L’influence de l’eau sur les propriétés mécaniques des roches a fait l’objet de peu d’études jusqu’à présent. Or dans de nombreuses situations, la différence entre le comportement mécanique de la roche sèche et saturée en eau peut être appréciable. De nouveaux champs d’application, tels que l’analyse des risques liés à l’après-mine ou les problématiques relatives au stockage souterrain des déchets nucléaires, requièrent actuellement une connaissance plus approfondie de ces aspects. Cette étude expérimentale se propose donc de contribuer à une meilleure compréhension du comportement hydromécanique de matériaux rocheux partiellement saturés. Pour ce faire, la démarche suivie a consisté à se baser sur des techniques et outils bien établis pour les sols (meubles), et à les adapter aux matériaux rocheux. Dans ce contexte, une première étude a été menée sur un matériau rocheux argileux, le schiste de Beringen, et a permis d’évaluer l’influence de la succion pour les états de compression simple. Suite à cette première étude, d’autres états de contrainte ont été envisagés, principalement au moyen de l’essai triaxial. Le contrôle de la succion en cours d’essai a demandé d’importantes transformations au système triaxial déjà disponible au laboratoire. En parallèle, un nouvel équipement, comprenant notamment un contrôle de la succion par la méthode de translation d’axes, a été conçu et mis en service. La suite du programme expérimental a été réalisée sur une roche poreuse et très homogène : le calcaire de Sorcy. A l’état sec, les résultats d’essais triaxiaux et polyaxiaux ont permis la construction de surfaces de charge tridimensionnelles. En plan méridien, comme pour d’autres roches poreuses, la résistance augmente avec la pression de confinement lorsque celle-ci reste assez faible (inférieure à 15 MPa environ) ; le comportement est fragile. Aux confinements plus élevés, le comportement devient ductile. En plan octaédrique, la forme de la surface évolue depuis le triangle jusqu’au cercle dans la partie fragile, puis continue à évoluer vers un triangle (inversé par rapport au premier) dans le domaine ductile. En conditions saturées, un ensemble cohérent de paramètres poroélastiques a été mesuré, parmi lesquels le coefficient de Biot (qui a été évalué à environ 0.85). La variabilité de ces paramètres entre échantillons et en fonction de l’état de contrainte a été examinée. Dans le domaine poroplastique, c’est la contrainte effective de Terzaghi qui se révèle contrôler le comportement mécanique, malgré que le coefficient de Biot soit inférieur à 1. En plan méridien, l’enveloppe obtenue pour le matériau saturé se rapproche de celle du matériau sec, moyennant une normalisation par rapport à sa longueur horizontale. Ceci suggère que la prise en compte des conditions non saturées pourrait se faire, comme souvent pour les sols, par l’ajout d’un axe supplémentaire : la succion. En conditions non saturées, les essais réalisés en conditions isotropes à succion contrôlée montrent une forte augmentation du module d’incompressibilité drainé avec la pression de confinement et une faible augmentation avec la succion. Ceci tend à conforter les hypothèses adoptées.

