As a consequence of the 2010 – 2011 Canterbury earthquake sequence, Christchurch experienced widespread liquefaction, vertical settlement and lateral spreading. These geological processes caused extensive damage to both housing and infrastructure, and increased the need for geotechnical investigation substantially. Cone Penetration Testing (CPT) has become the most common method for liquefaction assessment in Christchurch, and issues have been identified with the soil behaviour type, liquefaction potential and vertical settlement estimates, particularly in the north-western suburbs of Christchurch where soils consist mostly of silts, clayey silts and silty clays. The CPT soil behaviour type often appears to over-estimate the fines content within a soil, while the liquefaction potential and vertical settlement are often calculated higher than those measured after the Canterbury earthquake sequence. To investigate these issues, laboratory work was carried out on three adjacent CPT/borehole pairs from the Groynes Park subdivision in northern Christchurch. Boreholes were logged according to NZGS standards, separated into stratigraphic layers, and laboratory tests were conducted on representative samples. Comparison of these results with the CPT soil behaviour types provided valuable information, where 62% of soils on average were specified by the CPT at the Groynes Park subdivision as finer than what was actually present, 20% of soils on average were specified as coarser than what was actually present, and only 18% of soils on average were correctly classified by the CPT. Hence the CPT soil behaviour type is not accurately describing the stratigraphic profile at the Groynes Park subdivision, and it is understood that this is also the case in much of northwest Christchurch where similar soils are found. The computer software CLiq, by GeoLogismiki, uses assessment parameter constants which are able to be adjusted with each CPT file, in an attempt to make each more accurate. These parameter changes can in some cases substantially alter the results for liquefaction analysis. The sensitivity of the overall assessment method, raising and lowering the water table, lowering the soil behaviour type index, Ic, liquefaction cutoff value, the layer detection option, and the weighting factor option, were analysed by comparison with a set of ‘base settings’. The investigation confirmed that liquefaction analysis results can be very sensitive to the parameters selected, and demonstrated the dependency of the soil behaviour type on the soil behaviour type index, as the tested assessment parameters made very little to no changes to the soil behaviour type plots. The soil behaviour type index, Ic, developed by Robertson and Wride (1998) has been used to define a soil’s behaviour type, which is defined according to a set of numerical boundaries. In addition to this, the liquefaction cutoff point is defined as Ic > 2.6, whereby it is assumed that any soils with an Ic value above this will not liquefy due to clay-like tendencies (Robertson and Wride, 1998). The method has been identified in this thesis as being potentially unsuitable for some areas of Christchurch as it was developed for mostly sandy soils. An alternative methodology involving adjustment of the Robertson and Wride (1998) soil behaviour type boundaries is proposed as follows:  Ic < 1.31 – Gravelly sand to dense sand  1.31 < Ic < 1.90 – Sands: clean sand to silty sand  1.90 < Ic < 2.50 – Sand mixtures: silty sand to sandy silt  2.50 < Ic < 3.20 – Silt mixtures: clayey silt to silty clay  3.20 < Ic < 3.60 – Clays: silty clay to clay  Ic > 3.60 – Organics soils: peats. When the soil behaviour type boundary changes were applied to 15 test sites throughout Christchurch, 67% showed an improved change of soil behaviour type, while the remaining 33% remained unchanged, because they consisted almost entirely of sand. Within these boundary changes, the liquefaction cutoff point was moved from Ic > 2.6 to Ic > 2.5 and altered the liquefaction potential and vertical settlement to more realistic ii values. This confirmed that the overall soil behaviour type boundary changes appear to solve both the soil behaviour type issues and reduce the overestimation of liquefaction potential and vertical settlement. This thesis acts as a starting point towards researching the issues discussed. In particular, future work which would be useful includes investigation of the CLiq assessment parameter adjustments, and those which would be most suitable for use in clay-rich soils such as those in Christchurch. In particular consideration of how the water table can be better assessed when perched layers of water exist, with the limitation that only one elevation can be entered into CLiq. Additionally, a useful investigation would be a comparison of the known liquefaction and settlements from the Canterbury earthquake sequence with the liquefaction and settlement potentials calculated in CLiq for equivalent shaking conditions. This would enable the difference between the two to be accurately defined, and a suitable adjustment applied. Finally, inconsistencies between the Laser-Sizer and Hydrometer should be investigated, as the Laser-Sizer under-estimated the fines content by up to one third of the Hydrometer values.

