Imperial College London

Professor David Potts

Faculty of EngineeringDepartment of Civil and Environmental Engineering

Professor
 
 
 
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Contact

 

+44 (0)20 7594 6084d.potts

 
 
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Location

 

505Skempton BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

433 results found

Gawecka K, Taborda D, Potts D, Sailer E, Cui W, Zdravkovic Let al., 2020, Finite element modelling of heat transfer in ground source energy systems with heat exchanger pipes, International Journal of Geomechanics, Vol: 20, Pages: 04020041-1-04020041-14, ISSN: 1532-3641

Ground source energy systems (GSES) utilise low enthalpy geothermal energy and have been recognised as an efficient means of providing low carbon space heating and cooling. This study focuses on GSES where the exchange of heat between the ground and the building is achieved by circulating a fluid through heat exchanger pipes. Although numerical analysis is a powerful tool for exploring the performance of such systems, simulating the highly advective flows inside the heat exchanger pipes can be problematic. This paper presents an efficient approach for modelling these systems using the finite element method (FEM). The pipes are discretised with line elements and the conductive-advective heat flux along them is solved using the Petrov-Galerkin FEM instead of the conventional Galerkin FEM. Following extensive numerical studies, a modelling approach for simulating heat exchanger pipes, which employs line elements and a special material with enhanced thermal properties, is developed. The modelling approach is then adopted in three-dimensional simulations of two thermal response tests, with an excellent match between the computed and measured temperatures being obtained.

Journal article

Cui W, Potts DM, Pedro AMG, Zdravkovic Let al., Numerical assessment of the effects of end-restraints and a pre-existing fissure on the interpretation of triaxial tests on stiff clays, Geotechnique: international journal of soil mechanics, ISSN: 0016-8505

Conventional laboratory triaxial tests apply axi-symmetric boundary conditions to a cylindrical sample which has an axi-symmetric geometry. For a homogeneous sample this implies that the deformed shape of the sample should maintain an axi-symmetric geometry during the test. Consequently, the sample should deform in a barrelling mode and if slip planes develop they should define a cup and cone like failure surface. However, in many triaxial tests such behaviour is not observed, especially as failure is approached when a planar slip surface develops. Such a deformation mode is not axi-symmetric. One reason for this behaviour is that a fissure pre-exists in the sample. Employing hydro-mechanically coupled 3D finite element analyses, this paper investigates the influence of a single fissure in a triaxial sample of stiff clay on its behaviour throughout the test, focusing on the fissure position, orientation, strength and stiffness, in conjunction with the sample’s end-restraints (rough or smooth). The effects are quantified in terms of the samples’ overall stiffness and strength, indicating that the presence of a fissure can affect the very small strain stiffness, and that it has a significant effect on the strength of the sample, demonstrating that the conventional methods used to interpret laboratory tests may give unconservative results. The results also show a significant effect of the conditions at the top and bottom surfaces of the sample, where in particular the lateral restraint and rough ends introduce “bending” in the sample.

Journal article

Gawecka K, Cui W, Taborda D, Potts D, Zdravkovic L, Loukas Aet al., Predictive modelling of thermo-active tunnels in London Clay, Geotechnique: international journal of soil mechanics, ISSN: 0016-8505

Journal article

Sailer E, Taborda D, Zdravkovic L, Potts DMet al., A novel method for designing thermo-active retaining walls using two dimensional analyses, Proceedings of the Institution of Civil Engineers: Geotechnical Engineering, ISSN: 1353-2618

Journal article

Cui W, Tsiampousi A, Potts D, Gawecka K, Zdravkovic Let al., Numerical modelling of time-dependent thermally induced excess pore fluid pressures in a saturated soil, Journal of Geotechnical and Geoenvironmental Engineering - ASCE, Vol: 146, Pages: 04020007-1-04020007-15, ISSN: 0733-9410

