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1
Ulvestad, Anders. "Consolidation Settlement of Suction Caissons." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for bygg, anlegg og transport, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19504.
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Consolidation settlement analysis is an essential part of the design process for suction caissons. However it is a complex task since soil volume important for settlement analyses is directly affected by the installation process. Consolidation settlements have been found to be the critical design criterion in several subsea developments, adequate and correct analysis is therefore vital. The FEM code PLAXIS has been used to evaluate the reconsolidation process after completed installation of the suction caisson. Emphasize has been placed on studying the shear strength increase with time along the skirt walls. During consolidation dissipation of excess pore pressures result in higher effective stresses. Consequently the modeled undrained shear strength increases. However the increase is small compared to the expected increase in shear strength due to the set-up phenomenon. To account for the deviation an adjusted simulation procedure incorporating incremental increase of friction angle in the interface zones has been suggested. The results were found to be reasonable with respect to final consolidation settlements and development of mobilized shear strength with time.Adequate modeling of the changes in the interface zones adjacent to the caisson walls during consolidation is vital for correct prediction of long term settlements. Modeled undrained shear strength with time have huge impact on the analysis results due to different mobilization of the surrounding soil. Appropriate evaluation of soil structure interaction is essential to assess the reliability of the analysis. Taking into account changes of the soil volume important for settlement analysis is also vital. A simple physical model test has been performed. Due to delays and relatively short test period the results were inconclusive. However the importance of considering short term set-up effects has been underlined by recorded resistance and physical observations in the field.
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Pinna, Rodney. "Buckling of suction caissons during installation." University of Western Australia. School of Civil Engineering, 2003. http://theses.library.uwa.edu.au/adt-WU2004.0008.
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Suction caissons are a foundation system for offshore structures which offer a number of advantages over traditional piled foundations. In particular, due to the method of installation used, they are well suited for deep-water applications. The suction caisson consists of an open ended cylindrical shell, which is installed below the seabed in a sequence which consists of two loading phases. The caisson is first installed part way under self weight, with the installation being completed by lowering the pressure within the cylinder and thus allowing the ambient water pressure to force the caisson into the ground. This thesis examines a number of structural issues which result from the form of the caisson — essentially a thin walled cylinder — and the interaction of the caisson with the surrounding soil during installation. To do this, variational analysis and nonlinear finite element analysis are employed to examine the buckling and collapse behaviour of these cylinders. In particular, two issues are considered; the influence of the open end, and the interaction between the cylinder and soil on the buckling and collapse loads. First, the behaviour of open ended cylinders is considered, where the boundary condition at the open end is allowed to vary continuously from completely free to pinned, by the use of a variable lateral spring. This lateral spring restraint may be considered to represent the intermediate restraint provided by a ring stiffener which is not fully effective. The effect of various combinations of boundary conditions is accounted for by the use of a multiplier on the lower bound to the buckling load of a cylinder with classical supports. The variable spring at the open end may also be considered to be an initial, simple representation of the effect of soil restraint on the buckling load. More complex representations of the soil restraint are also considered. A nondimensional factor is proposed to account for the influence of this spring on the buckling load. One combination of boundary conditions, where the upper end of the caisson is pinned, and the lower end free (referred to as a PF boundary condition), is found to have buckling and collapse behaviour which is unusual for cylindrical shells. Buckling loads for such shells are much lower than would be found for cylinders with more typical boundary conditions, and of similar dimensions. More unusually however, PF cylinders are shown to have positive postbuckling strength. The behaviour is found to be a result of the large flexibility which results from the low restraint provided by the PF boundary conditions. This is shown by continuously decreasing the flexibility of the cylinder, by increasing the axial restraint at the pinned end. It is shown that this results in a large increase in buckling load, and a return to more usual levels of imperfection sensitivity. In particular, with an intermediate level of axial restraint, buckling loads and imperfection sensitivity are intermediate between those of PF shells with no, and with full, axial restraint. Overall however, collapse loads for PF cylinders with no additional restraint are well below those of cylinders with stiffer boundary conditions, for equal geometries. Eigenvalue buckling of cylinders fully and partially embedded in an elastic material are examined, and two analytical solutions are proposed. One of these is an extension of a method previously proposed by Seide (1962), for core filled cylinders, to pin ended cylinders which have support from both a core and a surrounding material. The second method represents the elastic support as a two parameter foundation. While more approximate than the first method, this method allows for the examination of a wider range of boundary conditions, and of partial embedment. It is found that the buckling load of the shell/soil system decreases as the embedment ratio decreases. Collapse of fully and partially embedded cylinders is also examined, using nonlinear finite element analysis. The influence of plasticity in the soil is also considered. For cylinders with small imperfections, it is found that the collapse load shows a large increase over that of the same cylinder with no soil support. However, as the size of initial geometric imperfections increases, it is found that the collapse load rapidly approaches that of the unsupported cylinder. In particular, in weak soils the gain in strength over the unsupported shell may be minimal. The exception to this is again PF cylinders. As these have relatively low collapse loads, even very weak soils are able to offer an increase in collapse load over the unsupported case. Finally, a summary of these results is provided in the form of guidance for design of such structures.
