Foundation Installation / Extraction
An Assessment of the Accuracy of SRD Methodologies for OWF Monopile Installation against a North Europe Driving Records Database
As monopile foundations diameter scales up with the larger turbines and increasing water depth, installation feasibility is becoming a greater risk in the offshore wind industry. Experience has shown that current drivability methodologies miscalculate the soil resistance to driving (SRD) when compared to actual driving data, resulting in additional installation costs and overestimation of pile fatigue. For the current study, two hundred sixty (260) driving logs from four offshore wind farms (OWF) in different areas of the North Sea have been selected and back calculated using standard industry SRD methodologies, namely Alm & Hamre (2001), Toolan & Fox (1977) and Stevens et al. (1982). The investigated pile driving records cover a broad range of soil conditions both in terms of soil type (sand dominated, clay dominated and layered soil profiles), soil strength (easy to hard driving conditions), monopile diameters and penetration depths. The accuracy of each method has been quantitatively evaluated, with the results underpinning the industry concern of the inadequacy of the existing SRD formulations to predict the drivability of OWF monopiles and illustrating the need for development of new SRD methodologies, tailored to the Offshore Wind industry.
Keywords: pile driving, back-calculation, statistical analysis, offshore wind farms
| 05-01Perikleous.pdf | An Assessment of the Accuracy of SRD Methodologies for OWF Monopile Installation against a North Europe Driving Records Database | Georgios Perikleous Themis Stergiou Sandra Meissl | Ørsted Ørsted Ørsted |
Effects of Vibratory Driving of Monopiles on Soil Conditions and Their Cyclic Lateral Load Bearing Behavior
The paper presents some results of an experimental study on the cyclic lateral loaddisplacement behavior of vibratory driven monopiles in dense sand. The test setup and the measurement devices used are explained. Subsequently, the results of pore water and earth pressure measurement of three experiments are presented. These results are set in relation to the cyclic lateral load displacement behavior of the piles. The presented results are based on two tests with vibratory-driven piles; one with a cavitational and one with a non-cavitational vibration mode. In order to relate these experimental results to an usual monopile installation method, a third test with an impact driven pile is presented.
Keywords: vibratory driven, impact driven, 1-g model test, cyclic lateral load behavior
| 05-02Labenski.pdf | Effects of Vibratory Driving of Monopiles on Soil Conditions and Their Cyclic Lateral Load Bearing Behavior | Bastian Hoffmann Johannes Labenski Christian Moormann | University Stuttgart Arcadis Germany GmbH University Stuttgart |
Experience from Full-Scale Suction Caisson Trial Installations at the Seagreen Offshore Wind Farm
“This paper details experience gained from full-scale suction caisson trial installations at the planned Seagreen offshore wind farm, which is located in the Firth of Forth, offshore Scotland. Issues encountered during the trial campaign are discussed and key conclusions provided.
A total of 30 trial installations were undertaken across 20 locations; these comprised 25 monotonic tests, 3 cyclic tests and 2 set down tests. Trial installations were conducted in very dense sands, overconsolidated clays and complex layered soils representative of the wide range of ground conditions present at the site. The main objectives were to prove the feasibility of suction caisson installation across the site and calibrate future predictions of installation resistance.
Successful trial installations were conducted at 19 of the 20 locations. Observations confirmed installation feasibility in various strata, including high strength clays and layered profiles, without indication of piping or plug failure. The single installation refusal highlighted that the presence of high resistance and high permeability surficial layers was a critical consideration for suction caisson installation. With this experience, isolated areas of the site were deemed unsuitable for suction caissons and mitigations planned accordingly, thereby reducing foundation installation risk.
Quantitative back-analysis of the trial installation results enabled improved site-specific predictions of foundation installation resistance, thereby further de-risking suction caisson foundation design and identifying areas for potential design optimisation. The results of the back-analysis also meant more areas of the site were considered feasible for suction caisson installation. Performance of the trial installation campaign therefore provided notable benefits to de-risking the project and to lowering overall foundation cost.”
