Byron W. Byrne

University of Oxford | OX · Department of Engineering Science

This paper describes the results obtained from a field testing campaign on laterally loaded monopiles conducted at Cowden, UK, where the soil consists principally of a heavily overconsolidated glacial till. These tests formed part of the PISA project on the development of improved design methods for monopile foundations for offshore wind turbines....

The results obtained from a field testing campaign on laterally loaded monopiles, conducted at a dense sand site in Dunkirk, northern France are described. These tests formed part of the PISA project on the development of improved design methods for monopile foundations for offshore wind turbines. Results obtained from monotonic loading tests on pi...

The PISA project was a combined field testing/numerical modelling study with the aim of developing improved design procedures for large-diameter piles subjected to lateral loading. This paper describes the development of a three-dimensional finite-element model for the medium-scale pile tests that were conducted in Cowden till as part of the PISA w...

The paper presents the development of a three-dimensional finite-element model for pile tests in dense Dunkirk sand, conducted as part of the PISA project. The project was aimed at developing improved design methods for laterally loaded piles, as used in offshore wind turbine foundations. The importance of the consistent and integrated interpretati...

Offshore wind turbines in shallow coastal waters are typically supported on monopile foundations. Although three-dimensional (3D) finite-element methods are available for the design of monopiles in this context, much of the routine design work is currently conducted using simplified one-dimensional (1D) models based on the p–y method. The p–y metho...

Chalk is a soft biomicrite composed of silt-sized crushable CaCO3 aggregates. Chalk's response to cyclic loading depends critically on its sensitive micro fabric and state, which may be altered significantly by high-pressure compression, dynamic impact or prior large-strain repetitive shearing. This paper reports high-resolution undrained cyclic tr...

Chalk is a highly variable cemented biomicrite limestone that can show widely different rock strengths and patterns of micro to macro fissuring and jointing, due to variations in depositional environments and local geological histories. This paper describes the characterisation of a very weak to weak, low-to medium-density chalk through in situ pro...

Offshore wind turbines (OWT) are emerging as a crucial component of renewable energy in Europe, reinforcing the importance of efficient and reliable foundation designs to ensure long-term economic viability. The determination small strain stiffness parameters of soil, including shear stiffness (G0 ), shear degradation (G/G0 ), linear (γtl) and volu...

Project-specific advanced laboratory testing is employed increasingly frequently in site investigations for major offshore projects. Such testing needs to focus on characterising properties under in-situ conditions, while also catering for the effects of foundation installation and subsequent service conditions, including cyclic loading. Low-to-med...

Driven piles support a substantial number of offshore wind turbines, near-shore bridges, and port facilities. Designing and installing these piles can be challenging in Chalk, a porous, low-density, weak carbonate rock prevalent beneath vast areas of NW Europe. Designers currently have limited guidance on driveability, axial capacity, lateral pile...

Offshore pile design presents multiple challenges in low-to-medium density chalks, whose sensitivity and brittleness often leads to very low driving resistances. Also, existing design rules have proved unable to give reliable predictions for axial and lateral resistances under offshore field loading conditions. This paper summarises how the ALPACA...

In jacket foundations, the overturning moments caused by winds/waves are transferred to the piles mostly in the form of axial loads; understanding the complex mechanics of soil-pile interaction under axial loads has been a key subject in offshore wind turbines (OWT) design. In this paper, the application of a numerical modelling approach called 'Hy...

Progressive buckling of thin-walled open-ended piles can occasionally occur during installation, especially when the pile penetrates through hard materials, or where there are subsea obstructions, typically in clays, such as boulders. The distortion initiated at the pile tip due to a boulder collision can propagate and lead to premature refusal of...

Monopiles are the most widespread foundation option for offshore wind turbines. The PISA (pile soil analysis) joint industry research established a one-dimensional (1D) model for calculating the monotonic behaviour of laterally loaded monopiles by using a parametric equation to represent the soil reaction components. During the current PICASO proje...

