Publications
396 results found
Byrne BW, McAdam RA, Burd H, et al., 2019, PISA: new design methods for offshore wind turbine monopiles, Proceedings of the Society for Underwater Technology Offshore Site Investigation and Geotechnics 8th International Conference on “Smarter Solutions for Future Offshore Developments"
Byrne BW, Burd HJ, Zdravkovic L, et al., 2019, PISA Design Methods for Offshore Wind Turbine Monopiles, Offshore Technology Conference
Liu TF, Quinteros VS, Jardine RJ, et al., 2019, A unified database of ring shear steel-interface tests on sandy-silty soils
Characterisation of shearing behaviour at soil-structure interfaces is critical in the analysis and design of a wide range of geotechnical structures. Large-displacement ring shear interface testing employing preshearing stages has been recognised as a robust approach for characterising interface resistance, particularly when large relative displacements are developed between soil and interface during either installation or operation. Such tests are applied in practical design approaches, for example in the ICP method for driven piles (Jardine et al., 2005). This paper presents a database of interface shearing tests involving sandy-silty soils that contain low percentage (≤ 20%) of non-plastic fines, integrating outcomes from research and project studies conducted at Imperial College London and the Norwegian Geotechnical Institute using Bishop Ring Shear apparatuses. The outcomes enable a critical review of the potential effects of a wide range of factors, including: soil physical index properties (grading, fines content); interface characteristics (material type, surface roughness); and applied testing conditions (shear rate and normal effective stress). Trends identified from the datasets are integrated with previously reported studies to indicate the interface shear strength parameters that may be adopted for preliminary design with non-plastic sandy-silty soils on the basis of simple index tests.
Ciantia MO, O’Sullivan C, Jardine RJ, 2019, Pile penetration in crushable soils: Insights from micromechanical modelling, Pages: 298-317
A 3D discrete element model (DEM) was used to simulate calibration chamber experiments of a cone shaped tip pile penetrating into crushable granular media. Both monotonic and cyclic jacking are considered. Particle crushing is simulated by employing a rigorous breakage criterion applied to elasto-brittle spheres. Particle scaling is used to limit the number of particles considered and it is shown that, above a threshold limit, the penetration curves become scale independent, provided a scalable crushing model is used. The particle crushing model parameters were calibrated by matching triaxial and one-dimensional compression tests. The DEM model could capture the stress measurements made around a model pile during and after its penetration into sand relatively well. The particle-scale mechanics that underlie the observed macroscopic responses are analysed, placing emphasis on the distribution of crushing events around the pile tip and distributions of particle stresses and forces around the shaft. Comparing simulations made with crushable and uncrushable grains, and analysing the particle displacement fields, provides insights into one of the mechanisms proposed for the well-known, yet not fully understood, marked shaft capacity increases developed over time by piles driven in sands.
Byrne BW, Burd HJ, Gavin K, et al., 2019, PISA: Recent developments in offshore wind turbine monopile design, 1st Vietnam Symposium on Advances in Offshore Engineering, Publisher: Springer
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 key research elements completed. The paper concludes with a brief description of the anticipated impact of the work and describes initiatives that have followed since.
Buckley R, Jardine R, Kontoe S, et al., 2018, Effective stress regime around a jacked steel pile during installation, ageing and load testing in chalk, Canadian Geotechnical Journal, Vol: 55, Pages: 1577-1591, ISSN: 0008-3674
This paper reports experiments with 102 mm diameter closed-ended instrumented Imperial College piles (ICPs) jacked into low- to medium-density chalk at a well-characterized UK test site. The “ICP” instruments allowed the effective stress regime surrounding the pile shaft to be tracked during pile installation, equalization periods of up to 2.5 months, and load testing under static tension and one-way axial cyclic loading. Installation resistances are shown to be dominated by the pile tip loads. Low installation shaft stresses and radial effective stresses were measured that correlated with local cone penetration test (CPT) tip resistances. Marked shaft total stress reductions and steep stress gradients are demonstrated in the vicinity of the pile tip. The local interface shaft effective stress paths developed during static and cyclic loading displayed trends that resemble those seen in comparable tests in sands. Shaft failure followed the Coulomb law and constrained interface dilation was apparent as the pile experienced drained loading to failure, although with a lesser degree of radial expansion than with sands. Radial effective stresses were also found to fall with time after installation, leading to reductions in shaft capacity as proven by subsequent static tension testing. The jacked, closed-ended, piles’ ageing trends contrast sharply with those found with open piles driven at the same site, indicating that ageing is affected by pile tip geometry and (or) installation method.