Keywords: Suction caisson, foundation installation, offshore wind
| 05-03Jones.pdf | Experience from Full-Scale Suction Caisson Trial Installations at the Seagreen Offshore Wind Farm | Lewis Jones Andrew Harding | SSE Renewables SPT Offshore |
GDP: A New Technology for Gentle Driving of (Mono)Piles
Large monopiles with, for instance, 8 m diameter and total length of 80 m (30-40 m embedded in the ground) are commonly adopted in current offshore wind practice in suitable geotechnical conditions. Piles of such size require large impact hammers to ensure successful pile driving in a variety of soil conditions. Environmental constraints regarding underwater noise during pile installation add to the numerous challenges associated with monopile installation. It is necessary to explore alternative installation approaches, which are of less impact on the sea life (lower noise emissions) and at the same time do not compromise adequate operational performance of the foundation. To address this challenge, the Gentle Driving of Piles (GDP) JIP has been launched in the Netherlands. The experimental scope of the project includes pile installation using impact hammering, axial vibratory driving, and a novel vibratory installation method named Gentle Pile Driving, based on simultaneous application of low-frequency/axial and high-frequency/torsional vibrations. This paper overviews activities and preliminary results after the first year of project, particularly regarding the development of a new GDP vibrohammer and the execution of 1/10-scale field tests.
Keywords: offshore wind, monopile, pile installation, vibratory driving, field testing, cyclic lateral load testing, sand, underwater noise
| 05-04Tehrani.pdf | GDP: A New Technology for Gentle Driving of (Mono)Piles | Andrei V. Metrikine Apostolos Tsouvalas Maxim L. A. Segeren Ahmed S. K. Elkadi Faraz S. Tehrani Sergio S. Gómez Rob Atkinson Federico Pisanò Evangelos Kementzetzidis Athanasios Tsetas Timo Molenkamp Kees van Beek Peter de Vries | Delft University of Technology Delft University of Technology Delft University of Technology Deltares Deltares Delft University of Technology Delft Offshore Turbine Delft University of Technology Delft University of Technology Delft University of Technology Delft University of Technology Delft University of Technology Delft University of Technology |
Hydraulic Pile Extraction Scale Tests (HyPE-ST): Experimental Design & Preliminary Results
Decommissioning of offshore wind farms at the end of their operational life requires full or partial removal of foundation structures such as monopiles. Removing entire piles is more sustainable, economical, and less hazardous in terms of Health & Safety (H&S) than partial removal. This is because e.g. underwater cutting can be avoided, and no steel remains in the seabed. A promising method for full pile removal is hydraulic extraction. This method involves sealing the pile after removal of the top structure, and pressurizing water inside its void, thus forcing the pile to move upwards. Before applying this method offshore at full scale using expensive vessels and equipment, a better understanding of the pile-fluid-soil interaction in different soil types is needed. To accomplish this, a testing campaign has taken place as part of a Joint Industry Project. Tests are performed at scales of 1:20 and 1:30 for a prototype monopile with a diameter of 8 m. Four different soil conditions were used: medium dense sand, dense sand, medium stiff clay, and layered soil. The piles were installed by impact driving. During the extraction process, several parameters have been monitored including pressure, flow, pile displacement and plug displacement. This paper describes the test program and shares first insights from the results.
Keywords: monopile, decommissioning, offshore wind, sustainability, circular economy
| 05-05Atkinson.pdf | Hydraulic Pile Extraction Scale Tests (HyPE-ST): Experimental Design & Preliminary Results | T. Balder D. A. de Lange A. S. K. Elkadi P. J. P. Egberts W. J. A. P. Beuckelaers M. Coronel J. van Dijk R. Atkinson H. J. Luger | Deltares Deltares Deltares TNO Jan De Nul NV Innogy IHC IQIP Delft Offshore Turbine BV Deltares |
Insights into the Driveability of Large Diameter Piles
Keywords: pile, driveability, signal matching, shaft resistance, end bearing, friction fatigue
| 05-06Cathie.pdf | Insights into the Driveability of Large Diameter Piles | David Cathie Christophe Jaeck Erdem Ozsu Sylvie Raymackers | Cathie Cathie Cathie DEME Offshore |
Large Diameter Monopile Buckling Due to Localized Force – A Numerical Study
In the last decade, the industry of fixed offshore wind farms has developed significantly, leading to important reductions of the global cost of the plants. Generally speaking, about 30% of the total cost of a wind offshore plant, including the installation activities, is related to foundations. In the view of optimising the management of the plant, strong efforts have been done to reduce the costs of the foundation, preserving the planned design while assuring a safe and reliable performance. From the practical point of view, the most diffused foundation, i.e., the monopile, is of special interest. Cost optimisation of the foundation suggests to increase the diameter and to reduce the wall thickness of the monopile, increasing the risk of pile tip damage, particularly frequent in soils where localized inclusions like flints or boulders are present. A higher potential tip damage is the undesired counterpart of the geometry optimisation and it may induce unacceptable economic consequences. This study, based on numerical analyses, is focalized on the buckling of the pile tip subjected to a variously inclined localized force, acting on the edge of the pile base. Results are collected in diagrams, which can be used in design procedures.
