Physical modelling of the push-over capacity of a jack-up structure on sand in a geotechnical centrifuge

2009 ◽  
Vol 46 (2) ◽  
pp. 190-207 ◽  
Author(s):  
B. Bienen ◽  
M. J. Cassidy ◽  
C. Gaudin
Keyword(s):  
Wind Waves ◽  
Physical Modelling ◽  
Three Dimensions ◽  
Combined Loading ◽  
Silica Sand ◽  
Foundation Soil ◽  
Experimental Development ◽  
Dense Sand ◽  
Geotechnical Centrifuge ◽  
Jack Up

Offshore jack-up drilling rigs are subjected to loading from wind, waves, and current in addition to their self-weight. This applies combined loading in all six degrees-of-freedom in space on the footings. Although the foundation–soil interaction is crucial to the overall response of a jack-up structure, current state-of-the-art models to predict jack-up footing behaviour, developed using data from single footing experiments, have not been validated for such multi-footing systems under general combined loading. This paper introduces the experimental development of a three-legged model jack-up and loading apparatus designed to investigate the rig’s response — in particular the footing load paths — under combined loading in three dimensions. Push-over experiments were performed in a geotechnical beam centrifuge on silica sand. Experimental results of two tests on dense sand are discussed, highlighting differences in response and mode of failure depending on the loading direction of the jack-up. The importance of three-dimensional modelling is also stressed by experimentally demonstrating that the symmetric load case is not necessarily conservative.

Influence of Spud-Can-Soil Interaction Modeling and Parameters on the Reliability Index of Neka Drilling Jack-Up Platform

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
M. R. Emami Azadi
Keyword(s):  
Reliability Index ◽  
Clayey Soil ◽  
Interaction Model ◽  
Soil Parameters ◽  
The Caspian Sea ◽  
Foundation Soil ◽  
Soil System ◽  
Dense Sand ◽  
Interaction Modeling ◽  
Jack Up

In the present study, the influence of spud-can-soil modeling and parameters on the reliability index of jack-up platform is investigated. Neka platform is studied as a case, which is a three-leg drilling jack-up type platform located in water depth of about 91 m in the Caspian Sea region. Various spud-can-soil interaction models such as pinned, fixed-base, hyperelastic, and nonlinear elastoplastic spud-can models are applied. The soil type is varied from loose to dense sand and also from soft NC clay to very stiff OC Clay. The effect of bias and coefficient of variation (COV) of the spud-can-soil interaction modeling and also the soil parameters such as the effective interface soil friction angle and also the undrained shear strength of clayey soil are studied. The results showed that inclusion of spud-can-soil interaction may have a considerable effect on the reliability of the jack-up platform. In particular, the bias and COV of soil have shown to have more significant effect on the reliability of jack-up platform in loose sand and soft clayey type soils. It is also found that bias in strength modeling of jack-up itself has less profound effect on the reliability index of the jack-up-foundation-soil system. Importance factors of spud-can-soil modeling are found to be quite considerable. The key aspect is that the inclusion of jack-up-spud-can-soil interaction is more crucial with respect to the reliability of jack-up platform than the choice of interaction model itself.

Push-Over Response of a Jack-Up on Sand of Different Relative Densities

2009 ◽  
Author(s):  
Britta Bienen ◽  
Mark J. Cassidy ◽  
Christophe Gaudin
Keyword(s):  
Wind Waves ◽  
Scaled Model ◽  
Environmental Loading ◽  
Complex Load ◽  
Geotechnical Centrifuge ◽  
Overall Response ◽  
Load Paths ◽  
Numerical Predictions ◽  
Macro Element ◽  
Jack Up

