324 results found
Dominguez-Quintans C, Quinteros VS, Carraro JAH, et al., Quality assessment of a new in-mould slurry deposition method for triaxial specimen reconstitution of clean and silty sands, 7th International Symposium on Deformation Characteristics of Geomaterials - IS Glasgow 2019
An innovative specimen reconstitution technique for sandy and silty soils that simulates underwater deposition is presented and evaluated. The technique is an upgraded version for triaxial testing of the well-established slurry deposition method. This novel setup integrates the reconstitution mould and the mixing tube into a single unit to avoid transferring the sample from the mixing tube to the mould. This subtle, but critical, modification enables reconstitution of very loose specimens as sample transfer disturbance, which can be significant, is eliminated. The quality of specimens prepared by the new reconstitution method was assessed by experiments on a clean sand from the UK (Ham River sand) and a silty sand from Norway (Øysand). The method, as any slurry-based procedure, is capable of producing homogeneous specimens with high initial degree of saturation, even in the absence of back pressure. The procedure is shown to be suitable for sands with or without fines. Moreover, the new method is able to achieve a wide range of initial void ratios, from very loose to very dense, without imposing any particle crushing in the latter case.
Jardine R, Geotechnics, energy and climate change: The 56th Rankine Lecture, Géotechnique, ISSN: 0016-8505
Geotechnical Engineering has matured sufficiently to contribute to resolving some of society’s grand challenges. The 56th Rankine Lecture considered one of the most pressing global problems: maintaining vital energy supplies while also recognising, mitigating and reducing the climate consequences of fossil fuel consumption. This written version reports geotechnical research relating to these wide-ranging issues, considering paired topics within its three main parts and illustrating these with specific practical examples. Part 1 focuses on supporting offshore hydrocarbon production, considering advances in understanding and designing the driven piles that support most continental shelf platforms, before moving to the large underwater landslides that can affect deeper water developments. Part 2 describes investigations into the geotechnical impact of climate change in a permafrost region and a peatland study that contributes to alleviating flood risks exacerbated by climate change. Part 3 outlines research that is improving the economics of renewable offshore wind energy for multi-pile and monopile supported turbines. Integrating geology and rigorous analysis with advanced laboratory and field experiments is shown to be essential to resolving the complex geotechnical problems considered, as is careful full-scale checking and monitoring. Close cooperation with co-workers from industry and academia was central to the studies described and the contributions of many collaborators are emphasised. The concluding section identifies examples of significant questions from each of the six topic areas that remain to be resolved fully.
Carroll R, Carotenuto P, Dano C, et al., Field experiments at three sites to investigate the effects of age on steel piles driven in sand, Géotechnique, Pages: 1-21, ISSN: 0016-8505
Taborda D, Zdravkovic L, Potts DM, et al., Finite element modelling of laterally loaded piles in a dense marine sand at Dunkirk, Géotechnique, ISSN: 0016-8505
The paper presentsthedevelopment of a three-dimensional finite element model for pile tests in dense Dunkirk sand,conducted as part of the PISA project.The projectwas aimed at developing improved design methods for laterally loadedpiles, as used in offshore wind turbine foundations. The importance of the consistent and integrated interpretation of the soil data from laboratory and field investigations is particularly emphasised. The chosen constitutive model for sand is an enhanced version of the state parameter-based bounding surface plasticity model, which, crucially, is able to reproduce the dependency of sand behaviour on void ratio and stress level. The predictions from three-dimensional finite element analyses,performed before the field tests, show good agreement with the measured behaviour, proving the adequacy of the developed numerical model and the calibration process for the constitutive model. This numerical model directly facilitated the development of new soil reaction curves for use in Winkler-type design models for laterally loaded piles in natural marine sands.
Zdravkovic L, Taborda D, Potts D, et al., Finite element modelling of laterally loaded piles in a stiff glacial clay till at Cowden, Géotechnique, ISSN: 0016-8505
The PISA project was a combined field testing/numerical modelling study with the aim ofdevelopingimproved design procedures for large diameter piles subjected to lateral loading. This paper describes the development ofa three-dimensional finite elementmodel for the medium-scale pile tests that were conducted in Cowden tillas part of the PISA work.The paper places particular emphasis on the consistent interpretation of the soil data determined from the available field and laboratory information.An enhancedversion of the modified Cam clay model was employedin the numerical analyses, featuring a non-linear Hvorslevsurface, a generalised shape for the yield and plastic potential surfaces in the deviatoric planeand a non-linear formulation for the elastic shear modulus.Three-dimensional finite element analyses were performed prior to the field tests.Excellent agreement between the measured and simulated behaviourfora range of pile geometrieswas observed, demonstrating the accuracy of the numerical model and the adequacy of the calibration process for theconstitutive model.The developed numerical modelconfirmed the premise of the PISA design method that site-specific ground characterisation and advanced numerical modelling candirectly facilitate the development of additionalsoil reaction curves for use in new design models for laterally loaded piles in a stiff clay till.
