Conleth O'Loughlin

University of Western Australia | UWA · Centre for Offshore Foundation Systems

The cone penetration test (CPT) is widely used to determine soil stratigraphy and soil characteristics. Moreover, correlations derived from CPT measurements are used increasingly in geotechnical design, for instance, to estimate the bearing capacity of foundations and soil liquefaction susceptibility. Correlations based on the results of cyclic CPT...

Shallow foundations can mobilize uplift resistance due to the negative excess pore pressure generated underneath the foun-dation. However, quantifying the magnitude of this uplift resistance remains uncertain due to the dependence on uplift rate, with differentresponses expected for surface foundations and skirted foundations. This paper attempts t...

Floating offshore infrastructure requires geotechnical anchorage for station-keeping. Dynamically embedded anchors are anchors that free-fall through the water column and embed in the seafloor through kinetic energy at impact, enabling efficient installation into soft seabeds. Dynamic installation of plate anchors is an alternative to static embedm...

This paper presents and discusses results from a series of cone, vane and footing tests in a carbonate silty sand, conducted in a geotechnical centrifuge, that investigate how drainage effects scale with the diameter of the device/foundation. The tests involved different penetration and rotational velocities to quantify how velocity influences the...

Cyclic loading features in many applications. Questions important for design include: Does the monotonic capacity increase or decrease following cyclic loading? How does foundation rotation, stiffness and damping evolve? This is investigated here for suction caissons in sand, looking to applications as foundations for offshore wind turbines where c...

The accurate quantification of the temporal changes in seabed strength allows for more reliable and less conservative geotechnical design. A recently developed effective stress framework, established within a one-dimensional computational domain to quantify changes in soil strength due to pore pressure generation and dissipation, has been extended...

The undrained shear strength of contractive fine-grained soils changes with time, reducing due to pore pressure generation and increasing during consolidation. There is an increasing appetite to recognise these temporal soil strength changes in offshore geotechnical design, as it provides a basis for potentially less conservative designs. Contribut...

Motivation for this paper stems from experimental investigations that consider how the vertical capacity of a horizontal circular plate anchor in clay changes due to consolidation. These experiments produced interesting time-dependent measurements that prompted a follow-on study, designed to explore the underlying mechanisms. The new experimental d...

Plate anchors have become an attractive technology for anchoring offshore floating facilities such as floating renewable energy devices because they provide high holding capacity relative to their dry weight. This allows for the use of smaller anchors (relative to a driven or suction-installed pile), which provide cost savings on production, transp...

Geotechnical centrifuge modelling has (for decades) aided our understanding of real-world foundation behaviour. When used in combination with numerical/analytical analysis, the outcome is robust design practice. With world attention on the pursuit of renewable energy, including offshore wind, this paper explores the differentiators to oil and gas g...

Suction-embedded plate anchors (SEPLAs) utilise a suction caisson to install a plate anchor positioned near the base of the caisson. This eliminates much of the geotechnical uncertainty surrounding the final position of the anchors (relative to drag anchors), whilst also providing significant economic benefit as the caisson is reused between instal...

This paper presents the results of centrifuge model tests on bucket foundations conducted in clean silica sand to simulate the loading conditions which apply at the windward leg of a three-legged offshore wind turbine jacket structure. Load sharing response between bucket skirt and soil, and the concurrent suction pressure under the bucket lid, was...

Suction caissons are being increasingly considered as foundations for offshore wind turbine jacket structures. Suction caissons are installed through self-weight and application of under pressure, achieved by pumping water from the caisson interior. However, in some instances alternative installation strategies need to be considered to ensure compl...

The undrained shear strength of fine-grained soils changes with time, reducing due to pore pressure generation, and increasing during consolidation. This paper describes an effective stress framework, implemented within a two-dimensional computational domain, that relates generation of pore pressure to accumulated plastic shear strain, allowing und...

Helical piles are being increasingly considered for offshore applications as they avoid the acoustic emissions associated with pile driving, and they provide additional capacity relative to a driven pile. In this paper, we consider the installation and tensile capacity of helical piles through a combination of centrifuge experiments and large defor...

Suction bucket jackets are increasingly being used to support bottom-fixed offshore wind turbines. It is generally assumed that contact between the underside of the bucket lid and the seabed is mandatory to safeguard against additional settlement. Lid contact is usually ensured by underwater grout injection, albeit this has a significant impact of...

Plate anchors are an attractive technology for mooring floating facilities; as relative to piles, suction caissons, and drag anchors, they provide a much higher capacity relative to their mass. Plate anchors may experience an extreme loading event that will cause geotechnical failure, although they will still retain a residual capacity. The displac...