Σκοπός της παρούσας Διατριβής Ειδίκευσης είναι η ανάλυση, η παρουσίαση και η αξιολόγηση των γεωτεχνικών συνθηκών της πόλης των Πατρών, σε σχέση με την εκδήλωση του φαινόμενου της ρευστοποίησης και τις συνθήκες γεωλογικής καταλληλότητας για τις προς δόμηση περιοχές. Στα πλαίσια της διατριβής πραγματοποιήθηκαν γεωτεχνικές έρευνες για είκοσι πέντε (25) γεωτρήσεις που έχουν διανοιχθεί κατά μήκος της πόλης των Πατρών, και αξιολογήθηκαν τα αποτελέσματα των επί τόπου και των εργαστηριακών δοκιμών. Με τη βοήθεια του λογισμικού Petal υπολογίστηκε ο συντελεστής ασφάλειας για ρευστοποίηση σε κάθε γεώτρηση και συντάχθηκαν χάρτες ζωνών επικινδυνότητας για την πόλη των Πατρών. Η έρευνα αυτή πραγματοποιήθηκε για δύο σεισμικά γεγονότα. Για το σεισμό των Πατρών το 1993 με μέγεθος 5.4 Richter και το σεισμό του Αιγίου το 1995 με μέγεθος 6.2 Richter. / The aim of this MSc Project is the presentation, the analysis and the assessment of the geotechnical conditions in city of Patras, Western Greece, for liquefaction phenomenon and geological suitability for construction purposes. In this project were done geotechnical surveys for twenty-five (25) boreholes in area of Patras, and assessment insitu and laboratory tests. Using Petal program we can estimate the factor of safety against liquefaction. The data used to perform mapping, in some zones of liquefaction risk. The survey based on seismic facts. The first one was the earthquake in 1993 in city of Patras with magnitude 5.4 Richter and the second one was the earthquake in city of Aigio in 1995 with magnitude 6.2 Richter.

In the period between September 2010 and December 2011, Christchurch was shaken by a series of strong earthquakes including the MW7.1 4 September 2010, Mw 6.2 22 February 2011, MW6.2 13 June 2011 and MW6.0 23 December 2011 earthquakes. These earthquakes produced very strong ground motions throughout the city and surrounding areas that resulted in soil liquefaction and lateral spreading causing substantial damage to buildings, infrastructure and the community. The stopbank network along the Kaiapoi and Avon River suffered extensive damage with repairs projected to take several years to complete. This presented an opportunity to undertake a case-study on a regional scale of the effects of liquefaction on a stopbank system. Ultimately, this information can be used to determine simple performance-based concepts that can be applied in practice to improve the resilience of river protection works. The research presented in this thesis draws from data collected following the 4th September 2010 and 22nd February 2011 earthquakes. The stopbank damage is categorised into seven key deformation modes that were interpreted from aerial photographs, consultant reports, damage photographs and site visits. Each deformation mode provides an assessment of the observed mechanism of failure behind liquefaction-induced stopbank damage and the factors that influence a particular style of deformation. The deformation modes have been used to create a severity classification for the whole stopbank system, being ‘no or low damage’ and ‘major or severe damage’, in order to discriminate the indicators and factors that contribute to ‘major to severe damage’ from the factors that contribute to all levels of damage a number of calculated, land damage, stopbank damage and geomorphological parameters were analysed and compared at 178 locations along the Kaiapoi and Avon River stopbank systems. A critical liquefiable layer was present at every location with relatively consistent geotechnical parameters (cone resistance (qc), soil behaviour type (Ic) and Factor of Safety (FoS)) across the study site. In 95% of the cases the critical layer occurred within two times the Height of the Free Face (HFF,). A statistical analysis of the geotechnical factors relating to the critical layer was undertaken in order to find correlations between specific deformation modes and geotechnical factors. It was found that each individual deformation mode involves a complex interplay of factors that are difficult to represent through correlative analysis. There was, however, sufficient data to derive the key factors that have affected the severity of deformation. It was concluded that stopbank damage is directly related to the presence of liquefaction in the ground materials beneath the stopbanks, but is not critical in determining the type or severity of damage, instead it is merely the triggering mechanism. Once liquefaction is triggered it is the gravity-induced deformation that causes the damage rather than the shaking duration. Lateral spreading and specifically the depositional setting was found to be the key aspect in determining the severity and type of deformation along the stopbank system. The presence or absence of abandoned or old river channels and point bar deposits was found to significantly influence the severity and type of deformation. A review of digital elevation models and old maps along the Kaiapoi River found that all of the ‘major to severe’ damage observed occurred within or directly adjacent to an abandoned river channel. Whilst a review of the geomorphology along the Avon River showed that every location within a point bar deposit suffered some form of damage, due to the depositional environment creating a deposit highly susceptible to liquefaction.

