2v. (various paging) : / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (D.Sc.)--University of Adelaide, Dept. of Physiology, 1975

Petroleum exploration and production in recent years have moved into increasingly deeper water off the continental shelf. Some of these facilities are anchored in water depths in excess of 1000 meters. Exploration and production in deep water present new technological challenges where traditional fixed platforms have given way to floating structures. Today suction caissons are the most commonly used anchorage system for permanent offshore oil production facility. The objective of this study is to numerically predict the ultimate capacity of suction caissons in normally consolidated and lightly overconsolidated clays. Representative soil profile from the Gulf of Mexico and the North Sea are taken and analyzed for suction caissons with length over diameter ratios of 2, 4, 6 & 8. Normalized failure load interaction diagrams are generated for each of the cases. The location of optimum attachment point is also reported for each of the cases. General purpose finite element computer program ABAQUS is used for the numerical prediction. The finite element study is carried out with three-dimensional models using hybrid elements. A simplified elastic perfectly plastic model with von-Mises yield criterion is used for the study. The saturated clay is treated as an incompressible material. Results of the study compares well with existing simplified method for estimating load capacity of suction caisson anchors.

In the study, wave reflection, transmission, and energy dissipation with a caisson-type breakwater have been investigated experimentally. Three different sizes of grain are used to construct the porous base, they are 16mm, 25mm, and 35mm, respectively.Single and double layers of porous base are considered. Hydraulic test, porous media choice is glass ball.Wave conditions must be consistent with the scope of the linear wave theory. Two different depths are used to construct,they are 40 cm and 72 cm. Do a single trial of all size. Double size 16mm and 35mm diameter glass ball is a test. Recording the test process, and then analyze energy consumption. Water area's characteristics and pore area's characteristics are calculated by the Newton¡¦s method and the Ward¡¦s method. It is the substitute for the dispersion equation is also correct. During the course of a series, the draft of caisson is deeper, the convergence is harder. But the increase and decrease the mode number or the draft, and sometimes increase the possible of convergence. As the number of cutting layer are more complex than other predecessors, particularly in the large number of required mode, when the composition of the matrix of boundary conditions greater complexity. In the caisson area calculated pore velocity, or on behalf of the later is very large, so it's easy in the solution process, generate positive infinity or negative infinity error. As the caisson-type breakwater with a shorter wavelength, the frictional resistance influences bigger. At this time, reflectance and transmittance has the Drop tendency.When the wavelength is longer, the frictional resistance influences smaller. Most of the energy reflection because the caisson of less permeable. The caisson-type breakwater got the wave force to increase. The effect is bad in the Wave force reduced. If the static water surface above the pore structure, the caisson-type breakwater can be reduction of about 30% to 40% off the energy. If the static water surface under the pore structure, the caisson-type breakwater wave damping efficiency is better. Usually remove 30% to 70% energy. Sometimes, it¡¦s up to about 90%.Reflectivity of the caisson breakwater is larger, but the transmissivity is lower. For the waters behind the breakwater, the protective effect is significant. Transmissivity trend is arranged according to media size. As the media size smaller, the transmissivity is smaller, the reflectivity is higher. At the same depth, double-size model compared with other single-size model of the wave forces reduced is better. Whether long or short period, double-size model's performance is relatively stable. Except to a long cycle time, the wave damping efficiency has a larger range. Other cycles are at the lower position.

Petroleum exploration and production in recent years have moved into increasingly deeper water off the continental shelf. Some of these facilities are anchored in water depths in excess of 1000 meters. Exploration and production in deep water present new technological challenges where traditional fixed platforms have given way to floating structures. Today suction caissons are the most commonly used anchorage system for permanent offshore oil production facility. The objective of this study is to numerically predict the ultimate capacity of suction caissons in normally consolidated and lightly overconsolidated clays. Representative soil profile from the Gulf of Mexico and the North Sea are taken and analyzed for suction caissons with length over diameter ratios of 2, 4, 6 & 8. Normalized failure load interaction diagrams are generated for each of the cases. The location of optimum attachment point is also reported for each of the cases. General purpose finite element computer program ABAQUS is used for the numerical prediction. The finite element study is carried out with three-dimensional models using hybrid elements. A simplified elastic perfectly plastic model with von-Mises yield criterion is used for the study. The saturated clay is treated as an incompressible material. Results of the study compares well with existing simplified method for estimating load capacity of suction caisson anchors.