A temperature rise in soils is usually accompanied by an increase in excess pore fluid pressure due to the differential thermal expansion coefficients of the pore fluid and the soil particles. To model the transient behaviour of this thermally induced excess pore fluid pressure in geotechnical problems, a coupled THM formulation was employed in this study, which accounts for the non-linear temperature-dependent behaviour of both the soil permeability and the thermal expansion coefficient of the pore fluid. Numerical analyses of validation exercises (where there is an analytical solution), as well as of existing triaxial and centrifuge heating tests on Kaolin clay, were carried out in the current paper. The obtained numerical results exhibited good agreement with the analytical solution and experimental measurements respectively, demonstrating good capabilities of the applied numerical facilities and providing insight into the mechanism behind the observed evolution of the thermally induced pore fluid pressure. The numerical results further highlighted the importance of accounting for the temperature-dependent nature of the soil permeability and the thermal expansion coefficient of the pore fluid, commonly ignored in geotechnical numerical analysis.

Journal article

Zdravković L, Potts DM, 2020, Keynote Lecture: Application of Advanced Numerical Analysis in Geotechnical Engineering Design, Lecture Notes in Civil Engineering, Pages: 1009-1022

© Springer Nature Singapore Pte Ltd. 2020. Geotechnical analysis is an integral part of the geotechnical design process. It is performed with the aim of assessing the stability and serviceability of geotechnical structures and their interaction with the natural and built environment. The complexities of many geotechnical problems and requirements for long-term design solutions increasingly require the use of advanced numerical analysis. This paper explores the application of advanced numerical tools in the lifecycle assessment of infrastructure slopes in stiff clays and of earthfill infrastructure embankments.

Book chapter

Burd HJ, Taborda D, Zdravkovic L, Abadie CN, Byrne BW, Houlsby GT, Gavin K, Igoe D, Jardine RJ, Martin CM, McAdam RA, Pedro AMG, Potts DMet al., PISA design model for monopiles for offshore wind turbines: application to a marine sand, Geotechnique, ISSN: 0016-8505

This paper describes a one dimensional (1D) computational model for the analysis and design oflaterally-loaded monopile foundations for offshore wind turbine applications. The model represents themonopile as an embedded beam and specially-formulated functions, referred to as soil reactioncurves, are employed to represent the various components of soil reaction that are assumed to act onthe 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 foroffshore wind applications. The overall framework of the model, and an application to a stiff glacialclay till soil, is described in a companion paper (Byrne et al. 2019b); the current paper describes analternative formulation that has been developed for soil reaction curves that are applicable tomonopiles installed at offshore homogenous sand sites, for drained loading. The 1D model iscalibrated using data from a set of three dimensional finite element analyses, conducted over acalibration space comprising pile geometries, loading configurations and soil relative densities thatspan typical design values. The performance of the model is demonstrated by the analysis of exampledesign cases. The current form of the model is applicable to homogeneous soil and monotonicloading, although extensions to soil layering and cyclic loading are possible.

Journal article

Byrne BW, Houlsby GT, Burd HJ, Gavin K, Igoe D, Jardine RJ, Martin CM, McAdam RA, Potts DM, Taborda D, Zdravkovic Let al., PISA design model for monopiles for offshore wind turbines: application to a stiff glacial clay till, Geotechnique, ISSN: 0016-8505

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

Journal article

Cui W, Potts DM, Zdravković L, Gawecka KA, Tsiampousi Aet al., 2019, Formulation and application of 3D THM-coupled zero-thickness interface elements, Computers and Geotechnics, Vol: 116, Pages: 1-11, ISSN: 0266-352X

Interface elements are frequently employed in finite element (FE) analyses to represent soil-structure interfaces or rock joints. The modelling of coupled thermo-hydro-mechanical (THM) problems in geotechnical engineering requires equally a coupled and robust THM formulation for interface elements. This paper presents such a formulation which is capable of reproducing the coupled THM behaviour of discontinuities and soil-structure boundaries, and is compatible with other types of finite elements used to discretise the soil and structural domains (e.g. solid and shell elements). The coupled THM three-dimensional (3D) zero-thickness interface element is implemented into the bespoke FE code employed in this research and its features are verified using a number of numerical exercises. To demonstrate their performance, the proposed interface elements are employed in the simulation of the coupled THM behaviour of a fissured triaxial sample subjected to a thermal load and the influence of the presence of fissures on soil behaviour is presented.