In this thesis primarily structural induced liquefaction potential was aimed to be analyzed. Also the effect of base isolation systems both on structural performance and liquefaction potential was studied. FLAC software was chosen for the analyses so that structure and soil could be modeled together. By these means the soil structure interaction effects were also examined. Four different structures and three different sites were analyzed under two different input motions. All the structures were also analyzed as base isolated. It was mainly found that depending on the structural type and for a certain depth the liquefaction potential could be higher under the structure than the one in the free field. Also it was concluded that base isolation systems were very effective for decreasing the story drifts, shear forces in the structure and liquefaction potential in the soil. It was also found that the interaction took place between structure, soil and input motions.

[Formulae and special characters can not be reproduced here. Please see the pdf version of the Abstract for an accurate reproduction.] The thesis provides a comprehensive study on the behaviour of sand with a small amount of fines [i.e.1/3 plastic fines and 2/3 non-plastic fines]. The work is carried out experimentally under axi-symmetric conditions using the triaxial apparatus. Conventional drained triaxial tests are conducted on isotropic consolidated specimens and all the tests indicate that sand with fines does not manifest any unusual behaviour under drained conditions. However in undrained shearing the so-called ???reverse behaviour??? is noted. The study demonstrates that the reverse behaviour conforms to the critical state framework because significant changes in the position and geometry of the critical state [CS] and isotropic consolidation [IL] lines are caused by the presence of fines. These changes cannot be adequately modelled by the intergranular void ratio as proposed by Thevanayagam and Mohan (2000). This study also demonstrates that the original state parameter [special character] as proposed by Been and Jefferies (1985) is not an adequate parameter to predict the undrained behaviour trend. A new parameter termed ???modified state parameter??? [special character] is proposed to account for the combined effects of density and confining pressure. The suitability of the modified state parameter to characterise the response of parent sand and sand with fines is assessed for a range of void ratios and confining pressures. The effect of drained stress history is an important factor affecting the subsequent undrained response. Drained pre-shearing to failure is found to improve considerably the subsequent undrained response to the extent that liquefaction may not occur. Different drained pre-shearing histories have different effects on the undrained response. However in these tests [special character] has limitations in quantifying the subsequent undrained stress-strain response. Hence, a new framework of ???yielding parameter??? [special character] extends the capability of [special character] and additional data is presented to demonstrate the suitability of this concept. The implementation of [special character] depends on whether the previous stress state reached during the stress history is below or at failure. The effects of drained pre-shearing on the position and movement of failure surface are investigated. It is found that drained pre-shearing to failure at larger confining pressures has the effect of shifting upwards part of the drained failure surface. The shift at larger stress ratios [special character] may be described in terms of dilatancy and modified state parameter at failure. The so-called strain path tests are conducted to study the influence of strain increment ratio on the deformation behaviour of sand with fines. It is found that the value of [special character] has significant effects on the stress-strain behaviour. Along negative [special character] paths the soil strain softens in the form of decreasing the shear resistance before reaching the failure state. In contrast, along positive [special character] paths the soil strain hardens to an asymptotic stress ratio. The asymptotic stress ratio decreases with increasing [special character] along a linear relationship. The framework of [special character] cannot quantify the stress-strain response along positive and negative strain paths. Consequently an ???instability parameter??? [special character] is proposed to extend the capabilities of [special character] and the reliability of this parameter is further assessed. The behaviour along a range of positive and negative [special character] paths is investigated on pre-sheared specimens. In negative [special character] the effective stress paths reach a surface located higher than the monotonic failure surface on which they trace downward towards the origin of stress space. The results indicate this surface may be the same as the drained failure envelope which has been shifted as a result of drained pre-shearing. In positive [special character] paths a large improvement is noted in both the strength and stiffness of the soil. Note The parameters [special character] and [special character] are all generalisations of [special character] so that the behaviour under complex conditions can be characterised.

