigraphy and the interpretation of geoparameters with depth in an efficient, economic, [...]

The mechanical properties of clays are influenced by the characteristics of the fluid in the pore space. The liquid limit reacts differently to the permittivity, e, of the fluid: for smectites the slopes are positive, for kaolinite and illite they are negative and smaller. This dissimilarity can be explained by the structural differences between swelling smectites with solvated interlayer cations and nonswelling clay minerals such as kaolinite and illite. Undrained shear strengths, [c.sub.u], of Ca-smectite, but not Na-smectite, correlate with the actual fluid ratio. Regressing [c.sub.u] against the liquidity index, [I.sub.L], yields two different regression lines for Na-smectite and Ca-smectite. For the first time it is shown that normalizing [c.sub.u] to the [epsilon] of the pore fluid results in a single regression line for both smectitic clay types. As kaolinites and illites possess significantly less exchangeable cations than smectites, this yields significantly smaller ranges for Atterberg limits and reduces the impact of [epsilon] on almost pure particleparticle interactions. In addition, the much larger particle sizes of the kaolinite and illite may dominate the undrained shear strengths, as normalization of [c.sub.u] to [epsilon] did not change the relationship to either the actual water content or the liquidity index. Key words: undrained shear strength, pore fluid, Atterberg limits, clays. Les proprietes mecaniques des argiles sont egalement influencees par les caracteristiques du fluide dans l'espace poreux. La limite de liquide reagit differemment a la permittivite, e, du fluide : pour les smectites, les pentes sont positives, pour la kaolinite et l'illite elles sont negatives et plus petites. Cette dissemblance peut s'expliquer par les differences structurelles entre les smectites gonflantes avec des cations intercalaires solvates et les mineraux argileux non gonflants tels que la kaolinite et l'illite. Les resistances au cisaillement non drainees, [c.sub.u], de la Casmectite, mais pas de Na-smectite, sont en correlation avec le taux de fluide reel. La regression de [c.sub.u] par rapport a l'indice de liquidite, IL, donne deux lignes de regression differentes pour les Na-smectite et Ca-smectite. Pour la premiere fois, il est montre que lorsque [c.sub.u] est normalise par rapport au e du fluide interstitiel, il en resulte une seule ligne de regression pour les deux types d'argile smectique. Comme les kaolinites et les illites possedent significativement moins de cations echangeables que les smectites, ceci donne des plages significativement plus petites pour les limites d'Atterberg et reduit l'impact de e sur les interactions particule-particule presque pures. En outre, les tailles de particules beaucoup plus grandes de la kaolinite et de l'illite peuvent dominer les resistances au cisaillement non drainees, car la normalisation de [c.sub.u] a [epsilon] n'a pas modifie les relations avec la teneur en eau reelle ni avec l'indice de liquidite. [Traduit par la Redaction] Mots-cles: resistance au cisaillement non drainee, fluide poreux, limites d'Atterberg, argiles., Introduction Leakage and spillage of diesel and gasoline from pipelines, processing plants or from abandoned fuel stations contaminates the surrounding soil. Clay minerals in these soils may mitigate the extent [...]

Dynamic loadings, induced by earthquakes and other causes, will lead to the cyclic variation of both shear stress and normal stress components on the soil elements. A series of cyclic triaxial tests with and without variable confining pressure were carried out to investigate the coupling effects of cyclic shear stress and cyclic normal stress on the normalized shear modulus, G/[G.sub.max], characteristics of saturated clays. Results indicated that both the phase differences and ratios between the cyclic deviatoric stress and cyclic confining pressure exerted a constant and pronounced influence on the G/[G.sub.max], indicating that the G/[G.sub.max] properties under combined loadings will be more representative of actual field conditions than from single-loading conditions. A modified hyperbolic model considering the effects of cyclic confining pressure was further proposed. Key words: shear modulus, dynamic properties, cyclic confining pressure, triaxial tests, clays. Les charges dynamiques, induites par les tremblements de terre et d'autres causes, meneront la fois la variation cyclique des composantes de la contrainte de cisaillement et de la contrainte normale sur les elements de sol. Une serie d'essais triaxiaux cycliques avec et sans la pression de confinement variable ont ete effectues pour etudier les effets de couplage de la contrainte de cisaillement cyclique et de la contrainte normale cyclique sur les caracteristiques du module de cisaillement normalise G/[G.sub.max] des argiles saturees. Les resultats ont indique que les differences de phase et les ratios entre la contrainte deviatorique cyclique et la pression de confinement cyclique ont exerce une influence marquee et constante sur le G/[G.sub.max], indiquant que les proprietes G/[G.sub.max] sous des charges combinees seront plus representatives des conditions reelles sur le terrain que dans des conditions de charge unique. Un modele hyperbolique modifie tenant compte des effets de la pression de confinement cyclique est en outre propose. [Traduit par la Redaction] Mots-cles : module de cisaillement, proprietes dynamiques, pression de confinement cyclique, essais triaxiaux, argiles., Introduction Water-saturated, fine-grained soil deposits can be subjected to undrained cyclic loads induced by earthquakes, pile driving, explosions, ocean wave storms, and other causes. The dynamic response under such loads [...]