Journal article

Avgerinos V, Potts DM, Standing JR, Wan MSP, Ieronymaki ES, Boukin K, Whittle AJet al., 2019, Predicting tunnelling-induced ground movements and interpreting field measurements using numerical analysis: Crossrail case study at Hyde Park DISCUSSION, Géotechnique, Vol: 69, Pages: 936-939, ISSN: 0016-8505

Journal article

Sailer E, Taborda D, Zdravkovic L, Potts D, Pang MHet al., Long-term thermal performance of a thermo-active retaining wall, XVII European Conference on Soil Mechanics and Geotechnical Engineering

Conference paper

Liu R, Taborda D, Gawecka K, Cui W, Potts Det al., Computational study on the effects of boundary conditions on the modelled thermally induced axial stresses in thermo-active piles, XVII European Conference on Soil Mechanics and Geotechnical Engineering

Conference paper

Taborda D, Zdravkovic L, Potts DM, Burd HJ, Byrne BW, Gavin K, Houlsby GT, Jardine RJ, Liu T, Martin CM, McAdam RAet 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.

Journal article

Sailer E, Taborda DMG, Zdravkovic L, Potts DMet al., 2019, Assessing the impact of vertical heat exchangers on the response of a retaining wall, 7th International Symposium on Deformation Characteristics of Geomaterials (IS-Glasgow 2019), Publisher: EDP Sciences, ISSN: 2267-1242

Shallow geothermal energy systems, e.g. borehole heat exchangers or thermo-active structures, provide sustainable space heating and cooling by exchanging heat with the ground. When installed within densely built urban environments, the thermo-hydro-mechanical (THM) interactions occurring due to changes in ground temperature, such as soil deformation and development of excess pore water pressures, may affect the mechanical behaviour of adjacent underground structures. This paper investigates the effects of vertical heat exchangers installed near a deep basement by performing fully coupled THM finite element analyses using the Imperial College Finite Element Program. Different heat exchanger configurations are considered and their influence on the response of the basement wall is assessed in two-dimensional plane strain analyses, where different methods of modelling the heat sources in this type of analysis are employed to evaluate their effect on the temperature field and the non-isothermal soil response.

Conference paper

Ghiadistri G, Zdravković L, Potts DM, Tsiampousi Aet al., 2019, Calibration of a double structure constitutive model for unsaturated compacted soils, 7th International Symposium on Deformation Characteristics of Geomaterials (IS-Glasgow 2019), Publisher: EDP Sciences, Pages: 1-6

This paper describes a calibration procedure for the double structure constitutive model ICDSM (Imperial College Double Structure Model), developed for highly expansive clays, when the model is applied to MX-80 bentonite. Firstly, the model calibration process is discussed and organised in a number of hierarchical steps. These steps involve the estimation of the macrostructural parameters that can be derived from oedometer, isotropic and triaxial laboratory data. Estimation of the microstructural parameters is more challenging due to the limited knowledge of an expansive clay’s fabric and of the physico-chemical phenomena that control its evolution upon wetting. Nevertheless, this paper discusses the available sources of data and identifies the appropriate information that is needed to characterise the micro-structural behaviour of the bentonite. Finally, through the simulation of a swelling pressure test on a bentonite plug, the hydration of the material is studied as a hydro-mechanical coupled process. Particular attention is devoted to the evolution of the stress state of the sample, which is compared to the experimental measurements in order to demonstrate that the constitutive model accurately reproduces the expansive behaviour of MX-80 bentonite.