Keywords: offshore monopile foundation, pile driving, pile tip damage, buckling, shells, finite element modelling
| 05-07Cornaggia.pdf | Large Diameter Monopile Buckling Due to Localized Force – A Numerical Study | Emilio Nicolini Aram Cornaggia Anna Pandolfi | Cathie Associates Politecnico di Milano Politecnico di Milano |
Numerical Simulation of the Installation of Suction Buckets Using MPM
Suction buckets (or caissons) have traditionally been used for oil and gas related projects. Over the last few years, the use of suction buckets increased significantly in the offshore renewables sector. For example, 31 suction bucket jackets were installed for wind farms in the North Sea in 2018. To reduce costs, there is a need for a design optimization for this type of foundations. Experimental studies have been carried out to investigate the prediction of the installation pressure, mostly focusing on single- or two-layer soil configurations. Lab or field test experiments are sometimes extremely expensive, and they mostly focus on limited configurations, such as the dimensions of the structure and the soil type conditions. Experimental tests on complex scenarios remain very challenging. Nowadays, numerical methods demonstrate important capabilities in simulating large deformation problems such as the installation of objects. Using this technique, several experiments can be virtually reproduced with significantly less costs. This paper shows the simulation of the installation of a suction bucket using the Material Point Method (MPM). Ideal homogeneous purely cohesive and frictional soils have been investigated, and the effect of water flow has also been studied. MPM results are in good agreement with the analytical predictions, justifying the use of MPM for more complex problems.
Keywords: suction, installation, underpressure, offshore, material point method, MPM
| 05-08Alderlieste.pdf | Numerical Simulation of the Installation of Suction Buckets Using MPM | M. Martinelli E. A. Alderlieste V. Galavi H. J. Luger | Deltares Deltares Deltares Deltares |
Physical Modelling of Pile Tip Damage Arising from Impact Driving
There have been a number of incidents worldwide where pile tip damage has occurred during pile driving, generally requiring costly remedial actions. The number of such occurrences has increased recently, consistent with the trend of increasing diameter tubular piles, which are increasingly thin-walled relative to the diameter, used to support offshore wind turbines either as monopiles or as part of a jacket structure. As the wind industry moves into new regions of the world, challenging soil conditions are becoming more common, in particular with increasing risks from embedded boulders or partially weathered soft rocks including chalk and limestone. Pile tip damage may occur as a rather abrupt tip ‘crumpling’, or as a more gradual progressive ‘extrusion buckle’. Both are likely to be triggered by localised heterogeneous hard zones within the sediments, with the rate of growth determined by the stiffness of the surrounding soil matrix. The paper reports some results from a pilot series of centrifuge model tests where thin-walled piles were driven in flight into a sand bed containing thin layers of either ‘gravel’ (representing boulders of up to 30% of the pile diameter), or weakly cemented material. Tip damage varying from barely perceptible to rather extreme was triggered, resulting in increasing driving resistance and premature refusal.
