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Several seismic properties of Lake Maracaibo are unique and difficult to understand. However, studies show that the two principal factors that affect the seismic data are likely to be the low compressional and shear wave velocities generated by the gassy sediment in the mud layer, and the high attenuation of the compressional and shear waves. This mud layer sediment is heavy and is not suspended in the water. Furthermore, it is compacted enough to support shear stresses and, therefore, has a finite shear wave velocity. In theory, the gas content of the sediment reduces the compressional wave velocity by an order of magnitude below the values for water saturated sediments, but in Lake Maracaibo several studies show that gassy sediment reduces the compressional wave velocity from 1500 m/s to between 300 m/s and 700 m/s. This situation produces high attenuation of the compressional waves that are traveling through the sediment in the first 100 m. However, the results of seismic modeling show that this velocity has to be between 700 m/s and 900 m/s in order to get reasonable results, at least in the study area. The results show that there are very important lithological differences between the zones with and without gassy sediments in the mud layer. The best match between the raw data and the synthetic seismogram was found when an embedded rigid shale layer was located within the mud layer, in the first 100 m. Unrealistic results were produced when the rigid shale layer was removed in the modeling. This rigid layer produces a destructive interference in the Stoneley wave that could be observed in the seismic data and the synthetic seismogram. In this research, the attenuation quality factor Q, an intrinsic property of rock, will be studied. Common attenuation mechanisms include grain sliding, viscous flow of pore fluid or gas, viscous relaxation and other features. Additionally, it will be shown that other factors can be proposed to account for the attenuation of compressional and shear waves in Lake Maracaibo sediments. They include: the viscous losses between the particles and the fluid immediately above the mud layer; and the solid friction losses between the particles, the mud layer and the gassy sediment. This research shows That the attenuation in the mud layer in the zone with gassy sediment is very different from the attenuation in the zone without gassy sediment, and that the compressional wave attenuation is larger in the mud layer zone with gassy sediment than in the mud layer zone without gassy sediment. Finally, the research shows that the ringing is an important phenomenon associated with the low velocity in the mud layer and that this ringing has more frequency content in the zone without gassy sediment than in the zone with gassy sediment.

The study presents a numerical analysis of series of unanticipated events that took place upon the excavation of a landfill in a deep deposit of clayey soil in southwestern Ontario, Canada. During the excavation of a landfill cell to be used for waste disposal, unexpected lateral slope movements were observed followed by gas and water venting in several locations (while the excavation in low permeability clayey till was about 14m above the underlying aquifer). The clayey till is known to be underlain by permeable, natural gas bearing rock, and gas has been diffusing through the clayey deposit over about the last 13,000-15,000 years. Preliminary 2D and 3D elasto-plastic effective stress analyses using conventional soil mechanics –similar to what was used in design- are used to capture the general behaviour of the excavation. However, the analyses revealed the need for model modification to account for other governing factors (gassy soil and hydrofracturing) to be able to explain the mechanism that might have lead to the evolution of gas vents and upward water flow through the thick shale aquitard. The clayey deposit contains silty sand lenses at different elevations. The upward diffusion of methane and chloride from the bedrock aquifer through the clay till is modelled and the potential for chloride migration contributing to the exsolution of methane due to reduction in methane solubility is discussed. Two approaches to modelling the lenses are examined where gas exsolution either occurs prior to or during the excavation. The FE model is modified to account for hydrofacturing and gassy soil behaviour (for sand lenses). 2D and 3D forensic modelling studies are presented examining the potential causes for the unanticipated movements and the gas and water venting observed during the excavation. The model investigates the role of presence of gassy sand lenses and of the presence of a discontinuous weak sandy clayey silt layer between the bedrock and the low permeability till on the hydrofracturing path and gas venting. Finally, a parametric study is conducted to examine the effect of different parameters on the soil behaviour when excavated. Recommendations regarding further excavations within the same soil deposit are presented. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2012-08-23 16:33:05.062