Conference paper

Pedro A, Zdravkovic L, Potts D, Almeida e Sousa Jet al., 2019, Numerical modelling of the Ivens shaft construction in Lisbon, Portugal, Proceedings of the ICE - Geotechnical Engineering, Vol: 172, Pages: 263-282, ISSN: 1353-2618

The traditional use of shafts is that of simple geotechnical structures, built to provide direct access to the subsoil to either access existing facilities, or to provide a launch chamber for new excavations. More recently, shafts have been constructed with complex geometries and directly incorporated as part of a permanent basement or metro station. One such complex structure is the Ivens shaft in Lisbon, Portugal, which is yet to be built. The construction of this shaft represents a geotechnical challenge due to its complex shape and location in central Lisbon, surrounded by several historic buildings and having in its close vicinity the Baixa-Chiado metro station. This paper presents a sophisticated 3D numerical simulation of the Ivens shaft construction, with a focus on assessing its effect on the existing buildings and the metro station and on the structural forces induced in its lining. The importance of integrating in the analysis the appropriate constitutive modelling of the different formations, the realistic initialisation of the ground conditions and the stiffness of the buildings, is discussed in detail. Although this is a class A prediction of a specific case study, it provides an insight into the general soil-structure interaction of a complex underground excavation.

Journal article

Sailer E, Taborda D, Zdravkovic L, Potts Det al., 2019, Fundamentals of the coupled thermo-hydro-mechanical behaviour of thermo-active retaining walls, Computers and Geotechnics, Vol: 109, Pages: 189-203, ISSN: 0266-352X

Geotechnical structures can be employed to provide renewable and cost-effective thermal energy to buildings. To date, limited field studies regarding thermo-active retaining walls exist and therefore their mechanical response under non-isothermal conditions requires further research to comprehend their behaviour. This paper investigates the response of a hypothetical thermo-active diaphragm wall by performing finite element analysis to characterise in detail its short and long term response. The soil-structure interaction mechanisms arising from the coupled thermo-hydro-mechanical nature of soil behaviour are for the first time identified and shown to be complex and highly non-linear. Subsequently, simpler modelling approaches are used to isolate and quantify the impact of the various identified mechanisms on the design of thermo-active retaining walls. It is concluded that simpler approaches tend to overestimate structural forces developing due to temperature changes in the retaining wall, while severely underestimating the associated ground movements, which are highly influenced by the development of thermally-induced excess pore water pressures. Furthermore, the results suggest that the behaviour of thermo-active retaining walls is highly transient in nature, as a result of the high rates of heat transfer and pore water pressure dissipation under plane strain assumptions.

Journal article

Wan MSP, Standing JR, Potts DM, Burland JBet al., 2019, Pore water pressure and total horizontal stress response to EPBM tunnelling in London Clay, Géotechnique, Vol: 69, Pages: 434-457, ISSN: 0016-8505

The ground response, in terms of surface and subsurface displacements, to twin-bore Crossrail tunnel construction beneath a research monitoring site in Hyde Park, London, using earth-pressure-balance machines (EPBMs) in London Clay, has recently been reported in two companion papers by the authors. This third paper presents and discusses corresponding changes in pore water pressure and total horizontal stress measured using multi-level piezometers and pushed-in spade cells. The three papers together provide a comprehensive and completely unique field monitoring case history of the short-term ground response to EPBM tunnelling in London Clay, making them invaluable for validating future numerical analyses. The fully grouted vibrating-wire piezometers were able to measure the rapid pore water pressure changes around the tunnels as they were constructed. Five distinct immediate pore water pressure responses are identified, induced by different stages of the tunnel drives as the EPBMs approached and passed the instruments. The responses are correlated with tunnel-boring machine operation variables and a postulated arching mechanism, identified for the first time through field measurements. The sense and magnitude of changes in horizontal total stress were reasonable and are correlated with overall pore water pressure changes. Both responses are linked where possible with measured subsurface displacements and generally correlate well, at least qualitatively. Limitations to the measurements and influencing factors are also discussed.

Journal article

Tsaparli V, Kontoe S, Taborda D, Potts Det al., 2019, A case study of liquefaction: demonstrating the application of an advanced model and understanding the pitfalls of the simplified procedure, Géotechnique, ISSN: 0016-8505