This paper presents a new approach, called the Modulus Weighting Method (MWM), for estimating the static stiffness of suction caisson foundations in layered soil conditions. The existing simplified design models for estimating caisson stiffness are limited to non-layered soil conditions, but layered conditions are often found in real-world scenario...

Soils exhibit non-linear stress-strain behaviour, even at relatively low strain levels. Existing Winkler models for suction caisson foundations cannot capture this small-strain, non-linear soil behaviour. To address this issue, this paper describes a new non-linear elastic Winkler model for the uniaxial loading of suction caissons. The soil reactio...

This paper explores the application of a numerical method for modeling pseudorandom cyclic loading, at very large cycle numbers , to the design of offshore wind turbine foundations. The work expands the development of a novel constitutive modeling framework, the hyper-plastic accelerated ratcheting model (HARM), for which the key constitutive equat...

Low-to-medium-density chalk can be destructured to soft putty by high-pressure compression, dynamic impact or large-strain repetitive shearing. These process all occur during pile driving and affect subsequent static and cyclic load-carrying capacities. This paper reports undrained triaxial experiments on destructured chalk, which show distinctly t...

This paper describes a finite element study of the uplift behaviour of a plane strain pipe segment embedded in modified Cam clay soil. The primary aim of this study is to explore the role of rate effects on pipe uplift capacity and the transition between drained and undrained behaviour using coupled-consolidation analyses. The velocities considered...

Large-diameter open caissons are an increasingly common means of constructing underground storage and attenuation tanks, as well as launch and reception shafts for tunnel-boring machines. A ‘cutting face’ at the base of the caisson wall, resembling an inclined ring footing, is typically used to aid the sinking phase. This paper describes a suite of...

Monopile foundations supporting offshore wind turbines are exposed to cyclic lateral loading, which can cause accumulated pile displacement or rotation and evolution of the dynamic response. To inform the development of improved design methods, the monopile's response to cyclic lateral loading has been explored through small-scale physical modeling...

Suction caisson foundations provide options for new foundation systems for offshore structures, particularly for wind turbine applications. During the foundation design process, it is necessary to make reliable predictions of the stiffness of the foundation, since this has an important influence on the dynamic performance of the overall support str...

The PISA design model is a procedure for the analysis of monopile foundations for offshore wind turbine applications. This design model has been previously calibrated for homogeneous soils; this paper extends the modelling approach to the analysis of monopiles installed at sites where the soil profile is layered. The paper describes a computational...

Robust design of offshore wind turbine foundations requires that the ultimate capacity is acceptable. In addition the accumulated deformations over 25 years of operational life, typically 10 8 cycles, must also be limited. This paper outlines a numerical method for modelling the response of monopiles to monotonic and cyclic lateral loading to very...

This paper reports the use of optical fiber Bragg-grating (FBG) sensors to monitor the stress waves generated below ground during pile driving, combined with measurements using conventional pile driving analyzer (PDA) sensors mounted at the pile head. Fourteen tubular steel piles with a diameter of 508 mm and embedded length-to-diameter ratios of 6...

Scour erosion processes can occur at seabed level around offshore wind turbine monopile foundations. These scour processes are often especially severe at sites where mobile sediments, such as sands, are present in the superficial seabed soils. Loss of local soil support to the monopile, caused by scour erosion, can lead to significant changes in th...

Large-diameter open caissons are a widely used construction solution for deep foundations, underground storage and attenuation tanks, pumping stations, and launch and reception shafts for tunnel boring machines. The sinking phase presents a number of challenges during construction including maintaining caisson verticality, controlling the rate of s...

This paper describes a one-dimensional (1D) computational model for the analysis and design of laterally loaded monopile foundations for offshore wind turbine applications. The model represents the monopile as an embedded beam and specially formulated functions, referred to as soil reaction curves, are employed to represent the various components o...

The simulation of additional soil overburden pressure through the use of a surcharge system is a technique commonly adopted in laboratory testing of pipe–soil interaction. This paper examines the influence of surcharge boundary conditions and pressure level on the axial sliding behaviour of a trenched pipeline surrounded by sand backfill. A novel t...