This paper proposes a novel model that can predict the displacement of suction caisson anchors under monotonic and cyclic loading. Failure is assumed to occur when the accumulative monotonic and cyclic displacement along the load attachment point is over 60% of the diameter of the anchor. The anchors will go through lateral failure when the accumulative monotonic and cyclic displacement along the loading direction at the load attachment point is over 30% of the diameter. Hence, it is important to predict this displacement and therefore determine the expected failure of the anchor. However, it is difficult to predict displacement using the modern software without knowing the material properties of the soil and piles. Hence a new model that relies only on the normalized static load (Fa/Ff), normalized cyclic load (Fcy/Ff ), loading angle (Θ), and the number of cycles (N) is proposed. The inputs for training of the proposed model are (Fa/Ff), (Fcy/Ff), (Θ), (α) and (N). The output of the model will be the displacement normalized by the diameter of the anchor. To generalize the trained model, unused sets of data are used to validate the model. Furthermore, a comparative study is performed to evaluate the effectiveness of the proposed model. It is shown from extensive simulation that the model can accurately predict the normalized displacement of suction caisson anchors.

This paper proposes a novel model that can predict the displacement of suction caisson anchors under monotonic and cyclic loading. Failure is assumed to occur when the accumulative monotonic and cyclic displacement along the load attachment point is over 60% of the diameter of the anchor. The anchors will go through lateral failure when the accumulative monotonic and cyclic displacement along the loading direction at the load attachment point is over 30% of the diameter. Hence, it is important to predict this displacement and therefore determine the expected failure of the anchor. However, it is difficult to predict displacement using the modern software without knowing the material properties of the soil and piles. Hence a new model that relies only on the normalized static load (Fa/Ff), normalized cyclic load (Fcy/Ff ), loading angle (Θ), and the number of cycles (N) is proposed. The inputs for training of the proposed model are (Fa/Ff), (Fcy/Ff), (Θ), (α) and (N). The output of the model will be the displacement normalized by the diameter of the anchor. To generalize the trained model, unused sets of data are used to validate the model. Furthermore, a comparative study is performed to evaluate the effectiveness of the proposed model. It is shown from extensive simulation that the model can accurately predict the normalized displacement of suction caisson anchors.

Deep foundations, such as piles and suction caissons, are used throughout an offshore oil and gas production facility in deepwater. Ideally, the values of geotechnical properties for foundation design are determined by results from geotechnical investigation programs performed at the site of the foundation. However, the locations for facilities are not known exactly when soil borings are drilled and the footprint of a facility in deepwater can be very large with numerous foundation elements spread out over miles. Therefore, it is not generally feasible to perform a site-specific investigation for every foundation element. The objective of this research is to assess, analyze and model spatial variability in geotechnical properties for offshore foundations. A total of 97 geotechnical investigations from 14 offshore project sites covering the past twenty years of deepwater development in the Gulf of Mexico are compiled into a database. The geologic setting is primarily a normally to slightly overconsolidated marine clay, and the property of interest for the design of deep foundations is the undrained shear strength. The magnitude and characteristics of variability in design undrained shear strengths are analyzed quantitatively and graphically. Geostatistical models that describe spatial variability in the design shear strength properties to the distance away from the available information are developed and calibrated with available information from the database. Finally, a methodology is presented for incorporating the models into a reliability-based design framework to account for spatial variability in foundation capacity. Design examples are presented to demonstrate the use of the reliability methodology. Based on the design undrained shear strength profiles for the past 20 years in this Gulf of Mexico deepwater area, the design undrained shear strength varies spatially but does not depend on the time or method for site investigations. There are nonlinear spatial relationships in the point shear strength laterally and vertically due to stratigraphy such that depth-averaged shear strengths are correlated over further distances than point shear strengths. The depositional forces are an important factor causing spatial variations in the undrained shear strength, with greater variation and less spatial correlation in the more recent hemipelagic deposits (about upper 60 feet) than the deeper turbidite deposits and along the shelf versus off the shelf. The increased conservatism required in deep foundation design due to spatial variability when site specific strength data are not available is generally small with less than a five percent increase required in design capacity in this geologic setting. / text