The paper describes the anisotropic undrained stiffness behaviour of four medium-plasticity heavily overconsolidated UK stiff marine clays as revealed through hollow cylinder testing. The experiments contributed to two broader studies on stiff-to-hard London, Gault, Kimmeridge, and Oxford clay strata. They involved static and dynamic testing of multiple highquality natural specimens sampled at similar depths from inland sites. This paper explores the directional dependency of the clays' highly nonlinear undrained stiffness characteristics. New data-analysis approaches are outlined that allow the stiffnesses associated with one-dimensional vertical, horizontal, or pure horizontal shear modes to be isolated in complex undrained stress paths. In the presented experiments, loading progressed from in situ stresses to reach ultimate failure at a range of final major principal stress orientation angles a (defined in the vertical plane) while keeping fixed values of the intermediate principal stress ratio, b. The tests reveal strong undrained stiffness anisotropy that can impact significantly on the prediction and understanding of ground deformation patterns in numerous geotechnical engineering applications. Key words: clays, laboratory tests, stiffness, anisotropy, stress path. Ce document decrit l'anisotropie du comportement rheologique en conditions non drainees de quatre argiles marines britanniques, rigides, fortement surconsolidees et de moyenne plasticite, telle que revelee par des essais sur eprouvettes cylindriques creuses. Ces experiences faisaient partie de deux plus larges etudes portant sur les strates d'argile rigide a dure de Londres, du Gault, de Kimmeridge et d'Oxford. Elles comprenaient des essais statiques et dynamiques sur plusieurs echantillons naturels de haute qualite provenant de profondeurs similaires sur la terre ferme. Cet article explore l'influence de l'orientation des contraintes sur les caracteristiques extremement non lineaires de rigidite des argiles en conditions non drainees. Il y est propose une approche nouvelle de l'analyse des resultats permettant d'isoler, a partir de chemins de contrainte non draines complexes, les parametres du tenseur rheologique associes aux modes de sollicitation purement horizontale, purement verticale, ou de cisaillement pure. Dans les experiences presentees, les chemins de contrainte partant de l'etat in situ se deroulaient de maniere a atteindre la rupture a un eventail d'angles finaux d'orientation de la contrainte principale majeure (par rapport a la vertical), tout en conservant des valeurs fixes du rapport de contrainte principale intermediaire, b. Les tests revelerent une forte anisotropie de la rigidite non drainee pouvant avoir un impact significatif sur la prediction et la comprehension des modes de deformation du sol dans de nombreuses applications d'ingenierie geotechnique. Mots-cles: argiles, essais de laboratoire, rigidite, anisotropie, chemin de contrainte., Introduction Much of the UK's civil engineering infrastructure and several of its major cities are built on stiff overconsolidated, geologically aged, clays. The clays' highly nonlinear stiffness characteristics have an [...]

The deformation of clayey soil under repeated cycles of unloading and reloading has been investigated in oedometer tests using both undisturbed and reconstituted Ariake clay samples. The test results indicate that even for repeated unloading-reloading in the overconsolidated stress range, the deformation of the soil sample is not purely elastic and there is an accumulation of permanent deformation. Based on the test results, a model has been proposed for predicting unloading-reloading- induced deformation. The proposed model has been used to simulate the behaviour of a clayey soil deposit in the Saga Plain, Japan, in response to groundwater fluctuation. Good agreement between the simulation and the field measurements indicates that the proposed model can be used to predict land subsidence induced by groundwater fluctuations. Key words: groundwater fluctuation, land subsidence, oedometer test, repeated unloading-reloading. La deformation des sols argileux sous l'effet de cycles repetes de dechargement et rechargement a ete etudiee par l'intermediaire d'essais redometriques en utilisant a fois des echantillons d'argile d'Ariake reconstituee et non remaniee. Les resultats des essais montrent que, meme pour des cycles de dechargement-rechargement repetes dans le domaine de contraintes surconsolide, la deformation de l'echantillon de sol n'est pas purement elastique et qu'il y a une accumulation de deformations permanentes. A partir des resultats des essais, un modele a ete propose pour predire la formation induite par le cycle de dechargement-rechargement. Le modele propose a ete utilise pour simuler le comportement d'un depot de sol argileux dans la plaine de Saga, au Japon, en reponse aux fluctuations de la nappe phreatique. Une bonne concordance entre la simulation et les mesures effectuees sur le terrain montre que le modele propose peut etre utilise pour predire l'affaissement du sol induit par les fluctuations de la nappe phreatique. [Traduit par la Redaction] Mots-cles: fluctuations de la nappe phreatique, affaissement du sol, essai redometrique, cycles de dechargement- rechargement repetes., Introduction There are many large cities around the world located on soft clay deposits. Due to excessive pumping of groundwater for domestic, industrial, and agricultural uses, sometimes occurring over decades, [...]

