Imperial College London

Dr David M. G. Taborda

Faculty of EngineeringDepartment of Civil and Environmental Engineering

Senior Lecturer
 
 
 
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Contact

 

+44 (0)20 7594 6033d.taborda Website

 
 
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Assistant

 

Ms Sue Feller +44 (0)20 7594 6077

 
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Location

 

432Skempton BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

107 results found

Zdravković L, Potts DM, Taborda DMG, 2021, Integrating laboratory and field testing into advanced geotechnical design, Geomechanics for Energy and the Environment, Vol: 27, Pages: 1-21, ISSN: 2352-3808

Contemporary geotechnical design often requires the use of advanced numerical analysis, if it is to take account of the complex nature of many geotechnical problems. One crucial aspect of such analyses is the realistic representation of the facets of soil behaviour that are dominant in any given problem, which in turn requires a careful selection of an appropriate constitutive model and derivation of model parameters from the available, and often disparate, experimental data. This paper uses the authors’ experience of advanced numerical analysis and constitutive modelling to emphasise the importance of close integration of the process involved with interpreting experimental data with the process of selecting and calibrating advanced constitutive models, in successfully predicting the response of geotechnical structures.

Journal article

Gawecka K, Cui W, Taborda D, Potts D, Zdravkovic L, Loukas Aet al., 2021, Predictive modelling of thermo-active tunnels in London Clay, Geotechnique: international journal of soil mechanics, Vol: 71, Pages: 735-748, ISSN: 0016-8505

Thermo-active structures are underground facilities which enable the exchange of thermal energy between the ground and the overlying buildings, thus providing renewable means of space heating and cooling. Although this technology is becoming increasingly popular, the behaviour of geotechnical structures under additional thermal loading is still not fully understood. This paper focuses on the use of underground tunnels as thermo-active structures and explains their behaviour through a series of finite element analyses based on an existing case study of isothermal tunnels in London Clay. The bespoke finite element codeI CFEP is adopted which is capable of simulating the fully coupled thermo-hydro-mechanical behaviour of porous materials. The complex coupled interactions between the tunnel and the surrounding soil are explored bycomparing results from selected types of coupledand uncoupled simulations. It is demonstratedthat: (1) the thermally-induceddeformation of the tunnel and the ground are more critical design aspects than the thermally-induced forces in the tunnel lining, and (2) the modelling approach in terms of the type of analysis, as well as the assumed permeability of the tunnel lining, have a significant effect on the computed tunnel response and,hence, must be chosen carefully

Journal article

Sailer E, Taborda DMG, Zdravkovic L, Potts DM, Cui Wet al., 2021, Thermo-hydro-mechanical interactions in porous media: implications on thermo-active retaining walls, Computers and Geotechnics, Vol: 135, Pages: 1-16, ISSN: 0266-352X

Thermo-active structures exchange heat with the ground to provide thermal energy to buildings. Consequently, the ground is subjected to changes in temperature, inducing thermo-hydro-mechanical (THM) interactions within the soil. To provide insights into the origin and manifestations of the main mechanisms taking place in complex fully THM-coupled finite element (FE) analyses, simple, one-dimensional problems are firstly analysed in this paper and compared to analytical expressions developed for determining thermally-induced excess pore water pressures in undrained problems with different displacement restraints. Subsequently, various dimensionless parameters are established to evaluate the impact of varying ground properties on the observed THM interactions and their evolution with time. Finally, the findings from simple one-dimensional problems are verified in the context of THM modelling of thermo-active retaining walls, where the structural response of walls is shown to be highly transient and influenced by different phenomena prevailing over different periods involving thermal expansion of soils, volumetric deformations due to pore water generation and dissipation, and interactions with mechanical boundary conditions. The results also highlight the importance of performing fully coupled THM analyses and of a correct estimation of the hydraulic and thermal properties to guarantee a safe design of thermo-active structures.

Journal article

Sailer E, Taborda D, Zdravkovic L, Potts DMet al., 2020, 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

Thermo-active retaining walls are geotechnical structures employed as heat exchangers to provide low carbon dioxide heating and cooling to buildings. To assess the thermo-mechanical response of such structures, finite-element (FE) analyses are typically carried out. Due to the presence of heat exchanger pipes, the temperature distribution along the width of the wall is not uniform, implying that these problems are three-dimensional (3D) in nature. However, performing 3D FE analyses including elements to model the heat exchanger pipes to simulate the advective conductive heat transfer as well as thermo-hydro-mechanical coupling to reproduce the non-isothermal soil response accurately requires considerable computational effort. In this work, a novel approach to simulate thermo-active walls in 2D analyses was developed, which requires the sole use of thermal boundary conditions. This approach was found to reproduce average wall behaviour computed in 3D to a high degree of accuracy for numerous wall geometries, a wide range of thermal properties of soil and concrete, and different thermal boundary conditions along the exposed face of the wall. In addition, out-of-plane effects recorded in 3D analyses were assessed and an accurate simplified procedure to account for these when performing 2D analyses was developed.

