To see the other types of publications on this topic, follow the link: Offshore geotechnics.
Dissertations / Theses on the topic 'Offshore geotechnics'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 32 dissertations / theses for your research on the topic 'Offshore geotechnics.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Williams, Elizabeth S. "Upheaval buckling of offshore pipelines buried in loose and liquefiable soils." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:10c2cf4d-ab26-4f2c-82d9-35e15cfa03bc.
Full textAbstract:
Pipelines used for the transportation of oil and gas products offshore are often buried beneath the seabed for protection from mechanical damage and for thermal insulation. During high temperature and high pressure operations, these pipelines are susceptible to resurfacing behaviour known as upheaval buckling, a structural response that is strongly influenced by the resistance of the surrounding soil. Despite much previous research on pipe uplift, the influence of the initial soil state – particularly in loose and liquefiable soil conditions – on the uplift resistance and corresponding buckling behaviour of the pipe is not well understood. This thesis presents research that examines the implications of these backfill conditions in the context of the global behaviour of the pipeline. The work consists of plane-strain monotonic uplift experiments focusing on density, rate, and stress level effects on the initial pipe-soil response. This is followed by numerical modelling of the global buckling behaviour using the experimental data as inputs. Finally, plane-strain cyclic experiments examine the possibility of progressive upward displacements over a number of cycles causing eventual upheaval buckling. A key finding from the uplift tests is that very loose backfill conditions may result in a localised flow-around failure mechanism, associated with lower peak resistance and a softer force-displacement response than with the sliding block mechanism that is typically assumed. This leads to lower peak buckling loads/temperatures than those predicted by current design guidelines. High quality data from both the monotonic and cyclic experiments was used to assess and suggest improvements to design guidance for these conditions.
2
Dunne, Helen P. "Finite element limit analysis of offshore foundations on clay." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:ba9c9beb-e055-4f46-a9f9-b2d10bd292b7.
Full textAbstract:
Capacity analysis is a common preliminary step in the design of offshore foundations. Inaccuracies in traditional capacity analysis methods, and the advancement of numerical modelling capabilities, have increasingly led designers to optimise foundations using more complex methods. In this thesis, the ultimate limit state capacity of a range of foundation types is investigated using finite element limit analysis. Novel three-dimensional finite element limit analysis software is benchmarked against analytical solutions and conventional displacement finite element analysis. It is then used to find lower and upper bounds of foundation capacity, with adaptive mesh refinement used to reduce the bound gap over successive iterations of the solution. Rigid foundations subjected to short term loading on clay soil are analysed. The undrained soil is modelled as a rigid--plastic von Mises material, and attention is given to modelling any normal and/or shear stress limits at the foundation/soil interface. Shallow foundations, suction anchor foundations, and hybrid mudmat/pile foundations are considered. Realistic six degree-of-freedom load combinations are applied and results are reported in the form of normalised design charts, and tables, that are suitable for use in preliminary design. Relationships between loading combinations and failure mechanisms are also explored. A number of case studies based on authentic foundation designs are analysed. The results suggest that finite element limit analysis could provide an attractive alternative to displacement finite element analysis for preliminary foundation design calculations.
3
Muraleedharan, Atmaram. "Fatigue design and dynamic analysis of Steel catenary risers at Touch down zone with nonlinear soil structure interaction model under randomly generated waves." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
Find full textAbstract:
The offshore industry is moving deeper and deeper into the ocean depths and a subsequent technological advancement are inevitable factors. Steel Catenary Risers (SCRs) are the most popular type of deep water risers and are very important part of any deep-water developments. Although the simplicity in installation and the associated economic advantage makes it widely popular, these highly slender structures are very sensitive to dynamic loads and fatigue. Hang-off point where the riser is connected to the floater and Touch Down Zone (TDZ) where the riser interacts with the seabed are the two-important fatigue critical regions in an SCR.
Fatigue design at TDZ remains a challenging topic among riser engineers and the soil structure interaction here makes it extremely complex to design for fatigue. Linear soil structure models, which are popular among the design professionals due to its simplicity are extremely conservative and the industry is slowly moving towards the nonlinear soil models. This research investigates the effects of implementing the nonlinear soil model into the fatigue design of SCRs under randomly generated waves with detailed comparison with the linear soil model. The uncertainties related to estimation of fatigue damage at TDZ and the influence of duration of simulation are studied in detail and some significant observations and findings are presented in this research. A very extensive effort to understand the effect of different order of waves (of varying intensities) also formed a part of this study which yielded crucial results which opens new doors in this topic.
4
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.
Full textAbstract:
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.
5
Melling, Gregor J. "Hydrodynamic and geotechnical controls of scour around offshore monopiles." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/378992/.