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Byrne, Byron Walter. "Investigations of suction caissons in dense sand." Thesis, University of Oxford, 2000. http://ora.ox.ac.uk/objects/uuid:64c30b2e-155c-4642-9115-5e2bf5667af5.
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Offshore structures are used in a variety of applications ranging from the traditional oil and gas extraction facilities to emerging renewable energy concepts. These structures must be secured to the seabed in an efficient and cost effective manner. A novel approach is to use shallow inverted buckets as foundations, installed by suction, in place of the more usual piles. These foundations lead to cost savings through reduction in materials and in time required for installation. It is necessary to determine how these foundations perform under typical offshore loading conditions so that design calculations may be developed. This thesis presents experimental data from a comprehensive series of investigations aimed at determining the important mechanisms to consider in the design of these shallow foundations for dense sand. Initially the long term loading behaviour (e.g. wind and current) was investigated by conducting three degree of freedom loading {V:M/2R:H} tests on a foundation embedded in dry sand. The results were interpreted through existing work-hardening plasticity theories. The analysis of the data has suggested a number of improved modelling features. Cyclic and transient tests, representing wave loading, were carried out on a foundation embedded in an oil saturated sand. The novel feature of the cyclic loading was that a 'pseudo-random' load history (based on the 'NewWave' theory) was used to represent realistic loading paths. Of particular interest was the tensile load capacity of the foundation. The results observed suggested that for tensile loading serviceability requirements rather than capacity may govern design. Under combined-load cyclic conditions the results indicated that conventional plasticity theory would not provide a sufficient description of response. A new theory, termed 'continuous hyperplasticity' was used, reproducing the results with impressive accuracy. Surprisingly, under the conditions investigated, loading rate was found to have a negligible effect on response.
4
Chen, Wen. "Uniaxial behaviour of suction caissons in soft deposits in deepwater." University of Western Australia. School of Civil and Resource Engineering, 2005. http://theses.library.uwa.edu.au/adt-WU2005.0136.
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Suction caissons are a cost-effective alternative to traditional piles in deep to ultradeep waters. No design rule has been available on the axial capacity of suction caissons as part of the mooring system in soft sediments. In this research, a series of centrifuge tests were performed using instrumented model caissons, to investigate the axial capacity and radial stress changes around caissons during installation, consolidation and vertical pullout in normally consolidated, lightly overconsolidated and sensitive clays. Total pressure transducers instrumented on the caisson wall were calibrated for various conditions. The radial total stress acting on the external wall varied almost linearly during penetration and extraction of the caisson, with smaller gradients observed during post-consolidation pullout. Minimum difference was found in the penetration resistance and the radial total stress for caissons installed by jacking or by suction, suggesting that the mode of soil flow at the caisson tip is similar under these two types of installation. Observed soil heave showed that the soil particles at the caisson tip flow about evenly outside and inside the caisson during suction installation. Comparison was made between measurements and various theoretical predictions, on both the radial stress changes during caisson installation, and the radial effective stress after consolidation. Significant under-predictions on excess pore pressure changes, consolidation times and external shaft friction ratios were found for the NGI Method, based on the assumption that the caisson wall is accommodated entirely by inward motion of the clay during suction installation. Obvious over-predictions by the MTD approach were found in both stress changes and shaft capacity of the caissons. A simple form of cavity expansion method was found to give reasonable estimations of stress changes and post-consolidation external shaft friction. A model for predicting the penetration resistance of suction caissons in clay was evaluated. Upper and lower bound values of external shaft friction ratio during uplift loading after consolidation were derived. Uplift capacity of caissons under sustained loading and cyclic loading were investigated, revealing approximately 15 to 30% reduction of the capacity compared to that under monotonic loading. External shaft friction ratios and reverse end-bearing capacity factors were both found to be significantly lower than those under monotonic loading
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Supachawarote, Chairat. "Inclined load capacity of suction caisson in clay." University of Western Australia. School of Civil and Resource Engineering, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0188.
