371 results found
Pan K, Liu XM, Yang ZX, et al., 2022, Closure to “Undrained Cyclic Response of K0-Consolidated Stiff Cretaceous Clay under Wheel Loading Conditions” by K. Pan, X. M. Liu, Z. X. Yang, R. J. Jardine, and Y. Q. Cai, Journal of Geotechnical and Geoenvironmental Engineering, Vol: 148, ISSN: 1090-0241
Lehane BM, Liu Z, Bittar EJ, et al., 2022, CPT-Based Axial Capacity Design Method for Driven Piles in Clay, Journal of Geotechnical and Geoenvironmental Engineering, Vol: 148, ISSN: 1090-0241
There are clear advantages in the establishment of reliable, direct cone penetration test (CPT) based methods for assessment of the axial capacity of driven piles. These advantages motivated the formation of a joint industry project (JIP) under the management of the Norwegian Geotechnical Institute (NGI), which initially led to the creation of a unified database of high-quality pile load tests in sand and clay. The unified database has the consensus approval of representatives of the profession and personnel in multiple companies from the offshore energy sector. This paper presents a component of the research from the second phase of the JIP, which had the objective of developing a new CPT-based method for driven piles in clay to unify several CPT-based methods that are in use today. First, a rational basis for the CPT-based formulation is described, using trends from instrumented pile tests; the description facilitates an understanding of the approach and illustrates its empirical nature and limitations. The unified database was used to calibrate the formulation and it led to good predictions for an independent database of pile load tests and for measured distributions of shaft friction.
Ushev ER, Jardine RJ, 2022, The mechanical behaviour of Bolders Bank till, Canadian Geotechnical Journal, ISSN: 0008-3674
Advanced sampling and testing techniques are applied to assess the mechanical behaviour of a stiff, silt-and-clay dominate, stony, low plasticity UK till whose genesis and post-depositional history imparted complex profiles of yielding pressures and shear strengths that differ considerably from those of K0 consolidated waterborne sediments. It is shown that the till reaches the limits of its elastic behaviour and undergoes Y1 yielding at very small strains, after which stiffness is non-linear. Tests reach stable critical-state failures at strains exceeding 25%. The Y1 yield surface is kinematic and, once engaged, travels with the effective stress path, as does a second Y2 surface. Stiffnesses vary with mean effective stress raised to fractional exponent ≈0.5. The till displays far more marked sample-size dependency and anisotropy in stiffness than in shear strength. It also shows significantly strain-rate dependent behaviour and displays an isotach response. The main features of the till’s shear strength and dilatancy behaviour can be synthesised within a critical state based interpretive framework that brings field and in-situ testing outcomes together with laboratory experiments conducted over a wide range of stress levels and over-consolidation ratios, considering both natural and reconstituted specimens.
Liu T, Ahmadi-Naghadeh R, Vinck K, et al., 2022, An experimental investigation into the behaviour of de-structured chalk under cyclic loading, Géotechnique, ISSN: 0016-8505
Low-to-medium density chalk can be de-structured to soft putty by high-pressure compression, dynamic impact or large-strain repetitive shearing. These process all occur during pile driving and affect subsequent static and cyclic load-carrying capacities. This paper reports undrained triaxial experiments on de-structured chalk, which shows distinctly time-dependent behaviour as well as highly non-linear stiffness, well-defined phase transformation (PT) and stable ultimate critical states under monotonic loading. Its response to high-level undrained cyclic loading invokes both contractive and dilative phases that lead to pore pressure build-up, leftward effective stress path drift, permanent strain accumulation, cyclic stiffness losses and increasing damping ratios that resemble those of silts. These outcomes are relatively insensitive to consolidation pressures and are distinctly different to those of the parent intact chalk. The maximum number of cycles that can be sustained under given combinations of mean and cyclic stresses are expressed in an interactive stress diagram which also identifies conditions under which cycling has no deleterious effect. Empirical correlations are proposed to predict the number of cycles to failure and mean effective stress drift trends under the most critical cyclic conditions. Specimens that survive long-term cycling present higher post-cyclic stiffnesses and shear strengths than equivalent ‘virgin’ specimens.