Full textAbstract:
Marine monopiles can suffer from removal of sediment around their foundations by waves and currents, a process termed scour, which can negatively affect structure stability and integrity of associated infrastructure. Scour is a function of the interaction of local hydrodynamics with the geotechnical properties of the seabed, the feedbacks of which are not well understood. Using the largest prototype scour data base available to date, assembled from field data routinely collected during the consents and design phase of wind farms, this study aims to offer a detailed characterisation of marine monopile scour and conduct critical testing of the current, experimentally-derived, state-of-the-art knowledge and practices. Scour research has been hampered by a dearth of prototype scour observations and much of the existing knowledge is derived from physical and numerical work which has had very little validation with field data. This study addresses the dearth of prototype scour analysis and by adding observations from 281 monopiles more than doubles the size of the currently existing knowledge base on marine monopile scour. Furthermore, the scope, variety and quality of data available in this study have enabled a wider-ranging and more in-depth and problem-focussed analysis of scour to be conducted. The data used in this study comes from a "natural offshore laboratory", consisting of three offshore wind farms in the Outer Thames Estuary, which were strategically chosen to minimise the flow variability within the data set in order to focus on identifying and quantifying the controls on scour exerted by the sea bed substrate. The effect of geotechnical conditions on scour is, so far, little understood as most scour research has focused on unconsolidated sandy sediments. Nevertheless, scour experiments in cohesive substrates have revealed the great complexity of the scour response in such materials. For this reason, quantitatively scrutinizing prototype scour in various substrate types and attempting to establish causal links between geotechnical properties and scour development from real data is important. In order to fulfill the remit of this study, the research is guided by a set of questions, derived from a review of the current scour framework, which pose testable hypotheses and identify knowledge gaps which will be evaluated throughout the course of the analysis. The outcomes of the study include an extensive quantitative description and contextualisation of observed scour with existing prototype observations, a critical validation of current knowledge and methods and an investigation of hydrodynamic and geotechnical controls on scour. Some key findings include improved predictive models for scour depth based on mean water depth as well as secondary relationships for lateral extent and scoured volume. For scour in consolidated and cohesive materials, equations for the estimation of scour-limiting material strength as a function of erosion depth are also proposed. The study concludes with a discussion of temporal, survey resolution and geotechnical issues and recommendations for optimised field data collection and survey strategy, alongside suggestions for additional research to fully resolve some of the findings of this research.
6
Orazalin, Zhandos Y. "Analysis of large deformation offshore geotechnical problems in soft clay." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111442.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 269-281).
Although finite element (FE) methods are well established for modeling geotechnical problems in soil masses and soil-structure interaction, most prior research on large deformation problems has been limited to simplified assumptions on drainage conditions and constitutive behavior. This thesis investigates two large deformation problems in soft clay and proposes a methodology for performing coupled flow and deformation analyses with advanced effective stress models. The first part of the research focuses on realistic 3-D finite element analyses (using AbaqusTM Standard) of a conductor (steel pipe pile) embedded within soft marine clay subjected to large lateral deformations caused by drift/drive-off of a drilling vessel. The proposed analyses use coupled pore pressure-displacement procedures together with the MIT-E3 soil model to represent the anisotropic, non-linear and inelastic effective stress-strain-strength properties of deepwater marine sediments with input parameters derived from a series of laboratory element tests performed on reconstituted Gulf of Mexico (GoM) clay. The numerical predictions are evaluated through comparison with experimental results from centrifuge tests with a well-instrumented model conductor. The FE results accurately predict the measured bending moment distribution along the length of the conductor and the spread of plastic strains within the conductor itself. The study has also shown the effects of soil behavior on local pile-soil interactions, enabling simplified analyses using macro-elements. The FE results have been used to calibrate input parameters for BWGG framework (Gerolymos & Gazetas, 2005), the Bouc-Wen (BW) model extended by Gerolymos and Gazetas (GG), that simulates generalized hysteretic pile-soil interactions and allows for degradation in soil resistance associated with geometric non-linearities. The second application considers the effects of partial drainage for large deformation, quasi-static piezocone penetration in clay. The proposed axisymmetric FE analysis procedure introduces automated remeshing and solution mapping technique (similar to RITSS; Hu & Randolph, 1998) within a commercial FE solver. We have analyzed the penetration resistance for a piezocone device using two elasto-plastic soil models (MCC, MIT-E3) and the recent elasto-viscoplastic MIT-SR soil model (Yuan, 2016) over a range of steady penetration velocities. The MCC predictions are in very good agreement with laboratory measurements of tip resistance and penetration pore pressures measured in centrifuge model tests in reconstituted kaolin. The results from more advanced soil models illustrate the impacts of anisotropic, rate dependent soil behavior on penetration tests in natural clays and are within the range of empirical measurements. The proposed analyses provide a complete framework that can now be used to investigate effects of partial drainage that occurs in piezocone tests for soils (such as silts) of intermediate permeability.
by Zhandos Y. Orazalin.
Ph. D.
7
Mondrago, Quevedo Monica. "Probabilistic modelling of geotechnical conditions for offshore wind turbine support structures." Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/9205.
Full textAbstract:
The geotechnical conditions of the soil can fluctuate greatly across the wind
farm. This is an issue since geotechnical modelling is the base of the structural
design of an offshore wind farm, and the efficient installation of the wind
turbines depends on its accuracy. This paper deals with the characterization of
the seabed, predicting the soil properties over the total affected area by a wind
farm, with the challenge to reduce the required data samples in the site
investigation under the number of installed wind turbines, to reduce its cost.
It is compared the prediction outcome from two different interpolation methods,
kriging and radial basis function, assessing their accuracy by the Mean-Squared
Error and the Goodness-of-Prediction Estimate, as well as with a visual
examination of their mapping; obtaining higher accuracy for radial basis function
and reducing to half the required sample points, from the initial value of installed
wind turbines.
In a second stage it is studied the soil effect over the foundation, analyzing the
results from a FEA, where different geometries of the structure are compared
submitted to different load cases to check its limit states. Those results show
that the foundation cost can increase four times due to the soil conditions,
taking into account only the steel volume, and demonstrating how important is
the soil characterization in the foundation design, as it gives the chance to
relocate those wind turbines that require more expensive foundations.
8
Laham, Noor. "Episodic DSS tests to measure changing strength for whole-life geotechnical design." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
Find full textAbstract:
Changes in seabed soil strength due to loading events during the life of a structure, affect the response of the structure to any future event. This change in soil strength due to loading events, in particular cyclic loads, was of great concern in the field of offshore geotechnics during the last decades. Allowing for these changes can have a beneficial outcome on the design. Studying the changes occurring in the soil can be mainly done using large scale centrifuge tests or Laboratory element testing, where the latter proved to be able to successfully illustrate soil strength changes during periods of cyclic loads and reconsolidation.