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This thesis investigates the capacity and failure mode of suction caissons under inclined loading. Parametric finite element analyses have been carried out to investigate the effects of caisson geometry, loading angle, padeye depth (i.e. load attachment point), soil profile and caisson-soil interface condition. Displacement-controlled analyses were carried out to determine the ultimate limit state of the suction caissons under inclined load and the results presented as interaction diagrams in VH load space. VH failure interaction diagrams are presented for both cases where the caisson-soil interface is fully-bonded and where a crack is allowed to form along the side of the caisson. An elliptical equation is fitted to the normalised VH failure interaction diagram to describe the general trend in the case where the caisson-soil interface is fully-bonded. Parametric study reveals that the failure envelope in the fully-bonded case could be scaled down (contracted failure envelope) to represent the holding capacity when a crack is allowed to form. A stronger effect of crack on the capacity was observed in the lightly overconsolidated soil, compared to the normally consolidated soil. The sensitivity of caisson capacity to the changes in load attachment position or loading angle was quantified based on the load-controlled analyses. It was found that, for caisson length to diameter ratios of up to 5, the optimal centreline loading depth (i.e. where the caisson translates with no rotation) is in the range 0.65L to 0.7L in normally consolidated soil, but becomes shallower for the lightly overconsolidated soil profile where the shear strength profile is more uniform. The reduction of holding capacity when the padeye position is shifted from the optimal location was also quantified for normally consolidated and lightly overconsolidated soil profiles at loading angle of 30 [degrees]. Upper bound analyses were carried out to augment the finite element study. Comparison of holding capacity and accompanying failure mechanisms obtained from the finite element and upper bound methods are made. It was found that the upper bound generally overpredicted the inclined load capacity obtained from the finite element analyses especially for the shorter caisson considered in this study. A correction factor is introduced to adjust the upper bound results for the optimal condition. Comparisons of non-optimal capacity were also made and showed that the agreement between the upper bound and finite element analyses are sensitive to the change in the centreline loading depth when the caisson-soil interface is fully bonded, but less so when a crack forms.
6
El-Gharbawy, Sherif Lotfy. "The pullout capacity of suction caisson foundations /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Senders, Marc. "Suction caissons in sand as tripod foundations for offshore wind turbines." University of Western Australia. School of Civil and Resource Engineering, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0163.
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[Truncated abstract] The demand for offshore wind turbines is increasing in densely populated areas, such as Europe. These constructions are typically founded on a gravity foundation or a large 'mono pile'. Gravity foundations can only be used at locations where strong soils exist and water depths are limited. Costs associated with a 'mono pile' type foundation contribute to a very large percentage of the total investment costs. This research, therefore, focuses upon a different foundation for offshore wind turbines, namely suction caissons beneath a tripod. This foundation can be used in all kinds of soil types and is cheaper than the 'mono pile' foundation, both in the amount of steel used and installation costs. Cheaper foundations can contribute to a more competitive price for offshore wind energy in comparison with other energy resources. To date, there have been relatively few studies to investigate the behaviour of this type of foundation during the installation process and during operational and ultimate loading for seabed conditions comprising dense sand. Two types of investigations were performed during this research to determine the behaviour of suction caissons beneath a tripod. Firstly, an existing computer program was extended to predict the typical loading conditions for a tripod foundation. Secondly, centrifuge tests on small scale suction caissons were performed to investigate the behaviour during the installation and loading phases. The computer program developed helped to quantify the likely ranges of environmental loading on an offshore wind turbine. For a typical 3 MW wind turbine of 90 m height, the vertical load is low at around 7 MN. During storm conditions the horizontal hydrodynamic load can be in the order of 4 MN. During normal working conditions the horizontal aerodynamic loads can reach 0.4 MN, but can increase to 1.2 MN when the pitch system malfunctions and gusts reach 30 m/s. This aerodynamic load will result in a very large contribution to the overturning moment, due to the high action point of this load. When the wind turbine is placed on top of a tripod, these large moments are counteracted by a push-pull system. ... The development of differential pressure was found to depend on the soil permeability, the extraction speed and a consolidation effect. During cyclic loading no obvious signs of a decrease in resistance were observed. During very fast cyclic loading differential pressures developed, which could increase the drained frictional resistance by approximately 40%. All centrifuge tests results were used to develop methods to predict or back calculate the installation process of suction caissons in sand and layered soil, and the behaviour during tensile and cyclic loading. These methods all use the cone resistance as the main input parameter and predict the force (or required suction) as a function of time, for a given rate of pumping or uplift displacement, in addition to the variation of suction with penetration (or force with uplift displacement). These new methods provide a useful tool in designing a reliable foundation for offshore wind turbines consisting of a tripod arrangement of suction caissons embedded in dense sand.
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Sgardeli, Christina G. (Georgia-Chrysouli C. ). "A finite element analysis of the pullout capacity of suction caissons in clay." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/53111.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2009.Includes bibliographical references (leaves 90-92).