Methods of computation for soil heave based on an 'equivalent' net normal stress path approach often have built-in assumptions regarding the relationship between in situ matric suction, overburden stress, and swell pressure. The term 'matric suction equivalent' has been previously defined as the difference between in situ state of stress projected on the net normal stress plane (represented by swell pressure) and overburden stress. Correlations between matric suction, overburden stress, and swell pressure for matric suction values in excess of the air-entry value have not been well studied and are explored here for expansive soils. Filter paper (in-contact) and constant volume swell pressure tests were performed on undisturbed tube samples of expansive soils taken from Arizona, Colorado, and Texas. In general, the ratio of the matric suction equivalent to the matric suction decreases with increasing soil suction. An empirical relationship was established in which the matric suction equivalent was found to be proportional to the logarithm of the matric suction for in situ matric suctions greater than a certain value, termed as the 'intercept matric suction'. A correlation between the intercept matric suction and the soil's plasticity index (PI) was found for the clays of this study. The developed correlations represent a method for obtaining approximate estimates of in situ matric suction for expansive soils from PI and swell pressure data. Implications of the study findings for the use of an equivalent net normal stress approach for estimation of soil heave are explored. Key words: expansive soils, unsaturated soils, matric suction, matric suction equivalent, swell pressure, degree of saturation, heave prediction. Les methodes de calculs de soulevement de sol basees sur une approche avec contrainte normale nette << equivalente >> comportent souvent des hypotheses sur le lien entre la succion matricielle in situ, la pression lithostatique et la pression de gonflement. Le terme<>a ete precedemment defini comme la difference entre l'etat de contrainte in situ projete sur le plan de la contrainte normale nette (representee par la pression de gonflement) et la pression lithostatique. Les liens entre la succion matricielle, la pression lithostatique et la pression de gonflement pour les valeurs de succion matricielle depassant la charge capillaire critique n'ont pas encore ete formellement etudies et sont examines ici dans le cas des sols expansifs. Des essais de pression de gonflement sur papier filtre (en contact avec les echantillons) et a volume constant ont ete realises sur des tubes d'echantillons non perturbes de sols expansifs preleves en Arizona, au Colorado et au Texas. De fa^on generale, le quotient de l'equivalent succion matricielle par la succion matricielle diminue lorsque la succion du sol augmente. Une relation empirique a montre que l'equivalent succion matricielle semblait etre proportionnel au logarithme de la succion matricielle dans le cas ou cette derniere etait superieure a une certaine valeur qualifiee de << succion matricielle au point d'intersection >>. Une correlation entre la succion matricielle au point d'intersection et l'indice de plasticite (IP) du sol a ete decouverte dans le cas des argiles etudiees ici. Les correlations ainsi mises en evidence constituent une methode permettant d'obtenir des estimations approximatives de la succion matricielle in situ dans le cas des sols expansifs a partir des valeurs de l'IP et de la pression de gonflement. On evoque enfin les repercussions des decouvertes realisees dans la presente etude sur l'utilisation d'approches avec contrainte normale nette equivalente pour estimer le soulevement des sols. [Traduit par la Redaction] Mots-cles: sols expansifs, sols non satures, succion matricielle, equivalent succion matricielle, pression de gonflement, degre de saturation, prediction du soulevement., Introduction The vertical swelling of an expansive soil layer is generally referred to as heave. Existing methods for computing heave in response to soil wetting typically follow either an actual [...]

The oedometer tests of remoulded deep clay in East China subjected to consolidation stresses ranging from 0.2 to 15.0 MPa were carried out. Both the measured compression curves and the curves of logarithmic permeability versus void ratio consist of two linear segments, among which the bilinear shape of the compression curves is less noticeable. The consolidation stress and void ratio at the intersection of two lines are around 2 MPa and 0.565 [+ or -] 0.015, respectively, and the corresponding saturated water content is very close to the reported saturated adsorbed water content. Lastly, but most importantly, the calculated microscopic pore size corresponding to the intersection point agrees well with the transitional range of the distance between two clay surfaces within which water molecules transform from bulk-liquid-like water into confined water. This is confirmed by experimental results available in the literature. Key words: clay, high consolidation stress, compressibility, microscopic mechanism. Des essais redometriques sur de l'argile profonde remaniee provenant de l'est de la Chine et soumise a des contraintes de consolidation variant de 0,2 a 15,0 MPa ont ete realises. Les courbes de compression mesurees de meme que les courbes de la permeabilite en logarithme versus l'indice des vides consistent en deux segments lineaires, dans lesquels la forme bilineaire des courbes de compression est moins apparente. La contrainte de consolidation et l'indice des vides a l'intersection de deux lignes sont d'environ 2 MPa et 0,565 [+ or -] 0,015, respectivement, et la teneur en eau a saturation correspondante est tres pres de la teneur en eau adsorbee saturee rapportee. Enfin, le plus important resultat est que la taille des pores microscopiques calculee correspondant au point d'intersection correspond bien avec les distances de transition entre deux surfaces d'argile dans lesquelles les molecules d'eau se transforment d'eau de type liquide a de l'eau confinee. Ceci est confirme par les resultats experimentaux disponibles dans la litterature. [Traduit par la Redaction] Mots-cles: argile, contrainte de consolidation elevee, compressibilite, mecanisme microscopique., Introduction There are over 100 deeply penetrating vertical shafts in East China. Most of them penetrate the Quaternary-age overburden layer, with an average thickness of over 200 m and a [...]