A new approach of life design known as “the whole life design” has been introduced lately to the industry “. Whole life design embraces the time-varying evolution of actions and resistances to create a continuous assessment of conditions of a structure.
This dissertation studies the possibility of one of the most famous element tests which is the “Direct simple shear testing” to capture the changing in strength under cyclic (i.e., episodic in this context) loads and the settlement of subsea layers for the whole life geotechnical design. The outcome of the DSS testing in addition to outcomes from other previous methods (eg T-bar penetrations and Triaxial testing) can form the basis for a new framework to be adopted in the future for demonstrating a whole life design for subsea structures.
In general, the project introduces the concept of whole-life geotechnical design through practical examples and shed lights on Direct simple shear testing ability to simulate specific cyclic loading scenarios. The topic closes with a discussion of next steps to enable whole-life geotechnical design to be more readily adopted in routine practice where appropriate.
9
Lewis, S. L. "The influence of geotechnical parameters on the efficiency of water jetted burial of underwater cables in cohesive sediments." Thesis, Bangor University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245853.
Full text
10
Villalobos, Jara Felipe Alberto. "Model testing of foundations for offshore wind turbines." Thesis, University of Oxford, 2006. http://ora.ox.ac.uk/objects/uuid:438cfe69-c8d4-4630-ab0b-482da5ea2839.
Full textAbstract:
Suction caissons are a new foundation option for offshore wind turbines. This thesis is focussed on the behaviour of suction caisson foundations in sand and in clay during installation, and under subsequent vertical and combined moment-lateral loadings. The research is based on extensive experimental work carried out using model scaled caissons. The analysis of the results allowed the determination of parameters for hyperplasticity models. Model caissons were vertically loaded in loose and dense sands to study in service states and plastic behaviour. Bearing capacity increased with the length of the caisson skirt. The bearing capacity formulation showed that the angle of friction mobilised was close to the critical state value for loose sands and close to those of peak values due to dilation for dense sands. The vertical load increased, though at a lower rate than during initial penetration, after large plastic displacements occurred. A hardening law formulation including this observed behaviour is suggested. In sand the installation of caissons by suction showed a drastic reduction in the net vertical load required to penetrate the caisson into the ground compared with that required to install caissons by pushing. This occurred due to the hydraulic gradients created by the suction. The theoretical formulations of the yield surface and flow rule were calibrated from the results of moment loading tests under low constant vertical loads. The fact that caissons exhibit moment capacity under tension loads was considered in the yield surface formulation. Results from symmetric and non symmetric cyclic moment loading tests showed that Masing’s rules were obeyed. Fully drained conditions, partially drained and undrained conditions were studied. Caisson rotation velocities scaled in the laboratory to represent those in the field induced undrained response for relevant periods of wave loading, a wide range of seabed permeabilities and prototype caisson dimensions. Under undrained conditions and low constant vertical loads the moment capacity of suction caissons was very small. Under partially drained conditions the moment capacity decreased with the increase of excess pore pressure. In clay, vertical cyclic loading around a mean vertical load of zero showed that in the short term the negative excess pore pressures generated during suction installation reduced vertical displacements. The yield surface and the flow rule were determined from moment swipe and constant vertical load tests. The moment capacity was found to depend on the ratio between the preload Vo and the ultimate bearing capacity Vu. Gapping response was observed during cyclic moment loading tests, but starting at smaller normalised rotations than in the field. The hysteresis loop shape obtained during gapping cannot be reproduced by means of the Masing’s rules.
11
Ngo-Tran, Cong Luan. "The analysis of offshore foundations subjected to combined loading." Thesis, University of Oxford, 1996. http://ora.ox.ac.uk/objects/uuid:96a07b7a-58f8-4a5d-9dfd-68509546368c.
Full textAbstract:
This thesis is concerned with four different types of offshore foundations, namely gravity foundations, jack-up foundations, the mudmats for piled jacket structures and caisson foundations for jacket structures. In most applications, these can be idealised as circular rigid foundations. Unlike onshore foundations, offshore foundations are subjected to large horizontal and moment loads. This research used the finite element method to examine the elastic behaviour and stability of circular footings under combined loading. Due to the circular shape of the footings and the combination of vertical, horizontal and moment loads, three dimensional finite element analysis was used. In-depth analyses of the elastic behaviour of circular footings under combined loading (V,H,M) were performed. The vertical stiffness coefficient was investigated using two dimensional axi-symmetric analyses whereas three dimensional analyses were used to examine the other coefficients. Different features of offshore foundations such as footing embedment and cone angle were taken into consideration. Based on the numerical results, a set of empirical expressions for elastic stiffness coefficient was derived. For footing stability calculations, large horizontal or moment loads can cause the footing to lose contact with the soil, or cause the footing to slide relative to the soil. In finite element analyses, this loss of contact and sliding are modelled by interface elements. A new zero-thickness iso-parametric interface element was formulated for both two and three dimensional analyses. An exact close formed solution for integration of the stress-strain relationship (for the two dimensional interface element) was found. The element is then used to explore footing stability. It was shown that by using a yield criteria which allows the interface to behave as either frictional or cohesive interface, depending upon the normal stress, numerical stability is achieved. The footing stability was examined by establishing the bearing capacity envelope. The envelopes for footings on undrained clays were established for surface flat strip footings and for surface flat circular footings. The effects of soil strength varying with depth, cone angle and embedment on the bearing capacity envelope were also investigated.
12
Tapper, Laith. "Bearing capacity of perforated offshore foundations under combined loading." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:4beb1f5c-24d9-4359-a973-95dda05e550d.