The complexity of advanced constitutive models often dictates that their capabilities are only demonstrated in the context of model testing under controlled conditions. In the case of earthquake engineering and liquefaction in particular, this restriction is magnified by the difficulties in measuring field behaviour under seismic loading. In this paper, the well documented case of the Canterbury Earthquake Sequence in New Zealand, for which extensive field and laboratory data are available, is utilised to demonstrate the accuracy of a bounding surface plasticity model in fully-coupled finite element analyses. A strong motion station with manifestation of liquefaction and the second highest peak vertical ground acceleration during the Mw 6.2 February 2011 event is modelled. An empirical assessment predicted no liquefaction for this station, making this an interesting case for rigorous numerical modelling. The calibration of the model aims at capturing both the laboratory tests and the field measurements in a consistent manner. The characterisation of the ground conditions is presented, while, to specify the bedrock motion, the records of two stations without liquefaction are deconvolved and scaled to account for wave attenuation with distance. The numerical predictions are compared to both the horizontal and vertical acceleration records and other field observations, showing a remarkable agreement, also demonstrating that the high vertical accelerations can be attributed to compressional resonance. The results provide further insights into the underperformance of the simplified procedure.

Journal article

Norambuena R, Tsaparli V, Kontoe S, Taborda D, Potts Det al., 2019, The effect of irregular seismic loading on the validity of the simplified liquefaction procedures, Obras y Proyectos, Pages: 42-50, ISSN: 0718-2805

Soil liquefaction has been one of the major hazards for civil engineering projects relating to earthquakes. The simplified liquefaction procedure which is used to assess liquefaction susceptibility in practice is still based on semi-empirical methods. These rely on the assumption that irregular seismic motions can be represented fully by an equivalent number of cycles of uniform stress amplitude, which is based on the peak acceleration measured at ground surface. Most methodologies used to calculate the equivalent number of cycles are based on Miner's damage concept developed for the fatigue analysis of metals. Several researchers have questioned the validity of this concept, as soils have a highly non-linear response. The present work investigates numerically the concept of the equivalent uniform amplitude cycles. Effective stress-based non-linear finite element analyses are performed with a modified bounding surface plasticity model that allows to realistically simulate liquefaction, reproducing the cyclic strength of sands accurately. The seismic response of a 15 m deep uniform level-ground sand deposit is simulated with full hydro-mechanical coupling to establish the benchmark extent of liquefaction zone. In parallel, the analyses are repeated assuming drained conditions to compute the irregular time-histories, which are then converted to an equivalent number of uniform amplitude cycles. The constant amplitude series are then applied in single element simple shear test simulations, with initial conditions those corresponding to the 7 m depth in the deposit. The results in terms of the predicted triggering of liquefaction are contrasted to the predictions of the fully coupled benchmark analyses at the corresponding depth to assess the validity of the Seed et al. (1975) methodology, based on Miner's cumulative damage concept.

Journal article

Cui W, Gawecka KA, Taborda D, Potts DM, Zdravkovic Let al., 2019, Time-step constraints for finite element analysis of two-dimensional transient heat diffusion, Computers and Geotechnics, Vol: 108, Pages: 1-6, ISSN: 0266-352X

In a FE analysis of transient heat transfer, a lower limit of the time-step size exists below which numerical oscillations of temperatures may occur. Although time-step constraints for simulating 1D heat diffusion have been well established in the literature, the conclusions cannot be directly applied to 2D cases. In this paper, both analytical and computational studies are carried out to obtain the time-step constraints for 2D linear and quadratic elements. It is noted that in the simulation of 2D heat diffusion employing quadratic elements is not always beneficial. Recommendations are provided on selecting the numerical scheme to minimise numerical oscillations.

Journal article

Byrne BW, Burd HJ, Gavin K, Houlsby GT, Jardine RJ, McAdam RA, Martin CM, Potts DM, Taborda DMG, Zdravkovic Let al., 2019, PISA: Recent developments in offshore wind turbine monopile design, 1st Vietnam Symposium on Advances in Offshore Engineering, Publisher: Springer

This paper provides a brief overview of the Pile Soil Analysis (PISA) project, recently completed in the UK. The research was aimed at developing new design methods for laterally loaded monopile foundations, such as those supporting offshore wind turbine structures. The paper first describes the background to the project and briefly outlines the key research elements completed. The paper concludes with a brief description of the anticipated impact of the work and describes initiatives that have followed since.