The drying suction--water content soil-water characteristic curves (SWCCs) of three clays (MX80 bentonite, yellow bentonite, and Speswhite kaolin) were experimentally determined using axis-translation, vapour equilibrium, and osmotic techniques. The shrinkage paths of the clays were established from Clod tests. The suction--water content SWCCs in conjunction with the Clod test results enabled establishing the suction--degree of saturation SWCCs and further determination of the air-entry values (AEVs) of the clays. Chemical analyses of the polyethylene glycol (PEG) solutions in the osmotic tests revealed an imbalance of the osmotic suctions between the expelled and the retained salts on either side of semi-permeable membranes. A decrease in the water content due to an applied suction for clays with significant osmotic efficiencies was explained by two mechanisms. In mechanism 1, the water content decrease prior to the air entry is controlled by the interparticle repulsive pressure, and in mechanism 2, a decrease in the degree of saturation following the air entry is primarily due to the matric suction. The agreements between the AEVs of the clays determined based on the osmotic suctions corresponding to various applied suctions and that determined from the suction--degree of saturation SWCCs were found to be very good. Key words: soil-water characteristic curve (SWCC), unsaturated soils, volume measurement, shrinkage, Clod test, clays. Les courbes de retention d'eau (CRE) en drainage de trois argiles (bentonite MX80, bentonite jaune, et kaolin Speswhite) ont ete determinees experimentalement a l'aide des techniques de translation de l'axe, equilibre de vapeur, et par osmose. Les trajectoires de retrait des argiles ont ete etablies a l'aide des essais de Clod. Les succions-teneurs en eau des CRE en plus des resultats des essais de Clod ont permis d'etablir la CRE succion-degre de saturation et de faire des determinations plus poussees des pressions a l'entree d'air (PEA) des argiles. Des analyses chimiques des solutions de polyethylene glycol (PEG) dans les essais par osmose ont revele une difference dans les succions osmotiques entre les sels expulses et retenus de chaque cote des membranes semi-permeables. Une diminution de la teneur en eau due a une succion appliquee pour les argiles ayant des efficacites osmotiques significatives est expliquee par deux mecanismes. Dans le mecanisme 1, la diminution de la teneur en eau avant la pression a l'entree d'air est controlee par la pression repulsive interparticule, et dans le mecanisme 2, une diminution du degre de saturation suite a la pression a l'entree d'air est principalement due a la succion matricielle. La correspondance entre les PEA des argiles determinees apartir des succions osmotiques associees adifferentes succions appliquees etcelles determinees a partir des CRE succion-degre de saturation est tres bonne. [Traduit par la Redaction] Mots-cles: courbe de retention d'eau (CRE), sols non satures, mesure du volume, retrait, essai de Clod, argiles., Introduction Clays are increasingly used in many countries for various important engineering applications. For example, bentonites are used in liner and cap systems for minimizing migration of contaminants of chemical [...]

The tests in this investigation were performed on a natural soft clay with plasticity index around 32%, which was K0 consolidated to a vertical stress of 2942 kPa and then [K.sub.0] unloaded to a vertical stress of 74 kPa (i.e., to the 'in situ' stress). The specimens so created were disturbed in various ways to study the effect of sample disturbance on the stress-strain relationships during undrained shearing and during drained [K.sub.0] loading (i.e., [K.sub.0] triaxial and oedometer tests). The results for two testing alternatives may be summarized as follows. Alternative 1: Allow the specimen to swell at the correct in situ effective stresses, but accept an initial water content that is higher than the in situ value. This alternative was found to give the best stress-strain relationships around the in situ effective stresses for undrained triaxial tests, but with undrained shear strength values up to about 20% too low, due to the swelling taking place during consolidation to the in situ effective stresses. Alternative 2: Prevent swelling by starting the test at effective stresses that are higher than the in situ stresses, but with a water content that is closer to the in situ value than if alternative 1 is chosen. Using only isotropic stresses prior to shearing, this alternative was found to give better undrained shear strength values (although up to about 14% too high) but strain values much too small around the in situ effective stresses. For oedometer tests, only alternative 2 was investigated. Also, for these tests, the strains around the in situ stress were too small, but preconsolidation stresses estimated from stress-strain curves were typically only around 60% of the true value. Key words: stiff clay, sample disturbance, undrained shear strength, preconsolidation stress, triaxial