Determination of an acceptable lower bound, large strain undrained shear strength of tailings is fundamental for evaluating the stability tailings storage facilities comprising loosely deposited tailings. Currently, techniques used include laboratory shear strength testing and in-situ measurements including the cone penetration test (CPT) and vane...

Layered soils are frequently encountered in intermediate water depths, where suction bucket jackets are considered an economically competitive foundation for offshore wind turbines. Permanent tilting can make the turbine inoperable, such that excessive differential movement between buckets must be avoided. This paper presents results from centrifug...

A series of CPT and skirt penetration tests have been conducted in carbonate silty sand in a range of drainage conditions ranging from fully drained to fully undrained. The drainage transition response for each has been quantified in order to provide guidance in how to use the results from field CPTs to predict soil resistance during the installati...

Rock berms are used to restrain flowlines from moving axially by adding vertical load to enhance resistance. Should the contact pressure be reduced at the flowline-berm interface, such as in response to ‘arching’ of the rock berm due to pipe settlement, this resistance may be substantially reduced. This study shows how the development of axial rest...

The performance of plate anchors in sand, relative to clay, is not well understood, particularly for the more realistic case of an inclined load. This paper investigates the effect of load inclination on horizontal plate anchors in sand through centrifuge tests and numerical finite-element simulations. The centrifuge tests were performed on rectang...

This paper examines the effect of consolidation on a shallowly embedded horizontal plate anchor in medium dense and dense sand using centrifuge tests, where the loading rate was varied over four orders of magnitude. The experimental results show a 4·8 to 5·5 times increase in anchor capacity as the consolidation condition changes from drained to un...

Dynamically embedded plate anchors (DEPLAs) are a relatively new anchor type that combine the advantages of dynamically installed anchors and conventional plate anchors. Through three dimensional finite element modelling, this paper first derives the combined loading yield surface of the anchor holding capacity in clay and then uses this yield surf...

Pipe clamping mattresses (PCMs) are a relatively new system for providing anchoring force to pipelines, to mitigate offshore flowline ‘walking’. They represent a cost-effective and highly efficient alternative to anchor piles, rock dump and conventional concrete mattresses. The system comprises a hinged concrete structure that clamps onto a section...

Single (or mono) suction buckets have been put forward by others as possible offshore wind turbine (OWT) foundations. This paper presents a series of centrifuge model tests conducted in dense sand to investigate their monotonic response for a range of drainage conditions. The results from the centrifuge tests suggest that the mono-bucket rotational...

The use of plate anchors on permanent offshore facilities with taut or semi-taut moorings requires a thorough understanding of their long-term capacity under sustained loading. In this paper, a programme of centrifuge tests and numerical simulations is reported to investigate the capacity of a plate anchor deeply embedded in normally consolidated c...

Suction buckets are expected to be increasingly used as foundations for offshore wind turbine (OWT) projects as they move to deeper water and monopiles become impractically large. Since OWTs are relatively light and operational loads include high overturning moments, potential exists for individual foundations to experience periods of net tension w...

This paper investigates the uplift capacity of horizontal plate anchors in sand through finite element analyses and centrifuge experiments. The finite element simulations adopt a sophisticated bounding surface plasticity model that accounts for stress- and density-dependent behaviour, as well as loading- and fabric-related anisotropic effects in sa...

This paper describes a centrifuge investigation on drained monotonic and cyclic capacity of a plate anchor in dry loose sand. The model rectangular plate anchor was pre-embedded vertically at an embedment depth of 5 times the plate width, and was loaded horizontally at the mudline with monotonic or irregular cyclic loading to failure. The anchor wa...

Key uncertainties in the assessment of subsea pipeline spans for fatigue due to vortex-induced vibrations (VIV) are the effective axial force, the soil spring stiffness, and the soil damping. To reduce these uncertainties, pluck tests have been carried out, to determine the natural frequency and damping of single and multiple spans. These are carri...

The paper examines the merit of a bounding surface plasticity model at both element and system level. The governing equations are based essentially on the parent bounding surface plasticity model reported by Dafalias and Manzari in 2004 with some simple yet practical changes to enable realistic predictions for monotonic loading along different load...

Wind and wave action on offshore wind turbines causes irregular cyclic loading on the foundation that can lead to rotation accumulation of the structure. Such loading is generally considered in design using ‘counting methods’ that decompose the time history of irregular cyclic loads into a series of cyclic load parcels of uniform amplitude. These p...

