121 results found
Morimoto T, Zhao B, Taborda D, et al., 2022, Critical appraisal of pore network models to simulate fluid flow through assemblies of spherical particles, Computers and Geotechnics, Vol: 150, Pages: 1-20, ISSN: 0266-352X
Coupled numerical models considering fluid flow and particle movement enable fundamental analyses of a variety of phenomena in geomechanics including seepage-induced instabilities. Amongst the various CFD (Computational Fluid Dynamics)-DEM (Discrete Element Method) coupled frameworks which have been proposed, Pore Network Models (PNMs) have the potential to simulate fluid flow in granular materials accurately with a low computational cost to enable simulations on Representative Volume Elements (RVEs). However, the current models of the local conductance between the connected pores are very simple, limiting the accuracy of PNMs. This study develops novel local conductance models by detailed analysisof existing analytical studies of fluid flow through different 3D lattice packings of uniform spheres. The performance of these new models relative to existing, simpler models is demonstrated using CFD simulations in which the flow in the pore space of random assemblies of polydisperse spheres is accurately resolved. The analyses show that the new models proposed here can more accurately predict the local and global permeabilities of specimens with a wide range of void ratios and polydispersities. These models do not require any optimisation via merging pores so that they can efficiently simulate systems with an evolving pore space topology.
Sailer E, Taborda D, Zdravkovic L, et al., 2022, A novel method for designing thermo-active retaining walls using two dimensional analyses, Proceedings of the Institution of Civil Engineers: Geotechnical Engineering, Vol: 175, Pages: 289-310, 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.
Loveridge F, Schellart A, Rees S, et al., 2022, The potential for heat recovery and thermal energy storage in the UK using buried infrastructure, Proceedings of the Institution of Civil Engineers - Smart Infrastructure and Construction, Vol: 175, Pages: 10-26
Dispersed space heating alone accounts for 40% of UK energy use and 20% of CO2 emissions. Tackling heating and building cooling demands is therefore critical to achieve net zero ambitions in the UK. The most energy efficient way to decarbonise heating and cooling is through the use of ground source heat pumps and district heating technology. However, capital costs are often high, sometimes prohibitively so. To reduce investment costs, it is proposed to use buried infrastructure as sources and stores of thermal energy. Barriers to this innovative approach include lack of knowledge about the actual net amount of recoverable energy, and impacts on the primary function of any buried infrastructure, as well as the need for new investment and governance strategies integrated across the energy and infrastructure sectors. Additional opportunities from thermal utilisation in buried infrastructure include the potential mitigation of damaging biological and/or chemical processes that may occur. This paper presents a first assessment of the scale of the opportunity for thermal energy recovery and storage linked to new and existing buried infrastructure, along with strategic measures to help reduce barriers and start the UK on the journey to achieving of its infrastructure energy potential.
Taborda D, Goncalves Pedro A, Pirrone A, 2022, A state parameter-dependent constitutive model for sands based on the Mohr-Coulomb failure criterion, Computers and Geotechnics, Vol: 148, ISSN: 0266-352X
Experimental data have demonstrated that a strong relationship exists between the state parameter and the peak strength and dilatancy characteristics of sands. This paper proposes a way of reproducing this behaviour using a modified Mohr-Coulomb failure criterion, which retains its simplicity while improving substantially its modelling capabilities. The formulated constitutive model is calibrated for Nevada sand following a well-defined procedure and used in the prediction of four centrifuge tests investigating the behaviour of axially loaded footings. It is shown that the proposed model reproduces well both the element tests and the morecomplex footing problems, demonstrating its usefulness for engineering practice. Moreover, a simplified version which does not require the definition of the Critical State Line is proposed for situations when this aspect of soil behaviour cannot be determined with confidence. It is shown that such simplification results in only slightly less accurate predictions than the full version of the model, while simulating aspects of soil response that cannot be reproduced using constant values for strength and dilatancy parameters.
Liu R, Taborda D, Fisher A, et al., 2021, Development of a practical heat of hydration model for concrete curing for geotechnical applications, Geotechnical Research, Vol: 9, ISSN: 2052-6156
Thermal integrity profiling (TIP) is a common non-destructive technique to evaluate the quality of construction of piles by analysing the temperature fields due to heat of hydration from freshly cast concrete piles. For this process to be accurate, a reliable concrete heat of hydration model is required. This paper proposes a practical and simple to calibrate four parameter model for the prediction of concrete heat of hydration. This model has been shown to be able to reproduce the evolution of heat of hydration measured in laboratory tests, as well as field measurements of temperature within curing concrete piles, as part of a thermal integrity profiling (TIP) operation performed at a site in London. With the simplicity of the model and the small number of model parameters involved, this model can be easily and quickly calibrated, enabling quick predictions of expected temperatures for subsequent casts using the same concrete mix.