Jardine R, Buckley R, Kontoe S, et al., 2018, Behaviour of piles driven in chalk, Chalk 2018, Publisher: ICE Publishing
Driving resistance is difficult to predict in chalk strata, with both pile free-fall self-weight ‘runs’ and refusals being reported. Axial capacity is also highly uncertain after driving. This paper reviews recent research that has explored these topics. Programmes of onshore tests and novel, high-value offshore, experiments involving static, dynamic and cyclic loading are described. The key findings form the basis of the Chalk ICP-18 approach for estimating the driving resistance and axial capacity of piles driven in low-to medium-density chalk. The new approach is presented and the highly significant impact of set-up after driving is emphasised. It is shown that Chalk ICP-18 overcomes the main limitations of the industry’s current design guidelines by addressing the underlying physical mechanisms. While further tests are required to enlarge the available test database, the new approach is able to provide better predictions for tests available from suitably characterised sites. A new Joint Industry Project is outlined that extends the research to cover further axial, lateral, static and cyclic loading cases.
Jardine RJ, Yang ZX, 2018, Joint research into the behaviour of driven piles, China–Europe Conference on Geotechnical Engineering, Publisher: Springer, Pages: 961-972, ISSN: 1866-8755
Large driven piles are used widely in both onshore and offshore construction. Predicting their limiting capacities and load-displacement behaviour under a range of static and cyclic, axial, lateral and moment loading conditions is critical to many engineering applications. This paper reviews relevant recent joint research by groups at Imperial College London (ICL) and Zhejiang University China (ZJU). Two tracks of enquiry are outlined: (i) assembling and analysing a major and open database of high quality load tests conducted on industrial scale piles at well characterised sites; and (ii) modelling the effective stress regime developed around piles driven in sands. Both avenues of research are vital to enabling scientifically well-founded and yet industrially credible improvements to practical pile design methods. The scope of future joint research is also outlined.
Altuhafi F, Jardine RJ, Georgiannou VN, et al., 2018, Effects of particle breakage and stress reversal on the behaviour of sand around displacement piles, Géotechnique, Vol: 68, Pages: 546-555, ISSN: 0016-8505
The stresses acting in the soil mass adjacent to the tips and shafts of displacement piles during installation and loading in medium-dense sand have been simulated in triaxial stress path tests on Fontainebleau NE34 sand. The very high normal and shear stresses recorded in calibration chamber model pile tests involving the same sand were first reproduced in high-pressure triaxial tests, so changing the sand's physical properties markedly. The behaviour of the mutated sand was then examined in second, lower stress, stages of the same experiments, demonstrating important changes in the sand's mechanical behaviour, including a significant increase in the angle of shearing resistance and a relocation of the sand's critical state line in the e−log p′ plane. Image analysis confirmed changes in the sand particles' micro-characteristics. The particles' size distributions altered and grain surface roughness increased markedly, while particle sphericity was only mildly affected. Similar surface roughness changes were noted between the particulate characteristics of specimens examined after the triaxial laboratory tests and those sampled from around the shafts of the calibration chamber model piles.
Buckley RM, Jardine R, Kontoe S, et al., 2018, Ageing and cyclic behaviour of axially loaded piles driven in chalk, Geotechnique: international journal of soil mechanics, Vol: 68, Pages: 146-161, ISSN: 0016-8505
This paper reports a programme of static and cyclic loading tests on seven open steel tubes driven in low- to medium-density chalk at a well-characterised test site, describing their response to driving, ageing in situ and loading under both static and cyclic conditions. Back analysis of dynamic monitoring identifies the distributions of notably low shaft resistances that develop during installation, showing that these depend strongly on the relative pile tip depth (h/R). The shaft capacities available to ‘virgin’ piles are shown to increase markedly after driving, following a hyperbolic trend that led to a fivefold gain after 250 days. Pre-failed piles do not follow the same trend when re-tested. Pile exhumation confirmed that driving remoulded the chalk, creating a puttified zone around the shaft. Excess pore water pressure dissipation, which is likely to have been rapid during and after driving, led to markedly lower water contents close to the shaft. Axial cyclic testing conducted around 250 days after driving led to a range of responses, from manifesting stable behaviour over 1000 cycles to failing after low numbers of cycles after developing sharp losses of static capacity. The dependence of permanent displacement on the cyclic loading parameters is explored and characterised. The experiments provide the first systematic study of which the authors are aware into the effects of undisturbed ageing and cyclic loading on previously unfailed piles driven in chalk. Potential predictive tools may now be tested against the reported field measurements.
