393 results found
Wen K, Kontoe S, Jardine RJ, et al., 2023, An axial load transfer model for piles driven in chalk, Journal of Geotechnical and Geoenvironmental Engineering, Vol: 149, Pages: 1-17, ISSN: 1090-0241
Chalk is encountered under large areas of Northern Europe and other locations worldwide, and a wide range of onshore and offshore structures are founded on piles driven in chalk. The safe and economical design of these structures is challenging because of current uncertainties regarding their axial capacity and load-displacement behavior. This work builds on recent research into the axial capacity of open-ended driven piles by proposing new shaft and base load transfer models for chalk that employ geotechnical properties measured directly in laboratory and in-situ tests. First, this study set out a new closed-form elastic analysis of the initial tension loading response. Then, a new nonlinear shaft model was proposed that captures the radial variation in properties induced by pile installation in chalk and uncouples the piles’ stiffness responses from their ultimate local shaft resistances, which are predicted independently. A new base model was also outlined that predicts the loading response based on the chalk’s small-strain stiffness and cone penetration test (CPT) cone resistances. The models are shown to offer good load-displacement predictions for 0.139-m to 1.8-m diameter piles tested between 20 and 600 days after driving at several sites. Improved reliability and accuracy are demonstrated through comparison with existing load-transfer methods.
Lehane BM, Liu Z, Bittar EJ, et al., 2023, Closure to "CPT-Based Axial Capacity Design Method for Driven Piles in Clay", JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING, Vol: 149, ISSN: 1090-0241
Vinck K, Liu T, Mawet J, et al., 2023, Field tests on large scale instrumented piles driven in Chalk: results and interpretation, Canadian Geotechnical Journal, Vol: 60, Pages: 1475-1490, ISSN: 0008-3674
The design of large open steel piles driven at chalk sites suffers from considerable uncertainty, leading to major difficulties in many significant onshore and offshore projects. This paper describes recent instrumented driving, monotonic testing to failure and re-strike tests conducted on large open steel piles driven in primarily low- to medium-density chalk at a site in North-western France. The experiments are described and interpreted with reference to a high-quality site characterisation, dynamic and static methods of test analysis and alternative predictive design approaches. Important new conclusions flow regarding driving behaviour, the set-up that took place over up to 65 days after installation and the resistances available under compression and tension loading. Surprisingly large differences are shown between tension and compression shaft capacity which are postulated to be due to Poisson straining in the steel pile shaft and its interaction with the surrounding chalk mass. The field tests contribute to building a high-quality dataset that allows proposed axial capacity design methods to be tested and potentially refined to provide reliable and representative design tools.
Wen K, Kontoe S, Jardine RJ, et al., 2023, Assessment of time effects on capacities of large-scale piles driven in dense sands, Canadian Geotechnical Journal, Vol: 60, Pages: 1015-1035, ISSN: 0008-3674
This paper considers the axial resistances of open-ended, highly instrumented, 763 mm diameter steel pipe piles driven in sands for the EURIPIDES (EURopean Initiative on PIles in DEnse Sands) project at a well characterised research site at Eemshaven, in the northern Netherlands. It offers new analyses of previously unreported dynamic tests and considers their relationship to four heavily instrumented static compression tests. Rigorous signal matching employing two distinct pile-soil interaction models is reported, supported by careful sensitivity analyses, to interpret the recorded driving signals. The back-calculated shaft resistance profiles show good agreement between the models as well as calculations performed with a global wave equation analysis approach. The study highlights the need to account for the internal soil column resistance. The combined interpretation of the dynamic and static test data indicates a 50% gain in shaft resistance over the ten days after driving and threefold shaft capacity growth over a total period of 533 days after driving. The outcomes have important implications for driven pile design and field quality monitoring; the case history contributes an important benchmark in the study of long-term set-up trends.
Pedone G, Kontoe S, Zdravkovic L, et al., 2023, A sensitivity study on the mechanical properties of interface elements adopted in finite element analyses to simulate the interaction between soil and laterally loaded piles, 10th European Conference on Numerical Methods in Geotechnical Engineering, Publisher: International Society for Soil Mechanics and Geotechnical Engineering
An increasing number of offshore energy structures have been built recently on driven piles, ranging from jack-et piles with typical length-to-diameter (L/D) ratios of 10-40 to monopiles with far lower L/D ratios. The load-displacementbehaviour of these foundations can be investigated by means of Finite Element (FE) analyses, for instance following the designmethodology developed by the PISA Joint Industry Project (JIP). A challenging aspect of the modelling, for piles loaded eitheraxially or laterally, is the simulation of the behaviour at the soil-pile interface with the adoption of suitable formulations for theinterface elements and with representative mechanical properties. This paper presents a sensitivity study conducted on both theelastic and plastic properties of interface elements adopted in FE analyses of laterally loaded piles driven in chalk. The studybenefited from the extensive field and laboratory test results collected during the ALPACA JIP and the corresponding piletests. The aim of the paper is to provide guidance for numerical modelling on the selection of the most appropriate mechanicalproperties of interface elements to be used in the analyses of soil-pile interaction under lateral loading.