tests, oedometer tests. Les essais dans cette etude ont ete realises sur de l'argile molle naturelle avec un indice de plasticite d'environ 32 %, qui a ete consolidee en [K.sub.0] a une contrainte verticale de 2942 kPa et ensuite dechargee en [K.sub.0] a une contrainte verticale de 74 kPa (c'est-a-dire la contrainte <>). Les echantillons ainsi crees ont ete remanies de differentes facons pour etudier l'effet du remaniement des echantillons sur les relations contrainte-deformation durant le cisaillement non draine et durant le chargement en [K.sub.0] draine (c'est-a-dire essais triaxiaux-K0 et redometriques). Les resultats des deux alternatives d'essai suivantes peuvent etre resumes comme suit. Alternative 1: Permet a l'echantillon de gonfler aux contraintes effectives in situ correctes, mais on doit accepter une teneur en eau initiale qui est superieure a la valeur in situ. Cette alternative donne les meilleures relations contrainte-deformation autour des contraintes effectives in situ pour les essais triaxiaux non draines, mais la resistance au cisaillement est trop faible d'environ jusqu'a 20 %, en raison du gonflement qui se produit durant la consolidation aux contraintes effectives in situ. Alternative 2 : Empecher le gonflement en commencant l'essai a des contraintes effectives superieures aux contraintes in situ, mais d'une teneur en eau qui est plus pres de la valeur in situ qu'a l'alternative 1. Puisqu'elle applique les contraintes isotropes seulement avant le cisaillement, cette alternative s'est averee donner de meilleurs resultats de resistance au cisaillement non draine (malgre des valeurs jusqu'a environ 14 % trop elevees), mais aussi des deformations trop faibles pres des contraintes effectives in situ. Pour les essais redometriques, seulement l'alternative 2 a ete evaluee. Pour ces essais, les deformations pres de la contrainte in situ etaient aussi trop faibles, mais les contraintes de preconsolidation estimees a partir des courbes de contrainte-deformation etaient typiquement seulement a 60 % de la valeur reelle. [Traduit par la Redaction] Mots-cles : argile rigide, remaniement des echantillons, resistance au cisaillement non draine, contrainte de preconsolidation, essais triaxiaux, essais redometriques., Introduction Reconsolidation of strongly disturbed, stiff, and very over consolidated clay specimens to the in situ effective stresses in connection with triaxial tests sometimes ends up with swelling of the [...]

This paper examines the influence of reproducing the stress history of a natural soil deposit during laboratory reconsolidation on the subsequent response and behavior of heavily overconsolidated Bootlegger Cove Formation (BCF) clays under both monotonic and cyclic loadings. The results are compared with a conventional reconsolidation technique wherein a specimen is directly [K.sub.0]-reconsolidated to the in situ effective stresses, and no stress history of the overconsolidated soil deposit is reproduced. Monotonic and cyclic experiments under triaxial conditions were conducted and their results compared in terms of stress-strain-strength responses with emphasis on shear stiffness degradation, to show the significant difference in the responses between the stress-probe sets. Additionally, comparison with field and in situ measurements are presented to validate procedures, judge the accuracy of the experiments, and evaluate the effects of tube sampling. Key words: reconsolidation, stress history, sampling disturbance, stiffness degradation, monotonic and cyclic loading. Cet article examine l'influence de la reproduction de l'historique des contraintes d'un depot de sol naturel lors de sa reconsolidation en laboratoire sur le comportement subsequent d'argiles fortement surconsolidees provenant de la formation Bootlegger Cove (BCF) soumises a des charges monotoniques et cycliques. Les resultats sont compares a une technique de reconsolidation conventionnelle dans laquelle un echantillon est reconsolide en [K.sub.0] directement aux contraintes effectives in situ, et aucun historique des contraintes du depot de sol surconsolide n'est reproduit. Des essais monotoniques et cycliques en conditions triaxiales ont ete realises, et leurs resultats sont compares en termes de comportement en contrainte-deformation-resistance, avec une emphase sur la degradation de la rigidite en cisaillement, pour demontrer la difference significative entre les reponses des series d'essais en contrainte. De plus, des comparaisons entre les mesures de terrain et in situ sont presentes pour valider les procedures, pour juger de la justesse des essais, et pour evaluer les effets de l'echantillonnage par tubes. [Traduit par la Redaction] Mots-cles : reconsolidation, historique des contraintes, perturbation d'echantillonnage, degradation de la rigidite, chargement monotonique et cyclique., Introduction Laboratory testing of soil samples has the advantage over field testing in that the laboratory test's boundary conditions are explicitly known and high-quality stress-strain data can be obtained to [...]