Suction caissons are increasingly becoming the foundation of choice for offshore structures in deep water. They are used extensively in Tension Leg Platforms and provide the most efficient foundations for many offshore wind turbine structures. One of their major advantages is the ability to withstand large uplift forces by mobilizing shear on their external and internal surface and by the suction forces induced in the enclosed soil plug. These suction forces can be relied upon for short-term loading, while the behaviour of the soil remains undrained, but are more questionable for the sustained loading induced by storms and loop currents. This study uses finite element analysis to investigate the uplift capacity of suction caissons under three loading conditions: a) short-term undrained loading, b) long-term drained loading and c) sustained loading for short and long periods of time. The study compares the capacity from 5 different geometries with length to diameter ratios, L/d = 0.5,0.65,1,2 and 3 under these three loading conditions. For the sustained loading case, a minimum time under which the load can be sustained is established for different load levels. The commercial finite element program Plaxis is used and a Mohr-Coulomb model is assumed for the soil. Comparisons are presented between the results of this study, the theoretical Mohr-Coulomb model predictions and other finite element analysis found in the research for undrained and drained loading.
by Christina G. Sgardeli.
M.Eng.
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Tran, Manh Ngoc. "Installation of Suction Caissons in Dense Sand and the Influence of Silt and Cemented Layers." University of Sydney, 2006. http://hdl.handle.net/2123/4064.
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Doctor of PhilosophySuction caissons have been used in the offshore industry in the last two decades as both temporary mooring anchorages and permanent foundation systems. Although there have been more than 500 suction caissons installed in various locations around the world,understanding of this concept is still limited. This thesis investigates the installation aspect of suction caissons, focusing on the installation in dense sand and layered soils, where sand is inter-bedded by silt and weakly cemented layers. The research was mainly experimental, at both normal gravity and elevated acceleration levels in a geotechnical centrifuge, with some numerical simulations to complement the experimental observations. This study firstly explored the suction caisson installation response in the laboratory at 1g. The influence and effect of different design parameters, which include caisson size and wall thickness, and operational parameters including pumping rate and the use of surcharge were investigated in dense silica sand. The sand heave inside the caisson formed during these installations was also recorded and compared between tests. The 1g study also investigated the possibility of installing suction caissons in layered sand-silt soil, where caissons were installed by both slow and rapid pumping. The heave formation in this case is also discussed. The mechanism of heave formation in dense sand and deformation of the silt layer was further investigated using a half-caisson model and the particle image velocimetry (PIV) technique. The installation response at prototype soil stress conditions was then investigated in a geotechnical centrifuge. The effects of caisson size, wall thickness, as well as surcharge were investigated in various types of sand, including silica sand, calcareous sand dredged from the North Rankin site in the North West Shelf (Australia), and mixed soil where silica sand was mixed with different contents of silica flour. Comparison with the 1g results was also made. The general trend for the suction pressure during installation in homogenous sand was identified. The installation in layered soil was also investigated in the centrifuge. The installation tests were performed in various sand-silt profiles, where the silt layers were on the surface and embedded within the sand. Comparison with the results in homogenous sand was made to explore the influence of the silt layer. Installations in calcareous sand with cemented layers were also conducted. The penetration mechanism through the cemented layer is discussed, and also compared with the penetration mechanism through the silt layer. Finite element modelling was performed to simulate key installation behaviour. In particular, it was applied to simulate the sand deformation observed in the PIV tests. The likely loosening range of the internal sand plug during suction installation in silica sand was estimated. By investigating the development of hydraulic gradient along the inner wall, the principle underlying the suction response for different combinations of selfweight and wall thickness was identified. FE modelling was also performed to explore the influence of the hydraulic blockage by the silt layer. This study found that the caissons could penetrate into all soils by suction installation. Among the key findings are the observations that the suction pressure increases with depth following a distinct pressure slope, corresponding to a critical hydraulic condition along the inner wall; and the installation was possible in both layered sand-silt and uncemented-cemented soils if sufficient pumping was available. While the caisson could penetrate the weakly cemented layers well with no notable adverse effects, problems were observed in the installation in layered sand-silt soil. These include piping failure in slow pumping rate installation at 1g, and the formation of extremely unstable soil heave during installation.
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Tran, Manh Ngoc. "Installation of Suction Caissons in Dense Sand and the Influence of Silt and Cemented Layers." Thesis, The University of Sydney, 2005. http://hdl.handle.net/2123/4064.