Saskatchewan Highways and Transportation (SDHT) rely on dense-graded hot mix asphalt concrete mixes for construction and rehabilitation of asphalt pavement surfaced highways. As a result of increased commercial truck traffic on the provincial road network, over the last two decades, some of Saskatchewans recently placed dense graded hot mix asphalt concrete (HMAC) pavements have been observed to show a susceptibility to premature permanent deformation in the asphalt mix. One of the aggregate properties thought to have significant influence on mix performance under traffic loading is the shape of the aggregate. Specifically, the physical properties of the fine aggregate (smaller than 5 mm in diameter) are of particular importance in dense graded mixes. Although empirical evidence suggests that there are performance benefits associated with using angular fine aggregate, the relationship of this parameter on mechanistic mix performance and resistance to permanent deformation has not yet been clearly defined.<p>The primary objective of this research was to conduct laboratory analysis to determine the physical, empirical, and mechanistic behaviour sensitivity to the proportion of manufactured and natural fine aggregate in SDHT Type 72 hot mix asphalt concrete. The second objective of this research was to compare the mechanistic behaviour of the Type 72 mixes considered in this research to conventional SDHT Type 70 structural hot mix asphalt concrete.<p>Physical and mechanistic properties of a SDHT Type 72 mix at levels of 20, 40, and 60 percent manufactured fines as a portion of total fines (smaller than 5 mm), and for a SDHT Type 70 mix (which contained 38 percent manufactured fines) were evaluated. Ten repeat samples were compacted for each mix using 75-blow Marshall compaction, and ten samples for each mix were compacted using the Superpave gyratory compaction protocols. Marshall stability and flow testing was conducted on the Marshall-compacted samples. Triaxial frequency sweep testing was conducted on the gyratory-compacted samples using the Rapid Triaxial Tester (RaTT) at 20°C. The testing was conducted at axial loading frequencies of 10 and 0.5 Hz, and at deviatoric stress states of 370, 425, and 500 kPa, respectively. The resulting dynamic modulus, axial and radial microstrains, Poissons ratio, and phase angle were evaluated.<p>The research hypothesis stated that the increased amount of manufactured fines improves mechanistic properties of the Type 72 mix under typical field state conditions, and Type 72 mix with increased manufactured fines can exhibit mechanistic properties equivalent to or exceeding those of a typical type 70 mix. <p>Based on the improved densification properties, increased Marshall stability, increased dynamic modulus, and reduced radial and axial strains, it was demonstrated that increasing manufactured fines content in the SDHT Type 72 mix does improve the mechanistic properties of this dense-graded asphalt mix. It should be noted that there appears to be a minimum level of manufactured fines content that is required to affect mix response to loading, and that this threshold lies somewhere between 40 and 60 percent manufactured fines content for the Type 72 mix tested as part of this research.<p>Further, the Type 72 mix exhibited comparable or improved mechanistic properties relative to the Type 70 mix, which SDHT consider a structural mix. This is illustrated by the Type 72 mix with 60 percent manufactured fines resulting in higher Marshall stability and dynamic modulus, and lower axial microstrains than the Type 70 mix evaluated in this study.<p>It is recommended that other Type 72 and Type 70 mixes are evaluated using similar testing protocols. In addition, field test sections should be used to further verify the research hypothesis investigated here. <p>Economic analysis indicates that substantial savings in life cycle costs of SHDT asphalt concrete surfaced roadways can be realized by engineering well-performing, rut-resistant mixes. The life cycle costs can be reduced annually by approximately $7.4 million, which translates into $102.5 million savings over 18 years, during which the entire pavement network would be resurfaced with well-performing asphalt concrete mixes.<p>Further, enhanced crushing of smaller aggregate top size decreases the amount of rejected material, and increases manufactured fines to coarse aggregate ratio, resulting not only in better engineering properties, but also in the optimized use of the provinces diminishing gravel resources. Pressures on aggregate sources are also reduced by improving life cycle performance of Saskatchewan asphalt concrete pavements. The total potential aggregate savings that can be realized by implementing well-performing Type 72 HMAC mixes amount to 4.3 million metric tonnes of aggregate in the next 42 years. These aggregate savings can help decrease the predicted shortage of aggregate between 2007 and 2049 by approximately 6 percent. The total potential cost savings after 18 years of paving 500 km per year with rut-resistant, well-performing HMAC mixes amount to $112.4 million in present value dollars. The 42 year savings amount to $193.7 million in present day dollars. It is recommended that a more detailed economic analysis be carried out.