Guo L, Cai Y, Jardine RJ, et al., 2018, Undrained behaviour of intact soft clay under cyclic paths that match vehicle loading conditions, Canadian Geotechnical Journal, Vol: 55, Pages: 90-106, ISSN: 1208-6010
Vehicle traffic loading appears to contribute significantly to long term settlement beneath highways, airport runways and metro lines in China. Wheel loading imposes cycles in both the magnitude and direction of the principal stresses acting on the soils beneath pavement or rail-track structures. Conventional cyclic triaxial testing, which is not capable of imposing such stress paths may underestimate how heavy traffic loading affects any underlying soft clay layers. Hollow cylinder apparatus (HCA) can simulate such traffic loading stress paths more accurately, including rotation of the principal stress directions. This paper presents a systematic experimental study of cyclic HCA (CHCA) tests on K0-consolidated saturated soft clay involving cyclic variations in both vertical and torsional shear stresses, along with a parallel programme of cyclic triaxial (CT) tests, considering the undrained response of saturated samples of intact soft clay. It is shown that when applied above certain critical cyclic stress ratios, principal stress rotation accelerates excess pore water pressure and permanent strain development. Corresponding changes are also seen in the resilient modulus and damping ratio trends. The discrepancies between the behaviour of CHCA and equivalent cyclic triaxial tests grow as the cyclic stress ratios increase.
Carotenuto P, Meyer VM, Stem PJ, et al., 2018, Installation and axial capacity of the Sheringham Shoal offshore wind farm monopiles - A case history, Pages: 117-122
The Sheringham Shoal offshore wind farm is located in the North Sea, approximately 20 km north of the Norfolk coast. At this location, Quaternary sediments of the Swarte Bank, Egmond Ground, Bolders Bank and Botney Cut Formations are found directly on top of the Cretaceous chalk. The chalk is thought to be similar to the high porosity upper Campanian (84-74 million years) chalks found in Norfolk and to be comprised of the Paramoudra and Beeston Chalks. Monopile foundations we re installed at the Sheringham Shoal Offshore Wind Farm in Summer 2011. Low driving resistances were encountered during installation of some of the monopiles, particularly in areas with shallow subcropping chalk. In some instances pile 'run-out' occurred (i.e. continued penetration under the weight of the pile and hammer alone). This paper presents a case history of the available information, including an overview of the geological and geotechnical conditions at the site together with the pile driving records. Results from back-analysis of the driving records to assess the Soil Resistance to Driving (SRD) are presented and provide possible explanations for the observed pile driving responses. The long-term axial capacity of the monopiles is discussed. The properties of the chalk are based on a review of the available literature and site-specific laboratory and field tests.
Doughty LJ, Buckley RM, Jardine RJ, 2018, Investigating the effect of ageing on the behaviour of chalk putty, Pages: 695-701
Substantial recent investment in offshore wind energy developments and other foundation projects in chalk dominated locations has created an urgent need for a better understanding of how driven piles behave in this variable and unpredictable material. Pile driving in chalk is known to create a remoulded zone of chalk 'putty' around the pile which mobilises low shaft resistance on installation; however, shaft capacity has been reported to increase over time through a process referred to as pile 'set-up' or ageing. Although field evidence of ageing has been reported, the potential role of the chalk putty's behaviour in the ageing process is not well understood. This is partly due to a lack of published laboratory testing on chalk samples which have been conditioned to represent the conditions adjacent to a pile after driving. This paper presents selected results from a suite of laboratory tests undertaken at Imperial College London. Specimens from intact Maas-trichtian Chalk were reduced to putty by Proctor compaction applied at natural water content and subjected to either drained or undrained ageing for periods of between 0 and 28 days. Consolidated undrained triaxial tests, with pore water pressure measurement and local strain measurements, were undertaken on the aged specimens, along with thixotropy testing on unconsolidated samples employing a fall cone. An interpretation of the test results within a critical state framework combined with a conceptual small strain stiffness model is presented. The ageing of chalk putty is shown to encompass a combination of consolidation, thixotropic hardening and re-cementation, with small increases in undrained shear strength seen due to thixotropic hardening, and larger increases in strength evident following consolidation.