Full textAbstract:
This thesis presents experimental work and numerical analysis that has been undertaken to assess the bearing capacity of perforated offshore foundations. Perforated foundations may be used to support subsea infrastructure, including as mudmats into which a number of perforations have been made, or as grillages which consist of a series of structurally connected strip footings. Larger gravity base foundations, such as for offshore wind turbines or oil and gas platforms, may adopt a single central perforation. The advantages of using perforated foundations can include reduced material requirements and easier offshore handling as a result of smaller weight and lower hydrodynamic forces during deployment. Limited guidance currently exists for assessing the bearing capacity of these foundation types. Bearing capacity of perforated foundations has been examined in this thesis under conditions of combined vertical, horizontal and moment loading which is typical in offshore settings. Undrained soil conditions have been considered, except for the case of grillages in which drained conditions are often most relevant. Experimental work has included centrifuge testing of ring and square annular foundations on clay, and 1g testing of grillage foundations on sand. Finite element modelling has also been undertaken to assess perforated foundation capacity. A Tresca material subroutine (UMAT) and an adaptive meshing scheme have been developed to improve the accuracy of the finite element analysis carried out. The results showed that perforated foundations can be an efficient foundation solution for accommodating combined loading. As a ratio of their vertical load capacity, perforated foundations may be able to withstand higher moment and horizontal loads compared with unperforated foundations. The experimental and numerical results have been used to develop design expressions that could be employed by practitioners to estimate the vertical and combined load bearing capacity of these foundation types.
13
Chaudhry, Anjum Rashid. "Static pile-soil-pile interaction in offshore pile groups." Thesis, University of Oxford, 1994. http://ora.ox.ac.uk/objects/uuid:7b4c8d56-184f-4c8d-98c9-2d9c69a1ef55.
Full textAbstract:
This thesis is a theoretical study, using both finite element and boundary element methods, of the behaviour of single-piles and pile groups under vertical and lateral loading. It offers an improved understanding of the soil-structure interaction that occurs in pile groups, particularly closely spaced piles subjected to lateral loads. The potential of a two- dimensional idealisation of what is a three-dimensional problem is demonstrated by achieving real insight into the complex nature of pile-soil and pile-soil-pile interaction in pile groups. A new load transfer mechanism is presented for a rigid, axially loaded vertical pile. From this an improvement is then derived to the analytical solution for pile head settlement given by Randolph and Wroth (1978). The improved mechanism has the further merit that it can be applied also to solutions for flexible piles and pile groups. The improved analytical solution is further adapted in the development of two correcting layers specifically for vertically loaded piles to model infinite boundaries in the finite element model. The correcting layers help in establishing superiority of the finite element method over the boundary element method. To model pile-soil interaction, a purely cohesive interface element is developed and then validated by performing various two-dimensional test problems, including stability analysis of flat surface footings. Footing-soil interface tension is successfully modelled in this way - an outcome that entails a significant modification to the Hansen (1970) bearing capacity solution. Stability analysis is also carried out of conical footings using a three-dimensional finite element model: the results help to explain the applicability of the existing bearing capacity theories to conical footings. The ultimate lateral soil reaction is determined and various pile loading stages are investigated through parametric studies. Study of the stage immediately following pile installation (i.e. the consolidation stage) highlights the need to develop an effective stress analysis for laterally loaded piles. Pile-soil interaction is studied using the cohesive interface element presented earlier, which proves to be quite successful in smoothing out the stress discontinuities around the pile. A new material model for frictional soils is presented, and validated by using it to model an extension test: it captures well post-peak behaviour and takes care of the effects of dilation on the response of laterally loaded piles. Finally, mechanisms of interaction in closely spaced pile groups are studied. Simple analytical expressions are derived which quantify the effects of interaction. A new method of analysis is presented for single-piles and pile groups which offers a considerable degree of reliability without having to do either impossibly expensive full scale field tests or prohibitively expensive full three-dimensional analysis using the currently available computers.
14
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.
Full textAbstract:
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.
15
Mangal, Jan Krishna. "Partially-drained loading of shallow foundations on sand." Thesis, University of Oxford, 1999. http://ora.ox.ac.uk/objects/uuid:205bf0bc-b801-4648-a556-8dba0d113cba.
Full textAbstract:
Wave loading on offshore structures founded on sand can result in partially drained response of the foundation soil. The characteristics of the rate of loading, the permeability of the soil, and the size of the foundation affect the degree of partial drainage. Partial drainage refers to situations where pore pressures develop in the soil, and the response of the soil is neither fully drained nor undrained. This thesis is concerned with the effects of loading rate, and consequent drainage, on the behaviour of a flat footing that is founded on the surface of a saturated sand base. The results of physical tests performed in the laboratory on a model-sized footing are reported. The footing was founded on oil-saturated fine sand and was subjected to combined loading. The effect of the vertical, horizontal, and rotational displacements are reported. The response of the footing is analysed in the context of existing drained foundation models that are based on work hardening plasticity theory. The rate dependency of the vertical load:deformation behaviour and the combined yield surfaces are described.
16
Martin, Christopher Michael. "Physical and numerical modelling of offshore foundations under combined loads." Thesis, University of Oxford, 1994. http://ora.ox.ac.uk/objects/uuid:b582fb74-7a1b-4be9-884d-0daa9fda7c7b.