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Suction caissons have been used in the offshore industry in the last two decades as both temporary mooring anchorages and permanent foundation systems. Although there have been more than 500 suction caissons installed in various locations around the world,understanding of this concept is still limited. This thesis investigates the installation aspect of suction caissons, focusing on the installation in dense sand and layered soils, where sand is inter-bedded by silt and weakly cemented layers. The research was mainly experimental, at both normal gravity and elevated acceleration levels in a geotechnical centrifuge, with some numerical simulations to complement the experimental observations. This study firstly explored the suction caisson installation response in the laboratory at 1g. The influence and effect of different design parameters, which include caisson size and wall thickness, and operational parameters including pumping rate and the use of surcharge were investigated in dense silica sand. The sand heave inside the caisson formed during these installations was also recorded and compared between tests. The 1g study also investigated the possibility of installing suction caissons in layered sand-silt soil, where caissons were installed by both slow and rapid pumping. The heave formation in this case is also discussed. The mechanism of heave formation in dense sand and deformation of the silt layer was further investigated using a half-caisson model and the particle image velocimetry (PIV) technique. The installation response at prototype soil stress conditions was then investigated in a geotechnical centrifuge. The effects of caisson size, wall thickness, as well as surcharge were investigated in various types of sand, including silica sand, calcareous sand dredged from the North Rankin site in the North West Shelf (Australia), and mixed soil where silica sand was mixed with different contents of silica flour. Comparison with the 1g results was also made. The general trend for the suction pressure during installation in homogenous sand was identified. The installation in layered soil was also investigated in the centrifuge. The installation tests were performed in various sand-silt profiles, where the silt layers were on the surface and embedded within the sand. Comparison with the results in homogenous sand was made to explore the influence of the silt layer. Installations in calcareous sand with cemented layers were also conducted. The penetration mechanism through the cemented layer is discussed, and also compared with the penetration mechanism through the silt layer. Finite element modelling was performed to simulate key installation behaviour. In particular, it was applied to simulate the sand deformation observed in the PIV tests. The likely loosening range of the internal sand plug during suction installation in silica sand was estimated. By investigating the development of hydraulic gradient along the inner wall, the principle underlying the suction response for different combinations of selfweight and wall thickness was identified. FE modelling was also performed to explore the influence of the hydraulic blockage by the silt layer. This study found that the caissons could penetrate into all soils by suction installation. Among the key findings are the observations that the suction pressure increases with depth following a distinct pressure slope, corresponding to a critical hydraulic condition along the inner wall; and the installation was possible in both layered sand-silt and uncemented-cemented soils if sufficient pumping was available. While the caisson could penetrate the weakly cemented layers well with no notable adverse effects, problems were observed in the installation in layered sand-silt soil. These include piping failure in slow pumping rate installation at 1g, and the formation of extremely unstable soil heave during installation.
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Stapelfeldt, Marc [Verfasser]. "The influence of the drainage regime on the installation and the response to vertical cyclic loading of suction caissons / Marc Stapelfeldt." Hamburg : Universitätsbibliothek der Technischen Universität Hamburg-Harburg, 2021. http://d-nb.info/1226854575/34.
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Zhou, Hongjie. "Numerical study of geotechnical penetration problems for offshore applications." University of Western Australia. Centre for Offshore Foundation Systems, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0239.
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The research carried out in this thesis has concentrated on the application of numerical solutions to geotechnical penetration problems in offshore engineering. Several important issues closely relevant to deep-water oil and gas developments were investigated, covering installation of suction caisson foundations, interpretation of fullflow penetrometers and shallow penetration of a cylindrical object (submarine pipeline or T-bar), all in clayey sediments such as are often encountered in deep-water sites. These problems are commonly characterised by large vertical movements of structural elements relative to the seabed. A large deformation finite element method was adopted and further developed to simulate these challenging problems, referred to as Remeshing and Interpolation Technique with Small Strain. In this approach, a sequence of small strain Lagrangian increments, remeshing and interpolation of stresses and material properties are repeated until the required displacement has been reached. This technique is able to model relative motion between the penetrating objects and the soil, which is critical for evaluating soil heave inside the caissons, the effect of penetration-induced remoulding on the resistance of full-flow penetrometers, and influence of soil surface heave on the embedment of pipelines. '...' Simple expressions were presented allowing the resistance factors for the T-bar and ball penetrometers to be expressed as a function of the rate and strain-softening parameters. By considering average strength conditions during penetration and extraction of these full-flow penetrometers, an approximate expression was derived that allowed estimation of the hypothetical resistance factor with no strain-softening, and hence an initial estimate of the stain-rate dependency of the soil. Further simulations of cyclic penetration tests showed that a cyclic range of three diameters of the penetrometers was sufficient to avoid overlap of the failure mechanism at the extremes and mid-point of the cyclic range. The ball had higher resistance factors compared with the T-bar, but with similar cyclic resistance degradation curves, which could be fitted accurately by simple expressions consistent with the strain-softening soil model adopted. Based on the curve fitting, more accurate equations were proposed to deduce the resistance factor with no strain-softening, compared with that suggested previously based on the resistances measured in the first cycle of penetration and extraction. The strain-rate dependency was similar in intact or post-cyclic soil for a given rate parameter. The resistance factor for the post-cyclic condition was higher than that for the initial conditions, to some degree depending upon soil sensitivity and brittleness parameter. For the shallow penetration of a cylindrical object, the penetration resistance profile observed from centrifuge model tests was very well captured by the numerical simulation. The mechanism of shear band shedding was reproduced by the numerical technique, although the frequency of the shear band generation and the exact shape of the heave profile were not correctly captured, which were limited by the simple strainsoftening soil model adopted.