Morimoto T, O'Sullivan C, Taborda D, 2021, Exploiting DEM to Link Thermal Conduction and Elastic Stiffness in Granular Materials, Journal of Engineering Mechanics, Vol: 148, ISSN: 0733-9399
Estimating the effective thermal conductivity (ETC) of granular materials is important in various engineering disciplines. The ETC of a granular material is not unique, rather it depends upon the material's packing characteristics, i.e. porosity and coordination number. Directly measuring the ETC of granular materials with a particular packing density and subjected to specific stress conditions is experimentally challenging. There is a need to develop reliable, indirect experimental methods to measure the ETC of granular materials. Here we explore the possibility of linking the ETC of granular materials to their elastic moduli.This study used a thermal pipe network model implemented in a Discrete Element Method (DEM) code to generate ETC data for ideal, virtual two-phase granular samples with stagnant pore fluid. Parametric studies considered the sensitivity of the ETC to the sample packing. Data from small deformation probes were used to explore links between the samples' elastic moduli and their ETCs. The results provide a theoretical background for the development of an indirect experimental method to predict the ETC or trends in the variation in the ETC by considering stiffness data which are relatively straightforward to acquire. The study shows how DEM can be used as a sophisticated thought experiment to explore novel ideas for developing experimental procedures.
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.
Gawecka K, Cui W, Taborda D, et 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
Sailer E, Taborda DMG, Zdravkovic L, et 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.
Morimoto T, O'Sullivan C, Taborda D, 2021, Analytical and DEM studies of thermal stress in granular materials, Powders and Grains 2021, Publisher: EDP Sciences, Pages: 1-4, ISSN: 2100-014X
The ability to predict thermal-induced stresses in granular materials is of practical importance across a range of disciplines ranging from process engineering to geotechnical engineering. This study presents an analytical formula to predict thermal-induced stress increments in mono-disperse granular materials subject to an initial isotropic stress state. A complementary series of DEM simulations were carried out to explore the applicability of the proposed analytical formula. The comparative analysis showed that the proposed expression can accurately predict stress changes in packings where there are negligible particle displacements as a consequence of the thermal loading (e.g. regular packings and medium/dense random packings); however large errors were observed in loose samples with a random packing.
Lopez AR, Tsiampousi A, Taborda DMG, et al., 2021, Numerical investigation into time-dependent effects on short-term tunnelling-induced ground response in London Clay, 10th International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground (IS-Cambridge), Publisher: ROUTLEDGE, Pages: 597-604
Moeller JK, Kontoe S, Taborda D, et 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.
Grammatikopoulou A, Schroeder FC, Pedone G, et al., 2020, 3D finite element analysis of monopiles and its application in offshore wind farm design, 4th International Symposium on Frontiers in Offshore Geotechnics
Zdravkovic L, Taborda DMG, Potts DM, 2020, Effect of interface conditions on the response of laterally loaded monopiles in sand, 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
Tsaparli V, Kontoe S, Taborda D, et 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.
Liu R, Sailer E, Taborda D, et 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.
Sailer E, Taborda D, Zdravkovic L, et 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.
Burd HJ, Beuckelaers WJAP, Byrne BW, et al., 2020, New data analysis methods for instrumented medium scale monopile field tests, Géotechnique, Vol: 70, Pages: 961-969, ISSN: 0016-8505
The PISA Joint Industry Research Project was concerned with the development of improved design methods for monopile foundations in offshore wind applications. PISA involved large-scale pile tests in overconsolidated glacial till at Cowden, north-east England, and in dense, normally consolidated marine sand at Dunkirk, northern France. This paper describes the experimental set-up for pile testing, with unique features of load-application mechanisms and built-in fibre optic strain gauges. New procedures are described for the interpretation of pile loading data, and specifically for providing precise interpretation of pile displacements.
Burd HJ, Taborda D, Zdravkovic L, et al., 2020, PISA design model for monopiles for offshore wind turbines: application to a marine sand, Geotechnique, Vol: 70, Pages: 1048-1066, ISSN: 0016-8505
This paper describes a one-dimensional (1D) computational model for the analysis and design of laterally loaded monopile foundations for offshore wind turbine applications. The model represents the monopile as an embedded beam and specially formulated functions, referred to as soil reaction curves, are employed to represent the various components of soil reaction that are assumed to act on the pile. This design model was an outcome of a recently completed joint industry research project – known as PISA – on the development of new procedures for the design of monopile foundations for offshore wind applications. The overall framework of the model, and an application to a stiff glacial clay till soil, is described in a companion paper by Byrne and co-workers; the current paper describes an alternative formulation that has been developed for soil reaction curves that are applicable to monopiles installed at offshore homogeneous sand sites, for drained loading. The 1D model is calibrated using data from a set of three-dimensional finite-element analyses, conducted over a calibration space comprising pile geometries, loading configurations and soil relative densities that span typical design values. The performance of the model is demonstrated by the analysis of example design cases. The current form of the model is applicable to homogeneous soil and monotonic loading, although extensions to soil layering and cyclic loading are possible.
