The study of the shear behavior of particulate (soil) – continuum (man-made material) interfaces has received significant attention during the last three decades. The historical belief that the particulate – continuum interface represents the weak link in most geotechnical systems has been shown to be incorrect for many situations. Namely, prescribing properties of the continuum material, such as its surface roughness and hardness, can result in interface strengths that are equal to the contacting soil mass internal shear strength. This research expands the engineering implications of these findings by studying the response of interface systems in different loading conditions. Specifically, the axial and torsional shear modes are studied in detail. Throughout this thesis it is shown that taking an engineering approach to design the loading conditions induced to the interface system can result in interface strengths that exceed the previously considered limiting shear strength of the contacting soil. Fundamental experimental and numerical studies on specimens of different types of sand subjected to torsional and axial interface shear highlighted the inherent differences of these processes. Specifically, micro-scale soil deformation measurements showed that torsional shear induces larger soil deformations as compared to axial shear, as well as complex volume-change tendencies consisting of dilation and contraction in the primary and secondary shear zones. Studies on the global response of torsional and axial shear tests showed that they are affected differently by soil properties such as particle angularity and roughness. This difference in global behavior highlights the benefits of making systems that transfer load to the contacting soil in different manners available for use in geotechnical engineering. Discrete Element Modeling (DEM) simulations allowed for internal information of the specimens to be studied, such as their fabric and shear-induced loading conditions. These findings allowed for the development of links between the measured micro-scale behavior and the observed global-scale response. The understanding of the behavior of torsional and axial interfaces has allowed provides a framework for the development of enhanced geotechnical systems and applications. The global response of torsional shear found to induce larger cyclic contractive tendencies within the contacting soil mass. Therefore, this shear mode is more desirable than the conventional axial shear for the study of phenomena that depend on soil contractive behavior, such as liquefaction. A study on the influence of surface roughness form revealed that surfaces with periodic profiles of protruding elements that prevent clogging are capable of mobilizing interface friction angles that are 20 to 60% larger than the soil friction angle. These findings have direct implications in engineering design since their implementation can result in more resilient and sustainable geotechnical systems.

The results from an experimental study on the dynamic properties of sand with nonplastic silt are presented. Combined resonant column and torsional shear equipment is used to evaluate the effects of confining pressure, shearing strain, frequency, and number of cycles of loading on the dynamic properties of silty sand. The goal of this study is to determine if relationships in the literature for sands and gravels are accurate for predicting the shear modulus and material damping characteristics of soil with nonplastic fines or if the incorporation of a fines content parameter improves predictions. This goal was primarily accomplished by reconstituting and testing samples of an alluvial deposit from Dillon Dam, Dillon, Colorado according to predetermined gradation curves with variable amounts of non-plastic fines. Among the findings of this investigation are: (1) soil parameters such as Cu and D50 can be related to dynamic properties of soils with up to 25% fines, (2) the effects of non-plastic fines on the small-strain dynamic properties of soils are not very pronounced for soils with less than 25% fines, and (3) an increase in the amount of non-plastic fines in uniform soils or soils with more than 25% fines generally results in lower values of small-strain shear modulus, higher values of small-strain material damping, and more linear G/Gmax - log([gamma]) and D - log([gamma]) curves. The effect of non-contacting, larger granular particles in a finer soil matrix is also investigated along with the impact of removing larger particles from laboratory samples. / text