, 2018, Author Index, Chalk 2018 Engineering in Chalk, Publisher: ICE Publishing
Burd HJ, Byrne BW, McAdam R, et al., 2017, Foundation Design of Offshore Wind Structures, TC209 Workshop on Foundation Design of Offshore Wind Structures, 19th International Conference on Soil Mechanics and Geotechnical Engineering
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 a new one-dimensional (1D) design model. The resulting 1D design model is based on the same basic assumptions and principles that underlie the current p-y method, but the method is extended to include additional components of soil reaction acting on the pile, and enhanced to provide an improved representation of the soil-pile interaction behaviour. Mathematical functions – termed ‘soil reaction curves’ – are employed to represent the individual soil reaction components in the 1D design model. Values of the parameters needed to specify the soil reaction curves for a particular design scenario are determined using a set of 3D finite element calibration analyses. The PISA research was focused on two particular soil types (overconsolidated clay till and dense sand) that commonly occur in north European coastal waters. The current paper provides an overview of the field testing and 3D modelling aspects of the project, and then focuses on the development, calibration and application of the PISA design approach for monopiles in dense sand.
Buckley R, Jardine R, Kontoe S, et al., 2017, Field investigations into the axial loading response of displacement piles in chalk, Proceedings of the 8th International Conference on Offshore Site Investigation and Geotechnics: Smarter Solutions for Future Offshore Developments, Publisher: Th e Society for Underwater Technology, Pages: 1178-1185
Buckley R, Kontoe S, Jardine R, et al., 2017, Common pitfalls of pile driving resistance analysis - A case study of the Wikinger offshore windfarm, 978-0-906940-57-0, Publisher: Society for Underwater Technology, Pages: 1246-1253
Brosse AM, Jardine RJ, Nishimura S, 2017, The undrained shear strength anisotropy of four Jurassic to Eocene stiff clays, Géotechnique, Vol: 67, Pages: 653-671, ISSN: 0016-8505
The shear strength of heavily overconsolidated, stiff-to-hard plastic clays is crucial to their stability and also influential on the ground movements they develop in many geotechnical engineering applications. This paper considers the shear strength anisotropy of the London, Gault, Kimmeridge and Oxford clays through advanced hollow cylinder experiments on multiple high-quality samples taken at similar depths from inland sites where the geotechnical profiles have been established by comprehensive laboratory and in situ testing. Suites of undrained tests are reported, which loaded specimens from their in situ stress states to reach ultimate failure at pre-defined final major principal stress axis orientations defined in the vertical plane, while also controlling or monitoring the intermediate principal stress ratio, b. Both stress path and simple shear tests were undertaken with the hollow cylinder apparatus, which offers key advantages over conventional simple shear equipment. The interpretation reveals patterns of marked shear strength anisotropy that impact significantly on numerous geotechnical engineering applications.
Liu T, Aghakouchak A, Taborda DMG, et al., 2017, Advanced laboratory characterization of a fine marine sand from Dunkirk, France, 19th International Conference on Soil Mechanics and Geotechnical Engineering, Publisher: ICSMGE, Pages: 439-442
Dense fine marine sand is encountered at the Dunkirk ZIP Les Huttes test site located in northern France that has beenemployed extensively for research into pile behaviour. Laboratory testing of the sand is required to fully characterise site conditionsand determine parameter inputs for analysing the field pile experiments. This paper summarises some of the comprehensivelaboratory testing programmes undertaken to investigate the sand’s mechanical behaviour, including stress-strain relationships,stiffness and strength anisotropy, cyclic behaviour, and interface shear properties. The paper first reviews the site’s geotechnicalconditions and their potential variations over time. The stringent laboratory requirements that are necessary for the accuratemeasurement of shear stiffness, strength, and creep strains are then discussed, before presenting illustrative results regarding thesand’s small strain stiffness and time-dependent behaviour. The importance of reproducing site conditions and stress states are alsoaddressed in relation to integrating the laboratory research with field observations and analyses of both recent and historical pilingexperiments at the Dunkirk test site.