Keywords: extrusion buckling, pile tip damage, centrifuge tests, monopiles, pile driving
| 05-09Nietiedt.pdf | Physical Modelling of Pile Tip Damage Arising from Impact Driving | Juliano A. Nietiedt Mark F. Randolph Christophe Gaudin James Doherty Dan Kallehave Jens Gengenbach Avi Shonberg | The University of Western Australia The University of Western Australia The University of Western Australia The University of Western Australia Ørsted Offshore Ørsted Offshore Ørsted Offshore |
Pile Design, Installation and Back-Analysis of 54 in Piles in Gravels at the Wiriagar Deep Platform in Berau Bay, Indonesia
The paper reports the design, installation, and back-analysis of six 54-inch driven steel piles in dense sands and gravels at the Wiriagar Deep A platform in Berau Bay, Papua Barat, Indonesia. Pile design required to incorporate the presence of thick gravel layers and the potential interaction of the piles with adjacent well conductors during installation or during drilling activities. Installation design required to consider the lack of industry recommendations for the derivation of Soil Resistance during Driving (SRD) in gravel and selection of fit for purpose piling equipment. Dedicated site investigations were carried out to acquire data that would enable pile capacity and drivability predictions. Geological analysis of the origin and distribution of the gravels provided additional context that was incorporated to the installation engineering studies. Pile design mitigation measures included setting the conductor tip below the proposed pile tip depth and strengthening the tip of the piles. Installation mitigations included full instrumentation and monitoring of the piles during driving and the mobilization of a pile top drilling spread. The pile driving instrumentation data enabled efficient management of the installation programme and limited the requirement to implement the installation mitigations available. A companion paper (Pua et al, 2020) provides a detailed description of the instrumentation programme for the Wiriagar Deep A platform adopted during installation. The data acquired also confirmed the uncertainties previously published for pile driving in gravels and the challenges to characterize their in-situ relative density and behaviour during driving. The pile driving monitoring data suggests degradation of shaft resistance during driving in a similar way to friction fatigue effects. The pile instrumentation data also enabled evaluation of the change of pile capacity with time as re-strikes were performed at selected time intervals and confirm the pile design suitability.
Keywords: piles, gravel, drivability, instrumentation, Tangguh
| 05-10Pua.pdf | Pile Design, Installation and Back-Analysis of 54 in Piles in Gravels at the Wiriagar Deep Platform in Berau Bay, Indonesia | Hugo Galanes-Alvarez Achmad Makmur Philippe Jeanjean Chee Peng Pua | BP Exploration Operating Company Ltd. BP Indonesia BP America, Inc. Somehsa Geosciences Pte Ltd. |
Pile Driving Instrumentation of 54-Inch Piles in Gravels at the Wiriagar Deep Platform in Berau Bay, Indonesia
The paper presents the results and findings of instrumentation monitoring during the driving of six 54-inch open-ended steel piles and fourteen 30-inch conductors through dense to very dense sand and gravel layers at the Wiriagar Deep A platform in Berau Bay, Papua Barat, Indonesia. Monitoring of pile driving was carried out with a Pile Driving AnalyserR (PDA) which provided data such as energy transmitted into the pile, driving stresses and the estimated soil resistance to driving for each hammer blow. The transmitted energy was used to evaluate the hammer performance and to control the pile driving fatigue damage by adjusting the hammer efficiency. The driving stresses also helped to minimize non-uniform impact at the pile or conductor top, and to ensure that stresses within the pile were below the allowable limit, especially at the pile tip when driving through the gravel layers. Pile monitoring data was successfully acquired for all sections of all piles, delivering a highquality continuous dataset for all piling operations. Signal matching analyses of the data from selected blows was conducted with the CAPWAPTM software which allowed for onsite evaluation of the soil resistance to driving including the shaft friction and end bearing. Comparison of the measured vs the predicted resistance was carried out in real time. Evaluation of the instrumentation data also enabled optimisation of the re-strike programme to determine the changes in pile capacity with time. A unique dataset of driving behaviour of small diameter conductors (30-in) and larger diameter piles (54-in) in gravel is now available, enabling optimised planning of future facilities in the area. A companion paper (GalanesAlvarez et al, 2020) describes the engineering design and assurance planning for the soil conditions encountered for this platform.