Suction buckets are becoming established as a viable foundation solution for offshore wind turbines. In sand, suction-induced seepage flow reduces effective stresses at the skirt tips, which decreases penetration resistance. However, layered seabeds are often encountered in areas of offshore wind farm development. The effect of the presence of a cl...

This paper describes a centrifuge study using novel penetrometer tests (T-bar and piezoball) and model foundation tests to explore through-life changes in the strength of a reconstituted natural carbonate silt. The test procedures include episodic cyclic loading, which involves intervals of pore pressure dissipation between cyclic packets. These lo...

Plate anchor technology is an efficient solution for mooring offshore floating facilities for oil and gas or renewable energy projects. When used with a taut mooring, the anchor is typically subjected to a maintained load component and intermittent episodes of cyclic loading throughout the design life. These loads, and the associated shearing, remo...

This study investigated the change in monotonic and cyclic capacity of a plate anchor across different degrees of consolidation in dense sand. To quantify the effect of consolidation on anchor capacity, a framework is introduced and validated using centrifuge model anchor test data. The centrifuge tests considered a rectangular plate loaded at vary...

Offshore wind energy has been explored as one of the sustainable energy forms for nearly 30 years, since the first offshore wind farm installed in Denmark in 1991. So far, monopile foundations are still the major foundation type in waters up to 30 m deep. Monopiles, or open steel pipe piles in general, are often installed by driving or vibration. T...

This paper describes a centrifuge study using a range of penetrometer tests (T-bar, piezocone and free-fall piezocone) to explore strength changes in a reconstituted, normally consolidated, natural calcareous silt. Various penetrometer test procedures were applied to measure the penetration resistances including monotonic, cyclic and twitch-type mo...

As part of a research project to develop a framework for quantifying cyclic effects on piles, centrifuge model tests on single piles and pile groups in dry silica sand were carried out at the Centre for Offshore Foundation Systems (COFS) in Perth, Australia. In addition, small-scale model tests (1g model tests) were undertaken at the University of...

An assessment of the conventional geotechnical design approach for cyclic loading of offshore shallow foundations is presented in the context of its applicability to new offshore architecture. Foundation response in normally consolidated clay has been investigated in a geotechnical centrifuge under vertical cyclic loading, indicative of that applie...

The response of rigid piles in sand to an inclined tensile load is poorly documented and understood, particularly when the load is cyclic. This is becoming relevant for floating marine renewable energy devices such as wave energy converters and floating wind turbines. This paper considers centrifuge data for rigid piles in dense sand subjected to d...

p>Geotechnical design of offshore shallow foundations is generally based on a cyclically degraded shear strength, typically determined from a shear strain or pore pressure accumulation procedure based on contour diagrams derived from laboratory tests. The procedure was initially developed for gravity-based structures and is now used for a wider ran...

Full-flow T-bar and ball penetrometer tests are often used to measure intact and remoulded soil strengths, with the latter determined after several large amplitude displacement cycles. In offshore design the remoulded soil strength is often the governing design parameter during installation of subsea infrastructure, whilst a ‘cyclic strength’ appli...

This paper reports on a series of centrifuge tests to investigate the feasibility and performance of a novel spudcan foundation design featuring a peripheral skirt with side openings. The ‘skirted spudcan’, designed and patented by Keppel, is particularly beneficial in layered seabeds with a clay layer overlaying sand. The purpose of the side openi...

Steel catenary risers (SCRs) are an efficient solution to transfer hydrocarbons from deep-water seabeds to floating facilities. SCR design requires an assessment of the fatigue life in the touchdown zone, where the riser interacts with the seabed, which relies on reliable estimates of the SCR–seabed stiffness over the design life. Current models fo...

The paper investigates the effect of stress history and shallow embedment on centrifuge cone penetration tests in sand. A series of centrifuge cone penetration tests were performed in loose and dense silica sand at g-levels ranging between 20 and 100 with corresponding overconsolidation ratio (OCR) between 1 and 5. Based on the measured cone tip re...

This paper addresses the selection of an appropriate consolidation coefficient for the analysis of drainage beneath foundations and pipelines in offshore geotechnical design. An emerging trend in the design of subsea infrastructure is the consideration of ‘whole life’ effects — namely the changes in soil properties and geotechnical capacity over th...

This study investigated the performance of two anchoring solutions (dynamically installed anchors and plate anchors) under taut mooring in clay using laboratory model tests. In the experiments, two instrumented anchors were pre-embedded vertically to the required depths before being loaded vertically. The monotonic capacity of the anchors was first...