Byrne B, McAdam RA, Burd HJ, et al., Monotonic laterally loaded pile testing in a stiff glacial clay till at Cowden, Géotechnique, ISSN: 0016-8505
This paper describes theresults obtained from a field testing campaign on laterally-loaded monopiles conducted at Cowden, UK, where the soil consists principally of aheavilyoverconsolidatedglacial till. These tests formed part of the PISA projecton the development of improved design methods for monopile foundations for offshore wind turbines. Results obtained for monotonic loading tests on piles of three different diameters (0.273m, 0.762m and 2.0m) are presented. The piles had length-to-diameter ratios (L/D) of between 3 and 10. Thetests includedthe application of monotonic loading incorporating periods of constant load to investigate creep effects,and investigations on the influence of loading rate. Data are presented on measured bending moments and inclinations induced in the piles. Inferred data on lateral displacements of the embedded section of the pilesare determined usingan optimisedstructural model. Thesefield data support the developmentof a new 1D modelling approach forthe design of monopile foundations for offshore wind turbines.They also form a unique database of field measurements in an overconsolidated clay, from lateral loading of piles at a vertical distance abovethe ground surface.
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.
Byrne BW, Burd HJ, Gavin K, et al., PISA: Recent Developments in Offshore Wind Turbine Monopile Design, 1st Vietnam Symposium on Advances in Offshore Engineering
Zdravkovic L, Jardine R, Taborda DMG, et al., Ground characterisation for PISA pile testing and analysis, Géotechnique, ISSN: 0016-8505
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 consolidated marine sand at Dunkirk, northern France. The paper presents the characterisationof the two sites, whichwas crucial to the design of the field experiments and advanced numerical modelling of the pile-soil interactions. The studies described, which had to be completed at an early stage of the PISA project, added new laboratory and field campaignsto historic investigations at both sites.Theyenabledanaccurate description ofsoilbehaviour from small strains to ultimate statesto be derived, allowing analyses to be undertaken that captured both the serviceability and limit statebehaviour of the test monopiles.
McAdam RA, Byrne BW, Houlsby GT, et al., Monotonic lateral loaded pile testing in a dense marine sand at Dunkirk, Géotechnique, ISSN: 0016-8505
Theresults obtained from a field testing campaignon laterally-loaded monopiles,conducted ata dense sand site inDunkirk, Northern Franceare described.These tests formed part of thePISA projecton the development of improved design methods for monopile foundations for offshore wind turbines. Results obtained frommonotonic loading tests on piles of three different diameters (0.273m, 0.762m and 2.0m) are presented. The piles had aspectratios (L/D) of between 3 and 10. Thetests consisted principally of the application of monotonic loads,incorporating periods of held constant load to investigate creep effects.The influence of loading ratewas also investigated. Data are presented on the overall load displacement behaviour of each of the test piles. Measured data on bending moments and inclinations induced in the pilesare also provided.Inferences are made forthe displacements in the embedded length of the piles. Thesefield data will support the development of a new 1D modelling approach forthe design of monopile foundations for offshore wind turbines.They also form a unique database of field measurements in a dense sand, from lateral loading of piles at a vertical distance abovethe ground surface.
Burd HJ, Beuckelaers WJAP, Byrne BW, et al., New data analysis methods for instrumented medium scale monopile field tests, Géotechnique, ISSN: 0016-8505
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, andin dense normally consolidated marine sand at Dunkirk, northern France. This paper describes the experimental set up for pile testing, with unique features of load-application mechanisms and built-in fibre optic strain gauges.New procedures are describedfor the interpretation of pile loading data, and specifically for providing precise interpretation of pile displacements.
Jardine RJ, Yang ZX, 2018, Joint research into the behaviour of driven piles, China–Europe Conference on Geotechnical Engineering, Pages: 961-972, ISSN: 1866-8755
© Springer Nature Switzerland AG 2018. 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, Vol: 68, Pages: 146-161, ISSN: 1751-7656
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 situand 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 250days.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, whichis 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 ofundisturbed ageingand cyclic loading onpreviously unfailedpiles driven in chalk. Potential predictive tools may now be tested against the reported field measurements.
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
Byrne BW, McAdam RA, Burd H, et al., 2017, 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"
Guo L, Cai Y, Jardine RJ, et al., 2017, 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.
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
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.
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.
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.
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.
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.
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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