Saskatchewan Highways and Transportation (SDHT) rely on dense-graded hot mix asphalt concrete mixes for construction and rehabilitation of asphalt pavement surfaced highways. As a result of increased commercial truck traffic on the provincial road network, over the last two decades, some of Saskatchewans recently placed dense graded hot mix asphalt concrete (HMAC) pavements have been observed to show a susceptibility to premature permanent deformation in the asphalt mix. One of the aggregate properties thought to have significant influence on mix performance under traffic loading is the shape of the aggregate. Specifically, the physical properties of the fine aggregate (smaller than 5 mm in diameter) are of particular importance in dense graded mixes. Although empirical evidence suggests that there are performance benefits associated with using angular fine aggregate, the relationship of this parameter on mechanistic mix performance and resistance to permanent deformation has not yet been clearly defined.<p>The primary objective of this research was to conduct laboratory analysis to determine the physical, empirical, and mechanistic behaviour sensitivity to the proportion of manufactured and natural fine aggregate in SDHT Type 72 hot mix asphalt concrete. The second objective of this research was to compare the mechanistic behaviour of the Type 72 mixes considered in this research to conventional SDHT Type 70 structural hot mix asphalt concrete.<p>Physical and mechanistic properties of a SDHT Type 72 mix at levels of 20, 40, and 60 percent manufactured fines as a portion of total fines (smaller than 5 mm), and for a SDHT Type 70 mix (which contained 38 percent manufactured fines) were evaluated. Ten repeat samples were compacted for each mix using 75-blow Marshall compaction, and ten samples for each mix were compacted using the Superpave gyratory compaction protocols. Marshall stability and flow testing was conducted on the Marshall-compacted samples. Triaxial frequency sweep testing was conducted on the gyratory-compacted samples using the Rapid Triaxial Tester (RaTT) at 20°C. The testing was conducted at axial loading frequencies of 10 and 0.5 Hz, and at deviatoric stress states of 370, 425, and 500 kPa, respectively. The resulting dynamic modulus, axial and radial microstrains, Poissons ratio, and phase angle were evaluated.<p>The research hypothesis stated that the increased amount of manufactured fines improves mechanistic properties of the Type 72 mix under typical field state conditions, and Type 72 mix with increased manufactured fines can exhibit mechanistic properties equivalent to or exceeding those of a typical type 70 mix. <p>Based on the improved densification properties, increased Marshall stability, increased dynamic modulus, and reduced radial and axial strains, it was demonstrated that increasing manufactured fines content in the SDHT Type 72 mix does improve the mechanistic properties of this dense-graded asphalt mix. It should be noted that there appears to be a minimum level of manufactured fines content that is required to affect mix response to loading, and that this threshold lies somewhere between 40 and 60 percent manufactured fines content for the Type 72 mix tested as part of this research.<p>Further, the Type 72 mix exhibited comparable or improved mechanistic properties relative to the Type 70 mix, which SDHT consider a structural mix. This is illustrated by the Type 72 mix with 60 percent manufactured fines resulting in higher Marshall stability and dynamic modulus, and lower axial microstrains than the Type 70 mix evaluated in this study.<p>It is recommended that other Type 72 and Type 70 mixes are evaluated using similar testing protocols. In addition, field test sections should be used to further verify the research hypothesis investigated here. <p>Economic analysis indicates that substantial savings in life cycle costs of SHDT asphalt concrete surfaced roadways can be realized by engineering well-performing, rut-resistant mixes. The life cycle costs can be reduced annually by approximately $7.4 million, which translates into $102.5 million savings over 18 years, during which the entire pavement network would be resurfaced with well-performing asphalt concrete mixes.<p>Further, enhanced crushing of smaller aggregate top size decreases the amount of rejected material, and increases manufactured fines to coarse aggregate ratio, resulting not only in better engineering properties, but also in the optimized use of the provinces diminishing gravel resources. Pressures on aggregate sources are also reduced by improving life cycle performance of Saskatchewan asphalt concrete pavements. The total potential aggregate savings that can be realized by implementing well-performing Type 72 HMAC mixes amount to 4.3 million metric tonnes of aggregate in the next 42 years. These aggregate savings can help decrease the predicted shortage of aggregate between 2007 and 2049 by approximately 6 percent. The total potential cost savings after 18 years of paving 500 km per year with rut-resistant, well-performing HMAC mixes amount to $112.4 million in present value dollars. The 42 year savings amount to $193.7 million in present day dollars. It is recommended that a more detailed economic analysis be carried out.