The test fill at Onsoy, close to the town of Fredrikstad in Norway, was built on a very soft marine clay with in situ vane strength as low as 11 kPa and a plasticity index varying from 34 to 50. The dimensions at the bottom of the long fill were 20 m x 60 m and the height 2.3 m. The fill, as placed, had a computed factor of safety against foundation failure of 1.35 based on in situ vane strength. The fill was allowed to sit for about 3 years (from 1972 to 1975) before it, in a second stage, was brought to failure by raising the height. The main purpose of the first stage was to study the stress-strain-time relationships for the soft clay and compare the values of geotechnical parameters determined by careful laboratory tests with those back-calculated from the observed field behaviour. The test fill foundation was heavily instrumented to measure clay deformations and pore pressures with time. Field observations showed that the Onsoy test fill turned out to be more of a drained loading case than an undrained case in spite of the fairly rapid construction of the fill. Actually, subsequent undrained triaxial and direct simple shear tests strongly indicate that the fill might have failed if less drainage had taken place, i.e., if the drainage paths had been longer and (or) if the coefficient of consolidation had been lower. Key words: test fill, Soft clay, field measurements, triaxial tests, in situ vane tests. Le site d'essai de remblayage de Onsoy, pres de la ville de Fredrikstad en Norvege, a ete construit sur de l'argile marine tres molle dont la resistance scissometrique est aussi faible que 11 kPa et dont l'indice de plasticite varie de 34 a 50. Les dimensions au bas du remblai sont de 20 m x 60 m et la hauteur est de 2,3 m. Le remblai, tel que place, comporte un facteur de securite calcule contre les ruptures de fondation de 1,35, base sur la resistance scissometrique in-situ. Le remblai a ete laisse en place pendant environ 3 ans (de 1972 a 1975) avant qu'il n'atteigne la rupture lors d'une deuxieme etape de rehaussement. L'objectif principal de la premiere etape etait d'etudier les relations contraintes-deformations-temps pour l'argile molle, et de comparer les valeurs des parametres geotechniques determines a partir d'essais de laboratoire a des valeurs retro-calcules a partir d'observations du comportement sur le terrain. La fondation du site remblaye a ete instrumentee avec de nombreux appareils pour mesurer des deformations dans l'argile et les pressions interstitielles avec le temps. Les observations sur le terrain ont demontre que le site de remblayage de Onsoy s'est avere un cas de chargement draine plutot qu'un cas non draine, malgre la construction relativement rapide du site. En fait, des essais triaxiaux non draines et de cisaillement simple directs subsequents ont fortement indique que le remblai aurait pu ceder si moins de drainage avait eu lieu, c'est-a-dire si les chemins de drainage avaient ete plus long et/ou si le coefficient de consolidation avait ete plus faible. [Traduit par la Redaction] Mots-cles: site d'essai de remblayage, argile molle, mesures de terrain, essais triaxiaux, essais scissometriques in- situ., Introduction In 1966 the Norwegian Geotechnical Institute (NGI) was engaged by Danish consulting firm Kampsax to assist with the investigation of problems with two highway projects in Thailand where test [...]

It is essential to prevent failures at a tunnel face during tunnel construction to protect existing structures and underground utilities. Many studies have investigated active failure in clay, but passive failure is often overlooked. The objectives of this study are to investigate passive failure as well as surface heave and excess pore-water pressure induced by tunnel face displacement in a geotechnical centrifuge. Long-term settlement and dissipation of excess pore-water pressure after passive failure are also investigated. For a tunnel located at a cover to diameter ratio of 2.1, soil in front of the tunnel face is displaced mainly forwards and upwards to the ground surface by the advancing tunnel face. The measured passive failure pressure is closely bounded by the best upper and lower bounds and agrees reasonably well with the cavity expansion solution. For a tunnel located at a cover to diameter ratio of 4.2, a localized failure mechanism is observed. There is a large discrepancy between the measured passive failure pressure and the upper bound solution. Both longitudinal and transverse surface heaves for tunnels located at cover to diameter ratios of 2.1 and 4.2 may be described by two-dimensional Gaussian distributions. The spherical cavity expansion solution appears to overestimate excess pore-water pressure upon passive failure for a tunnel located at a cover to diameter ratio of 2.1 An average of 90% degree of consolidation is reached at time factors of 0.9 and 1.5 for tunnels located at cover to diameter ratios of 2.1 and 4.2, respectively. Key words: tunnel face, passive failure, heave, pore-water pressure, clay. Il est essentiel de prevenir les ruptures de la face d'un tunnel durant la construction du tunnel pour proteger les structures existantes et les conduites de services enfouies. Plusieurs etudes se sont penchees sur la rupture active dans l'argile, mais la rupture passive est souvent negligee. Les objectifs de cette etude sont d'etudier la rupture passive ainsi que le soulevement de surface et la pression interstitielle excessive induits par le deplacement de la face d'un tunnel dans une centrifugeuse geotechnique. Les tassements a long terme et la dissipation des pressions interstitielles apres la rupture passive sont aussi evalues. Dans le cas d'un tunnel situe a un ratio couverture/diametre de 2,1, le sol devant la face du tunnel est deplace principalement vers l'avant et vers la surface du sol par la face du tunnel qui avance. La pression de rupture passive mesuree est incluse entre les meilleures frontieres inferieures et superieures et correspond assez bien avec la solution de l'expansion d'une cavite. Dans le cas d'un tunnel situe a un ratio couverture/diametre de 4,2, un mecanisme de rupture localise est observe. On observe une grande difference entre la pression de rupture passive mesuree et la solution a la frontiere superieure. Les soulevements de surface longitudinaux et transversaux pour des tunnels situes a des ratios couverture/diametre de 2,1 a 4,2 peuvent etre decrits par des distributions Gaussiennes en deux dimensions. La solution de l'expansion d'une cavite spherique semble surestimer la pression interstitielle lors de la rupture passive pour un tunnel situe a un ratio couverture/diametre de 2,1. Un degre de consolidation moyen de 90 % est atteint a un facteur de temps de 0,9 et 1,5 pour des tunnels situes a des ratios couverture/diametre de 2,1 et 4,2, respectivement. [Traduit par la Redaction] Mots-cles: face d'un tunnel, rupture passive, soulevement, pression interstitielle, argile., Introduction The construction of shallow tunnels for new underground transport systems in cities has great potential to damage existing structures and utilities. Engineers responsible for the tunnel construction must prevent [...]