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Cotter, Oliver. "Installation of suction caisson foundations for offshore renewable energy structures." Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.534163.
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Dekker, Marijn Johannes. "The Modelling of Suction Caisson Foundations for Multi-Footed Structures." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-27161.
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Suction caissons are a type of offshore foundation that allow for fast and noise-free installation and decommissioning of offshore structures. They have been used for 20 years in the oil and gas industry and are also becoming more common in the offshore wind sector as a promising way to cost reduction. SPT is a leading contractor for the installation of both single anchor piles and foundations on multiple caissons. The suction caissons are installed by applying a differential pressure between the inner and outer sides of the caissons, which pushes the caissons into the soil. When a platform is founded on multiple suction caissons, the way the wind and wave loads are transferred through the structure and various caissons into the soil will depend on the stiffness of both the platform and the caissons. The design of the substructure and suction caissons should thus be combined to include the effects of soil-structure interaction. This is currently done by modelling the suction caisson foundations as a set of linear-elastic springs attached to the substructure. These springs are however not able to capture the non-linear behaviour that is often characteristic for soils. A method has been developed to model the suction caisson foundations using non-linear springs. The characteristics of the springs are determined using FEM calculations with a nonlinear soil model in the geotechnical software PLAXIS. The springs are then implemented in a structural model of the substructure and the multiple foundations in the structural software SACS. The resulting loads on and displacements of the suction caisson foundations for a test load case have been compared to results from a complete FE model and a model that uses linear-elastic springs. The comparison has shown that the developed model gives results that match well with the results from the full FE model. The linear-elastic model on the other hand gives results that deviate significantly for high loads.When the stresses in the soil increase the soil will behave softer, leading to an increase of the displacements of the suction caissons for high loads. The substructure will help decrease large differences between the displacements of the suction caissons, resulting in a more even load distribution over the foundations and thus smaller design loads for the suction caissons. This allows for smaller suction caissons and savings of material and costs. The model with nonlinear springs is able to predict this behaviour of the soil and the substructure accurately and can be used to make a more efficient design of suction caisson foundations.
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Sharma, Partha Pratim. "Ultimate capacity of suction caisson in normally and lightly overconsolidated clays." Thesis, Texas A&M University, 2005. http://hdl.handle.net/1969.1/2460.
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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.
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Cox, James A. "Long-term serviceability behaviour of suction caisson supported offshore wind turbines." Thesis, University of Bristol, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.680352.
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Suction caissons have recently been considered as an alternative to monopile foundations for offshore wind turbines and met masts. By their nature, such structures have stringent limit states imposed on their design dictating the first modal frequency and the allowable structural rotations. The aim of this thesis is to assess how cyclic loading will affect the long-term serviceability behaviour of such an offshore structure. The behaviour of such a representative caisson system was assessed through the use of a series of scale model tests conducted in dry sand, replicating a fully drained prototype condition. These tests were designed to record the foundation stiffness, its evolution under cyclic loading, how the system accumulates rotation with loading cycles and the dynamic properties of a caisson system. This was conducted at a number of scales under single-g and multi-g conditions. Considering all of the experimentally obtained data it was possible to analyse and provide a prediction as to the long-term behaviour of such an offshore structure. It was discovered that the foundation stiffness was highly dependent on the strain level and under the application of cyclic loading the stiffness would tend to increase in a logarithmic manner. In addition it was found that when subjected to a cyclic load a caisson system will accumulate rotation in accordance with a power relationship. Finally the dynamic properties were found to closely match pre-existing formulations describing a simple dynamic system. Considering these results it was possible to produce an analytical model to describe the evolution of serviceability of a caisson founded offshore structure. Latterly this model was applied to a series of representative cyclic loading test to examine the validity of the complete model.
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Mucolli, Gent. "Fuzzy modeling of suction anchor behavior based on cyclic model tests data." Digital WPI, 2016. https://digitalcommons.wpi.edu/etd-theses/1313.
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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.
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Cauble, Douglas Frederick. "An experimental investigation of the behavior of a model suction caisson in a cohesive soil." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10734.