Journal article

Moeller JK, Kontoe S, Taborda D, Potts Det al., 2020, Maximum depth of liquefaction based on fully-coupled time domain site response analysis, 4th International Symposium on Frontiers in Offshore Geotechnics

Soil susceptibility to liquefaction is most commonly assessed in engineering practice using empirical correlations of in-situ tests with observed surface manifestations of liquefaction in case histories. This simplified design method further incorporates a correction factor for varying overburden pressure, derived from laboratory data, and provides expressions for earthquake induced shear stresses based on simplified one-dimensional equivalent linear site response analysis. The resulting factor of safety against liquefaction is only valid for the depths represented in the laboratory test data, case history data and the site response analyses, i.e. a maximum depth of 20 m. In order to evaluate the susceptibility of soils at larger depths, one-dimensional time-domain site response analyses are carried out, showing the extent of the liquefied zone for sand deposits of different depths. This study evaluates the performance of a bounding surface plasticity model in comparison with a nonlinear elastic cyclic model regarding the amplification and damping of certain frequency contents of shear waves propagating through deep soil deposits. These findings are of particular relevance for applications in offshore geotechnical engineering, where liquefaction in large depths can have severe effects on the load-carrying capacity of deep pile foundations.

Conference paper

Tsaparli V, Kontoe S, Taborda D, Potts Det al., 2020, Resonance as the source of high vertical accelerations: field demonstration and impact on offshore wind turbines, 4th International Symposium on Frontiers in Offshore Geotechnics

Recent studies have demonstrated the significance of the vertical seismic acceleration component for offshore wind turbines, as their low natural period in this direction can result in significant excitation, potentially making this load case design-driving. Unexpectedly high vertical ground accelerations, well exceeding their horizontal counterparts, have also been recorded in a number of recent seismic events. This study explores the concept of resonance between the vertical seismic component and the natural frequency for compressional waves of fully saturated soil deposits, which can aggravate further the vertical accelerations at the top of structures of interest, using numerical analysis and monitoring data. The site response at a strong motion station that registered the second highest peak ground vertical acceleration during the 2011 Mw 6.2 Christchurch earthquake in New Zealand is modelled in finite element analyses. Two different depths are also considered: the first one is truncated at the interface of the softer surficial deposits with the stiff gravel horizon. This has been shown to be adequate for S-wave propagation modelling. Conversely, the second one models the full depth to bedrock. Despite the number of uncertainties involved, the results validate the concept of resonance in compression against field measurements and demonstrate the importance of the modelled depth in the case of vertical site response analysis.

Conference paper

Sailer E, Taborda D, Zdravkovic L, Potts Det al., 2020, Simplified methods for designing thermo-active retaining walls, 2nd International Conference on Energy Geotechnics (ICEGT2020), Publisher: EDP Sciences, Pages: 06011-06011, ISSN: 2267-1242

Thermo-active retaining structures are geotechnical structures employed to provide thermal energy to buildings for space heating and cooling through heat exchanger pipes embedded within the concrete structure. Consequently, the design of these structures needs to consider both the long-term energy efficiency as well as the thermo-mechanical response in terms of stability and serviceability. Transient finite element analyses can be carried out to evaluate the behaviour of thermo-active walls, where the heat exchanger pipes are explicitly modelled, thus requiring three-dimensional (3D) analyses. However, performing long-term 3D finite element analyses is computationally expensive. For this reason, in this study, new approaches are presented that allow the thermal or thermo-mechanical design of thermo-active walls to be carried out by performing two-dimensional (2D) plane strain analyses. Two methods, which are based on different design criteria, are proposed and their performance in replicating the three-dimensional behaviour is assessed. Furthermore, the factors affecting the 2D approximations for the two modelling approaches are evaluated, where particular emphasis is given to the influence of the simulated boundary condition along the exposed face of the retaining wall.