Byrne B, McAdam RA, Burd HJ, et al., 2020, Monotonic laterally loaded pile testing in a stiff glacial clay till at Cowden, Géotechnique, Vol: 70, Pages: 970-985, ISSN: 0016-8505
This paper describes the results obtained from a field testing campaign on laterally loaded monopiles conducted at Cowden, UK, where the soil consists principally of a heavily overconsolidated glacial till. These tests formed part of the PISA project on the development of improved design methods for monopile foundations for offshore wind turbines. Results obtained for monotonic loading tests on piles of three different diameters (0·273 m, 0·762 m and 2·0 m) are presented. The piles had length-to-diameter ratios (L/D) of between 3 and 10. The tests included the application of monotonic loading incorporating periods of constant load to investigate creep effects, and investigations on the influence of loading rate. Data are presented on measured bending moments and inclinations induced in the piles. Inferred data on lateral displacements of the embedded section of the piles are determined using an optimised structural model. These field data support the development of a new one-dimensional modelling approach for the design of monopile foundations for offshore wind turbines. They also form a unique database of field measurements in an overconsolidated clay, from lateral loading of piles at a vertical distance above the ground surface.
Zdravkovic L, Jardine R, Taborda DMG, et al., 2020, Ground characterisation for PISA pile testing and analysis, Géotechnique, Vol: 70, Pages: 945-960, ISSN: 0016-8505
This paper is the first of a set of linked publications on the PISA Joint Industry Research Project, which was concerned with the development of improved design methods for monopile foundations in offshore wind applications. PISA involved large-scale pile tests in overconsolidated glacial till at Cowden, north-east England, and in dense, normally consolidated marine sand at Dunkirk, northern France. The paper presents the characterisation of the two sites, which was crucial to the design of the field experiments and advanced numerical modelling of the pile–soil interactions. The studies described, which had to be completed at an early stage of the PISA project, added new laboratory and field campaigns to historic investigations at both sites. They enabled an accurate description of soil behaviour from small strains to ultimate states to be derived, allowing analyses to be undertaken that captured both the serviceability and limit state behaviour of the test monopiles.
McAdam RA, Byrne BW, Houlsby GT, et al., 2020, Monotonic lateral loaded pile testing in a dense marine sand at Dunkirk, Géotechnique, Vol: 70, Pages: 986-998, ISSN: 0016-8505
The results obtained from a field testing campaign on laterally loaded monopiles, conducted at a dense sand site in Dunkirk, northern France are described. These tests formed part of the PISA project on the development of improved design methods for monopile foundations for offshore wind turbines. Results obtained from monotonic loading tests on piles of three different diameters (0·273 m, 0·762 m and 2·0 m) are presented. The piles had length-to-diameter ratios (L/D) of between 3 and 10. The tests consisted principally of the application of monotonic loads, incorporating periods of held constant load to investigate creep effects. The influence of loading rate was also investigated. Data are presented on the overall load–displacement behaviour of each of the test piles. Measured data on bending moments and inclinations induced in the piles are also provided. Inferences are made for the displacements in the embedded length of the piles. These field data will support the development of a new one-dimensional modelling approach for the design of monopile foundations for offshore wind turbines. They also form a unique database of field measurements in a dense sand, from lateral loading of piles at a vertical distance above the ground surface.