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Unida, Roberto. "An investigation on the offshore wind energy potential in Italy and its deployment with floating turbines." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
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The thesis aim is to offer a general assessment of potential of offshore wind deployment in Italy. More specifically, it aids with the identification of the most promising locations and estimates the levelized cost of energy of the areas found suitable. Furthermore, the thesis develops a simple technical feasibility study at one of these sites, which specifically focuses on the design of the wind turbines foundations, considering and comparing different geotechnical solutions.
It is been found that, in Italy, the offshore area suitable for the installation of wind farms is approximately 110,000 km2, with an estimated theoretical annual energy production of 188.25 TWh, more than half of the Italian electricity need. Locations identified as promising are the Adriatic Sea, and the Ionian Sea of the Apulia region and the South-West part of Sicily. For these areas the LCOE analysis has yielded values ranging between 90 $/kWh to 130 $/kWh, in line with European average. The case of study indicated that anchors’ cost strongly depends on local met-ocean conditions, as it is found by comparing the results obtained for the Italian case study with Hywind Scotland pilot floating wind farm, used as benchmark. Comparison between two different anchor solutions has also shown that the foundation choice has also a significant impact on the overall cost for a plant set-up.
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Floridia, Daniele. "Hybrid foundations for offshore wind turbines." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amslaurea.unibo.it/3284/.
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Nowadays offshore wind turbines represents a valid answer for energy production but with an increasing in costs mainly due to foundation technology required. Hybrid foundations composed by suction caissons over which is welded a tower supporting the nacelle and the blades allows a strong costs reduction. Here a monopod configuration is studied in a sandy soil in a 10 m water depth. Bearing capacity, sliding resistance and pull-out resistance are evaluated. In a second part the installation process occurring in four steps is analysed. considering also the effect of stress enhancement due to frictional forces opposing to penetration growing at skirt sides both inside and outside. In a three dimensional finite element model using Straus7 the soil non-linearity is considered in an approximate way through an iterative procedure using the Yokota empirical decay curves.
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Chen, Ching-Hsiang active 2013. "Performance of suction caissons with a small aspect ratio." 2013. http://hdl.handle.net/2152/23092.
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Suction caissons with a smaller aspect (length to diameter) ratio are increasingly used for supporting offshore structures, such as wind turbines and oil and gas production facilities. The design of these stubbier foundations is usually governed by lateral loads from wind, waves, or currents. It is desired to have more physical understanding of the behavior of less slender suction caissons under cyclic lateral loading condition and to have robust design tools for analyzing these laterally loaded caissons.
In this study, one-g model tests with 1:25 and 1:50 suction can foundation scale models with an aspect ratio of one are conducted in five different soil profiles: normally consolidated clay, overconsolidated clay, loose siliceous sand, cemented siliceous sand, and cemented calcareous sand. This test program involves monitoring settlements, lateral displacements (walking), tilt, lateral load and pore water pressures in the suction can during two-way cyclic lateral loading at one, three and five degrees of rotation. The model foundations are monitored during installation, axial load tests, and pullout tests.
In one and two-degree (±0.5 and ±1 degree) rotation tests, the suction can does not have significant walking or settlement in all the five soil profiles after 1000 load cycles. However, more significant walking or settlement may occur at extreme conditions such as the 5-degree (±2.5 degrees) rotation tests. Gaps between the foundation wall and the soil may also form in these extreme conditions in overconsolidated clay, cemented siliceous sand, and cemented calcareous sand.
Plastic limit analysis, finite element analysis, and finite difference analysis are used to evaluate the laterally loaded suction can in clay. The plastic limit analysis originally developed for more slender suction caissons appears to predict a lateral capacity close to the measured short-term static capacity of the caisson with an aspect ratio of one when undisturbed undrained shear strength of soil is used. However, this plastic limit model underestimates the long-term cyclic lateral load capacity of the caisson when the remolded undrained shear strength was used. The finite element model developed in this study can simulate the development and effect of a gap between the foundation and surrounding soil as observed in the experiments in overconsolidated clay. The lateral load-displacement response predicted by this finite element model matches well with the experimental data. Finally, finite difference analysis for a rigid caisson with lateral and rotational springs was developed by fitting the lateral load-displacement response of the suction can in clay. The calibrated p-y curves for rigid caisson are significantly stiffer and have higher ultimate resistance than the p-y curves recommended by API which is consistent with other studies. This finite difference model provides an efficient approach to analyze a laterally loaded caisson with a small aspect ratio in clay.text
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El-Sherbiny, Rami Mahmoud Gilbert Robert B. Olson Roy E. "Performance of suction caisson anchors in normally consolidated clay." 2005. http://repositories.lib.utexas.edu/bitstream/handle/2152/1900/elsherbinyd11657.pdf.
