Due to the similarity between the geometry and full displacement installation method of a cone penetrometer and displacement pile, the axial capacity of displacement piles is often assessed using data from a cone penetration test (CPT). As there are many more factors influencing pile axial capacity than affecting CPT cone resistance, there are a wide range of CPT-based empirical design methods in use. These methods have various levels of predictive success, which usually depends upon the soil conditions, pile geometry, pile installation method, and time between installations and loading. An improved understanding of the basis and reliability of respective design methods is essential to improve the quality of predictions in the absence of site specific load test data. This thesis explores the influence of soil state and drainage conditions on piezocone penetration test (CPTU) tip resistance (qc) and penetration pore pressures (u2). For cone penetration testing identified as 'drained', factors influencing the correlation between cone tip resistance and displacement pile shaft friction in sand are investigated through (i) a review of previous research and the performance of existing design methods; (ii) centrifuge studies of piles of differing widths with measurements of local lateral stress; (iii) field tension tests at different times between installation and loading for uninstrumented driven piles with different diameters and end conditions; and (iv) field tension tests at different times between installation and loading on closed ended strain gauged jacked segmented model piles with different installation sequences. CPTU qc and u2 are primarily controlled by soil state and drainage conditions, with effective stress strength parameters and soil stiffness also influencing the measurements. The primary mechanisms identified to control the correlation between cone tip resistance and shaft friction on displacement piles are identified as; (i) the initial increase in radial stress due to soil displaced during installation of a pile; (ii) different levels of soil displacement induced by open, closed, and partially plugged piles; (iii) reduction in radial stress behind the pile tip; (iv) additional reduction in radial stress with continued pile penetration (friction fatigue); (v) changes in radial stress during loading; (vi) constant volume interface friction angle between soil and steel; and (vii) changes in the effects of the above mentioned mechanisms with time between installation and loading. The relative effect of each of these factors is investigated in this thesis.

Evaluations of stress history and the geostatic state of stress of soils are ascertained on the basis of field geophysical measurements that provide paired complementary types of shear waves. It is well-established that multiple types of shear waves occur in the ground due to their directional and polarization properties. The shear wave velocity (Vs) provides the magnitude of small strain stiffness (G0) which depends on effective stress, void ratio, stress history, and other factors (cementation, age, saturation). Herein, this study examines a hierarchy of shear wave modes with different directions of propagation and particle motion from in-situ geophysical tests (HH, VH, and HV) and laboratory bender element data. A special compiled database from well-documented worldwide sites is assembled where full profiles of stress state, stress history, and several paired modes of Vs profiles have been obtained from crosshole tests (CHT), downhole tests (DHT), and rotary crosshole (RCHT). Reference profiles of the lateral stress coefficient (K0) are available from direct in-situ measurements (self-boring pressuremeter, hydrofracture, and push-in spade cells). Stress history is documented in terms of yield stress ratio (YSR) from consolidation testing and careful engineering geology studies. A methodology is developed that relates both the YSR and K0 to stiffness ratios obtained from directional shear wave velocities. In further efforts, means to extract reliable shear wave profiles from continuous downhole testing via a new GT autosource and seismic piezocone testing are outlined and applied to results from three test sites in Windsor/VA, Norfolk/VA, and Richmond/BC. A driving impetus to this research involves the geologic conditions at the US Dept. of Energy's Savannah River Site (SRS) in South Carolina. Here, the overburden soils in the upper 60 m depths consist of very old Miocene and Eocene sediments, primarily layered deposits of sands, clayey sands, silty sands, and interbedded clays which exhibit an apparent and unusual stress history profile. Special geologic conditions include the dissolutioning of old calcareous sediments (Santee Formation) at depths of 40 to 50 m below grade, similar to karstic limestone deposits. As a consequence, caves, voids, and infilled soft soil zones occur within the soil matrix at these elevations, probably resulting in localized collapse of the overlying soil column. Based on conventional laboratory and in-situ test data conducted during geotechnical investigations at SRS, available interpretative relationships for assessing the soil stress history and geostatic stress states show scattered and inconsistent results. Complications abound in the systematic assessments of these geomaterials due to effects of very old ageing, cementation, desiccation, and diagenesis, as evidenced by unusual in-situ shear wave velocity profiles that decrease in magnitude with depth, as measured by CHT and DHT. Based on the findings of this study, it is recommended that a new set of shear wave velocity measurements be made at SRS to obtain HH waves (and complementary VH waves) needed for an independent assessment of YSR in the upper soil column.

