Development of a force–resultant model for spudcan footings on loose sand under combined loads

Spudcans are typical foundations used in shallow to moderate-depth water oil and gas fields to support jack-up drilling units. Understanding the behaviour of spudcans under combined loadings is crucial to the overall response of the jack-up structure. This paper presents the development of a strain-hardening plasticity model for a spudcan footing on loose sand. Most of the model components are developed from direct centrifuge observations. The centrifuge tests were performed at an acceleration of 100 times that of the Earth’s gravity on a model spudcan footing subjected to combined vertical, horizontal, and moment loads. All the experiments have been designed and conducted to allow the results to be interpreted with a strain-hardening plasticity framework. Combined loads were applied by using a novel apparatus, which enables independent vertical, horizontal, and rotational movements of the footing. Test results also revealed the existence of a three dimensional sliding surface that intersects with the conventional yield surface. This additional surface has been defined analytically. Retrospective simulation of the experimental data using the plasticity model confirms the model’s capability for use in predicting the behaviour of larger spudcan applications offshore.

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A plasticity model for spudcan foundations in soft clay

Canadian Geotechnical Journal ◽

10.1139/cgj-2013-0269 ◽

2014 ◽

Vol 51 (6) ◽

pp. 629-646 ◽

Cited By ~ 18

Author(s):

Youhu Zhang ◽

Mark J. Cassidy ◽

Britta Bienen

Keyword(s):

Finite Element ◽

Load Capacity ◽

Soft Clay ◽

Plasticity Model ◽

Vertical Load ◽

Geotechnical Centrifuge ◽

Centrifuge Tests ◽

Model Components ◽

Jack Up ◽

Selection Of

A plasticity model for predicting the load displacement behaviour of a typical spudcan foundation for offshore jack-up platforms under combined vertical, horizontal, and moment loading in soft clay is presented. Results from geotechnical centrifuge experiments of a spudcan embedded vertically to 0.7, 1.0, and 1.45 footing diameters are described. Augmented with finite element results, these centrifuge experiments are used to evaluate the plasticity model components. As a result of soil backflow on top of the spudcan, enhanced combined bearing capacity was measured and this is reflected in increased yield surface size. A tensile vertical load capacity is also incorporated. The excellent predictive capabilities of the model are demonstrated by retrospectively simulating a selection of centrifuge tests.

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Eulerian finite element simulation of spudcan–pile interaction

Canadian Geotechnical Journal ◽

10.1139/cgj-2012-0288 ◽

2013 ◽

Vol 50 (6) ◽

pp. 595-608 ◽

Cited By ~ 23

Author(s):

Kee Kiat Tho ◽

Chun Fai Leung ◽

Yean Khow Chow ◽

Somsak Swaddiwudhipong

Keyword(s):

Numerical Model ◽

Oil And Gas ◽

Interaction Analysis ◽

Numerical Technique ◽

Three Dimensional ◽

Numerical Approach ◽

Gas Drilling ◽

Pile Interaction ◽

Offshore Oil And Gas ◽

Jack Up

Jack-up rigs are commonly employed to perform offshore oil and gas drilling. During the installation of the spudcan foundation, the large volume of soil displaced may induce severe stresses on the piles supporting the adjacent platform. The increasing numbers of jack-up rigs being deployed at close proximity to piled platforms accentuates the need for research into quantifying the effect of spudcan penetration on adjacent piles. The main difficulty with the numerical simulation of spudcan–pile interaction lies in the need to model continuous spudcan penetration in a three-dimensional (3-D) modeling space. In this paper, the three-dimensional Eulerian numerical technique is adopted to perform a coupled interaction analysis whereby the process of continuous spudcan penetration is simulated and the corresponding pile responses are obtained. The salient features of the proposed numerical approach with particular emphasis on the incorporation of a pile in the numerical model are first described. The validation of the numerical model against centrifuge experimental data under different geometric configurations and soil profiles are then presented. The final part of this paper demonstrates the usefulness of the proposed numerical approach through a series of parametric studies. This numerical approach can be readily applied to perform site-specific assessment to mitigate the risks associated with spudcan–pile interaction.

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Interaction Assessment of Diagonally-Spaced Identical Corrosion Defects and Fully-Aligned Unequal-Sized Corrosion Defects Under Combined Loads

Journal of Pressure Vessel Technology ◽

10.1115/1.4053116 ◽

2021 ◽

Author(s):

Shulong Zhang ◽

Wenxing Zhou

Keyword(s):

Finite Element ◽

Internal Pressure ◽

Oil And Gas ◽

Three Dimensional ◽

Element Model ◽

Interaction Effects ◽

Longitudinal Compression ◽

Combined Loads ◽

Corrosion Defects ◽

The Finite Element Model

Abstract In this study, the interaction effects of closely-spaced corrosion defects on the burst capacity of oil and gas pipelines under combined internal pressure and longitudinal compression are investigated by using parametric three-dimensional elasto-plastic finite element analyses. Full-scale burst tests reported in the literature are used to validate the finite element model. It is observed that the interaction effects of diagonally-spaced defects on the burst capacity is strongly related to the overlapping portion of the defect width or circumferential spacing between the two defects. The analysis results indicate that the strongest interaction between diagonally-spaced defects under combined loads occurs if the defects have zero circumferential separation. The interaction weakens as the defects are more and more overlapped or separated circumferentially. It is also observed that the interaction effect associated with longitudinally- or circumferentially-aligned, unequal-sized corrosion defects is negligible under the internal pressure only or combined loads.

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Three-Dimensional Pushover Analysis of a Jack-Up Platform

Volume 2: Structures, Safety and Reliability ◽

10.1115/omae2012-83619 ◽

2012 ◽

Author(s):

Ning Cheng ◽

Mehrdad Kimiaei ◽

Mark J. Cassidy

Keyword(s):

Oil And Gas ◽

Numerical Solutions ◽

Progressive Failure ◽

Pushover Analysis ◽

Three Dimensional ◽

Offshore Wind ◽

Foundation Soil ◽

Oil And Gas Exploration ◽

Plastic Behaviour ◽

Jack Up

Jack-ups, as the name indicates, are self-elevating units consisting of a floatable hull and, usually, three truss work or circular legs. As a mobile structure, jack-ups are mainly utilized for oil and gas exploration and maintenance purposes in shallow to medium water (up to 120 meters), though they have recently seen application in the construction of offshore wind energy infrastructure. The use of the finite element method for structural analyses of jack-ups is a common practice. However, most jack-up models remain elastic with the yielding of structural members or even the soil around the spudcan not accounted for. This paper describes the development of a comprehensive and integrated elasto-plastic jack-up model in ABAQUS [1]. This model is representative of a modern jack-up structure, and it can capture geometrical nonlinearities and plastic behaviour of the structural and soil materials. In this study, the discretisation of the structural elements, the choice of elements, the elasto-plastic behaviour of the material, and the mesh generation are described. Numerical results of a series of static pushover analyses for this sophisticated model under extreme loads are presented. The sensitivity of the results to the structural configurations is discussed. For instance, the choice of sectional properties of the chord member and the assumption of the behaviour of the spudcan (jack-up foundation)-soil interaction are shown to be critical to the prediction of the ultimate strength of the platform and the progressive failure mechanism. In conclusion, generic issues associated with static pushover analyses of jack-ups are discussed and possible numerical solutions are proposed.

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