Au cours des 50 dernières années, l’étude du phénomène de liquéfaction de sols sableux saturés ont fait l'objet de nombreuses recherches en laboratoire. La plupart de ces recherches antérieures se sont concentrées sur la liquéfaction de sables propres, en supposant que la présence de fines limite le développement de la surpression interstitielle et donc le risque de liquéfaction. Cependant, les sables sableux naturels se trouvent généralement dans la nature sous la forme d'un mélange de sable et de fines et, l’influence de ces fines sur le risque de liquéfaction de ce type de matériau n'est toujours pas claire. En effet, on trouve des résultats contradictoires, dans la littérature, sur l'effet des particules fines sur le phénomène de liquéfaction des sables. Dans ce contexte, l’objectif principal de ce travail expérimental est de clarifier et de quantifier l’influence des particules fines présentes au sein d’une matrice sableuse sur l’initiation et le développement du phénomène de liquéfaction. On s’est intéressé, en particulier, à la nature des particules fines (plastique/non-plastique), à leur proportion au sein de la matrice, à l’état de compacité de la matrice et à l’état de contrainte initial (état de consolidation). A cet effet, à l'aide d'un nouveau dispositif triaxial servo-hydraulique, une série d'essais monotones et cycliques ont été effectués afin de clarifier cet effet. Les résultats expérimentaux montrent que l'augmentation de la proportion de fines non plastiques augmente la résistance à la liquéfaction du mélange sous chargements monotone et cyclique. Par contre, cette tendance est inversée pour les mélanges qui contiennent des fines plastiques. Enfin, une comparaison a été établie entre le comportement de ces sols sous cisaillement monotone et cyclique non drainé en termes d'évaluation du déclenchement du phénomène d'instabilité et d'autres paramètres mécaniques / Since the last 50 years, the study of the phenomenon of liquefaction of saturated sandy soils has been a topic of extensive laboratory research. Most of the earlier research has focused on the liquefaction of clean sands assuming that the presence of fines resists the development of pore water pressure as well as the risk of liquefaction. However, natural sand is found in nature under the form of a mixture of sand and fines and, the influence of these fines on the liquefaction risk of this type of material is still unclear. In fact, we could find contradictory results in the literature review of the effect of fine particles on the sand liquefaction phenomenon. In this context, the main objective of this study is to clarify and quantify the influence of fine particles (plastic and non-plastic) present in a sandy matrix on the initiation and development of the liquefaction phenomenon .We’ve focused, in particular, on the nature of fine particles (plastic/non-plastic), their proportion in the matrix, the matrix compactness condition and initial stress state (state consolidation). For this purpose, with the aid of a new triaxial servo-hydraulic device, a series of monotonic and cyclic tests were done in order to clarify this effect. Experimental results show that the increase in non-plastic fines increases the resistance to liquefaction of the mixture under both monotonic and cyclic loading. However, this trend is reversed for the mixtures containing plastic fines. Finally a comparison has been established between the behavior of these soils under undrained monotonic and cyclic shearing in terms of evaluation of the initiation of instability phenomenon and other mechanical parameters