Cette thèse de doctorat porte sur la réponse des fondations caisson dans du sable pour les éoliennes en mer soumises à des chargements monotones et cycliques combinés. Le processus de défaillance et l’enveloppe de rupture (diagramme de capacité portante) d’une fondation en caisson dans du sable soumise à des chargements monotones combinés sont premièrement étudiés à l’aide du modèle constitutif de Mohr-Coulomb. La méthode Lagrangian-Smoothed Particle Hydrodynamics Combinée (CLSPH) est adoptée pour prendre en compte les grandes déformations et les limites de l'approche sont mises en évidence. Une loi constitutive basée sur la notion de l’état critique pour le sable récemment mis au point (SIMSAND) est ensuite introduite et utilisée avec la méthode CLSPH. Des tests d’effondrement du sol dans un canal rectangulaire et d’une colonne granulaire en prenant en compte différentes géométries sont simulés afin de valider l’approche en termes de morphologie de dépôt final, des profils d’écoulement et de zones non perturbées. La méthode CLSPH et le modèle SIMSAND sont ensuite utilisés pour étudier le diagramme de capacité portante des fondations caisson dans du sable. Différents paramètres ayant une incidence sur la forme et la taille de l'enveloppe de rupture sont pris en compte, tels que la densité et la rigidité du sol, la résistance au frottement, la rupture des grains, la géométrie et les dimensions de la fondation. Une formule analytique est introduite pour décrire la surface de rupture 3D capable à reproduire les résultats numériques. Sur la base de la formule analytique proposée, un macro-élément pour des fondations caisson dans du sable soumises à des chargements monotones et cycliques est finalement développé dans le cadre de l'hypoplasticité. L’outil numérique proposé est validé avec des résultats expérimentaux. / This PhD thesis deals with the response of caisson foundations in sand for offshore wind turbines submitted to combined monotonic and cyclic loadings. First, the failure process and failure envelope (or bearing capacity diagram) of a caisson foundation in sand under combined monotonic loadings is investigated using the conventional Mohr-Coulomb constitutive model. A Combined Lagrangian-Smoothed Particle Hydrodynamics(CLSPH) method is adopted to consider large deformations and the limitations of the approach are highlighted. A recently developed critical state model for sand (SIMSAND) is then introduced and combined with the CLSPH method. Rectangular channel soil collapse tests and granular column collapse tests considering different aspect ratios are simulated to validate the approach in terms of final deposit morphologies, flow profiles and undisturbed areas.The CLSPH method and the SIMSAND model are then used to investigate the bearing capacity diagram of the caisson foundation in sand. Different parameters affecting the shape and size of the failure envelope are considered, as soil density and stiffness, friction strength, grain breakage, geometry and aspect ratio of the foundation. An analytical formula is introduced to describe the 3D failure surface reproducing the numerical results. Based on the proposed analytical formula, a macro-element for the caisson foundation in sand submitted to monotonic and cyclic loadings is finally developed within the framework of hypoplasticity. Validation is provided through comparison with experimental results.