On location offshore, jack-up structures are subject to environmental loading from wind, waves and current in addition to self-weight. Over the operational period of the jack-up, the environmental loading on a given site may not be unidirectional along the jack-up’s ‘axis of symmetry’ but may act from different directions and/or be non-collinear (i.e. wind acting from a different direction than waves and current), resulting in complex load paths at the spudcan footings. This paper discusses load paths obtained from experiments on a scaled model jack-up for two different horizontal loading directions and illustrate the implications of spudcan load paths for the overall response of a jack-up to failure. Similar tests were performed at two different relative sand densities, allowing the influence of relative density on jack-up behavior to be investigated. Similitude to the prototype was achieved by conducting the experiments in a geotechnical centrifuge at 200g. The paper concludes with numerical predictions of the experimentally measured response, using a macro-element to model the soil-spudcan interaction coupled to a structural finite element program. The footing macro-element has been developed based on plasticity theory and single footing experiments, but its ability to predict the respective load paths of each of the spudcans in a multi-footing system is demonstrated here. The paper further provides the experimentally measured jack-up push-over capacity and numerical predictions in the context of recommendations of current guidelines. This highlights the requirement of nonlinear elasto-plastic modelling of the load-displacement behavior of the jack-up foundations in order to predict the overall response of the system.

Three-dimensional numerical analysis of centrifuge experiments on a model jack-up drilling rig on sand

2009 ◽  
Vol 46 (2) ◽  
pp. 208-224 ◽  
Author(s):  
B. Bienen ◽  
M. J. Cassidy
Keyword(s):  
Soil Analysis ◽  
Shallow Foundation ◽  
Integrated Modelling ◽  
Foundation Soil ◽  
Geotechnical Centrifuge ◽  
Drilling Rig ◽  
Numerical Predictions ◽  
Current Loading ◽  
Jack Up ◽  
Current Guidelines

Jack-up drilling rigs are usually founded on three shallow footings. Under wind, wave, and current loading offshore, the footings of these tall multi-footing systems transfer large moment loads in addition to self-weight, horizontal load, and even torsion to the underlying soil. To be able to deploy a jack-up safely at a particular offshore site, the unit’s capacity to withstand a 50 year return period storm is required to be checked in accordance with current guidelines (Site specific assessment of mobile jack-up units, The Society of Naval Architects & Marine Engineers). As the overall system behaviour is influenced significantly by the footing restraint, models that account for the complex nonlinear foundation–soil interaction behaviour are required to be integrated with the structural and loading models. Displacement-hardening plasticity theory has been suggested as an appropriate framework to formulate force-resultant models to predict shallow foundation behaviour. Recent research has extended such a model to account for six degree-of-freedom loading of circular footings on sand, allowing integrated structure–soil analysis in three dimensions. This paper discusses “class A” numerical predictions of experiments on a model jack-up in a geotechnical centrifuge, using the integrated modelling approach, and critically evaluates the predictive performance. The numerical simulations are shown to represent a significant improvement compared with the method outlined in the current guidelines.

scholarly journals Experimental and numerical investigation of the effect of vertical loading on the lateral behaviour of monopiles in sand

2021 ◽  
Author(s):  
Qiang Li ◽  
Kenneth Gavin ◽  
Amin Askarinejad ◽  
Luke J Prendergast
Keyword(s):  
Slenderness Ratio ◽  
Offshore Wind ◽  
Combined Loading ◽  
Initial Stiffness ◽  
Dense Sand ◽  
Geotechnical Centrifuge ◽  
Lateral Capacity ◽  
Vertical Loading ◽  
Load Tests ◽  
Observed Behaviour

The influence of combined loading on the response of monopiles used to support offshore wind turbines (OWTs) is investigated in this paper. In current practice, resistance of monopiles to vertical and lateral loading is considered separately. As OWT size has increased, the slenderness ratio (pile length, L, normalised by diameter, D) has decreased, and foundations are tending towards intermediate footings with geometries between those of piles and shallow foundations. Whilst load interaction effects are not significant for slender piles, they are critical for shallow footings. Previous research on pile load interaction has resulted in conflicting findings, potentially arising from variations in boundary conditions and pile slenderness. In this study, monotonic lateral load tests were conducted in a geotechnical centrifuge on vertically loaded monopiles in dense sand. Results indicate that for piles with L/D = 5, increasing vertical loading improved pile initial stiffness and lateral capacity. A similar trend was observed for piles with L/D = 3, when vertical loading was below ≈ 45% of the pile’s ultimate vertical capacity. For higher vertical loads considered, results tended towards the behaviour observed for shallow footings. Numerical analyses conducted show that changes in mean effective stress are potentially responsible for the observed behaviour.