Liquefaction is a phenomenon that occurs in loose saturated sand deposits that are subjected to earthquake loading. This phenomenon can cause massive displacements and significant destruction. Many methods for mitigating liquefaction have been proposed and investigated including compaction, drainage, and grouting. One such liquefaction mitigation technique involves the addition of bentonite fines to the pore spaces of a loose, saturated sand via permeation of an engineered clay suspension. This method of soil improvement has provided the basis and motivation for this research. Also, the effect of plastic and non-plastic fines on the static and cyclic response of sands is somewhat contradictory throughout the literature. Thus, the primary objective of this study was to characterize the affect of an engineered bentonite pore fluid on the undrained monotonic response of loose, saturated Ottawa sand in order to determine its feasibility for use as an effective method for liquefaction mitigation. The permeation of engineered bentonite suspensions is proposed as a passive site remediation technique. Thus, the suspensions were delivered to loose Ottawa sand specimens in the laboratory by permeation in a newly designed three-way split mold. This split mold was used to create easily tested specimens that would have an initial soil fabric similar to that expected after permeation in the field. The bentonite suspensions were treated with sodium pyrophosphate to reduce the initial yield stress and viscosity in order to allow for permeation. Three different bentonite suspensions were utilized throughout this study each having different properties and delivering slightly different amounts of bentonite to the loose, saturated sand. The affect of this engineered pore fluid on the undrained shear response of loose, saturated Ottawa sand was compared to the undrained shear response of clean sand and dry-mixed sand and bentonite. The specimen preparation method (dry-mixed or permeated) was shown to have a significant effect on the response of the sand specimens. While the dry-mixed specimens produced larger and more sustained positive pore water pressures than the clean sand (resulting in an increased tendency to flow), the permeated specimens showed a marked decrease in the generation of excess pore water pressures, displayed a more dilative response, and thus resulted in a soil structure that was less likely to flow. Finally, the results of tests on specimens permeated with engineered bentonite suspensions show that there is little to no change in the effective friction angle at critical state. A method for effectively testing permeated soil specimens was developed in this study. This method has laid the framework for further investigations into the use of engineered bentonite suspensions for liquefaction mitigation by permeation grouting. / text

In 2010 and 2011 Christchurch, New Zealand experienced a series of earthquakes that caused extensive damage across the city, but primarily to the Central Business District (CBD) and eastern suburbs. A major feature of the observed damage was extensive and severe soil liquefaction and associated ground damage, affecting buildings and infrastructure. The behaviour of soil during earthquake loading is a complex phenomena that can be most comprehensively analysed through advanced numerical simulations to aid engineers in the design of important buildings and critical facilities. These numerical simulations are highly dependent on the capabilities of the constitutive soil model to replicate the salient features of sand behaviour during cyclic loading, including liquefaction and cyclic mobility, such as the Stress-Density model. For robust analyses advanced soil models require extensive testing to derive engineering parameters under varying loading conditions for calibration. Prior to this research project little testing on Christchurch sands had been completed, and none from natural samples containing important features such as fabric and structure of the sand that may be influenced by the unique stress-history of the deposit. This research programme is focussed on the characterisation of Christchurch sands, as typically found in the CBD, to facilitate advanced soil modelling in both res earch and engineering practice - to simulate earthquake loading on proposed foundation design solutions including expensive ground improvement treatments. This has involved the use of a new Gel Push (GP) sampler to obtain undisturbed samples from below the ground-water table. Due to the variable nature of fluvial deposition, samples with a wide range of soil gradations, and accordingly soil index properties, were obtained from the sampling sites. The quality of the samples is comprehensively examined using available data from the ground investigation and laboratory testing. A meta-quality assessment was considered whereby a each method of evaluation contributed to the final quality index assigned to the specimen. The sampling sites were characterised with available geotechnical field-based test data, primarily