[pt] Com aumento da preocupação político-ambiental, torna-se imperativo desenvolver processos eficientes em termos econômicos e energéticos para a produção sustentável de combustíveis e produtos químicos. A liquefação hidrotérmica (HTL) é um processo para a transformação de materiais orgânicos, tais como bio-resíduos ou biomassa, em óleo bruto, em temperaturas usualmente inferiores a 400 graus Celsius sob altas pressões na presença de água, e, dependendo do processo, de um catalisador. Nesse contexto, é importante entender o comportamento de degradação térmica do material em atmosfera inerte, no sentido de se investigar a possibilidade de quebra das cadeias poliméricas inicias em moléculas menores, que, mediante pressão, poderão ser convertidas em novos produtos. Assim sendo, os objetivos do presente trabalho estão associados ao estudo termogravimétrico (TG) da degradação térmica da fibra do coco verde na presença de ferrita de cobalto (Fe2CoO4), utilizada no intuito de gerar um efeito catalítico, acelerando a degradação térmica das estruturas poliméricas presentes, e, que possa ser usada posteriormente em uma rota HTL. Os catalisadores foram produzidos a 1000 graus Celsius em diferentes tempos de calcinação (3h, 6h e 9h), sendo, nas misturas com a fibra, a fração mássica de óxido igual a 50 por cento. As amostras de interesse para a pesquisa foram caracterizadas mediante diferentes técnicas, tais como, a microscopia eletrônica de varredura, para o estudo da morfologia e composição elementar, difração de raios X, para a quantificação das fases presentes nas amostras de ferrita, e espectroscopia de infravermelho, visando à identificação das principais ligações químicas nas fibras, tanto antes quanto durante o tratamento térmico. Dentre todos os ensaios de TG realizados, os experimentos com o catalisador calcinado durante 9h homogeneizado com gral de ágata foi o que mostrou uma melhor resposta com relação à degradação térmica das fibras. Os resultados sugerem ainda que, tanto o tempo de calcinação, quanto a natureza do processo de mistura apresentam efeitos significativos sobre a cinética de degradação. / [en] With increasing political-environmental concern, it becomes imperative to develop efficient processes in economic and energy terms for the sustainable production of fuels and chemical products. Hydrothermal liquefaction (HTL) is a process for the transformation of organic materials such as bio-waste or biomass into crude oil at temperatures usually below 400 degrees Celsius under high pressures in the presence of water and, depending on the process, of a catalyst. In this context, it is important to understand the behavior of thermal degradation of the material under inert atmosphere, in order to investigate the possibility of breaking the initial polymer chains into smaller molecules, which, under pressure, can be converted into new products. The objectives of the present work are associated to the thermogravimetric study (TG) in the thermal degradation of the green coconut fiber in the presence of a cobalt ferrite (Fe2CoO4), used to generate a catalytic effect, accelerating the thermal degradation of the polymeric structures present, and which can be used later on an HTL route. The catalysts were produced at 1000 degrees Celsius at different calcination times (3h, 6h and 9h) and in the fiber mixtures, the oxide mass fraction was equal to 50 percent. The samples of interest for the research were characterized by different techniques, such as scanning electron microscopy, for the study of the morphology and elemental composition, X-ray diffraction, for the quantification of the phases present in the ferrite samples, and spectroscopy of Infrared, in order to identify the main chemical bonds in the fibers, both before and during the heat treatment. Among all the TG assays performed, the experiments with the catalyst calcined for 9h homogenized with mortar and pestle showed the best to the thermal degradation of the fibers. The results further suggest that both the calcination time and the nature of the blending process have significant effects on the degradation kinetics.