Full textAbstract:
In addition to vertical loads, the foundations of offshore structures are subjected to horizontal loads and overturning moments as a result of environmental (wind and wave) loading. The behaviour of circular footings on cohesive soil under conditions of combined vertical, horizontal and moment (V, H, M) loading is the primary concern of this thesis. A programme of physical model tests, involving combined loading of circular footings on reconstituted Speswhite kaolin, is reported. The shape of footing used is typical of the "spudcan" foundations of independent leg jack-up drilling platforms. Previous experience with combined loading of footings on sand has revealed that the observed load:displacement behaviour is best understood, and theoretically modelled, in terms of work hardening plasticity theory. The present tests on clay confirm this, and the results are interpreted to give empirical expressions for (i) the combined load yield surface in V:H:M space, and (ii) a suitable flow rule to allow prediction of the corresponding footing displacements (z, h, θ) during yielding. Extension to a complete plasticity model is achieved using theoretical stiffness factors to define elastic behaviour, and theoretical lower bound bearing capacity factors (derived specifically for this work) to define the size of the yield surface as a function of vertical penetration. The predictive capabilities of the numerical model are evaluated by retrospective simulation of various footing tests. Finally some plane frame structural analyses of a representative jack-up unit are described; some of these analyses incorporate the plasticity-based numerical model of spudcan footing behaviour under combined loads.
17
Santa, Maria Paulo Eduardo Lima de. "Behaviour of footings for offshore structures under combined loads." Thesis, University of Oxford, 1988. http://ora.ox.ac.uk/objects/uuid:50fb3d35-90b3-4685-9ace-0ec5a50014df.
Full textAbstract:
The lack of knowledge about the behaviour of footings for jack-up rigs under storm loads poses a design problem which can be tackled by model testing. The areas of prime concern are the ultimate loads on footings under combined loading, which affects the safety of the rig, and the rotational stiffness, which affects the interaction between the foundation and the structure. A programme of loading tests was performed on model footings on clay, and was divided into two stages: monotonic loading and cyclic loading. The clay samples were obtained by consolidating Speswhite kaolin slurry in cylindrical tanks 450mm in diameter. The strength and compressibility characteristics of the samples were verified by means of standard laboratory tests. The model footings were 50mm and 100mm in diameter and several shapes were tested: circular flat plate, cones of various angles and model spud-cans. Loads and displacements were monitored using appropriate instrumentation and a data logger. A series of central vertical loading tests provided data for comparison with existing bearing capacity theories. Combined loading tests were performed applying a displacement controlled horizontal load at a fixed height above the footing which was also subjected to a fixed vertical load. The main series of tests involved a parametric study of the relevant variables. Special tests allowed the assessment of the effect of embedment of the footing and the interaction of a flexible leg with the foundation. Cyclic loading tests were carried out using a load controlled system which applied a sinusoidal load simulating wave action. Effects of currents were investigated by introducing an offset to the loading cycle. The influence of amplitude and period of loading as well as the influence of vertical load were also investigated. Special tests were carried out to cover some peculiarities of real loading conditions. Fitting of a three-parameter hyperbola to the test results provided a systematic and accurate method of analysis of monotonic loading tests, leading to valuable information involving stiffness and ultimate loads. Analysis of cyclic loading tests yielded useful qualitative information regarding the progress of settlement and the variation of rotational stiffness and damping ratio with the number of cycles.
18
Nguyen-Sy, Lam. "The theoretical modelling of circular shallow foundation for offshore wind turbines." Thesis, University of Oxford, 2005. http://ora.ox.ac.uk/objects/uuid:fa4000fb-8de6-4093-b528-3e60d774dea0.
Full textAbstract:
Currently, much research is being directed at alternative energy sources to supply power for modern life of today and the future. One of the most promising sources is wind energy which can provide electrical power using wind turbines. The increase in the use of this type of energy requires greater consideration of design, installation and especially the cost of offshore wind turbines. This thesis will discuss the modelling of a novel type of shallow foundation for wind turbines under combined loads. The footing considered in this research is a circular caisson, which can be installed by the suction technique. The combined loads applied to this footing will be in three-dimensional space, with six degrees of freedom of external forces due to environmental conditions. At the same time, during the process of building up the model for a caisson, the theoretical analyses for shallow circular flat footing and spudcans also are established with the same principle. The responses of the soil will be considered in both elastic and plastic stages of behaviour, by using the framework of continuous plasticity based on thermodynamic principles. During this investigation, it is necessary to compare the numerical results with available experimental data to estimate suitable values of factors required to model each type of soil. There are five main goals of development of the model. Firstly, a new expression for plasticity theory which includes an experimentally determined single yield function is used to model the effects of combined cyclic loading of a circular footing on the behaviour of both sand and clay. This formulation based on thermodynamics allows the derivation of plastic solutions which automatically obey the laws of thermodynamics without any further assumptions. A result of this advantage is that non-associate plasticity, which is known to be a proper approximation for geotechnical material behaviour, is obtained logically and naturally. A FORTRAN source code called ISIS has been written as a tool for numerical analysis. Secondly, since there are some characteristics of the geometric shape and installation method which are quite different from that of spudcans and circular flat footing, another objective of this study is to adapt the current model which has been developed in ISIS for spudcans to the specific needs of caissons. The third goal of this research is the simulation of continuous loading history and a smooth transition in the stress-strain relationship from elastic to plastic behaviour. The model is developed from a single-yield-surface model to a continuous plasticity model (with an infinite number of yield surfaces) and then is discretized to a multiple-yield-surface model which can be implemented by numerical calculation to be able to capture with reasonable precision the hysteretic response of a foundation under cyclic loading. This can not be described by a conventional single-yield-surface model. Fourthly, as a method to simplify the numerical difficulties arising from the calculation process, a rate-dependent solution will be introduced. This modification is implemented by changing the dissipation function derived from the second law of thermodynamics. Finally, in order to control the model to capture the real behaviour, many parameters are proposed. A parametric study will be implemented to show the effects of these parameters on the solution.
19
Cassidy, Mark Jason. "Non-linear analysis of jack-up structures subjected to random waves." Thesis, University of Oxford, 1999. http://ora.ox.ac.uk/objects/uuid:02b96107-638b-4200-9fd7-fa49635594e3.
