As a result of tunnel construction, the ground level surface above will tend to collapse downward as the soil seeks to refill the missing tubular cavity. Many infrastructures that were originally built on that surface may also fall slightly or severely depending on the engineering design and execution of the tunneling project. Engineers then must factor in the development of ground subsidence, examining geotechnical and geological issues to construct a model that would otherwise predict the extent of vertical settlements. Their predictions could help to assess potential damages and make corrective actions. In this thesis submission, analytical methods from the classical elasticity were used to estimate surface displacements for a prospective tunnel. The analytical equation tied in the method of virtual images originating from Sagaseta with the classical Kirsch elastic solutions for stress-displacements of an infinite plate with hole in order to establish a solution of half-space. This approach will be similar to what Verruijt-Booker had developed after Sagaseta but will include higher-order terms to simulate an excavation process in a longitudinal direction below ground and thereby obtain a new subsidence equation including ground parameters associated with tunnel shape changes occurring at its base, springline (sideway point) and crown (top). These parameters were not previously reported by the Verruijt-Booker work or from current technical literature. In addition, the prescribed solution could include any Poisson’ ratios in which only the original Verruijt-Booker could be found correct for only incompressibility conditions (υ = 0.5). The Verruijt-Booker equation considered deep tunnels only. An extra term influencing the subsidence was included in the modified solution which is significant for shallow tunnels. The derived equations were applied to calculate surface deflections using data from a tunnel construction project to test its viability. Comparison analysis was made with the three methods to be described- Peck, Sagaseta, and Verruijt-Booker. In addition, a parametric study was made to examine the amount of subsidence changed when deciding to construct a tunnel from a shallow to deeper zone. Finally, a qualitative study of the derived equation and Verruijt-Booker was conducted to assess potential subsidence behaviour between shallow and deep tunnels.

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Thèses (M.Sc.A.)--Université de Sherbrooke (Canada), 2001. / Titre de l'écran-titre (visionné le 20 juin 2006). Publié aussi en version papier.

Thesis (M. Med. Sc.)--University of Hong Kong, 2005.

Th. doct.-ing.--Grenoble 1, 1985.