This study sought to determine whether a recently isolated slow-growing nonstarter lactic acid bacterium, Lactobacillus wasatchii sp. nov., could be implicated in late gassy defect in Cheddar cheese. I demonstrated that Lb. wasatchii grows readily in the laboratory under cheese-like stress conditions of 5% salt and pH 5.2, and has the potential to survive pasteurization. Lactobacillus wasatchii can co-utilize ribose and galactose to maximize its growth. Due to being an obligatory heterofermentative, Lb. wasatchii produces CO2 whenever it ferments a hexose such as galactose. A second investigation extended these findings by examining the growth and gas forming characteristics of Lb. wasatchii in Cheddar cheese. The optimum growth of Lb. wasatchii and highest levels of gas production were observed in cheese supplemented with ribose plus galactose, and stored at 12°C rather than 6°C. Lactobacillus wasatchii also grew readily and produced gas in Cheddar cheese even without added ribose and galactose, which corresponds with the ability of Lb. wasatchii to grow on starter cell lysate. A challenge still remains of how to easily enumerate Lb. wasatchii in cheese with a higher background population of other nonstarter lactic acid bacteria. The third set of experiments explored the consequences on growth and gas production of Lb. wasatchii in Cheddar cheese made with Streptococcus thermophilus. Using St. thermophilus in cheesemaking results in galactose accumulation, which Lb. wasatchii then can utilize for growth, causing release of CO2 with the end result of having blown Cheddar cheese. Results showed Lb. wasatchii or similar nonstarter lactic acid bacteria are likely to be particularly problematic in cheesemaking involving starter or adventitious St. thermophilus. From these observations, it was concluded that Lb. wasatchii is a contributor to late gassy defect in Cheddar cheese and may be widely present as part of the nonstarter lactic bacteria population but has been undetected up until now. The late gassy defect is more pronounced at temperatures used for accelerated ripening of cheese and when there are substantial residual levels of galactose in the cheese. Thus, researchers and cheese manufacturers now must consider slow-growing obligatory heterofermentative nonstarter lactic acid bacteria when dealing with late gassy defect in cheese.

Les évents de sécurité protègent de l'explosion les réacteurs chimiques sièges d'un emballement thermique de réaction. Pour les systèmes non tempérés (c'est à dire produisant majoritairement des gaz incondensables), les méthodes de dimensionnement des évents issues des travaux du DIERS sont très surdimensionnantes. Une méthode basée sur le principe de similitude, développée dans le cadre de l'ONU pour la famille des peroxydes, fournit des aires d'évent plus réalistes mais elle est très contraignante. Le présent travail a permis la réalisation d'un nouvel outil de dimensionnement en similitude pour scénario d'incendie : la maquette à 0,1 litre. Il s'agit d'une extension du calorimètre adiabatique VSP2. Cette maquette permet, à l'échelle du laboratoire, la réalisation de blowdowns et la détermination directe du rapport A/V de l'évent nécessaire, mais également le suivi en temps réel de la masse réactionnelle évacuée. <br />Nous avons validé l'utilisation de cette maquette à 0,1 litre (1 x 10-3 m-1 < A/V < 3,5 x 10-3 m-1) en comparant avec des blowdowns analogues effectués à l'INERIS dans le réacteur ONU 10 litres. Ces blowdowns ont été réalisés avec une solution d'hydroperoxyde de cumène (30% en masse) dans 2,2,4-triméthyl-1,3-pentanediol diiso-butyrate. Ces essais ont montré que la maquette à 0,1 litre conduit à des évents légèrement plus grands (0 à 50 %) que le réacteur ONU 10 litres. Elle se situe donc du côté de la sécurité, tout en étant beaucoup moins surdimensionnante que la méthode DIERS, et utilisable à l'échelle du laboratoire. La principale limite est due à des fuites thermiques dont il faut vérifier pour chaque système étudié que l'influence est négligeable. <br />Du point de vue compréhension, nos expériences montrent que, même si la décomposition de notre système ressemble à celle d'un système non tempéré (2 pics de pression), elle génère des vapeurs (produits de la décomposition) qui ont une forte influence sur le 2ème pic : ces vapeurs provoquent un ralentissement de la réaction et l'atténuation des températures maximales atteintes. On constate même une corrélation Pmax = f(Tmax). Ce comportement pourrait concerner la plupart (toutes ?) des décompositions. <br />Les mesures de masse évacuée ont permis de distinguer trois types de comportements qui illustrent l'influence de la pression dans le réacteur sur le « level swell ». La confrontation avec un modèle dynamique purement « gassy » a montré que l'évacuation de masse réactionnelle peut se traduire par une évacuation purement diphasique ou par une alternance gaz/ diphasique, que pour les hautes pressions l'évacuation est purement gazeuse au turnaround et que l'évacuation diphasique lors de la dépressurisation du second pic doit être imputée en grande partie à la présence de vapeur (ébullition). <br />Enfin, nous avons identifié et quantifié la contribution des différentes hypothèses au caractère surdimensionnant de la méthode DIERS appliquée à notre système hybride non tempéré. Parmi les hypothèses surdimensionnantes identifiées, celle qui suppose que le « turnaround » est gouverné par une égalité de débit volumique est de loin celle qui est la cause principale de surdimensionnement.