the Cone Penetrometer Test (CPT), supported by borehole sampling and shear-wave velocity testing. This characterisation provides a geo- logical context to the sampling sites and samples obtained for element testing. It also facilitated the evaluation of sample quality. The sampling sites were evaluated for liquefaction hazard using the industry standard empirical procedures, and showed good correlation to observations made following the 22 February 2011 earthquake. However, the empirical method over-predicted liquefaction occurrence during the preceding 4 September 2010 event, and under-predicted for the subsequent 13 June 2011 event. The reasons for these discrepancies are discussed. The response of the GP samples to monotonic and cyclic loading was measured in the laboratory through triaxial testing at the University of Canterbury geomechanics laboratory. The undisturbed samples were compared to reconstituted specimens formed in the lab in an attempt to quantify the effect of fabric and structure in the Christchurch sands. Further testing of moist tamped re- constituted specimens (MT) was conducted to define important state parameters and state-dependent properties including the Critical State Line (CSL), and the stress-strain curve for varying state index. To account for the wide-ranging soil gradations, selected representative specimens were used to define four distinct CSL. The input parameters for the Stress-Density Model (S-D) were derived from a suite of tests performed on each representative soil, and with reference to available GP sample data. The results of testing were scrutinised by comparing the data against expected trends. The influence of fabric and structure of the GP samples was observed to result in similar cyclic strength curves at 5 % Double Amplitude (DA) strain criteria, however on close inspection of the test data, clear differences emerged. The natural samples exhibited higher compressibility during initial loading cycles, but thereafter typically exhibited steady growth of plastic strain and excess pore water pressure towards and beyond the strain criteria and initial liquefaction, and no flow was observed. By contrast the reconstituted specimens exhibited a stiffer response during initial loading cycles, but exponential growth in strains and associated excess pore water pressure beyond phase-transformation, and particularly after initial liquefaction where large strains were mobilised in subsequent cycles. These behavioural differences were not well characterised by the cyclic strength curve at 5 % DA strain level, which showed a similar strength for both GP samples and MT specimens. A preliminary calibration of the S-D model for a range of soil gradations is derived from the suite of laboratory test data. Issues encountered include the influence of natural structure on the peak-strength–state index relationship, resulting in much higher peak strengths than typically observed for sands in the literature. For the S-D model this resulted in excessive stiffness to be modelled during cyclic mobility, when the state index becomes large momentarily, causing strain development to halt. This behaviour prevented modelling the observed re- sponse of silty sands to large strains, synonymous with “liquefaction”. Efforts to reduce this effect within the current formulation are proposed as well as future research to address this issue.

Pour étudier les déformations permanentes des enrobés bitumineux, la division SMIT du LCPC a mis au point un essai triaxial thermorégulé à pression de confinement constante. Un important travail de mise au point de l'essai et de vérification des mesures a été réalisé. Une première campagne expérimentale, portant sur des essais de fluage à contrainte imposée, a permis d'étudier l'influence des paramètres pression de confinement, déviateur de contraintes et température sur le comportement des enrobés bitumineux sous chargement statique. Ces essais ont, de plus, permis de valider le principe d'équivalence temps température en grandes déformations, avec confinement. Un modèle élasto-viscoplastique, permettant de prendre en compte l'application d'une pression de confinement, a été développé pour simuler les essais de fluage. Son principe est basé sur les observations expérimentales. Les applications visées sont l'étude de structures bitumineuses telles que les plates-formes industrielles ou aires de stationnement. Une deuxième campagne d'essais de compression cyclique sinusoïdale a ensuite été menée. Lors de ces essais, on mesure : les déformations cycliques, de l'ordre de 10−4 m/m, qui nous permettent d'obtenir des informations sur l'évolution de la rigidité du matériau (module complexe et coefficient de Poisson) et les déformations permanentes, de l'ordre de 10−2 m/m, qui donnent des informations sur la résistance à l'orniérage. L'influence des paramètres pression de confinement, température et fréquence a été étudiée. Des différences importantes de comportement ont été mises en évidence entre les essais statiques et cycliques, liées à la variation cyclique des contraintes.