Full textAbstract:
There is a steadily increasing demand for the use of jack-up units in deeper water and harsher environments. Confidence in their use in these environments requires jack-up analysis techniques to reflect accurately the physical processes occurring. This thesis is concerned with the models appropriate for the dynamic assessment of jack-ups, an important issue in long-term reliability considerations. The motivation is to achieve a balanced approach in considering the non-linearities in the structure, foundations and wave loading. A work hardening plasticity model is outlined for the combined vertical, moment and horizontal loading of spudcan footings on dense sand. Empirical expressions for the yield surface in combined load space and a flow rule for prediction of footing displacements during yield are given. Theoretical lower bound bearing capacity factors for conical footings in sand have been derived and are used in a strain-hardening law to define the variation in size of the yield surface with the plastic component of vertical penetration. The complete incremental numerical model has been implemented into a plane frame analysis program named JAKUP. The spectral content of wave loading is considered using NewWave theory, and the importance of random wave histories shown by constraining the deterministic NewWave into a completely random surface elevation. Using this technique, a method for determining short-term extreme response statistics for a sea-state is demonstrated. A numerical experiment on an example jack-up and central North Sea location is shown to emphasise the difference in long-term extreme response according to various footing assumptions. The role of sea-state severity in the variation of short-term extreme response statistics is also highlighted. Finally, probabilistic methods are used to develop further understanding of the response behaviour of jack-ups. A sensitivity study of influential variables (with probabilistic formulations as opposed to deterministic values) has been conducted using the response surface methodology.
20
Thompson, Richard Saint George. "Development of non-linear numerical models appropriate for the analysis of jack-up units." Thesis, University of Oxford, 1996. http://ora.ox.ac.uk/objects/uuid:5804719a-8643-49c3-a9f3-105f35dce9ca.
Full textAbstract:
Jack-up units have considerable economic significance because they are used to carry out a large proportion of the world's oil and gas exploration in water depths less than 90.0m. Due to the increase in use of jack-ups in harsher environments, analysis techniques assuming quasi-static and linear structural behaviour have had to be reassessed. This thesis is concerned with non-linear dynamic analysis methods appropriate for a jack-up assessment. Jack-up modelling requires realistic representation of the structure, the foundations and the environmental loading, together with the implementation of appropriate dynamic analysis algorithms. Techniques for each of these aspects of jack-up analysis are reviewed and the implementation of several of the methods in an advanced plane frame analysis program called JAKUP is described. Geometric non-linearity in the structure and work hardening plasticity at the foundations are accounted for in the program. Test cases are presented to verify the implementation of the methods and then some illustrative plane frame quasi-static and dynamic analyses are described. These simple models highlight the importance of accounting for dynamic motions in a jack-up analysis. For the quasi-static analyses, the assumption of pinned footing behaviour is seen to always result in the most conservative displacement and moment predictions. However, the analyses show that this is not always the case when dynamic amplification is accounted for.
21
Macaro, Giulia. "Distinct element modelling of pipe-soil interaction for offshore pipelines on granular soils." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:cf38c129-502f-4d7d-aa8c-fea5d95ad2d2.
Full textAbstract:
Offshore on-bottom pipelines are subjected to cycles of thermal and pressure-induced axial expansion, which can cause them to buckle laterally. For an elegant and cost-effective solution, lateral buckling is allowed in a controlled manner. Of the various design parameters, the soil resistance has the greatest associated uncertainty. Previous studies of lateral pipe-soil interaction have used laboratory model tests and continuum-based numerical methods. However, they are economically and computationally expensive, and have mostly been restricted to pipes on undrained clay. To overcome this limitation, this thesis introduces the distinct element method (DEM) as a novel numerical tool for the study of lateral pipe-soil interaction for partially embedded offshore pipelines on sandy seabeds. The DEM directly models the particulate nature of sandy soils, allowing large displacements of discrete bodies and providing insights into the mechanics of the soil at a particle level. Pipe{soil interaction is studied by DEM analyses through four separate research stages: (i) mechanical characterisation of the soil, (ii) specimen preparation and pipeline implementation, (iii) small displacement pipe loading tests and (iv) large displacement pipe loading tests. The soil is modelled as an assembly of spherical particles exchanging contact forces, energy and momentum when they interact. At the microscopic scale, a novel moment-relative rotation contact law is introduced to account for the irregular shape of real sand grains. At a macroscopic scale, the mechanical behaviour of the sand is calibrated using experimental triaxial test data. Additional work includes the numerical preparation of a soil assembly and the implementation of a pipeline object in the open-source DEM code Yade. A novel specimen preparation technique is developed to assemble a homogeneous sample at a desired relative density. The pipeline is implemented as a cylindrical body with a continuously curved surface and a specific mass. Small displacement loading tests are performed, with a segment of the pipeline interacting with a 3D prismatic soil domain, replicating plane strain conditions. The influence of particle size, domain thickness, loading velocity and damping are investigated. The findings provide valuable recommendations for performing DEM simulations of this problem, balancing numerical accuracy and computational effort. Large displacement loading tests are performed to validate the DEM approach and to obtain detailed insights into the nature of the pipe-soil interaction. Monotonic vertical and lateral loading simulations are quantitatively compared with laboratory results. To replicate realistic loading conditions of the pipeline on the seabed, cyclic large displacement tests are also performed. Both the monotonic and the cyclic tests show a good level of agreement with experimental results obtained in previous research. Moreover, the numerical analyses provide insights into the evolution of particle motion and the failure mechanism within the soil.
22
Li, Xinyao. "CENTRIFUGE MODELLING AND NUMERICAL SIMULATION OF NOVEL HYBRID FOUNDATIONS FOR OFFSHORE WIND TURBINES." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1594728306295576.