La consommation mondiale en énergie qui augmente progressivement a favorisé la recherche de ressources alternatives renouvelables. L’Europe a mis le développement de la filière de biogaz comme une priorité pour valoriser la matière organique et produire une énergie durable et un carburant propre. Plusieurs technologies ont été développées afin de produire le bio-méthane et ensuite le liquéfier. Cryo Pur a développé un procédé cryogénique où le biogaz est refroidi progressivement à 3 niveaux de température :-40 °C ; -75 °C et -120 °C. Dans un premier temps, la vapeur d’eau est extraite à -40 °C et à -75 °C, le biogaz sec ne contient plus alors que du méthane à une concentration de 65 % et du CO2 à 35 %. Le biogaz est alors refroidi jusqu’à -120 °C dans un système frigorifique en cascade intégrée pour capter le dioxyde de carbone jusqu’à une concentration résiduelle de 2 %. Une fois ce bio-méthane obtenu, il est liquéfié. A une pression de 15 bara et une température de -120 °C. Une étude énergétique et exergétique est menée et prend comme référence le pilote d’épuration et de liquéfaction Cryo Pur installé à la sortie de méthaniseurs de la station d’épuration de Valenton. Le CO2 est capté par givrage sur les ailettes d’échangeurs frigorifiques ; le dégivrage est effectué par un débit diphasique prélevé à l’étage -40 °C de la cascade intégrée. La thèse compare l’énergie récupérée par un dégivrage en phase liquide du CO2 avec donc une remontée en température jusqu’à -56 °C (température du point triple du CO2) et un dégivrage par sublimation du CO2 à une température bien inférieure à -56 °C qui fait l’objet d’une optimisation énergétique. La thèse mène aussi une étude énergétique et exergétique du procédé complet d’épuration de biogaz et de liquéfaction de bio-méthane avec récupération d’énergie par sublimation du dioxyde de carbone.Un banc d’essai est conçu pour évaluer la performance énergétique du procédé de dégivrage du CO2 par sublimation. Les différents éléments nécessaires de ce banc d’essai sont présentés avec leurs consommations énergétiques. Dans ce banc d’essai, le dégivrage du dioxyde de carbone par sublimation est effectué via un caloporteur qui récupère la froideur de sublimation du CO2 réduisant la puissance consommée par la cascade intégrée. Ce nouveau procédé a besoin d’une pompe à vide. La consommation de cette pompe à vide dépend de la pression de sublimation et fait l’objet d’une étude d’optimisation énergétique. La densité du CO2 varie énormément en fonction de la température et la pression de sublimation. Un modèle de calcul de l’évolution de l’épaisseur du givre au cours de la sublimation est présenté. Comme conclusion de cette partie, une comparaison est faite entre la consommation électrique spécifique du système installé à Valenton et celle du banc d’essai.D’autre part, la durée du cycle de givrage demande elle aussi une étude d’optimisation énergétique associée au dimensionnement de l’échangeur de captage du CO2. L’échangeur tube-ailettes avec la forme de l’ailette et les paramètres affectant le givrage du CO2 sont présentés. Une étude est effectuée pour répartir uniformément la masse de CO2 déposée sur la surface d’échange pour réduire le taux de blocage de l’échangeur et prolonger la durée de la phase de givrage. Une étude sur l’effet de la vitesse du biogaz et du glissement en température du réfrigérant sur la durée du cycle est menée ainsi qu’une étude sur les matériaux des ailettes et des tubes choisis afin de minimiser la surface d’échange en gardant la sortie du bio-méthane avec 2 % de CO2. / Global energy consumption, which is gradually increasing, has led to the search for alternative renewable resources. Europe has put the development of the biogas sector as a priority to enhance organic matter and produce sustainable energy and clean fuel. Several technologies have been developed to produce bio-methane and then to liquefy it. Cryo Pur developed a cryogenic process where the biogas is cooled gradually to 3 temperature levels: -40 ° C; -75 ° C and -120 °C. In a first step, the steam is extracted at -40 °C and at -75 ° C, the dry biogas contains 65 % methane and 35 % CO2. The biogas is then cooled to -120 °C in a low-temperature refrigeration system to capture carbon dioxide and obtain bio-methane with 2.5 % of CO2. Once this bio-methane is obtained, it is liquefied at a pressure of 15 bara and a temperature of -120 °C. An energy and exergy study is studied and takes as reference the pilot of purification and liquefaction Cryo Pur installed at the exit of digester of the purification station of Valenton. CO2 is captured by frosting on the fins of heat exchangers. The defrosting is carried out by a two-phase flow rate taken from the -40 °C stage of the low-temperature refrigeration system. The thesis compares the energy recovered by a liquid CO2 defrosted with a rise in temperature up to -56 °C (triple point temperature of CO2) and defrosting by sublimation of CO2 at a temperature much lower than - 56 ° C which is the subject of an