This paper attempts to explain how a normally consolidated lakebed sediment can have an undrained strength ratio of approximately unity, when the lithic component of the sediment is less than 3% by volume. The structured clay framework, coupled with sensitivity measurements of the sediment, show that the structure retains a very high strength in a...

Suction caissons have recently been considered as potential anchoring solutions for floating renewable devices (wind turbines and wave energy converters) in shallow waters, where-unlike for floating oil and gas applications in deep water-sandy seabeds are to be expected. This paper presents a simple framework to calculate the maximum drained capaci...

Suction buckets represent a viable solution as foundations for offshore wind turbines. Installation in sand is relatively straightforward, albeit with limited understanding of the resulting changes in soil state. This paper describes an experimental methodology that allows for visualisation and quantification of changes in soil state during suction...

Offshore wind turbines and their foundations experience loading from varying directions, yet understanding of the effect of changes in the direction of applied cyclic loading on foundation response remains limited. This study investigates the behaviour of a suction caisson foundation in sand over clay under various types of multidirectional cyclic...

This technical note considers experimental data on the long-term response of a suction caisson in sand and sand over clay to lateral cyclic loading. Installation of the caisson under suction in a geotechnical centrifuge provides insight into the contribution of this installation process, as well as the effects that soil drainage and consolidation i...

This note examines the interaction between the helices of a multi-helix anchor in terms of the mobilized drained capacity response in tension. Assessments are made on the basis of centrifuge tests in dense silica sand, supplemented with data from existing studies. The centrifuge tests were designed to isolate potential anchor installation effects f...

This paper considers data from centrifuge model tests on pile groups in silica sand involving lateral one-way cyclic loading. The influence of cyclic load amplitude, pile spacing within the pile group and number of cycles on the observed response are highlighted. Investigating the contribution of each pile on the lateral capacity shows leading row...

This paper presents a geotechnical engineering perspective on the design of anchoring systems for floating wind turbines and floating wave energy converters. It explores several transformational research directions in anchor technology and anchor design, moving away from standards established for floating oil and gas structures, and acknowledging t...

This paper presents a geotechnical engineering perspective on the design of anchoring systems for floating wind turbines and floating wave energy converters. It explores several transformational research directions in anchor technology and anchor design, moving away from standards established for floating oil and gas structures, and acknowledging t...

As part of a research project to develop a framework for quantifying cyclic effects on piles, centrifuge model tests on single piles and pile groups in dry silica sand have been carried out at the Centre for Offshore Foundation Systems (COFS) in Perth, Australia. The piles were subjected to lateral 1-way and 2-way cyclic loading, investigating the...

Plate anchors could be a solution for mooring offshore renewable energy devices in sand. Previous work has focused on the capacity of plate anchors when loaded normal to the plate. However, for field applications the anchor is mostly likely to be installed vertically, but then rotated from a vertical to non-vertical orientation as the mooring line...

Plate anchors could be a solution for mooring offshore renewable energy devices in sand. Previous work has focused on the capacity of plate anchors when loaded normal to the plate. However, for field applications the anchor is mostly likely to be installed vertically, but then rotated from a vertical to non-vertical orientation as the mooring line...

Suction buckets are an increasingly considered foundation option for offshore wind turbines. Although the required suction can be predicted well using existing methods, uncertainty remains around some input parameters, because the effects of suction installation on the soil state are not understood in detail. This paper visualises the mechanisms go...

This paper considers an alternative approach for multi-planar loading and multi degree-of-freedom movement in geotechnical centrifuge model tests. The multi degree-of-freedom loading system allows for vertical load control on the vertical axis, and either displacement or load control on the two horizontal axes, whilst allowing rotation about these...

This paper attempts to categorise geotechnical field site characterisation tools in a hierarchical manner, as appropriate for the progression from initial surveys to detailed geotechnical design of specific infrastructure. In general, the hierarchy reflects more the sophistication, and hence cost, of the field tools, although small-scale tools deve...

Free Fall Penetrometer (FFP) tests provide an efficient way to determine the penetration resistance at shallow depths in sandy soils, and are being used increasingly in geotechnical, geomorphological and coastal engineering applications. A limitation of free fall penetrometers is the effect of their high velocity on the penetration resistance. This...

Skirted foundations are a potential foundation solution for a range of offshore structures, including hydrocarbon and renewable energy platforms and subsea structures. Offshore foundations can be subject to cyclic loading from environmental, installation, and operational events affecting the geotechnical response. A series of centrifuge tests have...

The accumulation procedure on contour diagrams of she