Le cancer du sein est le cancer le plus fréquent chez la femme. Il demeure la cause de mortalité la plus importante chez les femmes âgées entre 35 et 55 ans. Au Canada, plus de 20 000 nouveaux cas sont diagnostiqués chaque année. Les études scientifiques démontrent que l'espérance de vie est étroitement liée à la précocité du diagnostic. Les moyens de diagnostic actuels comme la mammographie, l'échographie et la biopsie comportent certaines limitations. Par exemple, la mammographie permet de diagnostiquer la présence d’une masse suspecte dans le sein, mais ne peut en déterminer la nature (bénigne ou maligne). Les techniques d’imagerie complémentaires comme l'échographie ou l'imagerie par résonance magnétique (IRM) sont alors utilisées en complément, mais elles sont limitées quant à la sensibilité et la spécificité de leur diagnostic, principalement chez les jeunes femmes (< 50 ans) ou celles ayant un parenchyme dense. Par conséquent, nombreuses sont celles qui doivent subir une biopsie alors que leur lésions sont bénignes. Quelques voies de recherche sont privilégiées depuis peu pour réduire l`incertitude du diagnostic par imagerie ultrasonore. Dans ce contexte, l’élastographie dynamique est prometteuse. Cette technique est inspirée du geste médical de palpation et est basée sur la détermination de la rigidité des tissus, sachant que les lésions en général sont plus rigides que le tissu sain environnant. Le principe de cette technique est de générer des ondes de cisaillement et d'en étudier la propagation de ces ondes afin de remonter aux propriétés mécaniques du milieu via un problème inverse préétabli. Cette thèse vise le développement d'une nouvelle méthode d'élastographie dynamique pour le dépistage précoce des lésions mammaires. L'un des principaux problèmes des techniques d'élastographie dynamiques en utilisant la force de radiation est la forte atténuation des ondes de cisaillement. Après quelques longueurs d'onde de propagation, les amplitudes de déplacement diminuent considérablement et leur suivi devient difficile voir impossible. Ce problème affecte grandement la caractérisation des tissus biologiques. En outre, ces techniques ne donnent que l'information sur l'élasticité tandis que des études récentes montrent que certaines lésions bénignes ont les mêmes élasticités que des lésions malignes ce qui affecte la spécificité de ces techniques et motive la quantification de d'autres paramètres mécaniques (e.g.la viscosité). Le premier objectif de cette thèse consiste à optimiser la pression de radiation acoustique afin de rehausser l'amplitude des déplacements générés. Pour ce faire, un modèle analytique de prédiction de la fréquence de génération de la force de radiation a été développé. Une fois validé in vitro, ce modèle a servi pour la prédiction des fréquences optimales pour la génération de la force de radiation dans d'autres expérimentations in vitro et ex vivo sur des échantillons de tissu mammaire obtenus après mastectomie totale. Dans la continuité de ces travaux, un prototype de sonde ultrasonore conçu pour la génération d'un type spécifique d'ondes de cisaillement appelé ''onde de torsion'' a été développé. Le but est d'utiliser la force de radiation optimisée afin de générer des ondes de cisaillement adaptatives, et de monter leur utilité dans l'amélioration de l'amplitude des déplacements. Contrairement aux techniques élastographiques classiques, ce prototype permet la génération des ondes de cisaillement selon des parcours adaptatifs (e.g. circulaire, elliptique,…etc.) dépendamment de la forme de la lésion. L’optimisation des dépôts énergétiques induit une meilleure réponse mécanique du tissu et améliore le rapport signal sur bruit pour une meilleure quantification des paramètres viscoélastiques. Il est aussi question de consolider davantage les travaux de recherches antérieurs par un appui expérimental, et de prouver que ce type particulier d'onde de torsion peut mettre en résonance des structures. Ce phénomène de résonance des structures permet de rehausser davantage le contraste de déplacement entre les masses suspectes et le milieu environnant pour une meilleure détection. Enfin, dans le cadre de la quantification des paramètres viscoélastiques des tissus, la dernière étape consiste à développer un modèle inverse basé sur la propagation des ondes de cisaillement adaptatives pour l'estimation des paramètres viscoélastiques. L'estimation des paramètres viscoélastiques se fait via la résolution d'un problème inverse intégré dans un modèle numérique éléments finis. La robustesse de ce modèle a été étudiée afin de déterminer ces limites d'utilisation. Les résultats obtenus par ce modèle sont comparés à d'autres résultats (mêmes échantillons) obtenus par des méthodes de référence (e.g. Rheospectris) afin d'estimer la précision de la méthode développée. La quantification des paramètres mécaniques des lésions permet d'améliorer la sensibilité et la spécificité du diagnostic. La caractérisation tissulaire permet aussi une meilleure identification du type de lésion (malin ou bénin) ainsi que son évolution. Cette technique aide grandement les cliniciens dans le choix et la planification d'une prise en charge adaptée. / Breast cancer is the most frequent cancer in women and the leading cause of death for women between 35 