Ces travaux portent sur l’étude de l’influence du degré de saturation sur le comportement instable du sable de Fontainebleau sous sollicitations cycliques, et particulièrement vis-à-vis des risques de liquéfaction. Il s’agit d’évaluer expérimentalement le potentiel de liquéfaction d’un matériau granulaire en fonction de son degré de saturation initial. Pour cela, un cadre théorique est proposé, définissant trois zones d’états de saturation : une zone totalement saturée, dont le fluide poral est uniquement de l’eau ; une zone quasi-saturée, dont le fluide poral est constitué d’eau et d’air dissout ou occlus, et pour laquelle les effets de la succion sont négligés ; et une zone non saturée, caractérisée par une phase gazeuse continue, et des valeurs de succion positives. Les frontières du cadre théorique sont déterminées en termes de degrés de saturation. Chaque zone est ensuite investiguée expérimentalement. Une série d’essais triaxiaux cycliques est réalisée. Pour chaque essai, les conditions initiales de saturation sont fixées, et correspondent aux conditions de saturation déterminées dans le cadre théorique. Pour la zone non saturée, un équipement spécial de plaque tensiométrique est développé et mis en place au laboratoire afin d’imposer des conditions de succion initiales précises aux échantillons. Pour la zone quasi-saturée, les conditions de saturation initiale sont imposées via une courbe de calibration reliant le coefficient de Skempton B au degré de saturation, préalablement réalisée au laboratoire. Les résultats mettent en évidence que le sable de Fontainebleau liquéfie même lorsque le degré de saturation initial est inférieur à 100%. Plus particulièrement, tous les échantillons de la zone quasi-saturée montrent un état de liquéfaction totale à la fin du chargement cyclique. Les échantillons de la zone non saturée quant à eux ne montrent aucun signe de comportement instable sous l’action du chargement cyclique, pour les mêmes conditions de densité et de contrainte. Il semble donc que le schéma de répartition du fluide interstitiel joue un rôle fondamental dans le potentiel de liquéfaction d’un sable ; dans les conditions de densité et de contraintes testées ici, la phase gazeuse continue, et les valeurs de succion initiale positives permettent de préserver le matériau vis-à-vis du risque de liquéfaction. Au contraire, si la présence d’air sous forme dissout ou occlus permet de retarder le déclenchement des instabilités au sein du matériau granulaire, elle n’empêche pas la liquéfaction. / This work aims to study influence of saturation degree on unstable behavior under cyclic loading, and more specifically against risks of liquefaction. The potential of liquefaction of Fontainebleau sand is evaluated experimentally, in function of its initial degree of saturation. A theoretical frame is established, defining three areas of saturation states: a fully saturated zone, where pore fluid consists only of water; a nearly-saturated zone, where pore fluid consists of water and dissolved or occluded air, and where effects of suction are neglected; an unsaturated zone, where gaseous phase is considered as continuous, and suction is positive. Boundaries of this theoretical frame are defined in terms of saturation degree. Each zone is then experimentally investigated. Cyclic triaxial tests are performed. For each test, initial conditions of saturation are imposed, in agreement with saturation conditions parameters defined in the theoretical frame. For unsaturated zone investigation, a special equipment of Negative Water Column is developed and used in the laboratory in order to obtain initial conditions of suction in the sample. For nearly-saturated zone investigation, initial conditions of saturation are imposed through a calibration curve, linking Skempton coefficient B and saturation degree, previously obtained in the laboratory. Results show that Fontainebleau sand liquefies under cyclic loading, even when initial saturation degree is below 100%. More specifically, every sample tested on the nearly-saturated zone are in a complete state of liquefaction after cyclic loading is applied. Samples on the unsaturated zone did not show any sign of instability, under same conditions of stress applied and density. It seems that distribution pattern of pore fluids within granular material plays a major role regarding potential of liquefaction. In state of stress and density tested in this study, continuous air phase and positive suction prevent granular material from liquefaction. On the contrary, if dissolved or occluded air as a pore fluid delays the onset of instabilities and liquefaction, it does not prevent it.