Brosse A, Hosseini Kamal R, Jardine RJ, et al., 2017, The shear stiffness characteristics of four Eocene-to-Jurassic UK stiff clays, Géotechnique, Vol: 67, Pages: 242-259, ISSN: 0016-8505
<jats:p> A large proportion of the southern UK is underlain by stiff clays. Improving their geotechnical characterisation is important for many current and future infrastructure projects. This paper presents an integrated study of the complex stiffness behaviour of four key medium-plasticity, highly overconsolidated strata: the Gault, Kimmeridge, Oxford and London clays. The latter were deposited between the Jurassic and the Eocene under broadly similar marine conditions. Coordinated programmes of advanced static and dynamic laboratory measurements have been undertaken on high-quality samples, concentrating on samples taken from similar depths at inland sites and including triaxial and hollow cylinder stress path experiments employing high-resolution local strain, multi-axial bender element and resonant column techniques. A new approach was employed to interpret the hollow cylinder experiments and the laboratory measurements are examined in combination with independent field shear wave data. The clays' stiffness characteristics are shown to be markedly anisotropic, pressure dependent and highly non-linear. Synthesis allows key conclusions to be drawn regarding: the relative reliability of alternative measurement approaches; the potential spread of stiffness behaviours between the clays; and whether the clays' varying geological ages and burial depths have any systematic influence on their stiffness characteristics. The results have important geotechnical engineering implications. </jats:p>
Cai YQ, Guo L, Jardine RJ, et al., 2016, Stress–strain response of soft clay to traffic loading, Géotechnique, Vol: 67, Pages: 446-451, ISSN: 0016-8505
Approximately 25% of China's 120 000 km of expressway, as well as many new metro lines and airports, rest on soft clay deposits. However, service settlements are proving larger than expected, especially in southeast China. This note describes laboratory experiments on K0-consolidated intact samples of soft clay taken near Wenzhou, south-east China, that explore whether cyclic traffic wheel loading contributes significantly to the observed settlement trends. Cyclic triaxial (CT) tests are reported together with cyclic hollow cylinder (CHCA) experiments that imposed cardioid-shaped 2τzθ − (Δσz − Δσθ) stress paths. Cyclic principal stress axis rotation is shown to have an important influence on vertical straining. Once a certain threshold has been exceeded, the resilient and permanent strains developed in the CHCA tests become progressively larger than their counterparts in CT tests conducted at the same vertical cyclic stress ratio, with trends that diverge progressively as vertical cyclic stress ratio increases. Critical cyclic stress ratios can be defined that divide the response into (a) stable, (b) metastable and (c) unstable cyclic ranges. The novel experimental approach and high-quality data reported should aid practitioners and modellers in developing new analyses to address this economically significant geotechnical problem.
Brosse AM, Jardine RJ, Nishimura S, 2016, Undrained stiffness anisotropy from Hollow Cylinder experiments on four Eocene-to-Jurassic UK stiff clays, Canadian Geotechnical Journal, Vol: 54, Pages: 313-332, ISSN: 1208-6010
The paper describes the anisotropic undrained stiffness behaviour of four medium-plasticity heavily overconsolidated UK stiff marine clays as revealed through Hollow Cylinder testing. The experiments contributed to two broader studies on stiff-to-hard London, Gault, Kimmeridge, and Oxford clay strata. They involved static and dynamic testing of multiple high quality natural specimens sampled at similar depths from inland sites. This paper explores the directional dependency of the clays’ highly non-linear undrained stiffness characteristics. New data-analysis approaches are outlined that allow the stiffnesses associated with one dimensional vertical, horizontal or pure horizontal shear modes to be isolated in complex undrained stress paths. In the presented experiments, loading progressed from in-situ stresses to reach ultimate failure at a range of final major principal stress orientation angles α (defined in the vertical plane) while keeping fixed values of the intermediate principal stress ratio, b. The tests reveal strong undrained stiffness anisotropy that can impact significantly on the prediction and understanding of ground deformation patterns in numerous geotechnical engineering applications.