Wen K, Kontoe S, Jardine RICHARD, et al., 2023, Non-linear finite-element analysis of axially loaded piles driven in chalk, 10th European Conference on Numerical Methods in Geotechnical, Publisher: International Society for Soil Mechanics and Geotechnical Engineering
Driven piles are often employed to support onshore and offshore structures at low-density, porous weak carbonatechalk sites, which are encountered across Northern Europe and under the North and Baltic seas. Their efficient design is limitedby uncertainties regarding their ultimate axial capacity and load-displacement behaviour. Intensive axial testing has been under-taken recently for the ALPACA Joint Industry Project on piles driven at a UK chalk site, in conjunction with comprehensivechalk characterisation studies. This paper presents PLAXIS-2D numerical simulations of such piles' axial loading behaviour.The simulation accounts for three distinct zones of chalk identified around the pile shafts after installation. These comprise athin annular zone of de-structured, puttified, chalk and a second, thicker, annular zone of highly fractured chalk; both havedifferent mechanical properties compared to the surrounding parent intact chalk mass. The FE analyses investigate how shaftresistance, axial capacity and load-displacement behaviour develop differently in compression and tension tests.
Pan K, Zhou G, Yang Z, et al., 2023, Undrained cyclic loading behavior of stiff Eocene-to-Jurassic plastic, high OCR, clays, Canadian Geotechnical Journal, ISSN: 0008-3674
Assessing foundation response to cyclic loading is vital when designing transport infrastructure, such as road pavements and rail tracks, as well as offshore, port, and tall tower structures. While detailed guidance is available on characterizing many soil types’ cyclic behavior, relatively few studies have been reported on stiff, geologically aged, plastic clays. This paper addresses this gap in knowledge by reporting cyclic loading experiments on three natural stiff UK clays that were deposited and buried between the Jurassic Age and Eocene Epoch before geological unloading to their currently heavily over-consolidated states. High-quality samples taken at relatively shallow depths were reconsolidated to nominally in-situ K0 stresses in triaxial and hollow cylinder apparatus before imposing cyclic loading. The completely stable, metastable, or unstable outcomes invoked by different levels of undrained cyclic loading are interpreted within a kinematic yielding framework that is compatible with monotonic control experiments’ outcomes. The cyclic limits marking the onset of significant changes in permanent strain accumulation, pore pressure development, and stress-strain hysteresis demonstrate that the weathered Gault clay offers the lowest cyclic resistance. The experiments show that energy considerations provide a promising way of evaluating undrained pore pressure generation and stiffness degradation. They also provide a basis for developing cyclic constitutive models and analysis procedures for cyclic foundation design in stiff, high OCR, plastic clay strata.
Fu S, Yang Z, Jardine RJ, et al., 2023, Large deformation finite element simulation of deformation and strain fields resulting from closed-end displacement pile installation in sand, Journal of Geotechnical and Geoenvironmental Engineering, Vol: 149, Pages: 1-18, ISSN: 0733-9410
Displacement piles are driven to support a wide range of structures. However, analysis of the stress and strain fields developed during their installation remains one of the most challenging problems in geotechnical engineering. Advances in design methods, particularly for sand sites,have had to rely on an imperfect analogy between pile and CPT cone penetration processes, rather than modelling pile installation itself. Recent physical model experiments provide benchmark datasets that describe the stress and deformation patterns developed around displacement piles penetrating sand masses. Following from large deformation finite elementanalyses that captured the stresses measured in the Grenoble 3S-R calibration chamber NE34 sand experiments, this paper presents simulations of the displacements measured in equivalent high-quality experiments conducted at Purdue University with dense, angular, #2Q-ROK silica sand. A modified Mohr-Coulomb model with state-dependent parameters was calibrated to match element tests conducted by the Authors and an Arbitrary Lagrangian-Eulerian scheme was applied in the simulations. The evolution and distribution of the deformations induced by pile penetration are compared with the experiments. Predictions for the deformation and strain fields applying during and after pile installation are presented, showing broad agreement between the simulations and experiments. The predicted and measured pile capacities are also compared and contrasted. Points of divergence between the simulations and tests are highlighted and their implications for numerical modelling are discussed.