Le chapitre 9 de L'Eurocode 3 est le moyen le plus utilisé par les ingénieurs pour prédire la durée de vie des joints soudés, mais ce code ne donne qu'une seule courbe de résistance en fatigue pour chaque type de joint soudé, quel que soit l'acier utilisé. La résistance à la fatigue des assemblages soudés est particulièrement sensible à la géométrie du cordon déposé, ainsi qu'aux champs de contraintes introduits, soit par le procédé de soudage, soit par les défauts microscopiques inclus dans le soudage. Nous avons donc besoin d'une méthode locale telle la méthode volumétrique, qui a donné de bons résultats en fatigue, pour déterminer la contrainte effective dans la zone plastifiée à côté du cordon de soudure. Une étude numérique est réalisée sur un caisson soudé. La distribution et le gradient de contrainte permettent de calculer la contrainte effective. Les résultats numériques, comparés aux résultats expérimentaux, ont validé la méthode volumétrique sur ce type de structures soudées / The Chapter 9 of Eurocode 3 is one of the most widely adapted codes for fatigue life prediction of welded joints, the drawback of this code being the single curve fatigue strength for each type of welded joint produced regardless of the type of steel used. The fatigue strength of welded joints is particularly sensitive to the geometry of the weld bead and the stress fields which could potentially be introduced by the welding process or by other microscopic defects introduced by the welding. In this study the volumetric method, which has proven its validity in the study of fatigue, has been used to determine the effective stress in the plastic zone near the weld bead. Numerical simulations have been performed on a welded box to determine the stress distribution and gradient which would allow proper calculation of the effective stress. Both numerical simulations and experimental results support the validity of the volumetric method for such type of welded structures

Provas de carga dinâmicas em sete tubulões, de oito metros de comprimento e 0,60 m de diâmetro de fuste, sendo quatro com 1,5 m de base alargada, são apresentadas. Resistências mobilizadas determinadas pelo PDA e pela utilização de métodos que empregam medidas de repique elástico, em particular, os métodos de CHELLIS-VELLOSO e UTO et al. (1985) são comparadas. Várias seqüências de carregamento foram efetuadas, de modo a se ter uma ideia da influência de carregamentos sucessivos no comportamento dos tubulões. Constatou-se que o método de CHELLIS-VELLOSO apresentou resultados sofríveis em relação às resistências encontradas pelas análises CAPWAP, mas que melhoram à medida que sucessivos carregamentos são impostos aos tubulões, por causa do gradual comportamento de tubulões escavados em tubulões \"cravados\", pelo acúmulo de tensões residuais de cravação. Este fato pode ser corroborado pela aplicação do Princípio de Hamilton aos tubulões, fazendo crer que a realização de um ensaio de carregamento dinâmico em elementos de fundação moldados in loco necessita de uma suficiente penetração líquida deste elemento no terreno - da ordem do seu diâmetro, se este for de seção uniforme -, ou seja, sua transformação em um elemento de comportamento \"cravado\". Em alguns tubulões, provas de carga dinâmicas foram efetuadas com o solo em estado natural e inundado, a fim de se determinar a influência da colapsibilidade na resistência mobilizada, conforme o nível de energia aplicado. Verificou-se que em um tubulão submetido a uma inundação prévia do terreno por 48 h, as resistências mobilizadas foram inferiores às encontradas nos demais, para um mesmo nível de energia, muito provavelmente pela ação deletéria da água na colapsibilidade do solo em tela. / Dynamic Loading Tests (DLT) on seven caissons 8 m length and 0,60 m shaft diameter are presented, being four caissons with 1,5 m enlarged base diameter. Mobilized resistances determined both through PDA and rebound measurement methods as CHELLIS-VELLOSO and UTO et al. (1985) are compared. SeveraI successive loadings were performed in order to obtain assessment of the influence of the loading sequence in the caisson behavior. It was observed what CHELLIS-VELLOSO method showed very poor agreement with the obtained resistances through the CAPWAP analysis. Nevertheless, it was noted what the more the caissons are submitted to successive loadings, the closer are the results between CAPWAP analysis and CHELLIS-VELLOSO method, because the cast-in-place caisson is gradually switched to a driving caisson due to driving residual stress accumulations. To allow this to happen, it is necessary to have a net set value close to the shaft diameter in caisson without enlarged base. These facts were confirmed through the application Hamilton\'s Principle to tested caissons. In some caissons DLT were performed with natural and soaked soil conditions in order to know the collapsible influence in the mobilized resistances. lt was verified what 48 hours previous soaked soil resulted in lowest resistances than observed in the other caissons to the same energy level. This fact may justify the harmful action of the water in the reduction of resistance in collapsible soils.