Influence of Spud-Can-Soil Interaction Modeling and Parameters on the Reliability Index of Neka Drilling Jack-Up Platform

2008 ◽  
Author(s):  
M. R. Emami Azadi
Keyword(s):  
Reliability Index ◽  
Clayey Soil ◽  
Interaction Model ◽  
Friction Angle ◽  
Soil Parameters ◽  
Foundation Soil ◽  
Soil System ◽  
Dense Sand ◽  
Interaction Modeling ◽  
Jack Up

In the present study, the influence of spud-can-soil modeling and parameters on the reliability index of jack-up platform is investigated. Neka platform is studied as a case which is a 3-leg drilling jack-up type platform located in water depth of about 91m in Caspian Sea region. Various spud-can-soil interaction models such as pinned, fixed-base, hyper-elastic and non-linear elasto-plastic spud-can models are applied. The soil type is varied from loose to dense sand and also from soft NC-clay to very stiff OC-Clay. The effects of bias and COV of the spud-can-soil interaction modeling and also the soil parameters such as effective interface soil friction angle and also un-drained shear strength of clayey soil are studied. The results showed that inclusion of spud-can-soil interaction may have a considerable effect on the reliability of the Jack-up platform. In particular, the bias and COV of soil shown to have more significant influence on the reliability of jack-up platform in loose sand and soft clayey type soils. It is also found that bias in strength modeling of jack-up itself has less profound effect on the reliability index of the jack-up-foundation-soil system. Importance factors of spud-can-soil modeling are found to be quite considerable. The key aspect is that the inclusion of jack-up-spud-can-soil interaction is more crucial with respect to the reliability of jack-up platform than the choice of interaction model itself.

Numerical Study of the Combined Loading Envelope of a Skirted Spudcan Foundation

2014 ◽  
Author(s):  
Ning Cheng ◽  
Mark J. Cassidy ◽  
Yinghui Tian
Keyword(s):  
Clay Soil ◽  
Numerical Study ◽  
Failure Mechanisms ◽  
Small Strain ◽  
Offshore Structures ◽  
Combined Loading ◽  
Finite Element Analyses ◽  
Failure Envelope ◽  
Foundation Type ◽  
Jack Up

Foundations for offshore structures, such as mobile jack-up units, are subjected to large horizontal (H) and moment (M) loads in addition to changing vertical (V) loads. The use of a combined vertical, horizontal and moment (V-H-M) loading envelope to define foundation capacities has become increasingly applied in recent years. However, there is no study on the skirted spudcan, a new alternative foundation type to the conventional spudcan footing for jack-ups. In this study, the combined V-H-M yield envelope of a skirted spudcan foundation in clay soil is investigated with small strain finite element analyses using 3D modeling. The footing’s uniaxial bearing capacities and failure mechanisms are described. The failure envelope for the combined V-H-M loadings is presented. A comparison of the bearing capacities between the spudcan and skirted spudcan of various dimensions is also presented.

Predicting the overall horizontal bearing capacity of jack-up rigs using deck–foundation–soil-coupled model

2020 ◽  
pp. 147509022092590
Author(s):  
Qilin Yin ◽  
Jinjin Zhai ◽  
Sheng Dong
Keyword(s):  
Bearing Capacity ◽  
Failure Mode ◽  
Double Layer ◽  
Soft Clay ◽  
Coupled Model ◽  
Single Layer ◽  
Horizontal Load ◽  
Foundation Soil ◽  
Failure Envelopes ◽  
Jack Up

The overall bearing capacity of a jack-up rig under horizontal load is conducted using finite element models that consider the deck–foundation–soil interaction. In these models, the simplified horizontal load acts on the deck and increases until the platform loses its stability. The effects of the self-weight of the platform W and load direction α on the ultimate horizontal bearing capacity Hult are investigated, and W- Hult failure envelopes under different α conditions are obtained. Two typical seabed types, including the double-layer seabed of sand overlying soft clay and the single-layer seabed of sand, are considered. The results show that a critical self-weight Wcritical exists in the double-layer seabed. Based on Wcritical, the failure of the platform presents two different modes. When W <  Wcritical, the windward leg is pulled up, and Hult increases with the increase in W. When W >  Wcritical, the failure mode is the leeward leg or legs puncturing the bearing sand layer, and Hult decreases with the increase in W. In the single-layer seabed, the failure mode is the windward leg being pulled up, and Hult increases with the increase in W throughout the whole range. The W- Hult envelopes in these two types of seabeds are basically the same when W <  Wcritical.