Vinck K, Liu T, Jardine RJ, et al., 2022, Advanced in-situ and laboratory characterisation of the ALPACA chalk research site, Géotechnique, ISSN: 0016-8505
Low-to-medium density chalk at St Nicholas at Wade, UK, is characterised by intensive testing to inform the interpretation of axial and lateral tests on driven piles. The chalk de-structures when taken to large strains, especially under dynamic loading, leading to remarkably high pore pressures beneath penetrating CPT and driven pile tips, weak putty annuli around their shafts and degraded responses in full-displacement pressuremeter tests. Laboratory tests on carefully formed specimens explore the chalk's unstable structure and markedly time and rate-dependent mechanical behaviour. A clear hierarchy is found between profiles of peak strength with depth of Brazilian tension (BT), drained and undrained triaxial and direct simple shear (DSS) tests conducted from in-situ stress conditions. Highly instrumented triaxial tests reveal the chalk's unusual effective stress paths, markedly brittle failure behaviour from small strains and the effects of consolidating to higher than in-situ stresses. The chalk's mainly sub-vertical jointing and micro-fissuring leads to properties depending on specimen scale, with in-situ mass stiffnesses falling significantly below high-quality laboratory measurements and vertical Young's moduli exceeding horizontal stiffnesses. While compressive strength and stiffness appear relatively insensitive to effective stress levels, consolidation to higher pressures closes micro-fissures, increases stiffness and reduces anisotropy.
Ahmadi-Naghadeh R, Liu T, Vinck K, et al., 2022, A laboratory characterisation of the response of intact chalk to cyclic loading, Géotechnique, ISSN: 0016-8505
This paper reports the cyclic behaviour of chalk, which has yet to be studied comprehensively. Multiple undrained high-resolution cyclic triaxial experiments on low-to-medium density intact chalk, along with index and monotonic reference tests, define the conditions under which either thousands of cycles could be applied without any deleterious effect, or failure can be provoked under specified numbers of cycles. Intact chalk's response is shown to differ from that of most saturated soils tested under comparable conditions. While chalk can be reduced to putty by severe two-way displacement-controlled cycling, its behaviour proved stable and nearly linear visco-elastic over much of the one-way, stress controlled, loading space examined, with stiffness improving over thousands of cycles, without loss of undrained shear strength. However, in cases where cyclic failure occurred, the specimens showed little sign of cyclic damage before cracking and movements on discontinuities lead to sharp pore pressure reductions, non-uniform displacements and the onset of brittle collapse. Chalk's behaviour resembles the fatigue response of metals, concretes and rocks, where micro-shearing or cracking initiates on imperfections that generate stress concentrations; the experiments identify the key features that must be captured in any representative cyclic loading model.
Rimoy S, Silva M, Jardine RJ, 2022, Stability and load-displacement behaviour of axially cyclic loaded displacement piles in sands, Canadian Geotechnical Journal, ISSN: 0008-3674
Uncertainties regarding the axial cyclic behaviour of piles driven in sands led to an extended programme of calibration chamber instrumented pile experiments. Broad trends are identified and interpreted with reference to normalised cyclic loading parameters Qcyclic/QT, Qmean/QT and N. Cyclic damage is shown to be related to changes in the radial effective stress regime close to the shaft. While stable loading leads to little or no change as cycling continues in the sand masses’ effective stress regime, high-level cyclic loading can affect stresses far out into the sand mass. The test systems’ chamber-to-pile diameter ratio has a significant impact on outcomes. Piles installed in loose, fine, sand are far more susceptible to cyclic loading than in denser, coarser sand. Little or no change in pile stiffness was seen in tests that remained within the stable cyclic region, even over 10,000 or more cycles. Unstable tests lost their stiffness rapidly and metastable cases showed intermediate behaviours. The permanent deflections developed under cycling depend on the combined influence of Qcyclic/QT, Qmean/QT and N. While model tests provide many valuable insights into the behaviour of piles driven in sand, they are unable to capture some key features observed in the field.