Pedone G, Kontoe S, Zdravkovic L, et al., 2023, Numerical modelling of laterally loaded piles driven in low-to-medium density fractured chalk, Computers and Geotechnics, Vol: 156, Pages: 1-18, ISSN: 0266-352X
Chalk’s sensitive, variable nature poses difficulties for foundation designers. It can present as weak rock and yet be de-structured to very weak putty by dynamic or high-pressure loading. The development of multiple offshore wind farms at north European chalk sites led to the recent ALPACA Joint Industry Programme, which undertook intensive material characterisation and large-scale field testing at St Nicholas at Wade (SNW), Kent, UK to capture and better understand the behaviour of piles driven in fractured low-to-medium density chalk. Noting that lateral loading response is a vital design concern for monopile and jacket supported structures, this paper focuses on 3D Finite Element (FE) modelling of ALPACA’s monotonic lateral loading field tests on open-ended driven tubular steel piles. The brittle chalk is modelled with a strain-softening Mohr-Coulomb model combined with nonlocal regularisation, calibrated meticulously against the ALPACA characterisation dataset. A second, simpler modelling approach, adopting a perfectly-plastic Mohr-Coulomb model, is also explored as a simplified practical alternative. Both approaches can match field lateral capacity and bending moment distributions, after taking due account of pile installation and chalk fracturing effects. The analyses indicate how robust, accurate and cost-effective lateral loading design may be approached for low-to-medium density fractured chalks.
Buckley R, Jardine R, Kontoe S, et al., 2023, Axial cyclic loading of piles in low to medium density chalk, Geotechnique, ISSN: 1021-8637
Comprehensive field investigations into the axial cyclic loading behaviour of open-steel pipe piles driven and aged in low-to-medium density chalk identify the conditions under which behaviour is stable, unstable or metastable. Post-cycling monotonic tests confirmed that stable cycling enhanced pile capacity marginally, while unstable cases suffered potentially large losses of shaft capacity. Metastable conditions led to intermediate outcomes. The patterns by which axial deflections grew under cyclic loading varied systematically with the normalised loading parameters and could be captured by simple fitting expressions. Cyclic stiffnesses also varied with loading conditions, with the highest operational shear stiffnesses falling far below the in-situ seismic test values. The monotonic and cyclic axial responses of the test piles were controlled by the behaviour of, and conditions within, the reconsolidated, de-structured, chalk putty annuli formed around pile shafts during driving. Fibre-optic strain gauges identified progressive failure from the pile tip upwards. Large factors of safety were required for piles to survive repetitive loading under high-level, two-way, conditions involving low mean loads, while low amplitude one-way cycling had little impact. A simple ‘global’ prediction procedure employing interface shear and cyclic triaxial tests is shown to provide broadly representative predictions for field behaviour.
This paper describes research into the poorly understood axial behaviour of piles driven in chalk. Comprehensive dynamic and monotonic axial testing on 27, mostly instrumented, piles undertaken for the ALPACA Joint Industry Projects is reported and interpreted covering: diameters between 139mm and 1.8m; lengths from 3 to 18m; different pile material types; tip and groundwater conditions, and ages after driving. The experiments show the factors that influence resistance most strongly are: (i) pile end-conditions, (ii) slenderness ratio and flexibility, (iii) shaft material, (iv) age after driving, (vi) relative water table depth, and (vii) whether loading is compressive or tensile. Varying the factors systematically identified a remarkable average long-term shaft resistance range from below 11 kPa to more than 200 kPa for piles driven at the same low-to-medium density chalk test site in Kent (UK). Dynamic and static analyses demonstrate that soil resistances to driving (SRD) were generally well-predicted by the Chalk ICP-18 short-term formulation. Considering the piles’ long-term behaviour, the Chalk ICP-18 approach over-predicted capacity, while the widely used CIRIA approach proved over-conservative for most cases. The research enabled the development of a revised ‘ALPACA-SNW’ long-term capacity assessment method that matches the test outcomes far more faithfully.
Liu T, Ferreira PMV, Vinck K, et al., 2023, The behaviour of a low- to medium-density chalk under a wide range of pressure conditions, Soils and Foundations, Vol: 63, ISSN: 0038-0806
Experiments are described which provided the basis for advanced numerical modelling of large-scale axial and lateral pile tests undertaken chalk to assist the design of offshore wind and other projects in northern Europe. The research explored the mechanical behaviour of chalk from a UK research site under effective cell pressures up to 12.8 MPa. When sheared from low confining pressures the chalk’s interparticle bonds contribute a large proportion of the peak deviator stresses available to specimens that crack, bifurcate and dilate markedly after failing at relatively small strains. Progressively more ductile behaviour is seen as pressures are raised, with failures being delayed until increasingly large strains and stable critical states are attained. Loading invokes very stiff responses within the chalk’s (Y1) linear elastic limits and behaviour remains stiff, although non-linear, up to large-scale (Y3) yield points. Near-elliptical Y1 and Y3 yield loci can be defined in q-p′ stress space and a critical state v-p′ curve is identified. The chalk’s initially bonded, high porosity, structure is explored by normalising the shearing and compression state paths with reference to both critical state and intrinsic compression lines. The results have important implications for pile test analysis and practical design in this challenging geomaterial.