Jardine RJ, Yang ZX, Guo WB, 2016, Design method reliability assessment from an extended database of axial load tests on piles driven in sand, Canadian Geotechnical Journal, Vol: 54, Pages: 59-74, ISSN: 1208-6010
The accurate prediction of axial capacity remains a challenging task for piles driven in sands. Rigorous database studies have become key tools for assessing the efficacy of design methods. This paper employs the 117 high-quality entries in the recently developed Zhejiang University – Imperial College London (ZJU–ICL) database to check for potential biases between nine prediction procedures, considering a range of factors. The analysis highlights the critical importance of addressing age after driving, open and closed ends, tension versus compression, and concrete compared to steel. It also shows the hierarchy of reliability parameters associated with the alternative approaches. The “full” Imperial College pile (ICP) approach and The University of Western Australia (UWA) approaches are found to have significant advantages in eliminating potential biases. It is also argued that design load and resistance or safety factors should be varied to match the design and site investigation methods applied, as well as the loading uncertainty and degree of load cycling, which often vary between applications. Noting that predictions for base capacities Qb are inherently less reliable than for shaft Qs, especially in rapidly varying ground profiles, credible lower bound parameters (cone resistance, qc) are recommended for Qb assessment. It is also recommended that the potential effects of cycling be addressed carefully in cases that involve substantial environmental loading.
Jardine RJ, Brosse A, Coop MR, et al., 2015, Shear strength and stiffness anisotropy of geologically aged stiff clays., International Symposium on Deformation Behaviour of Geomaterials, Publisher: IOS Press, Pages: 156-191
This paper considers the deformation behaviour of four geologically aged, medium-plasticity, heavily overconsolidated stiff clays that affect a broad swathe of infrastructure projects in the SE of the United Kingdom. Static triaxial and hollow cylinder stress path experiments on high quality samples are examined along with dynamic multi-axial bender element and resonant-column measurements. Patterns of undrained shear strength anisotropy are revealed that are governed by the clays' meso and micro-structures. The clays are brittle in shear and their stiffness characteristics are shown to be markedly anisotropic, highly non-linear and pressure dependent. The results obtained have many implications for practical geotechnical engineering.
Aghakouchakn A, Sim WW, Jardine RJ, 2015, Stress-path laboratory tests to characterise the cyclic behaviour of piles driven in sands, Soils and Foundations, Vol: 55, Pages: 917-928, ISSN: 0038-0806
Recent publications have emphasised the importance of addressing cyclic behaviour when designing piled foundations. Laboratory tests may be conducted to provide site-specific cyclic soil characteristics, but questions arise concerning: (i) how to take into account the pile installation process and (ii) how to apply the results to assess pile capacity and deformation responses under cyclic loads. This paper describes an investigation into the cyclic behaviour of Dunkerque and NE34 Fontainebleau sands, performed to support and to help analyse field-scale and model pile cyclic loading tests on the same soils. Forty computer-controlled, locally instrumented, cyclic and static triaxial tests were performed, following testing schemes that were developed to reflect the conditions adjacent to the pile shafts. Assessments were made of how the cyclic variations in stress imposed during installation and the period allowing for the two types of sand to creep following such ‘installation’ effects, affect the response to subsequent cycling. Constant-volume cyclic tests, involving up to 4500 cycles, were imposed from alternative sets of initial conditions that revealed the relationships among the cyclic deviatoric amplitude, the changes in mean effective stress and the number of cycles as well as the permanent strain accumulation and the cyclic stiffness characteristics. Monotonic compression and extension tests are also presented for both sands to help frame their strength, stiffness and critical state properties. A synthesis with previously obtained cyclic pile test trends confirms the practical applicability of the results obtained.