Ushev E, Jardine R, 2022, The behaviour of Bolders Bank glacial till under undrained cyclic loading, Géotechnique, Vol: 72, Pages: 1-19, ISSN: 0016-8505
Analysis of foundation behaviour under repeated loading can be important to the design of offshore facilities, towers, bridges, wind turbines and other structures. Although detailed guidance is available on how some geomaterials behave under cycling, few such studies have been reported on the glacial formations that are widespread across parts of northern Europe and under the North and Baltic Seas. This paper presents a cyclic laboratory investigation involving block samples of Bolders Bank till, which is one of the most extensive North Sea glacial formations. Static and cyclic triaxial tests are reported on nominally identical, low-plasticity, high-overconsolidation-ratio specimens from Cowden, near Hull in the UK. Twenty-three cyclic tests are reported on specimens that were re-consolidated to K<jats:sub>0</jats:sub> stresses before experiencing up to 3500 undrained cycles involving a range of mean and cyclic shear stress combinations. The impacts of cycling on effective stress paths and strain development, cyclic stiffness and damping ratios are reported and interpreted with respect to parallel index, oedometer and monotonic triaxial compression and extension tests. Stable, metastable and unstable patterns of behaviour are identified, along with different cyclic failure modes. The styles of cyclic response are related to the till's static yielding behaviour. While the till can only manifest quasi-elastic behaviour within a very small (Y<jats:sub>1</jats:sub>) kinematic yield surface (KYS), a larger second (Y<jats:sub>2</jats:sub>) KYS is identified within which repeated loading leads to a non-linear yet stable response, with negligible mean effective stress drifts or stiffness degradation with low and stabilising strain accumulation rates. Cyclic paths that engage and relocate the Y<jats:sub>2</jats:sub> surface lead to greater permanent strains, mean effective stress drifts and stiffness decays that become progress
Pan K, Liu XM, Yang ZX, et al., 2021, Undrained cyclic response of K-0-consolidated stiff cretaceous clay under wheel loading conditions, Journal of Geotechnical and Geoenvironmental Engineering, Vol: 147, Pages: 1-16, ISSN: 0733-9410
Optimal whole life design for railways, highways, runways, and metro lines requires an accurate assessment of how their underlying geomaterials respond to large numbers of wheel-loading cycles. This paper presents an experimental study on a natural UK stiff clay with a cyclic triaxial (CT) and hollow cylinder apparatus (CHCA) that imposed K0 and wheel-loading stress conditions. The focus is on Gault clay, a high overconsolidation ratio (OCR) marine clay deposited in the Cretaceous, whose mechanical behavior is significantly anisotropic and in situ K0 values exceed unity. The clay outcrops under sections of most major highways radiating out of London, as well as the HS1 and new HS2 high-speed railways. The experimental investigation explored how the principal stress rotation implicit in wheel loading increases the magnitudes and changes the sign of vertical strain accumulation, as well as accelerating resilient modulus degradation and accentuating stress–strain hysteresis, all of which affect pavement or rail-track serviceability. The clay’s deformation and pore pressure responses are categorized into stable, metastable, and unstable patterns. Comparisons with related studies on low OCR, low K0 soft clay from Wenzhou in southeastern China, confirm the Gault clay’s generally stiffer prefailure behavior and different cyclic response. The stiff clay’s greater brittleness is also emphasized; particle reorientation occurs readily along distinct shear bands, leading to dramatic shear strength reductions that have a major impact on slope and foundation stability and call for appropriate caution in practical design.
Buckley R, Jardine R, Kontoe S, 2021, In situ testing in low-medium density structured chalk, 6th International Conference on Geotechnical and Geophysical Site Characterization
Pile driving in low- to medium-density chalk is subject to significant uncertainty. Predictions of “chalk resistance to driving” (CRD) often vary considerably from field driving behaviour, with both pile refusals and free falls under zero load being reported. However, recent field studies have led to better understanding of the processes that control the wide range of behaviour seen in the field. This paper describes the primary outcomes of the analysis of dynamic tests at an onshore and an offshore site and uses the results to propose a new method to predict CRD. The method is based on phenomena identified experimentally: the relationship between cone penetration resistance and CRD, the attenuation of local stresses as driving advances, and the operational effective stress interface shear failure characteristics. The proposed method is evaluated through back-analyses of driving records from independent pile installation cases that were not included in developing the method, but involved known ground conditions, hammer characteristics, and applied energies. The proposed method is shown to lead to more reliable predictions of CRD than the approaches currently applied by industry.