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El-Sherbiny, Rami Mahmoud. "Performance of suction caisson anchors in normally consolidated clay." Thesis, 2005. http://hdl.handle.net/2152/1900.
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Beemer, Ryan. "Analytical and Experimental Studies of Drag Embedment Anchors and Suction Caissons." Thesis, 2011. http://hdl.handle.net/1969.1/ETD-TAMU-2011-05-9263.
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The need for experimental and analytical modeling in the field of deep water offshore
anchoring technologies is high. Suction caisson and drag embedment anchors (DEA) are
common anchors used for mooring structures in deep water. The installation process of
drag embedment anchors has been highly empirical, employing a trial and error
methodology. In the past decade analytical methods have been derived for modeling
DEA installation trajectories. However, obtaining calibration data for these models has
not been economical. The development of a small scale experimental apparatus, known
as the Laponite Tank, was developed for this thesis. The Laponite Tank provides a quick
and economical means of measuring DEA trajectories, visually. The experimental data
can then be used for calibrating models. The installation process of suctions caissons
has benefited from from a more rational approach. Nevertheless, these methods require
refinement and removal methodology requires development. In this thesis, an algorithm
for modeling suction caisson installation in clay has been presented. An analytical
method and modeling algorithm for removal processes of suction caissons in clay was
also developed. The installation and removal models were calibrated to field data. These
analytical and experimental studies can provide a better understanding of installation of
drag embedment anchors and the installation and removal of suction caissons.
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Maniar, Dilip Rugnathbhai. "A computational procedure for simulation of suction caisson behavior under axial and inclined loads." Thesis, 2004. http://wwwlib.umi.com/cr/utexas/fullcit?p3143307.
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Maniar, Dilip Rugnathbhai Tassoulas John Lambros. "A computational procedure for simulation of suction caisson behavior under axial and inclined loads." 2004. http://wwwlib.umi.com/cr/utexas/fullcit?p3143307.
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Cao, Jianchun. "Centrifuge modeling and numerical analysis of the behaviour of suction caissons in clay /." 2003.
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Handayanu. "Failure mechanisms of suction caisson foundations in clay under vertical and inclined pullout loads /." 2001.
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Tran, Manh Ngoc. "Installation of suction caissons in dense sand and the influence of silt and cemented layers." Thesis, 2005. http://hdl.handle.net/2123/1197.
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Huang, Ting-Ting, and 黃亭亭. "Numerical study on installation pressure of suction caisson foundation for offshore wind turbine." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/vyt862.
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碩士國立中山大學
海洋環境及工程學系研究所
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The objective of this study is the mechanical behavior of suction bucket caisson under loadings. The formulations are derived based on the fundamental theories of ocean hydrodynamic and flow in porous medium and they are solved by the finite-difference methods. A benchmark validation was made before further simulation cases. Several penetration depths were assumed and two different suction pressures were given. Different boundary conditions were tested and the most reasonable one was suggested. Suction induced stresses in response to various suction pressures and penetration depths were studied. The overall lateral resistance and possible piping potential were investigated. As the penetration depth increases, the distribution of the normalize excess water pressure gradient inside the caisson wall is aligned with the wall and the excess water pressure at the caisson tip become smaller, whereas the normal stress and shear stress increase as does the penetration depth and the maximums stress is on the caisson tips. The suction induced stress will lead the friction stress within the caisson decrease, and the outer parts will increase. However, the maximum decrement of the effective soil stress at the inner corner of the caisson tip and the piping potential is 31.52 % in full penetration depth.
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Hsuan-ChiHung and 洪萱淇. "Numerical Analysis of Installation and Load-Bearing Behavior of Suction Caisson Foundations for Offshore Wind Turbines." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/20539348839566337954.
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碩士國立成功大學
土木工程學系
103
Suction caissons are considered as an alternative foundations for offshore wind turbines in Taiwan. This study presents numerical analyses of the installation process and bearing behavior of monopod suction caisson in sand with a finite difference technique. The results are validated with field test results in literature. It is shown that the application of suction inside the caisson is the main source for the penetration of foundations, and the soil stress distribution is symmetrical during the installation procedure. Under combined vertical, horizontal and moment loadings, the bearing capacity, sliding and overturning stability of foundations are analyzed. Among the three modes, the overturning stability is the dominated one for suction caissons stability. Comparisons with field testing results, show that the ultimate capacities from two dimension numerical simulations are smaller than the capacities of field tests.
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Cheon, Jeong Yeon. "Analysis of spatial variability in geotechnical data for offshore foundations." Thesis, 2010. http://hdl.handle.net/2152/ETD-UT-2010-12-2052.
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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