This paper is the first of a set of linked publications on the PISA Joint Industry Research Project, which was concerned with the development of improved design methods for monopile foundations in offshore wind applications. PISA involved large-scale pile tests in overconsolidated glacial till at Cowden, north-east England, and in dense, normally c...

The PISA Joint Industry Research Project was concerned with the development of improved design methods for monopile foundations in offshore wind applications. PISA involved large-scale pile tests in overconsolidated glacial till at Cowden, north-east England, and in dense, normally consolidated marine sand at Dunkirk, northern France. This paper de...

This paper describes an automated approach for determining the optimal dimensions (length and diameter) of a suction caisson foundation subject to lateral loads, to minimise the foundation weight, whilst satisfying installation requirements, serviceability and ultimate limit states. The design problem was cast as a constrained optimisation problem....

Monopiles supporting offshore wind turbines experience combined moment and horizontal loading which is both cyclic and complex – continuously varying in amplitude, direction and frequency. The accumulation of rotation with cyclic loading (ratcheting) is a key concern for monopile designers and has been explored in previous experimental studies, whe...

Chalk is present under large areas of NW Europe as a low-density, porous, weak carbonate rock. Large numbers of offshore wind turbines, bridges and port facilities rely on piles driven in chalk. Current European practice assumes ultimate shaft resistances that appear low in comparison with the Chalk’s unconfined compression strength and CPT cone re...

This paper provides a summary of the PIle Soil Analysis (PISA) project, completed in the UK during the period 2013 to 2018. The research led to the development of a new, computationally efficient, one dimensional design model for laterally loaded monopile foundations, particularly for offshore wind turbine support structures. The current form of th...

The failure envelope approach is widely used to assess the ultimate capacity of shallow foundations for combined loading, and to develop foundation macro-element models. Failure envelopes are typically determined by fitting appropriate functions to a set of discrete failure load data, determined either experimentally or numerically. However, curren...

This paper provides an overview of the PISA design model recently developed for laterally loaded offshore wind turbine monopiles through a major European joint-industry academic research project, the PISA Project. The focus was on large diameter, relatively rigid piles, with low length to diameter (L/D) ratios, embedded in clay soils of different s...

This paper presents an analytical methodology for calibration of the Hyperplastic Accelerated Ratcheting Model (HARM, Houlsby et al., 2017 [3]), based on a closed-form expression for the accumulation of ratcheting strain with cyclic history. The proposed method requires the fit of one test response and of a few continuous cyclic tests. The initial...

The failure envelope approach is commonly used to assess the capacity of shallow foundations under combined loading, but there is limited published work that compares the performance of various numerical procedures for determining failure envelopes. This paper addresses this issue by carrying out a detailed numerical study to evaluate the accuracy,...

This paper provides a brief overview of the Pile Soil Analysis (PISA) project, recently completed in the UK. The research was aimed at developing new design methods for laterally loaded monopile foundations, such as those supporting offshore wind turbine structures. The paper first describes the background to the project and briefly outlines the ke...

This paper presents experimental work aimed at improving understanding of the behaviour of rigid monopiles, in cohesionless soils, subjected to lateral cyclic loading. It involves 1g laboratory model tests, scaled to represent monopile foundations for offshore wind turbines. The test programme is designed to identify the key mechanisms governing pi...

Large-diameter open caissons are a widely-adopted solution for deep foundations, underground storage and attenuation tanks, pumping stations, and launch and reception shafts for tunnel boring machines. The sinking process presents a number of challenges including maintaining verticality of the caisson, controlling the rate of sinking, and minimizin...

Local and global scour around offshore wind turbine monopile foundations can lead to a reduction in system stiffness, and a consequential drop in the natural frequency of the combined monopiletower- nacelle structure. If unchecked this could lead to operational problems such as accelerated fatigue damage and de-rating or decommissioning of the turb...