Conference paper

Liu R, Sailer E, Taborda D, Potts Det al., 2020, Evaluating the impact of different pipe arrangements on the thermal performance of thermo-active piles, 2nd International Conference on Energy Geotechnics (ICEGT2020), Publisher: EDP Sciences, Pages: 05006-05006, ISSN: 2267-1242

Thermo-active piles are widely utilised for low carbon heating and cooling, and their uses are further encouraged in cities where there are obligations for developments larger than a certain threshold to generate a portion of their estimated energy use on site in a renewable manner. It is therefore important to model accurately the thermal performance of the designed thermo-active piles to ensure that such obligations are complied with. In this paper, the thermal performance of a thermo-active pile is quantified by the evolution with time of the power that can be harnessed from the pile, obtained from 3D thermo-hydro-mechanically coupled finite element analyses which include the simulation of a hot fluid flowing through heat exchanger pipes. Different pipe arrangements are considered in this study, in order to demonstrate the potential gains in efficiency arising from the installation of multiple U-loops within the pile. Furthermore, detailed analysis of the heat fluxes resulting from pipe-pile-soil interaction is carried out, illustrating the contribution of the different components of the system (concrete, near-field and far-field) to the overall storage of thermal energy.

Conference paper

Byrne BW, Houlsby GT, Burd HJ, Gavin K, Igoe D, Jardine RJ, Martin CM, McAdam RA, Potts DM, Taborda D, Zdravkovic Let 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

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., 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.

Journal article

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., 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.

Journal article

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

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., 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.

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., 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.

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., 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.

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., 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.

Journal article

Burd H, Abadie C, Byrne B, Houlsby G, Martin C, McAdam R, Jardine R, Pedro A, Potts D, Taborda D, Zdravkovic L, Andrade Met 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.

Journal article

Liu R, Sailer E, Taborda D, Potts D, Zdravkovic Let al., 2020, A practical method for calculating thermally-induced stresses in pile foundations used as heat exchangers, Computers and Geotechnics, Vol: 126, Pages: 1-16, ISSN: 0266-352X

Thermo-active piles are capable of providing both structural stability as foundations and low carbon heating and cooling as ground source heat exchangers. When subjected to heating or cooling, the soil surrounding the pile restricts its expansion or contraction, giving rise to thermally-induced axial stresses, which need to be considered during design. Previous numerical studies often assume axisymmetry of the problem and/or a simplification of the heating or cooling mechanism of the pile. To simulate accurately the development of thermallyinduced axial stresses, this paper presents a computational study comprising three dimensional fully coupled thermo-hydro-mechanical finite element analyses conducted using the Imperial College Finite Element Program (ICFEP), where the heating of a thermo-active pile is simulated by prescribing a flow of hot water through the heat exchanger pipes within the pile. The effects of pipe arrangement on thermally-induced axial stresses are investigated by considering three different cases – single U loop, double U-loop and triple U-loop. Since threedimensional analyses are computationally expensive, a simplified method using a combination of two-dimensional analyses is proposed to estimate the thermally-induced axial stresses, which is subsequently validated and shown to yield accurate results.

Journal article

Tsaparli V, Kontoe S, Taborda D, Potts Det al., 2020, A case study of liquefaction: demonstrating the application of an advanced model and understanding the pitfalls of the simplified procedure, Geotechnique: international journal of soil mechanics, Vol: 70, Pages: 538-558, 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

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

Byrne BW, Burd HJ, Zdravkovic L, McAdam RA, Taborda D, Houlsby GT, Jardine RJ, Martin CM, Potts DM, Gavin KGet al., 2019, PISA: new design methods for offshore wind turbine monopiles, Revue Francaise de Geotechnique, ISSN: 0181-0529

Journal article

Liu R, Taborda D, Gawecka K, Cui W, Potts Det al., 2019, 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

Sailer E, Taborda D, Zdravkovic L, Potts D, Pang MHet al., 2019, Long-term thermal performance of a thermo-active retaining wall, XVII European Conference on Soil Mechanics and Geotechnical Engineering

Conference paper

Araujo Santos LM, Coelho PALF, Ramos RC, Taborda Det al., 2019, Characterisation of liquefiable sands using the hollow cylinder apparatus, XVII European Conference on Soil Mechanics and Geotechnical Engineering

Conference paper

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

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

Byrne BW, McAdam RA, Burd H, Houlsby GT, Martin CM, Beuckelaers WJAP, Zdravkovic L, Taborda DMG, Potts DM, Jardine RJ, Ushev E, Liu T, Abadias Gomez D, Gavin K, Igoe D, Doherty P, Skov Gretlund J, Pacheco Andrade M, Muir Wood A, Schroeder FC, Turner S, Plummer MALet al., 2019, PISA: new design methods for offshore wind turbine monopiles, Proceedings of the Society for Underwater Technology Offshore Site Investigation and Geotechnics 8th International Conference on “Smarter Solutions for Future Offshore Developments"

Conference paper

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

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

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