Conference paper

Sailer E, Taborda DMG, Zdravkovic L, Potts DMet al., 2019, Numerical modelling of thermo-active shafts, 2nd Symposium in Energy Geotechnics, Pages: 97-104, ISSN: 1866-8755

© Springer Nature Switzerland AG 2019. Geotechnical structures, such as foundation piles, retaining walls and tunnel linings, are increasingly employed to produce geothermal energy for space heating and cooling. However, the exchange of heat between the structure and the ground induces additional structural forces and contributes to further structural and ground movements, which may affect the serviceability and stability of such structures. While numerous field and numerical studies exist regarding the response of geothermal piles, no investigations have been carried out to characterise the response of thermo-active shafts. This paper presents a numerical study of the short and long term behaviour of hypothetical thermo-active shafts through fully coupled thermo-hydro-mechanical (THM) finite element (FE) analyses using the Imperial College Finite Element Program (ICFEP), where the effect of changing the structure’s geometric characteristics is investigated.

Conference paper

Gawecka KA, Potts DM, Cui W, Taborda DMG, Zdravkovic Let al., 2018, A coupled thermo-hydro-mechanical finite element formulation of one-dimensional beam elements for three-dimensional analysis, Computers and Geotechnics, Vol: 104, Pages: 29-41, ISSN: 0266-352X

Finite element (FE) analysis in geotechnical engineering often involves entities which can be represented as one-dimensional elements in three-dimensions (e.g. structural components, drains, heat exchanger pipes). Although structural components require an FE formulation accounting only for their mechanical behaviour, for the latter two examples, a coupled approach is necessary. This paper presents the first complete coupled thermo-hydro-mechanical FE formulation for one-dimensional beam elements for three-dimensional analysis. The possibility of deactivating each of the systems enables simulation of both coupled and uncoupled behaviour, and hence a range of engineering problems. The performance of these elements is demonstrated through various numerical simulations.

Journal article

Zdravkovic L, Taborda D, Potts D, Abadias Gomez D, Burd HJ, Byrne BW, Gavin K, Houlsby GT, Jardine RJ, Martin CM, McAdam RA, Ushev Eet 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.

Journal article

Cui W, Potts DM, Zdravkovic L, Gawecka K, Taborda DMG, Tsiampousi Aet al., 2018, A coupled thermo-hydro-mechanical finite element formulation for curved beams in two-dimensions, Computers and Geotechnics, Vol: 103, Pages: 103-114, ISSN: 0266-352X

To enable the use of beam elements in the modelling of coupled thermo-hydro-mechanical (THM) geotechnical problems, a fully coupled and robust THM formulation is required. This paper presents such a formulation which allows both fluid flow and heat transfer along a 2D curved beam, while ensuring compatibility with coupled THM solid elements commonly used to discretise soils. Verification exercises and application with the proposed coupled beam element are carried out to demonstrate its satisfactory behaviour. The results of these analyses are compared against closed form solutions, solutions obtained using solid elements, and field measurements, showing an excellent agreement.

Journal article

Byrne B, McAdam RA, Burd HJ, Beuckelaers WJAP, Gavin K, Houlsby GT, Igoe D, Jardine RJ, Martin CM, Muir Wood A, Potts DM, Skov Gretlund J, Taborda D, Zdravkovic Let 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.

Journal article

Zdravkovic L, Jardine R, Taborda DMG, Abadias Gomez D, Burd HJ, Byrne BW, Gavin K, Houlsby GT, Igoe D, Liu T, Martin CM, McAdam RA, Muir Wood A, Potts D, Skov Gretlung J, Ushev Eet 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.

Journal article

McAdam RA, Byrne BW, Houlsby GT, Beuckelaers WJAP, Burd HJ, Gavin K, Igoe D, Jardine RJ, Martin CM, Muir Wood A, Potts DM, Skov Gretlund J, Taborda DMG, Zdravkovic Let 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.

Journal article

Burd HJ, Beuckelaers WJAP, Byrne BW, Gavin K, Houlsby GT, Igoe D, Jardine RJ, Martin CM, McAdam RA, Muir Wood A, Potts DM, Skov Gretlund J, Taborda DMG, Zdravkovic Let 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.

Journal article

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