Most existing Winkler models use non-linear elastic soil reactions to capture the non-linear be-haviour of foundations. These models cannot easily capture phenomena such as permanent displacement, hys-teresis and the influence of combined loading on the failure states. To resolve these shortcomings, an elasto-plastic Winkler model for suction caiss...

Suction caissons are a promising foundation concept for supporting offshore wind turbines. Compared to applications in the oil and gas industry, where most practical experience exists, significant differences arise in terms of load paths and magnitudes, soil type and caisson aspect ratio (skirt length to diameter). In a set of two companion papers,...

Suction caissons have been used for numerous oil and gas installations and are increasingly considered as a foundation solution for offshore wind turbines (OWTs). There can be significant differences between the two offshore energy applications in the load paths and magnitudes, soil type and caisson aspect ratio (skirt length to diameter). This pap...

This paper describes a full-scale laboratory study of the axial sliding behaviour of a trenched pipeline surrounded by sand backfill. Cyclic axial displacements are applied to a heavy pipe buried in a narrow trench (less than three pipe diameters wide), using various backfill cover depths and two different soils: dry Hostun sand and a damp, silty s...

Large-diameter open caissons are a widely-adopted solution for deep foundations, underground storage and attenuation tanks, pumping stations, and launch and reception shafts for tunnel boring machines. The sinking process presents a number of challenges including maintaining verticality of the caisson, controlling the rate of sinking, and minimizin...

This paper describes the outcome of a recently-completed research project – known as PISA – on the development of a new process for the design of monopile foundations for offshore wind turbine support structures. The PISA research was concerned with the use of field testing and three-dimensional (3D) finite element analysis to develop and calibrate...

In the PISA project, over 28 pile test are performed to investigate the behaviour of monopile foundations. These test piles are instrumented with inclinometers and displacement transducers above ground; a subset of the piles are instrumented below ground with inclinometers, extensometers and strain gauges. To analyse the data, processing tools are...

Improved design of laterally loaded monopiles is central to the development of current and future generation offshore wind farms. Previously established design methods have demonstrable shortcomings requiring new ideas and approaches to be developed, specific for the offshore wind turbine sector. The Pile Soil Analysis (PISA) Project, established i...

This paper outlines experimental and theoretical research exploring the response of rigid piles to cyclic lateral loading, relevant to large diameter monopiles for offshore wind applications. The experimental work comprised of 1-g laboratory scale model tests in sand, where up to 100,000 cycles were applied. The tests were designed specifically for...

This paper introduces sequential limit analysis (SLA) as a method for modelling large plastic deformations of purely cohesive materials such as undrained clay. The method involves solving a series of consecutive small-deformation plastic collapse problems using finite element limit analysis, thus ensuring high levels of accuracy, efficiency and rob...

A newly developed sequential limit analysis (SLA) technique is used to perform large-displacement numerical simulations relevant to thermally induced lateral buckling of untrenched subsea pipelines. A rigid plane-strain pipe segment, partially embedded in undrained clay, is subjected to cyclic lateral displacements with amplitudes of up to eight pi...

We present a theoretical model to describe the response of a one dimensional mechanical system under cyclic loading. Specifically, the model addresses the non-linear response on loading, hysteretic behaviour on unloading and reloading, and the phenomenon of ratcheting under very many cycles. The methods developed are formulated within the hyperplas...

Development of improved methods to capture the lateral cyclic behaviour of offshore wind monopiles through experimental and theoretical modelling

A theoretical model is proposed for a row of sub-arrays of tidal turbines aligned in a cross-stream fashion across part of a wide channel. This model builds on previous work investigating the behaviour of a single partial row array that split the problem into two flow scales; device and channel. In the present work, three flow scales are proposed:...

An open-dug caisson shaft is a form of top-down construction in which a concrete shaft is sunk into the ground using the weight of the shaft and additional kentledge, if required. Excavation at the base of the caisson shaft wall allows the structure to descend through the ground. A thorough understanding of the interaction between the caisson shaft...