Full text
23
Evans, Keith Martin. "A model study of the end bearing capacity of piles in layered calcareous soils." Thesis, University of Oxford, 1987. http://ora.ox.ac.uk/objects/uuid:574ae32d-bb91-4be7-aae6-d456f4c40b70.
Full textAbstract:
The results of a series of over 120 model tests to study the end bearing capacity of piles in layered calcareous soils are described. The tests were carried out on samples enclosed in a cylindrical testing chamber, 450 mm diameter and 450 mm high, which allowed independent control of horizontal and vertical stress in the range 25 kPa to 500 kPa. The samples consisted of a loose, uncemented calcareous sand consisting predominantly of foraminifera and mollusc micro-organisms (D50 = 0.2 mm, calcium carbonate content 92%). Into this was built a layer of the same material artificially cemented by a gypsum plaster. The layer had similar properties to naturally cemented deposits, and layers with unconfirmed crushing strengths in the range 500 kPa to 4000 kPa have been prepared. All samples were tested dry. Closed end model piles of 16mm diameter were jacked at 0.1mm/s into the sample, and continuous profiles of end bearing capacity obtained during penetration. A parametric study has been carried out to examine the effects on the bearing capacity of stress level, K0, cemented layer thickness (0.5 pile diameters to 5.0 pile diameters) and layer strength. In addition, tests have been conducted with different pile geometry, multiple cemented layers, and using dynamic installation techniques. The study has identified ranges of parameters for which brittle failure of the cemented layer occurs (low stress levels and high layer strengths) and ranges where the failure is ductile (high stresses and low layer strengths). Characteristic patterns have been observed of the variation of end bearing with position as a layer is penetrated. Examination of the samples after testing has revealed details of failure mechanisms. Simple procedures are proposed for modelling the bearing capacity of such layered systems, and some implications of the results for design methods are discussed.
24
Nouri, Hamid Reza. "Numerical Methods in Offshore Geotechnics: Applications to Submarine Landslides and Anchor Plates." Thesis, 2013. http://hdl.handle.net/1969.1/149513.
Full textAbstract:
The emphasis of this dissertation is on using numerical and plasticity based methods to study two main areas of offshore geotechnics.
The first part of this dissertation focuses on the undrained behavior of deeply embedded anchor plates under combined shear and torsion. Plate anchors are increasingly being used instead of typical foundation systems to anchor offshore floating platforms to sustain uplift operating forces. However extreme loading cases would create general loading conditions involving six degrees of freedom. The focus of my research was to evaluate the bearing capacity of plate anchors under two-way horizontal and torsional loading and to study the decreasing effect of torsional moment on the horizontal bearing capacity of these foundations. The study takes advantage of several approaches:
Numerical simulation (two and three dimensional finite element analysis)
Evaluating and modification of the available plasticity solutions
Developing equations for three degree-of-freedom yield locus surfaces
The same methodology is applied to evaluate the response of shallow foundations for subsea infrastructure subjected to significant eccentric horizontal loads.
The second part of this study focuses on offshore geohazards. Coastal communities and the offshore industry can be impacted directly by geohazards, such as submarine slope failures, or by tsunamis generated by the failed mass movements. This study aims at evaluating the triggering mechanisms of submarine landslide under cyclic wave and earthquake loading. A simple effective stress elasto-plastic model with a minimal number of parameters accounting for monotonic and cyclic response of fine-grained material is developed. The new constitutive soil model could be used to simulate case histories and conduct parametric study to evaluate the effect of slope inclination angle, the earthquake loading with different PGA, frequency content, and duration, as well as various deposition rates to simulate different over pressure levels. This study will generate more insight on the static and cyclic behavior of submarine slopes and influencing factors on their triggering mechanisms using more comprehensive and realistic modeling tools. Several objectives are defined: Developing an appropriate constitutive formulation, Evaluating the constitutive model and material parameters for available databases.
25
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.
Full textAbstract:
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
26
Ke-WeiChen and 陳克維. "Geotechnical Considerations of Suction Bucket Foundation Design for Offshore Wind Turbines." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/59234212558643397512.
Full text
27
Zadrozny, Katherine Elaine. "Documenting, demonstrating and enhancing an offshore geotechnical database for reliability-based foundation design." Thesis, 2013. http://hdl.handle.net/2152/23564.
Full textAbstract:
There is a large amount of geotechnical data. By putting it into a database, it can be applied to design reliable offshore foundations. The goal of this research is to improve the efficiency and transparency of the implementation of the previously developed reliability-based framework to streamline the process for analyzing and developing an offshore site in the Gulf of Mexico by looking at spatial variations among data sets.
This thesis documents how to store soil behavior information in the database and how to use that information for offshore foundation design. The process is illustrated through observing the steps with figures provided directly from the database so the user can more readily use the database to produce results. This makes the database more transparent for the user to follow the flow of information from input to analysis and to follow the calculation process as well. Enhancements were also made to the database to provide a more readily accessible interface. There is now an allowance of data to streamline the data input process. There is also a set amount of fifty data points to be used in each spatially conditioned analysis.
These detailed explanations and consistencies in data collection help the user to understand the models. This database provides a synthetic image of the site using both physical and statistical parameters where there might not be exact data at a desired foundation location. By providing the industry with a database that uses reliability-based design from actual data and spatial variation analysis, this project will continue to provide a more efficient design process.text
28
Carswell, Wystan. "Probabilistic Analysis of Offshore Wind Turbine Soil-Structure Interaction." 2012. https://scholarworks.umass.edu/theses/848.