The results of a study with undrained cyclic triaxial and direct simple shear (DSS) tests on high-quality undisturbed samples obtained from large blocks of a soft marine Norwegian clay are presented. Several tests with different average shear stresses, shear stress amplitudes, loading frequencies, and sample geometries have been performed on block samples taken from different depths. In tests with small average shear stresses, failure occurred due to large shear strain amplitudes, while large permanent shear strains were observed in tests with higher average shear stresses. Diagrams quantifying the undrained cyclic strength, permanent shear strain, shear strain amplitude, and permanent pore-water pressure dependent on average shear stress, shear stress amplitude, and number of cycles have been developed based on the test results. The undrained cyclic strength was found strongly dependent on loading frequency. Block samples from shallower depth showed a somewhat higher undrained cyclic strength. No influence of the height-to-diameter ratio of the samples (h/d = 1 and 2 were compared) could be found. A qualitative comparison of the test results with data for standard tube samples is provided. Key words: soft marine clay, block samples, undrained cyclic triaxial tests, undrained cyclic direct simple shear (DSS) tests. Les resultats d'une etude d'essais triaxiaux non draines cycliques et d'essais cycliques non draines en cisaillement simple direct (CSD) sur des echantillons de bonne qualite non remanies provenant de blocs d'argile molle norvegienne sont presentes. Plusieurs essais avec differentes moyennes et amplitudes de contraintes de cisaillement, frequences de chargement et geometries ont ete executes sur des echantillons en bloc de differentes profondeurs. Pour les essais de faible contrainte moyenne de cisaillement, la rupture est due aux amplitudes elevees de deplacement en cisaillement, tandis que des deplacements en cisaillement permanents eleves ont ete observes pour les essais de contrainte moyenne de cisaillement elevee. Des diagrammes quantifiant les resistances cycliques non drainees, les deplacements en cisaillement permanents, l'amplitude de deplacement en cisaillement et la pression interstitielle permanente, selon la contrainte moyenne de cisaillement, l'amplitude de la contrainte de cisaillement et le nombre de cycles ont ete developpes base sur les resultats de ces essais. Il est demontre que les resistances cycliques non drainees dependent de la frequence de chargement. Des echantillons moins profonds demontrent des resistances cycliques non drainees un peu plus elevees. Aucune influence du ratio hauteur/diametre des echantillons (h/d = 1 et 2 ont ete compares) n'a ete observee. Une comparaison qualitative des resultats des essais avec des echantillons en tube standards est presentee. [Traduit par la Redaction] Mots-cles : argile marine molle, echantillons en bloc, essais triaxiaux cycliques non draines, essais cycliques non draines en cisaillement simple direct (CSD)., Introduction The foundation design of offshore installations (gravity platforms, piled installations, suction anchors, wind turbines) or structures along the coast (harbours, breakwaters, storm-surge barriers) is governed by the bearing capacity [...]