Keywords: piles, gravel, pile monitoring, friction fatigue, drill-out, CAPWAP, Tangguh
| 05-11Galanes-Alvarez.pdf | Pile Driving Instrumentation of 54-Inch Piles in Gravels at the Wiriagar Deep Platform in Berau Bay, Indonesia | Chee Peng Pua D. S. Murthy Radha Rao Hugo Galanes-Alvarez, P. Jeanjean Achmad Makmur | Somehsa Geosciences Pte Ltd. Somehsa Geosciences Pte Ltd. Somehsa Geosciences Pte Ltd. BP Exploration Operating Company Ltd. BP America, Inc. BP Indonesia |
Plug Heave Phenomena during Pile Installation
Recently plug heave (soil rising within open ended tubular piles) phenomena caused, sometimes unexpected, problems in offshore developments. While some had relevant field experience concerning these effects and were prepared to deal with them, others were not forewarned and experienced the consequences at their cost. Surprisingly it turned out that, apart from suction installed piles, the plug heave phenomenon is not mentioned in recommended practices or industry standards, neither is it a topic in research literature. This paper is a first step to remedy this. Plug heave in long slender piles, where plug heave would not be expected up front by many, is discussed. The difference between static and dynamic installation conditions is shown to be an essential factor contributing to the development of plug heave in these piles. Finally, the use of pile installation templates is demonstrated to have a potential effect on (initial) plug heave. While accurate prediction of plug heave is shown to remain a challenge, providing insight in the mechanisms is easier. This insight is believed to be essential to create awareness and ensure that contractors and designers are not caught by surprise.
Keywords: plug heave, plugging, soil rise, pile installation
| 05-12Thijssen.pdf | Plug Heave Phenomena during Pile Installation | Dirk Luger René Thijssen | Deltares Royal Boskalis Westminster |
Suction Bucket Installation: Risks during the Installation Process
Future offshore wind farm projects are likely to be built further offshore in deeper water with larger wind turbine generators leading to increased foundation loads. Furthermore, in some regions, foundations must be installed without exceeding strict regulatory requirements on underwater noise. Thus, traditional foundation solutions are being pushed to their limits and there is a need for innovative foundation concepts. The suction bucket jacket (SBJ) is one such foundation solution which may address these challenges. SBJs are unique in that their geotechnical design may be governed by either installation or in place requirements. Therefore, understanding the installation process is crucial for an efficient and cost effective suction bucket foundation design. In addition to understanding the ground conditions and the expected resistance during the suction bucket installation, installation risks must also be considered. To this end, this paper examines installation data from twenty suction bucket jacket foundations installed in the German sector of the North Sea. The paper provides insight into the risks which may be encountered during the suction bucket installation process such as the effect of the installation process on the internal plug, the inclination of the structure during installation and the difficulties associated with real time monitoring of the installation process.
Keywords: suction bucket, installation risk, suction installation
| 05-13Harte.pdf | Suction Bucket Installation: Risks during the Installation Process | Avi Shonberg Michael Harte Amin Aghakouchak Morten Albjerg Liingaard | Ørsted Offshore Ørsted Offshore Ørsted Offshore Ørsted Offshore |
Suction Installation of Modular Bucket Foundation for Large Offshore Wind Turbines
Suction bucket foundation is named by many experts in offshore geotechnics as an alternative to pile foundations for offshore wind turbines as it is often more cost-effective. The suction installation process is noise-free and requires less operational time. A simple design of suction bucket is a steel cylindrical thin structure. A significant increase in size of foundation requires a higher pressure for installation and, at the same time, increases the probability of buckling failure. The proposed modular bucket consists of trapezoidal wall sections that are convenient for industrialization. The structure is significantly thinner than a circular bucket, resulting in a weight saving of 28% for full scale model with diameter equal 8 m (EUDP, 2018). This design has been analyzed for buckling resistance and results in much better performance. The paper includes also the installation tests on a medium-scale bucket models, both the round and modular. Results prove that the initially large penetration resistance in sand is highly reduced by the seepage flow induced by applied suction. Moreover, the comparison of results shows that the extra increase in jacking required load for modular bucket due to larger area is minimized almost to no difference in the required suction between circular and modular bucket model. These findings can contribute to a significant decrease in energy production costs for offshore wind turbines allowing installation of bigger turbines with reduced cost of the foundations.