The liquefaction resistance of a saturated medium sand with varying amount of non-plastic type F fly ash was evaluated by conducting cyclic triaxial tests. The test results were used to evaluate the effect of addition of various percentages of fly ash on the liquefaction resistance of Ottawa sand. The effect of cyclic shear stress and confining pressure on liquefaction resistance of the sand-fly ash mixtures was the main scope of this research. In addition, the Young's Modulus and Damping Ratio for sand-fly ash mixtures were also determined. A comprehensive experimental program was conducted in which 50 stress controlled cyclic triaxial tests were performed on a clean sand, sand containing 25%, 30%, 50% and 70% fly ash at a constant relative density of 50%. The results show that sand containing 25% fly ash has the highest liquefaction resistance under cyclic loading in comparison to clean sand and sand containing 30%, 50% and 70% fly ash. The cyclic resistance goes on decreasing as the fly ash content further increases. The test result also shows that the liquefaction resistance of the clean sand and sand containing 70% fly ii ash is almost same. The test results were also examined in terms of the conceptual framework of Thevanayagam (2000). The effects on liquefaction resistance were also measured in terms of pore water pressure generation and deformation of the sample. As the confining pressure increases, shear stress required to cause initial liquefaction of the sample also increases. Modulus of Elasticity was seen to increase with increase in confining pressure and decrease with increase in axial strain for all cases of sand-fly ash mixtures used in these tests. The damping ratio of the sample increases with the increase in axial strain upto about 1% and then it either decreases or remains constant thereafter. There was no clear correlation of damping ratio with confining pressure.

Earthquakes are natural calamities that occur as a result of sudden release of strain energy stored in fault planes. Earthquakes have been observed to cause huge damage to infrastructures and lives. Earthquakes result in development of fissures, abnormal or unequal movement of foundations, and loss of strength and stiffness of the soils. Liquefaction is attributed as a major cause for the loss of strength and stiffness of soil during earthquakes. In the past, liquefaction was attributed only to coarse-grained to medium-grained sand and was extensively studied but the fine-grained soils were generally considered as non-liquefiable. However, from observations during recent earthquakes, fine-grained soils having low plasticity (plasticity index (PI) <20) have experienced ground failures due to liquefaction or large deformations. Moreover, laboratory experiments show that not only saturated cohesionless soils but also fine-grained soils may liquefy if certain criteria are met. One of the parameters which influences the liquefaction characteristics of fine-grained soils is its plasticity. This study may become helpful in understanding the effect of plasticity on liquefaction resistance of fine-grained soils. The objective of this study were to investigate the (1) effect of plasticity on pore pressure built up and deformation characteristics of fine-grained soils, and (2) effects of cyclic shear stress on liquefaction resistance of fine-grained soils. A total of 24 tests were conducted using a stress controlled cyclic triaxial testing machine on identically prepared specimens at an initial effective confining pressure of 5.0psi. The plasticity index (PI) was varied from non-plastic (NP) to 14.53. Sil-Co-Sil #40, a non-plastic commercial silt (product of US Silica Company) and EPK Kaolin clay (product of Edgar Minerals Inc.) were used as base materials. These materials were mixed in different proportions to obtain desired plasticity index. Out of the twenty-four tests, eleven tests were conducted on clean silt samples. Among the tests on clean silt samples, four tests were conducted on specimens having a post consolidation void ratio of 0.74 to 0.76. Further, six tests were conducted on specimens having a post consolidation void ratio of 0.74 to 1.04 by using a cyclic stress ratio (CSR) of 0.2 and 0.25. Seventeen tests were grouped to study the influence of plasticity on liquefaction characteristics of fine-grained soil. The PI of specimens tested ranged from non-plastic (NP) to 14.53. Each of the specimens with a definite PI was tested at an initial confining pressure of 5.0 psi using a CSR of 0.2, 0.3, and 0.4. The results obtained from the tests were used to compare the effects of plasticity on liquefaction characteristics of fine-grained soils. Based on the limited tests conducted, it was observed that plasticity index had distinct influence on the cyclic strength of the samples. It was found that CSR required to cause a pre-determined strain in a given number of loading cycles reduces as the plasticity index increases from non-plastic (NP) to 3.46, but increases for soils having PI greater than 3.46. Moreover, the liquefaction resistance decreases with the increase in cyclic shear stress for all soils regardless of plasticity indices (PIs). The critical PI value corresponds to 15% of EPK clay content in the specimen which gives a PI of 3.46.