energy optimization. The thesis also conducts an energy and exergy study of the complete process of biogas and bio-methane liquefaction with the recovery of energy by sublimation of carbon dioxide.A test bench is designed to evaluate the energy performance of the CO2 defrosting process by sublimation. The various necessary elements of this test bench are presented with their energy consumption. In this test bench, the defrosting of the carbon dioxide by sublimation is carried out via a low-temperature heat-transfer fluid which recovers the energy sublimation of the CO2 reducing the power consumed by the low-temperature refrigeration system. This new process requires a vacuum pump. The consumption of this vacuum pump depends on the sublimation pressure and is the subject of an energy optimization study. The density of CO2 varies enormously depending on the temperature and the sublimation pressure. A model of the evolution of the thickness of the frost during the sublimation is presented. As a conclusion of this section, a comparison is made between the specific power consumption of the system installed at Valenton and that of the test bench.On the other hand, the duration of the frosting cycle also requires an energy optimization study associated with the design of the exchanger that capture the CO2. The tube-fins exchanger with the shape of the fin and the parameters affecting the CO2 frosting are presented. A study is carried out to uniformly distribution of the CO2 mass on the exchange surface to reduce the blocking rate of the exchanger and to extend the duration of the frosting phase. A study on the effect of biogas velocity and temperature slippage of the refrigerant over the cycle is carried out as well as a study on the materials of the fins and tubes selected in order to minimize the exchange surface and have the bio-methane with 2 % CO2.

L’engagement de l’Europe sur les énergies renouvelables amène à l’accélération du développement du biométhane comme énergie renouvelable. Les travaux de cette thèse portent sur une partie du procédé Cryo Pur qui est un procédé essentiellement frigorifique qui va permettre en refroidissant le biogaz de la température ambiante à -120 °C, de séparer successivement l’eau, le CO2 et des polluants pour obtenir du méthane et du CO2 liquides de hautes puretés. Les objectifs poursuivis sont méthodologiques et expérimentaux. La méthode est celle de l’intégration énergétique associée à une analyse exergétique du procédé. L’analyse intègre la production frigorifique et la production de chaleur par les groupes frigorifiques pour son utilisation dans le procédé de méthanisation. L’optimisation énergétique part de l’analyse exergétique et identifie les pertes des différentes étapes du procédé et intègre à la fois les productions frigorifiques aux différents niveaux de température et la production de chaleur utilisée dans le digesteur. Le besoin en chaleur du digesteur se situe autour de 50 à 55 °C pour les bactéries thermophiles. Pour l’épuration du biogaz et la liquéfaction du biométhane, les besoins frigorifiques se situent de la température ambiante jusqu’à-120 °C. Dans le procédé Cryo Pur, la production frigorifique s’effectue à 4 niveaux de températures : 2°C, -40 °C, -78 °C et -120 °C. La pompe à chaleur est couplée aux différents systèmes frigorifiques en refroidissant un frigoporteur à une température qui fait l’objet de l’optimisation globale du système de thermo-frigo-pompe. En effet la pompe à chaleur refroidit les condenseurs des 4 systèmes frigorifiques et la chaleur récupérée des groupes froids est valorisée à 55 °C par la pompe à chaleur.Complémentairement à cette optimisation énergétique globale, la thèse se focalise sur le givrage et dégivrage de l’eau contenue dans le biogaz. Cette opération consomme beaucoup d’énergie et un travail d’optimisation énergétique est mené pour minimiser la consommation d’énergie pour la déshumidification du biogaz de la température ambiante à -78 °C. La représentation des cycles associés au givrage et dégivrage de la glace hydrique et des pertes associées aux montées et descentes en température des masses métalliques des échangeurs requière une modélisation dynamique de ces phénomènes. Du point de vue expérimental les cycles de givrage et dégivrage de l’eau font l’objet d’une optimisation quant à leur gestion.Les travaux de la modélisation donneront lieu à dimensionner les échangeurs des cycles de givrage et de dégivrage. Le but finalement étant l’obtention d’un rendement exergétique le plus élevé possible. Les essais ont permis de valider les modèles d’échangeurs et des systèmes frigorifiques. L’optimisation intègre également le choix des mélanges des fluides frigorigènes. / Europe's commitment to renewable energy leads to accelerate the biomethane development as a renewable energy. The work of this thesis is based on the Cryo Pur process which is essentially a cooling process that will allow the biogas cooling from ambient temperature to -120 °C. While cooling the biogas, water vapor, CO2 