Buckley R, Byrne BW, Doherty JP, et al., 2021, Measurements of distributed strain during impact pile driving, Piling 2020, Publisher: ICE Publishing
This paper reports the use of optical Fibre Bragg Grating (FBG) sensors to monitor the stress waves generated below ground during pile driving, combined with measurements using conventional pile driving analyzer (PDA) sensors mounted at the pile head. Fourteen tubular steel piles with a diameter of 508 mm and embedded length to diameter ratios of 6 to 20 were impact driven at an established chalk test site in Kent, UK. The pile shafts were instrumented with multiple FBG strain gauges and pile head PDA sensors, which monitored the piles’ responses under each hammer blow. A high frequency (5 kHz) fibre optic interrogator allowed a previously unseen resolution of the stress wave propagation along the pile. Estimates of the base soil resistances to driving and distributions of shaft shear resistances were found through signal matching that compared time series of pile head PDA measurements and FBG strains measured below ground surface. Numerical solutions of the one-dimensional wave equation were optimised by taking account of the data from multiple FBG gauges, leading to significant advantages that have potential for widespread application in cases where high resolution strain measurements are made.
Buckley R, Jardine R, Byrne B, et al., 2020, Pile behaviour in low-medium density chalk: preliminary results from the ALPACA project, 4th International Symposium on Frontiers in Offshore Geotechnics
Byrne BW, McAdam RA, Beuckelaers WJAP, et al., 2020, Cyclic laterally loaded medium scale field pile testing for the PISA project, 4th International Symposium on Frontiers in Offshore Geotechnics
Jardine R, Ushev E, Liu T, 2020, The anisotropic stiffness and shear strength characteristics of a stiff glacial till, Journal of Geotechnical and Geoenvironmental Engineering - ASCE, Vol: 146, Pages: 1-18, ISSN: 0733-9410
Glacial tills are widespread across North America, northern and central Asia, and northern Europe, where they are also found under the Baltic, North, and Norwegian Seas. Their geological and geotechnical characterization is important to a wide range of onshore and offshore engineering projects. One aspect of tills on which little has been reported is their mechanical anisotropy. This paper reports coordinated hollow cylinder apparatus (HCA) tests, triaxial shearing, and small-strain stress probing experiments, supported by index testing, on high-quality samples of natural low-to-medium plasticity, high overconsolidation ratios (OCR) stiff clay-till from the Bolders Bank Formation at Cowden, near Hull in the UK. Material variability and sampling bias are inevitably introduced by the till’s erratic gravel particles and fissure systems, and these aspects are addressed carefully. The experiments investigated the till’s stiffness and shear strength anisotropy from its limited linear elastic range up to ultimate failure, showing that stiffnesses are higher in the horizontal direction than in the vertical and that higher undrained shear strengths develop under passive horizontal loading than active vertical loading. Comparisons are made between the till’s patterns of anisotropy and those applying to previously studied sediments, and reference is made to in situ stiffness measurements. The important implications of anisotropic behavior for geotechnical design and the interpretation of field tests are emphasized.
Zdravkovic L, Taborda D, Potts D, et al., 2020, Finite-element modelling of laterally loaded piles in a stiff glacial clay till at Cowden, Geotechnique: international journal of soil mechanics, Vol: 70, Pages: 999-1013, ISSN: 0016-8505
The PISA project was a combined field testing/numerical modelling study with the aim of developing improved design procedures for large-diameter piles subjected to lateral loading. This paper describes the development of a three-dimensional finite-element model for the medium-scale pile tests that were conducted in Cowden till as part of the PISA work. The paper places particular emphasis on the consistent interpretation of the soil data determined from the available field and laboratory information. An enhanced version of the modified Cam clay model was employed in the numerical analyses, featuring a non-linear Hvorslev surface, a generalised shape for the yield and plastic potential surfaces in the deviatoric plane and 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 behaviour for a range of pile geometries was observed, demonstrating the accuracy of the numerical model and the adequacy of the calibration process for the constitutive model. The developed numerical model confirmed the premise of the PISA design method that site-specific ground characterisation and advanced numerical modelling can directly facilitate the development of additional soil reaction curves for use in new design models for laterally loaded piles in a stiff clay till.