[pt] Este trabalho apresenta um estudo experimental detalhado do comportamento tensão-deformação-resistência de uma areia saturada submetida a uma condição tridimensional de carregamento. Os ensaios foram realizados nos equipamentos triaxiais cúbico e convencional. O equipamento triaxial cúbico apresenta a vantagem de controlar a magnitude das três tensões principais independentemente ( sigma 1 , sigma 2 , sigma 3 ) sob condições drenada e não drenada. Para o desenvolvimento do trabalho foi utilizada uma amostra de areia calcárea. Os corpos de prova utilizados foram moldados por pluviação submersa. No programa experimental foram realizados ensaios especiais, seguindo diferentes trajetórias de tensão. Este programa foi elaborado de modo a verificar a influência de cada parâmetro de tensão individualmente e os efeitos da anisotropia inicial de areias preparadas por pluviação submersa. Verifica-se através dos resultados de ensaios drenados que as deformações cisalhante e volumétrica são maiores na condição axissimétrica do que na de deformação plana. Tal observação equivale, em solicitações não drenadas, a um acréscimo de poropressão mais acentuado na condição axissimétrica. O comportamento anisotrópico de areias também é revelado com base em ensaios com diferentes direções ( alfa ) da tensão principal maior. Nos ensaios onde alfa = 90 graus Celsius (direção do carregamento perpendicular à de deposição do solo), ocorrem variações de deformação volumétrica e cisalhante bem mais acentuadas do que para alfa = 0 . O programa experimental mostrou ainda que areias calcáreas não cimentadas não apresentam comportamento tensão-deformação acentuadamente diferente do comportamento de areias de quartzo, mais usuais no Brasil. / [en] The subject of this dissertation is a detailed experimental study of the stress-strain-strength behavior of saturated sand under three-dimensional loading condition.The investigation was carried out in a cubic triaxial and a conventional apparatuses. The cubic triaxial apparatus has the advantage of independently controlling the magnitude of the three principal stresses (sigma1, sigma2, sigma3 ) under drained and undrained conditions. Reconstituted specimens of calcareous sand were used in all tests reported in this thesis.The specimens were prepared by pluviation of the sand in destilled water. Special tests were performed following different 3D stress paths. The experimental program was designed for checking the influence of each stress parameter individually. The effects of the inicial anisotropy of sands, caused by the water pluviation method, were also investigated.The results of the drained tests show that the shearing and volumetric strains are larger under axysimmetric than under plane strain condition. In undrained tests this observation would be equivalent to obtaining larger porepressure under axysimmetric conditions. The anisotropic behavior of sands is also noted in tests with different directions (alfa) of the major principal stress. In tests where alfa = 90 Celsius degrees ( direction of load perpendicular to pluviation) the variations in volumetric and shearing strains are much more accentuated than for alfa = 0.The experimental program also shows that the stress-strain behavior of uncemented calcareous sands is not significantly different from the behavior of quartz sands, which are more common in Brazil.