and 55 years old. In Canada, more than 20,000 new cases are diagnosed each year. Most of the previous works have shown that life expectancy is closely related to the precocity of diagnosis. Current diagnostic imaging methods such as mammography, sonography, MRI present limitations such as irradiation (mammography), low specificity and low resolution (sonography) and high cost (MRI). For example, about 95% of abnormalities detected by mammography are proven to be benign lesions after complementary examinations (biopsy). Sonography is useful as a complementary examination but the low resolution of its images, its low specificity (54% for women less than 50 years) and its operator dependent interpretation seriously limit the use of this modality alone. MRI is a non-invasive technique with a relatively high sensitivity (86% for women below 50 years), but its limitations are the high cost and the waiting time for medical examination, which dedicate it as a monitoring technique in high-risk patients. It is therefore necessary to examine new noninvasive and cost effective methods. In this context, dynamic elastography is a promising approach. It is an emerging quantitative medical imaging technique inspired from palpation and based on the determination of elastic properties (stiffness) of tissues. This thesis aims the development of a novel dynamic ultrasound elastography method for early detection of breast lesions. One of the main problems of dynamic elastography techniques using remote palpation (acoustic radiation force) is the strong attenuation of shear waves. After few wavelengths of propagation, displacement amplitudes considerably decrease and their tracking becomes difficult even impossible. This problem greatly affects biological tissue characterization. Moreover, these techniques give only the information about elasticity while recent studies show that some benign lesions have the same elasticity as malignant lesions which affect the specificity of these techniques and motivate investigation of other physical parameters (e.g. viscosity). The first objective of this thesis is to optimize the acoustic radiation force using frequency adaptation to enhance the amplitude of displacements. An analytical model has been developed to predict the optimal frequency for the generation of the radiation force. Once validated on phantoms (in vitro), this model was used for the prediction of the optimal frequencies for the generation of the radiation force in tissue mimicking phantoms and ex vivo human breast cancer samples obtained after total mastectomy. Gains in magnitude were between 20% to158% for in vitro measurements on agar-gelatin phantoms, and 170% to 336% for ex vivo measurements on a human breast sample, depending on focus depths and attenuations of tested samples. The signal-to-noise ratio was also improved by more than four folds with adapted sequences. We conclude that frequency adaptation is a complementary technique that is efficient for the optimization of displacement amplitudes. This technique can be used safely to optimize the deposited local acoustic energy, without increasing the risk of damaging tissues and transducer elements. In the second part of this thesis, a prototype of an ultrasound probe for the generation of a specific type of adaptive shear waves called ''adaptive torsional shear waves'' has been developed. The goal was to use the optimized radiation force (developed in the first part) to generate adaptive torsional shear wave, and prove their utility in improving the amplitude of displacement. During their inward propagation, the amplitude of displacement generated by torsional shear waves was enhanced and the signal to noise ratio improved due to the constructive interferences. Torsional shear waves can also resonate heterogeneities which further enhance the displacement contrast between suspicious masses and its surrounding medium. Finally, in the context of assessment of mechanical proprieties of tissue, the last step of this thesis is to develop an inverse problem based on the propagation of adaptive torsional shear waves to estimate the viscoelastic parameters. A finite element method (FEM) model was developed to solve the inverse wave propagation problem and obtain viscoelastic properties of interrogated media. The inverse problem was formulated and solved in the frequency domain and its robustness was evaluated. The proposed model was validated in vitro with two independent rheology methods on several homogeneous and heterogeneous breast tissue mimicking phantoms over a broad range of frequencies (up to 400Hz). The obtained results were in good agreement with reference rheology methods with discrepancies between 8% and 38% for shear modulus and from 9% to 67% for loss modulus. The robustness study showed that the proposed inverse problem solution yielded a good estimation of the storage (19%) and loss moduli (32%) even with very noisy signals.