Ushev ER, Jardine RJ, 2022, The mechanical behaviour of Bolders Bank till, Canadian Geotechnical Journal, Vol: 59, Pages: 2163-2183, 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.
Gao L, Guo N, Yang ZX, et al., 2022, MPM modeling of pile installation in sand: Contact improvement and quantitative analysis, Computers and Geotechnics, Vol: 151, ISSN: 0266-352X
The material point method (MPM), which is known to be advantageous in modeling large deformation and contact problems, is utilized in this study to simulate displacement pile installation in sand. A modified Bardenhagen’s contact algorithm is proposed that calculates the node-to-surface distances between the deformable soil mass and the rigid pile surface more effectively, along with a smoothing factor for the change of momenta between the contacting bodies. The modified algorithm is shown to produce more accurate and stable contact results. Three tests, namely, the rolling cylinder, the penetrating wedge, and the strip footing, are first conducted to demonstrate the validity of the modified algorithm. It is then applied to analyze the installation of a closed-ended pile, employing a state-dependent Mohr–Coulomb model to capture the sand’s state-dependent shearing behavior. Detailed analyses of the stress and deformation fields developed around the pile during steady penetration reveal quantitative agreement between the MPM predictions and published experiments, indicating that the approach holds promise for use in more sophisticated analyses designed to improve the understanding of industrially driven piles.
Pan K, Liu XM, Yang ZX, et al., 2022, Closure to "Undrained Cyclic Response of K-0-Consolidated Stiff Cretaceous Clay under Wheel Loading Conditions" by K. Pan, X. M. Liu, Z. X. Yang, R. J. Jardine, JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING, Vol: 148, ISSN: 1090-0241
Cathie D, Jardine RICHARD, Silvano R, et al., 2022, Pile setup in sand – the "PAGE" joint industry project, 11th International Conference on Stress Wave Theory and Design and Testing Methods for Deep Foundations (SW2022)
The reliability of long-term axial capacity predictions for large, offshore-scale, piles is uncertain. Current databases of static load tests include very few entries with diameters ≥ 1m, and none >2m. Also, most of the available tests were conducted at relatively early ages after driving. The PAGE Joint Industry Project addressed this knowledge gap by collating and analysing dynamic driving data from 25 offshore piles with 1.6 to 3.4m outside diameters and contrasting these with dynamic re-strike tests conducted between 1h and 1 year after driving. Systematic signal matching was performed with two independent codes that applied different soil models and the outcomes were compared with predictions from modern CPT-based static capacity design methods. Additional supporting analyses were performed on other piles, where static and dynamic tests had been conducted, to help assess the relationships between statically and dynamically measured resistances. Piles with 0.3 to 3.5m outside diameters followed broadly common trends overthe first 30 days after driving, with shaft capacities approximately doubling. While smaller (<1m) diameter piles driven at onshore/nearshore sites display marked further capacity growth, larger offshore piles showed little additionalcapacity gain after 30 days. The CPT-based Unified offshore pile design method offered conservative predictions for long-term shaft resistance, while no bias was apparent with the ICP-05 approach. An inverse relationship was identified between long-term shaft setup and diameter, which is ascribed to enhanced dilatancy applying at the pile-sand interface. The base capacities interpreted from dynamic analyses consistently fell far below the monotonic loading capacities predicted by current design methods and showed no significant trend to increase over time.
Liu T, Jardine RJ, Vinck K, et al., 2022, Optimization of advanced laboratory monotonic and cyclic triaxial testing on fine sands, Geotechnical Testing Journal, Vol: 45, Pages: 1087-1107, ISSN: 0149-6115
Monotonic and cyclic triaxial testing provides key information for a wide range of sensitivegeotechnical problems. This paper assesses the potential impact on stress-strain measure-ments of several error sources and discusses how test quality may be improved. External vol-ume gauges are shown to be subject to significant errors that depend on the pressure level.While high-resolution local radial strain measurement presents considerable challenges,especially in long-duration cyclic tests, problems with “floating” radial-belt and alternative“L-configuration” systems were overcome by steps that allow strains as low as 10−4 %tobe resolved reliably. Sample end conditions are shown more important than is commonly ap-preciated. Employing smooth, enlarged, and lubricated end platens can avoid the recording ofmisleadingly high shear resistances, which are most significant with relatively loose specimenstested under low effective stresses. Stiffnesses and dilation trends were also recorded morereliably in tests employing smooth, enlarged, and lubricated end platens. The arrangementsovercome significant strain errors even in tests employing local instruments and specimenswith initial height-to-diameter ratios of 2.
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: 0733-9410
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.
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.
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.
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, Vol: 59, Pages: 1358-1372, 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.
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.