Byrne BW, Houlsby GT, Burd HJ, et al., 2020, PISA design model for monopiles for offshore wind turbines: application to a stiff glacial clay till, Geotechnique, Vol: 70, Pages: 1030-1047, ISSN: 1021-8637
Offshore wind turbines in shallow coastal waters are typically supported on monopile foundations.Although three dimensional (3D) finite element methods are available for the design of monopiles inthis context, much of the routine design work is currently conducted using simplified one dimensional(1D) models based on the p-y method. The p-y method was originally developed for the relativelylarge embedded length-to-diameter ratio (L/D) piles that are typically employed in offshore oil and gasstructures. Concerns exist, however, that this analysis approach may not be appropriate formonopiles with the relatively low values of L/D that are typically adopted for offshore wind turbinestructures. This paper describes a new 1D design model for monopile foundations; the model isspecifically formulated for offshore wind turbine applications although the general approach could beadopted for other applications. The model draws on the conventional p-y approach, but extends it toinclude additional components of soil reaction that act on the pile. The 1D model is calibrated using aset of bespoke 3D finite element analyses of monopile performance, for pile characteristics andloading conditions that span a predefined design space. The calibrated 1D model provides results thatmatch those obtained from the 3D finite element calibration analysis, but at a fraction of thecomputational cost. Moreover, within the calibration space, the 1D model is capable of delivering highfidelity computations of monopile performance that can be used directly for design purposes. This 1Dmodelling approach is demonstrated for monopiles installed in a stiff overconsolidated glacial clay tillwith a typical North Sea strength and stiffness profile. Although the current form of the model hasbeen developed for homogeneous soil and monotonic loading, it forms a basis from which extensionsfor soil layering and cyclic loading can be developed. The general approach can be applied to otherfoundation and soil-structu
Zdravkovic L, Taborda D, Potts D, et al., 2020, Finite-element modelling of laterally loaded piles in a stiff glacial clay till at Cowden, Geotechnique: international journal of soil mechanics, Vol: 70, Pages: 999-1013, ISSN: 0016-8505
The PISA project was a combined field testing/numerical modelling study with the aim of developing improved design procedures for large-diameter piles subjected to lateral loading. This paper describes the development of a three-dimensional finite-element model for the medium-scale pile tests that were conducted in Cowden till as part of the PISA work. The paper places particular emphasis on the consistent interpretation of the soil data determined from the available field and laboratory information. An enhanced version of the modified Cam clay model was employed in the numerical analyses, featuring a non-linear Hvorslev surface, a generalised shape for the yield and plastic potential surfaces in the deviatoric plane and a non-linear formulation for the elastic shear modulus. Three-dimensional finite-element analyses were performed prior to the field tests. Excellent agreement between the measured and simulated behaviour for a range of pile geometries was observed, demonstrating the accuracy of the numerical model and the adequacy of the calibration process for the constitutive model. The developed numerical model confirmed the premise of the PISA design method that site-specific ground characterisation and advanced numerical modelling can directly facilitate the development of additional soil reaction curves for use in new design models for laterally loaded piles in a stiff clay till.
Taborda D, Zdravkovic L, Potts DM, et al., 2020, Finite-element modelling of laterally loaded piles in a dense marine sand at Dunkirk, Geotechnique: international journal of soil mechanics, Vol: 70, Pages: 1014-1029, ISSN: 0016-8505
The paper presents the development of a three-dimensional finite-element model for pile tests in dense Dunkirk sand, conducted as part of the PISA project. The project was aimed at developing improved design methods for laterally loaded piles, as used in offshore wind turbine foundations. The importance of the consistent and integrated interpretation of the soil data from laboratory and field investigations is particularly emphasised. The chosen constitutive model for sand is an enhanced version of the state parameter-based bounding surface plasticity model, which, crucially, is able to reproduce the dependency of sand behaviour on void ratio and stress level. The predictions from three-dimensional finite-element analyses, performed before the field tests, show good agreement with the measured behaviour, proving the adequacy of the developed numerical model and the calibration process for the constitutive model. This numerical model directly facilitated the development of new soil reaction curves for use in Winkler-type design models for laterally loaded piles in natural marine sands.
Burd H, Abadie C, Byrne B, et al., 2020, Application of the PISA design model to monopiles embedded in layered soils, Geotechnique, Vol: 70, Pages: 1067-1082, ISSN: 1021-8637
The PISA design model is a procedure for the analysis of monopile foundations for offshore windturbine applications. This design model has been previously calibrated for homogeneous soils; thispaper extends the modelling approach to the analysis of monopiles installed at sites where the soilprofile is layered. We describe a computational study on monopiles embedded in layered soilconfigurations comprising selected combinations of soft and stiff clay and sand at a range of relativedensities. The study comprises (i) analyses of monopile behaviour using detailed three dimensional(3D) finite element analysis, and (ii) calculations employing the PISA design model. Results from the3D analyses are used to explore the various influences that soil layering has on the performance ofthe monopile. The fidelity of the PISA design model is assessed by comparisons with data obtainedfrom equivalent 3D finite element analyses, demonstrating a good agreement in most cases. Thiscomparative study demonstrates that the PISA design model can be applied successfully to layeredsoil configurations, except in certain cases involving combinations of very soft clay and very densesand.
Liu R, Sailer E, Taborda D, et 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.
Tsaparli V, Kontoe S, Taborda D, et 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.
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.