Offshore developments for hydrocarbon resources have now progressed to water depths approaching 3000 m, with geotechnical design increasingly focused on soft sediments in the upper 30 m or so of the seabed. Due to the difficulties and high cost in recovering high-quality samples from deepwater sites, there is increasing dependence on in situ testing techniques for determining the geotechnical design parameters. This paper summarizes the findings from a joint industry project, undertaken by the Norwegian Geotechnical Institute and the Centre for Offshore Foundation Systems at The University of Western Australia, on the use of in situ testing for the characterization of deepwater soft soils. The project focused on theoretical and empirical studies for the interpretation of piezocone, T-bar, and ball penetration test data, linking the penetration resistance to shear strengths determined from in situ vane tests and laboratory tests on high-quality samples. Guidelines are summarized for interpreting in situ test data, particularly for estimating intact and remoulded undrained shear strengths from the penetration resistance measured by each type of penetrometer. Suggestions are also given for future development of in situ testing techniques to maximize the potential of in situ testing in characterization of deepwater soft soils. Key words: offshore soil investigations, soft clay, full flow penetrations, undrained shear strength. Les developpements des ressources d'hydrocarbures en mer atteignent maintenant des profondeurs de pres de 3000 m, et la conception geotechnique est de plus en plus centree [s.sub.ur] les sediments mous des premiers 30 m du fond marin. En raison des difficultes et des couts eleves associes a la recuperation d'echantillons de qualite des sites profonds, les techniques in situ voient leur utilisation augmenter lors de la determination des parametres geotechniques de conception. Cet article resume les resultats obtenus lors d'un projet industriel conjoint, entrepris par l'Institut geotechnique norvegien et par le Centre for Offshore Foundation Systems a l'Universite de Western Australia, [s.sub.ur] l'utilisation de methodes in situ pour la caracterisation des sols marins mous et profonds. Le projet s'est penche [s.sub.ur] les etudes theoriques et empiriques de l'interpretation des donnees provenant d' essais au piezocone, au T-bar et au penetrometre a bille, reliant la resistance a la penetration aux resistances en cisaillement determinees par des essais scissometriques in situ et en laboratoire effectues [s.sub.ur] des echantillons de qualite elevee. Des directives pour interpreter les donnees d'essais in situ sont resumees, en particulier pour l'estimation de la resistance au cisaillement non drainee intacte et remaniee a partir des resistances a la penetration obtenues pour chaque type de penetrometre. Des suggestions sont aussi fournies pour le developpement futur des techniques d'essai in situ afin de maximiser le potentiel de la caracterisation in situ des sols mous et profonds. Mots-cles : etudes des sols marins, argile molle, penetration en ecoulement complet, resistance au cisaillement non drainee. [Traduit par la Redaction], Introduction Geotechnical properties of near-surface seabed sediments are of increasing importance for deepwater hydrocarbon field developments, where offshore installations will typically comprise wellheads and subsea completions, pipelines, and shallow anchoring [...]

Quantifications Of uncertainties in soil shear strengths, including undrained shear strength of clay, are essential for geotechnical reliability-based design. In particular, how to reduce the uncertainties in undrained shear strengths based on all available information by correlation is a practical research subject, given the considerable cost of a typical site investigation. Although it is simple to reduce the uncertainties by correlation when the information is one dimensional (or univariate), it is quite challenging to reduce the uncertainties by using multivariate information through multiple correlations. This study proposes a systematic way of achieving multivariate correlations on undrained shear strengths. A set of simplified equations are obtained through Bayesian analysis for the purpose of reducing uncertainties: the inputs to the equations are the results of in situ or laboratory tests and the outputs are the updated mean values and coefficients of variation (c.o.v.s) of the undrained shear strengths. Two case studies are used to demonstrate the consistency of the proposed simplified equations. Results show that uncertainties in undrained shear strengths can be effectively reduced by incorporating multivariate information. Given that reliability-based design can justify more economical design with reduced uncertainties, the proposed equations essentially link the value of more and better tests directly to final design savings. Key words: uncertainty, undrained shear strength, in situ test, correlation. Bayesian analysis. La quantification des incertitudes dans les resistances au cisaillement des sols, incluant la resistance an cisaillement de l'argile, est essentielle pour la conception geotechnique basee sur la fiabilite. Un sujet de recherche pratique concerne les facons de reduire les incertitudes dans les resistances au cisaillement non drainees, basees sur toutes les informations disponibles par correlation, considerant le cout eleve d'une etude typique sur un site. Malgre le fait qu'il soil simple de reduire les incertitudes par correlation lorsque l'information est unidimensionnelle (ou univariee), il est neanmoins plus difficile de reduire les incertitudes a partir de donnees multivariees a correlation multiples. Cette etude propose une methode systematique pour obtenir des correlations multivariees sur des resistances au cisaillement non drainees. Une serie d'equations simplifies sont obtenues a 1'aide d'une analyse Bayesienne dans le but de reduire les incertitudes : les resultats d'essais in situ ou en laboratoire servent d'intrants pour les equations, les sortants etant les moyennes des valeurs et des coefficients de variation (c.o.v.s) pour les resistances au cisaillement non drainees. Deux etudes de cas sont presentees afin de demontrer la coherence des equations simplifies proposees. Les resultats montrent que les incertitudes dans les resistances au cisaillement non drainees peuvent effeclivement etre reduites en integrant des informations multivariees. Etant donne que la conception basee sur la fiabilite pent justifier des conceptions plus economiques avec des incertitudes reduites, les equations proposees font le lien direct entre la valeur d'essais meilleurs el plus nombreux et les economies a la conception finale. Mots-cles : incertitude, resistance au cisaillement non drainee, essai in situ, correlation, analyse Bayesienne. [Traduit par la Redaction], Introduction Uncertainties are commonly encountered in geotechnical engineering. Possible sources of these uncertainties may include inherent variabilities, measurement errors, modeling (or transformation) uncertainties, etc. More economical geotechnical designs can be [...]