Du fait de leurs propriétés physiques et chimiques exceptionnelles à haute température par rapport aux métaux, les composites de carbure de silicium (SiC) sont étudiés comme éventuel matériau de gainage du combustible nucléaire dans les réacteurs de fusion ou fission avancée futurs, ainsi que, depuis plus récemment, dans les réacteurs à eau légère existants. Les tubes composites SiC/SiC tressés en 2D, fabriqués par procédé d'infiltration chimique en phase vapeur (CVI), présentent un comportement mécanique anisotrope, faiblement déformable (~ 1%). La maîtrise des relations entre la microstructure, l’endommagement et le comportement macroscopique est essentielle pour optimiser précisément le dimensionnement structurel de ce matériau pour les applications envisagées. Un paramètre de fabrication important est l'angle de tressage, angle entre les torons de fibres et l'axe du tube. L'objectif de ce travail est de fournir une compréhension détaillée de la relation endommagement-microstructure, en particulier des effets de l'angle de tressage sur les mécanismes d’endommagement. Dans ce but, une étude combinant observations expérimentales à macro et micro-échelle et simulations numériques est menée. Les tubes composites sont d’abord étudiés par des essais de traction in situ sous tomographie par rayons X. Les expériences ont été réalisées sur la ligne PSICHE du synchrotron SOLEIL sous faisceau rose polychromatique. Les images tridimensionnelles sont analysées par la technique de corrélation d’image volumique (DVC), complétée par une série d'algorithmes de traitement d'image originaux, développés spécifiquement pour analyser les microstructures 3D, mesurer les déformations à travers l'épaisseur du tube, détecter et caractériser quantitativement le réseau de microfissures créées par le chargement mécanique. De plus, les microstructures réelles, décrites par les images de haute résolution issues des tests in situ, sont utilisées dans les simulations numériques multi-échelle. Les champs de contrainte à l’échelle microstructurale sont calculés en régime élastique par une technique utilisant la transformée de Fourier rapide (FFT). Ils permettent de mieux comprendre l'initiation des fissures et d’interpréter les observations expérimentales par une comparaison directe. Ces approches expérimentales et numériques sont appliquées à trois tubes présentant différents angles de tressage (30 °, 45 ° et 60 °). L’influence de l'angle de tressage sur l'initiation et l'évolution de l’endommagement à cœur des composites est ainsi mise en évidence / Because of their outstanding physical and chemical properties at high temperature, in comparison with metals, silicon carbide (SiC) composite materials are studied as possible nuclear fuel cladding materials either for future advanced fission/fusion reactors, or more recently, for the currently existing light water reactors. 2D-braided SiC/SiC composite tubes, manufactured by chemical vapor infiltration (CVI), exhibit an anisotropic, hardly deformable (~1%) mechanical behavior. Understanding the relations between the microstructure, the damage mechanisms and the macroscopic behavior is essential to optimize the structural design of this material for the considered applications. One important manufacturing parameter is the braiding angle, i.e. the angle between the fiber tows and the tube axis. The objective of this work is to provide a comprehensive understanding of the damage-microstructure relations, in particular of the effects of the braiding angle on the damage mechanisms. For this purpose, an investigation combining experimental observations at macro and micro-scale and numerical simulations is developed. The composite tubes are first studied through in situ tensile testing under X-ray computed tomography. Experiments were carried out on the PSICHE beamline at synchrotron SOLEIL using a pink polychromatic beam. The recorded 3D images are processed using the digital volume correlation (DVC) technique, extended by a series of advanced image processing algorithms specifically developed in order to analyze the 3D microstructures, to measure the deformations through the tube thickness, and to detect and quantitatively characterize the network of micro-cracks created by the mechanical loading. In addition, numerical simulations are performed on the real microstructures as observed in the high-resolution images recorded during the in situ tests. Stress fields are calculated at the microstructural scale in the elastic regime using a numerical tool based on the Fast Fourier Transform (FFT). They help to better understand crack initiation and interpret the experimental observations within one-to-one comparisons. Both the experimental and numerical approaches are applied to three tubes with different braiding angles (30°, 45° and 60°). The effect of the braiding angle on the initiation and evolution of damage in the bulk of the composite materials can thus be highlighted