and pollutants must be separated to obtain liquefied biomethane and bio CO2. The objectives pursued are methodological and experimental. The method used is the energy integration associated with an exergy analysis of the process. The analysis integrates the cooling production and the heat production by the refrigeration units for the use in the methanisation process. The energy optimization starts from the exergy analysis and identifies the losses of the various stages of the process and integrates both the cooling production at different temperature levels and the heat production used in the digester. The heat requirement of the digester is around 50 to 55 °C for the thermophilic bacteria. For the biogas upgrading and the liquefaction of biomethane, the cooling requirements are from ambient temperature to -120 °C. In the Cryo Pur process, refrigeration is carried out at 4 different temperature levels: 2 °C, -40 °C, -78 °C and -120 °C. The heat pump is coupled to the various refrigeration systems by cooling a refrigerant at a temperature which is the objective of the overall optimization of the heat pump system. The heat pump cools the condensers of the 4 refrigeration systems and the heat recovered from the refrigeration systems is upgraded to 55 °C by the heat pump.In addition to this overall energy optimization, the thesis focuses on the frosting and defrosting of the water contained in the biogas. This operation consumes a lot of energy. An energy optimization work is carried out to minimize the energy consumption for the dehumidification of biogas from ambient temperature to -78 ° C. The representation of the frosting and defrosting cycles and the losses associated with the temperature of the metallic mass of the heat exchangers requires a dynamic modeling. The dynamic modeling will lead to design the heat exchangers. The ultimate aim is to achieve the highest possible exergy efficiency. Tests made it possible to validate the models of the heat exchangers and refrigeration systems. The optimization also integrates the choice of refrigerant mixtures.

A thesis submitted to the Faculty of Engineering, Cape Peninsula University of Technology, Cape Town, in partial fulfilment of the requirements for the M-Tech Degree in Civil Engineering” Cape Town 16 MAY 2011 / Dwellings in impoverished and upper class urban areas of the Western Cape have undergone serious structural failure due to problematic underlying sand deposits, generally known as Cape Flats windblown found in areas such as Delft, Blue Downs and the Atlantic Beach Golf Estate. The problem is compounded further when moisture penetrates below the footings and reaches saturation in the winter months. When poorly graded sand with a high fines content is coupled with vibration (through earth tremors), liquefaction may occur and without proper precautions, this can lead to inadequate foundation design, more than expected settlement and eventual structural failure. Some sand deposits are highly contaminated with organic debris, leading to compressible and collapsible conditions. Little knowledge is locally available of liquefiable conditions in windblown dune sand and what long-term settlement can be expected. The Western Cape is not known as an area exposed to serious seismic activity, but an updated (and more locally applicable set of data) is needed to eliminate possible erroneous foundation design. Samples have been extracted from typical sandy sites in the Western Cape where windblown dune sand is evident. Laboratory tests have been carried out on representative samples for closer examination and have been placed inside a purpose built calibration chamber that facilitates easy densification and probe testing. A DMT (flat blade dilatometer) was used to hydraulically penetrate the chamber sand sample to varying depths (up to 800 mm). The device can measure (with reduction formula) horizontal stress, angle of friction, bearing capacity and settlement. An accelerometer was attached to the chamber wall and vibration measured with the sand in varying states of moisture. The DMT is an unexplored in-situ soil testing device in South Africa and so far the outcome indicates favourably compared to other devices such as the Dynamic Cone Penetrometer (DCP. The DMT has the ability to measure the in-situ stiffness, strength and stress history parameters of soil for better site characterisation. Settlement within the chamber is easily measured. The DMT has, for example, indicated that sand from the Philippi area are a problematic founding soil and should be treated with special care at shallow founding levels. The horizontal stress index is low and according to the available knowledge on soil stress history, these sand, coupled with low densities, can liquefy easily and result in structural damage. The West Coast dune sand, being coarser and easily consolidated, poses less of a problem under liquefiable conditions. A suitable terrain device for easy on-site manoeuvrability is required to assist the DMT in further testing.