Taborda D, Zdravkovic L, Potts DM, et al., 2020, Finite-element modelling of laterally loaded piles in a dense marine sand at Dunkirk, Geotechnique: international journal of soil mechanics, Vol: 70, Pages: 1014-1029, ISSN: 0016-8505
The paper presents the development of a three-dimensional finite-element model for pile tests in dense Dunkirk sand, conducted as part of the PISA project. The project was aimed at developing improved design methods for laterally loaded piles, as used in offshore wind turbine foundations. The importance of the consistent and integrated 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.
Byrne B, McAdam RA, Burd HJ, et al., 2020, Monotonic laterally loaded pile testing in a stiff glacial clay till at Cowden, Géotechnique, Vol: 70, Pages: 970-985, ISSN: 0016-8505
This paper describes the results obtained from a field testing campaign on laterally loaded monopiles conducted at Cowden, UK, where the soil consists principally of a heavily overconsolidated glacial till. These tests formed part of the PISA project on the development of improved design methods for monopile foundations for offshore wind turbines. Results obtained for monotonic loading tests on piles of three different diameters (0·273 m, 0·762 m and 2·0 m) are presented. The piles had length-to-diameter ratios (L/D) of between 3 and 10. The tests included the 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 piles are determined using an optimised structural model. These field data support the development of a new one-dimensional modelling approach for the 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 above the ground surface.
McAdam RA, Byrne BW, Houlsby GT, et al., 2020, Monotonic lateral loaded pile testing in a dense marine sand at Dunkirk, Géotechnique, Vol: 70, Pages: 986-998, ISSN: 0016-8505
The results obtained from a field testing campaign on laterally loaded monopiles, conducted at a dense sand site in Dunkirk, northern France are described. These tests formed part of the PISA project on the development of improved design methods for monopile foundations for offshore wind turbines. Results obtained from monotonic loading tests on piles of three different diameters (0·273 m, 0·762 m and 2·0 m) are presented. The piles had length-to-diameter ratios (L/D) of between 3 and 10. The tests consisted principally of the application of monotonic loads, incorporating periods of held constant load to investigate creep effects. The influence of loading rate was 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 piles are also provided. Inferences are made for the displacements in the embedded length of the piles. These field data will support the development of a new one-dimensional modelling approach for the 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 above the ground surface.
Zdravkovic L, Jardine R, Taborda DMG, et al., 2020, Ground characterisation for PISA pile testing and analysis, Géotechnique, Vol: 70, Pages: 945-960, 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 characterisation of the two sites, which was 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 campaigns to historic investigations at both sites. They enabled an accurate description of soil behaviour from small strains to ultimate states to be derived, allowing analyses to be undertaken that captured both the serviceability and limit state behaviour of the test monopiles.
Burd HJ, Beuckelaers WJAP, Byrne BW, et al., 2020, New data analysis methods for instrumented medium scale monopile field tests, Géotechnique, Vol: 70, Pages: 961-969, 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, and in 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 described for the interpretation of pile loading data, and specifically for providing precise interpretation of pile displacements.
Burd HJ, Taborda D, Zdravkovic L, et al., 2020, PISA design model for monopiles for offshore wind turbines: application to a marine sand, Geotechnique, Vol: 70, Pages: 1048-1066, ISSN: 0016-8505
This paper describes a one-dimensional (1D) computational model for the analysis and design of laterally loaded monopile foundations for offshore wind turbine applications. The model represents the monopile as an embedded beam and specially formulated functions, referred to as soil reaction curves, are employed to represent the various components of soil reaction that are assumed to act on the pile. This design model was an outcome of a recently completed joint industry research project – known as PISA – on the development of new procedures for the design of monopile foundations for offshore wind applications. The overall framework of the model, and an application to a stiff glacial clay till soil, is described in a companion paper by Byrne and co-workers; the current paper describes an alternative formulation that has been developed for soil reaction curves that are applicable to monopiles installed at offshore homogeneous sand sites, for drained loading. The 1D model is calibrated using data from a set of three-dimensional finite-element analyses, conducted over a calibration space comprising pile geometries, loading configurations and soil relative densities that span typical design values. The performance of the model is demonstrated by the analysis of example design cases. The current form of the model is applicable to homogeneous soil and monotonic loading, although extensions to soil layering and cyclic loading are possible.