Keywords: Modular bucket, Offshore wind turbines, Penetration resistance reduction
| 05-14Koteras.pdf | Suction Installation of Modular Bucket Foundation for Large Offshore Wind Turbines | Aleksandra K. Koteras Francisco M. G. Rodriguez Lars B. Ibsen | Aalborg University Aalborg University Aalborg University |
The Impact of Installation Method on Monotonic Loading of Monopiles in Sand
Monopiles are the most commonly used foundations for offshore wind turbines (OWTs). To date these are mostly impact driven into the seabed using high-capacity hammers. The noise and vibrations caused by driving create environmental concerns and the increasing size of these foundations has resulted in alternative installation methods being explored. In this paper a comparison is made between piles installed by vibration and driving. The results of full-scale field trials for pile pairs installed in dense sand by driving and vibration are presented. Lateral load tests were performed to determine the effect of installation method on the capacity and stiffness of the piles. In this paper 3D finite element model predictions of the pile response are reported. The soil model adopted was the HS small model in PLAXIS. The measured pile responses are compared to predictions made using soil parameters derived using correlations with Cone Penetration Test, CPT end resistance qc value (known herein as the direct approach) and through correlation with sand relative density. It is seen that the stiffness and capacity of the vibratory installed piles were lower than driven piles. The finite element model predictions using the input parameters based on relative density underestimate the stiffness response at low displacement levels whilst providing good predictions for displacements in excess of 2cm. The direct correlation approach provided good predictions of the initial response whilst over-estimating the stiffness for displacements above 2cm. The influence of sand creep on the field response of the piles and the performance of the numerical predictions is discussed.
Keywords: Monopile, CPT, sand, lateral loading, vibratory driving
| 05-15Eiksund.pdf | The Impact of Installation Method on Monotonic Loading of Monopiles in Sand | K. G. Gavin S. D. Blok G. R. Eiksund, Professor | Delft University of Technology GBM Works Norwegian University of Science and Technology |
The Influence of Friction Fatigue on Pile Drivability Predictions for Large Diameter Monopiles in the Bolders Bank Formation
Reliable drivability studies enable appropriate hammer selection, pile geometry optimization and safe, cost-effective pile installation. Friction Fatigue is a general term describing temporary changes in soil resistance around the pile shaft during pile installation. Friction Fatigue is affected by factors such as soil type, geotechnical properties and initial stress state. Impact hammer driving records for large diameter monopile foundations at a Southern North Sea offshore wind farm provide the link between dynamic soil resistance during driving and static soil resistance. The objective of this paper is to evaluate the influence of friction fatigue parameters for the glacial deposits of the Bolders Bank Formation which, in this area, comprised layered sequences of stiff, high strength, over-consolidated CLAY and dense to very dense SAND. The assessment utilizes and expands on the Alm and Hamre (2001) friction fatigue model in conjunction with the drivability software WEAP (2010). The results indicate that friction fatigue is a required component for drivability assessments in these soils and calibration can enable refinement of drivability predictions. Friction fatigue parameters can be modified to develop a drivability envelope for predictions. Different soil behaviour types defined through cone penetration testing, may also require different friction fatigue models to improve drivability predictions.
Keywords: Bolders Bank Formation, pile drivability, friction fatigue, monopile
| 05-16Giuliani.pdf | The Influence of Friction Fatigue on Pile Drivability Predictions for Large Diameter Monopiles in the Bolders Bank Formation | S. R. Davies G. Giuliani M. Vaziri | Xodus Ramboll Ramboll |
Vibratory Driving of a Monopile at a North Sea Site
This paper presents the outcomes of a post-installation study performed for the vibrohammer installation of a monopile at a platform located in the Dutch Sector of the North Sea. The monopile diameter was 4.7 m with a length of 40.5 m. The target penetration depth was 31.5 m below seafloor (BSF). The subsoil consisted of very dense fine to medium sands locally with few thin strata of silty sand and sandy silt. During the installation of the monopile, early pile refusal was encountered. The pile installation was subsequently completed using an impact hammer. This paper aims to highlight the importance of monitoring during pile installation and to review key parameters affecting the vibratory driving installation process.
Keywords: monitoring, vibratory driving, hammer installation, monopile
| 05-17Peralta.pdf | Vibratory Driving of a Monopile at a North Sea Site | A. Holeyman V. Whenham P. Peralta J.-C. Ballard S. Chenicheri Pulukul | UCLouvain Besix Fugro USA Marine, Inc. Fugro Geoconsulting Shell UK Ltd. |