Ce travail de thèse porte sur l'élaboration et la caractérisation de jonctions tunnel magnétiques (JTM) polycristallines à barrière d'oxyde de titane de strontium, SrTiO3, qui se situe parmi les nouvelles barrières tunnel aux bandes interdites les plus étroites, recensées par la littérature. De telles barrières pourraient répondre à un besoin applicatif crucial : avoir un produit résistance x surface, RA, plus faible dans les JTM, ou à son corollaire, avoir une épaisseur de barrière plus forte à RA égal tout en conservant une magnétorésistance tunnel, TMR, élevée. De précédents travaux ont montré que le SrTiO3 présente une température de cristallisation inhabituellement basse (< 400°C) lorsqu'il est déposé par pulvérisation par faisceau d'ions (IBS) ce qui peut le rendre compatible avec les électrodes magnétiques standards constitutives des JTM. Le dépôt par IBS restant une technique pour le moins exotique au regard de l'état de l'art des JTM, nous avons dans un premier temps élaboré des JTM à barrière d'oxyde de magnésium, MgO, matériau phare de la spintronique. Cette étude a permis de mettre en avant les paramètres spécifiques à cette technique de dépôt influant sur les propriétés de transport des JTM, notamment le type d'oxydation. Dans un second temps, nous avons réalisé des JTM CoFeB/SrTiO3/CoFeB par IBS à partir d'une cible céramique de SrTiO3, en nous inspirant du travail effectué sur le MgO. Les influences de plusieurs paramètres de dépôt, d'oxydation et de recuit ont été analysées, conduisant à deux tendances opposées avec des systèmes présentant soit à une TMR élevée (18 %), soit un RA faible (2.6 Ohm.µm²). Des JTM SrTiO3 ont ensuite été nanostructurées pour la première fois et les tests électriques ont montré que les JTM ayant un bas RA présentaient un comportement ohmique alors que celles ayant une TMR élevée présentaient le comportement tunnel attendu. De plus, ces dernières présentent un claquage diélectrique intrinsèque à l'oxyde. En parallèle, des études microstructurales ont montré une qualité morphologique des JTM SrTiO3 semblable à celle des JTM MgO à l'état de l'art. Toutefois, ces observations n'ont pas permis de statuer sur le caractère cristallisé ou non des barrières en SrTiO3. Plusieurs pistes visant à déterminer la température de cristallisation du SrTiO3 dans la gamme des épaisseurs extraordinairement faibles des barrières tunnel ont été proposées. / This work is focused on the development and the characterization of polycrystalline magnetic tunnel junctions (MTJ) with strontium titanium oxide barrier, SrTiO3, identified as a low band gap tunnel barrier by literature. Such barrier could fulfill the critical application requirement: having a lower resistance area product (RA) in MTJ, or its corollary, having a thicker barrier at constant RA, while keeping the tunnel magnetoresistance ratio (TMR) high enough. Former studies have shown that SrTiO3 deposited by ion beam sputtering (IBS) could crystallize at an unusual low temperature (< 400°C) which could make it compatible with the magnetic layers of MTJs. In a first place, MTJs with a tunnel barrier made of a well known material in spintronics, namely MgO, were deposited. This preliminary work allowed us to highlight the specific parameters affecting the transport properties in MTJs deposited by IBS, including the oxidation type. In a second place, CoFeB/SrTiO3/CoFeB MTJs were developed using IBS and a SrTiO3 ceramic target, learning from our experience on MgO based MTJs. Many combinations of different parameters (including deposition, oxidation and annealing parameters) were explored, leading to two opposite tendencies with systems having either a high TMR (up to 18 %) or a low RA (down to 2.6 Ohm.µm²). SrTiO3 based MTJs were then patterned for the first time and submitted to electrical tests. These tests showed that the MTJs having a low RA exhibited an ohmic behaviour while the MTJs having a large TMR showed the expected tunnel characteristics. Furthermore, the latter MTJs showed an intrinsic dielectric breakdown. In parallel, microstructural characterizations have shown that SrTiO3 based MTJs and MgO based MTJ were alike morphologically. Nevertheless, these observations alone were not enough to assess on the crystalline state of SrTiO3. Many possibilities/tracks aiming at determining the crystallisation temperature of SrTiO3, in the range of extremely low thicknesses used in MTJs, are identified.

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A solution to the current problem of wind tunnel wall interference could be achieved by ventilating the test section and thereby controlling the flow pattern around the model. The motivation for the slotted wall test section arises from the fact that a fully open jet and a fully closed jet introduce corrections of opposite sign to the wind tunnel data. This current work is limited to axisymmetric wind tunnels and solid blockage corrections. Such a tolerant axisymmetric wind tunnel (TAWT), which does not need any correction to the measured flow quantities and which is also independent of the test model shape and size would find wide application in the field of industrial aerodynamics. A numerical model based on a surface singularity potential flow method showed that at 70% OAR (open area ratio) for models of size up to 25% blockage and for three different shapes the tunnel design would yield results (coefficient of pressure) with less than 2% error while such models might need up to 75% data correction if tested in a solid wall wind tunnel. Experiments indicated good agreement with the numerical investigation and at 60% OAR the TAWT gave results close to free air results for all the models tested (up to 25% blockage). / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

M.Phil. / In today's world with its competitive environment there is a need to shorten product development time by using CFD (Computational Fluid Dynamics) to design an object for example a car, aeroplane or missile and to predict the forces that the wind will have on the object (design). To evaluate the correctness of the CFD results, the design or a scale model of the design must be tested in a wind tunnel by using a force balance. The wind tunnel balance is an apparatus used in the designing and testing of wings, shapes and profiles. In general a balance can be used in all aerodynamic designs to determine the forces on an object when it is moving through air. The aim of this project was to design and manufacture a three-component external balance for a low-speed wind tunnel using an axiomatic design method. It also covers the installation of the external wind tunnel balance to a wind tunnel with a computerized data acquisition capturing system, and performance evaluation of the wind tunnel balance.