Byrne BW, Houlsby GT, Burd HJ, et al., 2020, PISA design model for monopiles for offshore wind turbines: application to a stiff glacial clay till, Geotechnique, Vol: 70, Pages: 1030-1047, ISSN: 1021-8637
Offshore wind turbines in shallow coastal waters are typically supported on monopile foundations.Although three dimensional (3D) finite element methods are available for the design of monopiles inthis context, much of the routine design work is currently conducted using simplified one dimensional(1D) models based on the p-y method. The p-y method was originally developed for the relativelylarge embedded length-to-diameter ratio (L/D) piles that are typically employed in offshore oil and gasstructures. Concerns exist, however, that this analysis approach may not be appropriate formonopiles with the relatively low values of L/D that are typically adopted for offshore wind turbinestructures. This paper describes a new 1D design model for monopile foundations; the model isspecifically formulated for offshore wind turbine applications although the general approach could beadopted for other applications. The model draws on the conventional p-y approach, but extends it toinclude additional components of soil reaction that act on the pile. The 1D model is calibrated using aset of bespoke 3D finite element analyses of monopile performance, for pile characteristics andloading conditions that span a predefined design space. The calibrated 1D model provides results thatmatch those obtained from the 3D finite element calibration analysis, but at a fraction of thecomputational cost. Moreover, within the calibration space, the 1D model is capable of delivering highfidelity computations of monopile performance that can be used directly for design purposes. This 1Dmodelling approach is demonstrated for monopiles installed in a stiff overconsolidated glacial clay tillwith a typical North Sea strength and stiffness profile. Although the current form of the model hasbeen developed for homogeneous soil and monotonic loading, it forms a basis from which extensionsfor soil layering and cyclic loading can be developed. The general approach can be applied to otherfoundation and soil-structu
Burd H, Abadie C, Byrne B, et al., 2020, Application of the PISA design model to monopiles embedded in layered soils, Geotechnique, Vol: 70, Pages: 1067-1082, ISSN: 1021-8637
The PISA design model is a procedure for the analysis of monopile foundations for offshore windturbine applications. This design model has been previously calibrated for homogeneous soils; thispaper extends the modelling approach to the analysis of monopiles installed at sites where the soilprofile is layered. We describe a computational study on monopiles embedded in layered soilconfigurations comprising selected combinations of soft and stiff clay and sand at a range of relativedensities. The study comprises (i) analyses of monopile behaviour using detailed three dimensional(3D) finite element analysis, and (ii) calculations employing the PISA design model. Results from the3D analyses are used to explore the various influences that soil layering has on the performance ofthe monopile. The fidelity of the PISA design model is assessed by comparisons with data obtainedfrom equivalent 3D finite element analyses, demonstrating a good agreement in most cases. Thiscomparative study demonstrates that the PISA design model can be applied successfully to layeredsoil configurations, except in certain cases involving combinations of very soft clay and very densesand.
Buckley R, Jardine R, Kontoe S, et al., 2020, Full-scale observations of dynamic and static axial responses of offshore piles driven in chalk and tills, Géotechnique, Vol: 70, Pages: 657-681, ISSN: 0016-8505
This paper describes and interprets tests on piles driven through glacial tills and chalk at a Baltic Sea windfarm, covering an advance trial campaign and later production piling. The trials involved six instrumented 1.37m diameter steel open-ended tubes driven in water depths up to 42m. Three piles were tested statically, with dynamic re-strike tests on paired piles, at 12-15 week ages. Instrumented dynamic driving and re-strike monitoring followed on up to 3.7m diameter production piles. During driving, the shaft resistances developed at fixed depths below sea-bed fell markedly during driving, with particularly sharp reductions occurring in the chalk. Shaft resistances increased markedly after driving and good agreement was seen between long-term capacities interpreted from parallel static and dynamic tests. Analyses employing the sites’ geotechnical profiles show long-term shaft resistances in the chalk that far exceed those indicated by current design recommendations, while newly proposed procedures offer good predictions. The shaft capacities mobilised in the low-plasticity tills also grew significantly over time, within the broad ranges reported for sandy soils. The value of offshore field testing in improving project outcomes and design rules is demonstrated; the approach described may be applied to other difficult seabed conditions.