Centrifuge observations on combined loading of a strip footing on dense sand

Géotechnique ◽  
2013 ◽  
Vol 63 (5) ◽  
pp. 427-433 ◽  
Author(s):  
M. COCJIN ◽  
O. KUSAKABE
Keyword(s):  
Strip Footing ◽  
Combined Loading ◽  
Dense Sand

scholarly journals Development of novel apparatus to obtain soil resistance–displacement relationship for well conductor fatigue analysis

2017 ◽  
Vol 54 (10) ◽  
pp. 1435-1446 ◽  
Author(s):  
Arash Zakeri ◽  
Hendrik Sturm ◽  
Rune Dyvik ◽  
Philippe Jeanjean
Keyword(s):  
Cyclic Loading ◽  
Interaction Mechanism ◽  
Physical Modelling ◽  
Fatigue Analysis ◽  
Test Results ◽  
Major Step ◽  
Soil Response ◽  
Geotechnical Centrifuge ◽  
Field Samples ◽  
Stress Changes

An important aspect of deepwater well integrity is development of accurate conductor fatigue analysis due to cyclic loading during drilling operations. Fatigue damage in a structure occurs from stress changes in response to cyclic loading. In practice, the lateral cyclic soil response is typically modelled using Winkler lateral load–displacement (p–y) springs. However, recently developed soil models for conductor fatigue analysis are based on physical modelling in a geotechnical centrifuge. Notwithstanding the advantages of centrifuge modelling for investigating the conductor–soil interaction mechanism, development of simple laboratory tools to obtain p–y data directly from intact soil samples obtained from the field can also be very beneficial. This paper describes the development of a novel apparatus to obtain p–y and soil damping relationships from field samples specifically tailored for well conductor fatigue analysis. In addition, it compares test results obtained using reconstituted kaolin clay and intact natural Onsøy clay with centrifuge test results; ultimately demonstrating a satisfactory agreement between the two techniques. The results are highly encouraging and are believed to present a major step forward in deepwater well conductor fatigue analysis. The findings may also be beneficial to the offshore renewable energy sector.

Numerical Simulation of Spudcan Penetration Into Silica Sand and Prediction of Bearing Behaviour

2012 ◽  
Author(s):  
Tim Pucker ◽  
Britta Bienen ◽  
Sascha Henke
Keyword(s):  
Bearing Capacity ◽  
Oil And Gas ◽  
Cone Angle ◽  
Oil And Gas Industry ◽  
Friction Angle ◽  
Offshore Wind ◽  
Silica Sand ◽  
Gas Industry ◽  
Jack Up ◽  
Bearing Behavior

Prediction of the bearing behavior of vertical loaded shallow foundations is typically done using the classical bearing capacity approach. This approach is very sensitive to the friction angle assumed in the calculation. A conservative estimate of the bearing capacity is required for most applications, hence uncertainties in the friction angle may be absorbed by the safety factor applied. Spudcans are used to found mobile jack-up platforms in the oil and gas industry as well as in the offshore wind energy industry. Contrary to the classical approach, the bearing capacity of spudcans has to be predicted accurately. Spudcans are penetrated into the seabed and a continuous bearing failure proceeds until the target capacity is met. A Coupled Eulerian-Lagrangian (CEL) approach is used to simulate the penetration process of spudcans into silica sand. The sand is modeled using a hypoplastic constitutive model to capture the influence of the void ratio and stress state for example. A parametric study of foundation diameter and enclosed cone angle is presented. The numerical model is validated against results from centrifuge experiments of flat and conical circular footings penetrating into silica sand. A first empirical approach to estimate the bearing capacity depending on the diameter and enclosed cone angle is given for silica sand.

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