Offshore developments for hydrocarbon resources have now progressed to water depths approaching 2500 m. Due to the difficulties and high cost in recovering high quality samples from deepwater site, there is increasing reliance on in situ tests such as piezocone and full-flow (i.e. T-bar and ball) penetration tests for determining the geotechnical design parameters. This research was undertaken in collaboration with the Norwegian Geotechnical Institute (NGI), as part of a joint industry project, to improve the reliability of in situ tests in determining design parameters and to improve offshore site investigation practice in deepwater soft sediments. In this research, a worldwide high quality database was assembled and used to correlate intact and remoulded shear strengths (measured from laboratory and vane shear tests) with penetration resistances measured by piezocone, T-bar and ball penetrometers. The overall statistics showed similar and low levels of variability of resistance factors for intact shear strength (N-factors) for all three types of penetrometer. In the correlation between the remoulded penetration resistance and remoulded shear strength, the resistance factors for remoulded shear strength (Nrem-factors) were found higher than the N-factors. As a result, the resistance sensitivity is less than the strength sensitivity. The correlations between the derived N-factors and specific soil characteristics indicated that the piezocone N-factors are more influenced by rigidity index than those for the T-bar and ball penetrometers. The effect of strength anisotropy is only apparent in respect of N-factors for the T-bar and ball penetrometers correlated to shear strengths measured in triaxial compression. On the other hand, the Nrem-factors showed slight tendency to increase with increasing strength sensitivity but were insensitive to soil index properties. These findings suggest that the full-flow penetrometers may be used to estimate remoulded shear strength and are potentially prove more reliable than the piezocone in estimating average or vane shear strength for intact soil but the reverse is probably true for the estimation of triaxial compression strength.

The traditional radiation testing of space electronics has been used for more than fifty years to support the radiation hardness assurance. Its typical goal is to ensure reliable operation of the spacecraft in the harsh environment of space. This PhD research looks into the radiation testing from a different perspective; the goal is to develop radiation testing methods that are focused not only on the reliability of the components but also on a continuous radiation-induced degradation of their performance. Such data are crucial for the understanding of the impact of radiation on the measurement uncertainty of data acquisition systems onboard research space missions.

The majority of UK’s intermediate level radioactive waste is currently stored in 316L and 304L austenitic stainless steel containers in interim storage facilities for permanent disposal until a geological disposal facility has become available. The structural integrity of stainless steel canisters is required to persevere against environmental degradation for up to 500 years to assure a safe storage and disposal scheme. Hitherto existing severe localised corrosion observances on real waste storage containers after 10 years of exposure to an ambient atmosphere in an in-land warehouse in Culham at Oxfordshire, however, questioned the likelihood occurrence of stress corrosion cracking that may harm the canister’s functionality during long-term storage. The more corrosion resistant duplex stainless steel grade 2205, therefore, has been started to be manufactured as a replacement for the austenitic grades. Over decades, the threshold stress corrosion cracking temperature of austenitic stainless steels has been believed to be 50-60°C, but lab- and field-based research has shown that 304L and 316L may suffer from atmospheric stress corrosion cracking at ambient temperatures. Such an issue has not been reported to occur for the 2205 duplex steel, and its atmospheric stress corrosion cracking behaviour at low temperatures (40-50°C) has been sparsely studied which requires detailed investigations in this respect. Low temperature atmospheric stress corrosion cracking investigations on 2205 duplex stainless steel formed the framework of this PhD thesis with respect to the waste storage context. Long-term surface magnesium chloride deposition exposures at 50°C and 30% relative humidity for up to 15 months exhibited the occurrence of stress corrosion cracks, showing stress corrosion susceptibility of 2205 duplex stainless steel at 50°C.The amount of cold work increased the cracking susceptibility, with bending deformation being the most critical type of deformation mode among tensile and rolling type of cold work. The orientation of the microstructure deformation direction, i.e. whether the deformation occurred in transverse or rolling direction, played vital role in corrosion and cracking behaviour, as such that bending in transverse direction showed almost 3-times larger corrosion and stress corrosion cracking propensity. Welding simulation treatments by ageing processes at 750°C and 475°C exhibited substantial influences on the corrosion properties. It was shown that sensitisation ageing at 750°C can render the material enhanced susceptible to stress corrosion cracking at even low chloride deposition densities of ≤145 µm/cm². However, it could be shown that short-term heat treatments at 475°C can decrease corrosion and stress corrosion cracking susceptibility which may be used to improve the materials performance. Mechanistic understanding of stress corrosion cracking phenomena in light of a comprehensive microstructure characterisation was the main focus of this thesis.