Jardine R, Hight D, Potts D, 2020, Integrated research into the foundation behaviour of offshore energy production platforms, Geotechnical Engineering Journal of the SEAGS and AGSSEA, ISSN: 0046-5828
Buckley R, McAdam R, Byrne B, et al., 2020, Optimisation of impact pile driving using optical fibre Bragg grating measurements, Journal of Geotechnical and Geoenvironmental Engineering, Vol: 146, Pages: 1-15, ISSN: 0733-9410
This paper reports the use of optical Fibre Bragg Grating (FBG) sensors to monitor the stress waves generated below ground during pile driving, combined with measurements using conventional pile driving analyzer (PDA) sensors mounted at the pile head. Fourteen tubular steel piles with a diameter of 508 mm and embedded length to diameter ratios of 6 to 20 were impact driven at an established chalk test site in Kent, UK. The pile shafts were instrumented with multiple FBG strain gauges and pile head PDA sensors, which monitored the piles’ responses under each hammer blow. A high frequency (5kHz) fibre optic interrogator allowed a previously unseen resolution of the stress wave propagation along the pile. Estimates of the base soil resistances to driving and distributions of shaft shear resistances were found through signal matching that compared time series of pile head PDA measurements and FBG strains measured below ground surface. Numerical solutions of the onedimensional wave equation were optimised by taking account of the data from multiple FBG gauges, leading to significant advantages that have potential for widespread application in cases where high resolution strain measurements are made.
Yang Z, Gao Y, Jardine R, et al., 2020, Large deformation finite element simulation of displacement pile installation experiments in sand, ASCE Soil Mechanics and Foundation Division Journal, Vol: 146, ISSN: 0044-7994
Displacement piles are driven to support a wide rangeof structures. Predicting their axial limiting capacities and load-displacement behavior is critical to many such engineering applications. While field load tests may be conducted to check design assumptions, such tests can prove expensive and difficult to generalize. Numerical analyses undertaken to support design face uncertaintyover the potentially important effects of pile installationasno well-developed method exists to predict the stresses applying during and after driving. Recent experiments have provided evidence regarding the stresses and strains developed around displacement piles during installation in sandthat can help guiderepresentative numerical modeling. This paper contributes to this development by reporting large displacement numerical analysesand linking these to high-quality experiments. The Arbitrary Lagrangian-Eulerian (ALE) options available in ABAQUS/Explicit have been employed to simulate highly instrumented calibration chamber tests made with closed-ended pilespenetrated into sand. Predictions for the stress components developed during and afterpile installation are presented, along with measurements made by other authors of the corresponding strain fields. The simulations’ broad agreement with the available experimental evidenceindicatesthat the adopted ALE techniqueand soil modeling approach are appropriate for pile installation analysis in sands.
Carroll R, Carotenuto P, Dano C, et al., 2020, Field experiments at three sites to investigate the effects of age on steel piles driven in sand, Géotechnique, Vol: 70, Pages: 469-489, ISSN: 0016-8505
This paper investigates the influences that steel type, in situ soil properties, water table depth, pile diameter, roughness and driving procedures have on the ageing behaviour of piles driven in sand. Tension tests have been performed on 51 open-ended steel micro-piles, with 48 to 60 mm outside diameter, driven at well-established research sites at Larvik in Norway, Dunkirk in France and Blessington in Ireland to better understand the processes that control axial capacity set-up trends in the field. Mild steel, stainless and galvanised steel micro-piles were driven and left to age undisturbed for periods of between 2 h and 696 days before being subjected to first-time axial tension load tests. In addition to reporting and interpreting these experiments, further investigations of the sites’ geotechnical profiles are reported, including new piezocone and seismic cone penetration soundings as well as laboratory tests. Integration with earlier ageing studies at the same sites with larger (340 to 508 mm outside diameter) open-ended steel piles driven to 7 to 20 m embedments and experiments that varied the piles’ initial surface roughness shows that corrosion, pile scale, roughness, the bonding of soil particles and the driving process can all be highly significant. New insights are gained into the mechanisms that control the axial capacity of piles driven in sand.
Jardine R, 2020, Geotechnics, energy and climate change: The 56th Rankine Lecture, Géotechnique, Vol: 70, Pages: 3-59, 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.
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