Byrne BW, McAdam RA, Burd HJ, et al., 2015, Field testing of large diameter piles under lateralloading for offshore wind applications, 16th European Conference on Soil Mechanics and Geotechnical Engineering, Publisher: ICE Publishing
Offshore wind power in the UK, and around Europe, has the potential to deliver significant quantities of renewable energy. The foundation is a critical element in the design. The most common foundation design is a single large diameter pile, termed a monopile. Pile diameters of between 5m and 6m are routinely used, with diameters up to 10m or more, being considered for future designs. Questions have been raised as to whether current design methods for lateral loading are relevant to these very large diameter piles. To explore this problem a joint industry project, PISA, co-ordinated by DONG Energy and the Carbon Trust, has been established. The aim of the project is to develop a new design framework for laterally loaded piles based on new theoretical developments, numerical modelling and bench-marked against a suite of large scale field pile tests. The project began in August 2013 and is scheduled to complete during 2015. This paper briefly outlines the project, focusing on the design of the field testing. The testing involves three sizes of pile, from 0.27m in diameter through to 2.0m in diameter. Two sites will be used; a stiff clay site and a dense sand site. Tests will include monotonic loading and cyclic loading. A suite of site investigation will be carried out to aid interpretation of the field tests, and will involve in-situ testing, standard laboratory testing and more advanced laboratory testing.
Rimoy S, Silva M, Jardine R, et al., 2015, Field and model investigations into the influence of age on axial capacity of displacement piles in silica sands, Geotechnique, Vol: 65, Pages: 576-589, ISSN: 0016-8505
The axial capacities of piles driven in silica sands are known to grow over the months that follow installation, long after all driving-induced pore pressures have dissipated. However, there is uncertainty over the processes that govern the observed set-up and how they may vary from case to case. This paper evaluates three hypotheses against evidence from updated field test databases and laboratory investigations with highly instrumented and pressurised model piles. Potential influential factors are considered including: pile and sand particle sizes, installation style, access to free water, test conditions and external stress change cycles. Laboratory local stress measurements support the hypothesis that moderation, over time, of the extreme stress distributions developed during installation is a key contributor to capacity growth, while field tests confirm the action of enhanced dilation near the shaft. However, field and laboratory piles show paradoxically different ageing trends. The paper proposes that the fractured but compacted sand shear zone that forms around pile shafts during installation leads to set-up being far more significant with large field driven piles than in model tests.
Gavin K, Jardine RJ, Karlsrud K, et al., 2015, The Effects of Pile Ageing on the Shaft Capacity of Offshore Piles in Sand., International Symposium Frontiers in Offshore Geotechnics, Publisher: CRC Press, Pages: 129-151
A number of field studies suggest that the axial capacity of driven piles in sand increases withtime. Field test programmes were performed by a number of research groups to examine this aspect of pilebehaviour. The paper presents a summary of the findings from these experiments. It also reviews laboratorypile and element testing performed to provide further insights into the mechanisms controlling pile ageing.
Zwanenburg C, Jardine RJ, 2015, Laboratory, in situ and full-scale load tests to assess flood embankment stability on peat, Geotechnique: international journal of soil mechanics, Vol: 65, Pages: 309-326, ISSN: 0016-8505
The low submerged unit weights of peats usually lead to low effective self-weight stresses, stiffnesses and undrained shear strengths. These features, in combination with high compressibility, a propensity to creep and the uncertain effects of fibrous inclusions, make foundation stability hard to assess reliably. It is usual to apply high safety, or strong material reduction, factors in foundation design. However, over-conservatism can lead to undesirable environmental and financial costs. This paper describes full-scale field tests conducted on peat, with and without pre-loading, at Uitdam on the borders of Lake Markermeer, north of Amsterdam. The experiments investigated the peat layers' consolidation behaviour and their response under loading, including full shear failure. Noting the complex final test geometries and the large displacements developed, simple numerical analyses were undertaken to help interpret the failures within a Tresca and ‘consolidated undrained shear strength' framework. The trials that included modest pre-loading developed large vertical consolidation strains (up to 35%) and significant bearing capacity improvements. The field experiments provide a rich resource for testing advanced numerical techniques. They also allowed a range of practical characterisation techniques to be assessed and calibrated for flood dyke applications.
Yang ZX, Jardine RJ, Zhu BT, et al., 2015, Closure to "Stresses Developed around Displacement Piles Penetration in Sand" by Z. X. Yang, R. J. Jardine, B. T. Zhu, and S. Rimoy, JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING, Vol: 141, ISSN: 1090-0241
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