Full textAbstract:
A literature review of current design and analysis methods for offshore wind turbine (OWT) foundations is presented, focusing primarily on the monopile foundation. Laterally loaded monopile foundations are typically designed using the American Petroleum Institute (API) p-y method for offshore oil platforms, which presents several issues when extended to OWTs, mostly with respect to the large pile diameters required and the effect of cyclic loading from wind and waves. Although remedies have been proposed, none have been incorporated into current design standards. Foundations must be uniquely designed for each wind farm due to extreme dependence on site characteristics. The uncertainty in soil conditions as well as wind and wave loading is currently treated with a deterministic design procedure, though standards leave the door open for engineers to use a probability-based approach. This thesis uses probabilistic methods to examine the reliability of OWT pile foundations. A static two-dimensional analysis in MATLAB includes the nonlinearity of p-y soil spring stiffness, variation in soil properties, sensitivity to pile design parameters and loading conditions. Results are concluded with a natural frequency analysis.
29
Chen, Shuo-Ting, and 陳碩霆. "The Study of Localized Site Investigation Guideline and Geotechnical Parameters for Offshore Wind Farm." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/5h86va.
Full textAbstract:
碩士國立臺灣海洋大學
河海工程學系
105
Taiwan’s offshore wind farm industry is starting to launch, but lacked marine site investigation experiences and localized guideline in Taiwan. Therefore, how to establish the framework of offshore wind farm preparatory system and compose the site investigation guidelines which are suitable for Taiwan’s maritime environment and offshore wind farms become an important issue. This study was collected and discussed the codes or guidelines of international offshore wind farm site investigation, geotechnical design and EIA standard, including ABS, BV, BSH, DNV-GL, Euro code, IEC, NORSOK, SUT, and preparatory system including Denmark, UK, USA, Germany, China, HK, etc. This study also integrated the internal legislation or law and considering the local condition to propose the localized site investigation guideline for offshore wind farm and listed recommendations for preparatory system. Based on the related international codes and guidelines, this study was provided a suitable guideline of localized site investigation for offshore wind farm. This guideline not only explores the requirements to establish offshore wind farms, but also explains the details of site investigations such as geotechnical and geophysical survey. Specifically, this guideline combines those laws and standards; and makes it effective to Taiwan’s offshore wind industry. It could be improved the capacity of Taiwan’s offshore wind power development. As the basis of the important geotechnical parameters of offshore investigation suggestion by SUT and NORSOK standard, this study suggests several of essential geotechnical parameters and data which are necessary in the design phase. Research areas are situated in these four offshore wind farm areas, as Chang-Bin Fuhai phase II, the submarine cable route, and Si-Dao area. Collecting site investigation information, such as geophysics, geotechnical and drilling data, and the correlation of soil parameters and cone-penetration test data were discussed to establish geotechnical parameters and propose the suggestions for localization parameters. By using of the empirical formulas, this study shows most of the soil layers of site area are composed with sandy soils, and also has soft soil distribution. Besides, due to some deviations between the mean drilling data, laboratory tests are necessary to get accurate soil parameters, and should be aware of the risk of soft shallow soils in the maritine engineering of offshore wind farm. Keywords: offshore wind farm, preparatory system, site investigation guideline, geotechnical parameters, cone-penetration test (CPT)
30
Wu, Chia-Chi, and 吳佳騏. "A Study of Foundation Design Standard and Localization of Geotechnical Parameters for Offshore Wind Farm." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/29307834818540258070.
Full textAbstract:
碩士國立臺灣海洋大學
河海工程學系
103
Due to lack the related standard of offshore structure design and the experience of offshore geotechnical design in Taiwan, so how to establish the suitable the geotechnical design standard of offshore wind is required. The related offshore wind farm geotechnical design &; ground investigation standard around the world, including ABS, API, BSH, DNV, GL, IEC, NORSOK, Euro code were collected and reviewed in this study. The key point of offshore geological risk is discussed. And the Taiwan local offshore wind farm geotechnical design and ground investigation standard can be establish by review the certain offshore standard and make recommendations for domestic offshore wind farm certification requirement. On the other hand, this study according to the suggestion of geotechnical investigation by the Norsok Standard, the required valuable geotechnical parameters need to investigate is suggested. And according to the offshore wind farm geological section profiles, the reference geotechnical parameters are established. The geotechnical investigation data of Zhangbin offshore wind farm as in site exploration data and laboratory experimental data were collected in this study. Based on the in situ SPT and CPT with the geotechnical parameters were discussed. Meanwhile, the soil classification was performed by use of soil behavior index (Ic) for Cone Penetration Test (CPT). It could be found that there are many thin layer of soft soil existed in each bore hole. On the geotechnical design stage, the geotechnical problem caused by thin layer of soft soil must be concern with cautions.
31
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.
Full textAbstract:
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.
32
McCarthy, Katelyn Barbara. "Experimental in-plane behavior of a generic scale model drag embedment anchor in Kaolinite test beds." Thesis, 2011. http://hdl.handle.net/2152/ETD-UT-2011-05-3417.
Full textAbstract:
The trajectory and capacity are key components of the design of drag embedment anchor and drag-in vertically loaded anchors. This experimental testing program quantifies two factors that describe the anchor trajectory and capacity: the equilibrium bearing factor (Ne) and the tangential bearing factor (Ne). These factors can aid in the development of a numerical model of anchor behavior. A magnetometer device is used to track the orientation and location of the anchor during drag embedment. The results of the experimental testing program were compared with the results from a predictive model. The experimental program consisted of drag embedment tests with various testing conditions including different anchor line diameters and different initial pitch orientations. The results with the different anchor lines indicated that thinner anchor lines cause the anchor to dive deeper in the soil. The different initial pitch results indicate that regardless of the initial pitch of the anchor, the anchor rotates to a unique pitch trajectory within 2 fluke lengths.text