Publications
249 results found
Zdravkovic L, Taborda D, Potts D, et al., 2020, Finite-element modelling of laterally loaded piles in a stiff glacial clay till at Cowden, Geotechnique: international journal of soil mechanics, Vol: 70, Pages: 999-1013, ISSN: 0016-8505
The PISA project was a combined field testing/numerical modelling study with the aim of developing improved design procedures for large-diameter piles subjected to lateral loading. This paper describes the development of a three-dimensional finite-element model for the medium-scale pile tests that were conducted in Cowden till as part of the PISA work. The paper places particular emphasis on the consistent interpretation of the soil data determined from the available field and laboratory information. An enhanced version of the modified Cam clay model was employed in the numerical analyses, featuring a non-linear Hvorslev surface, a generalised shape for the yield and plastic potential surfaces in the deviatoric plane and a non-linear formulation for the elastic shear modulus. Three-dimensional finite-element analyses were performed prior to the field tests. Excellent agreement between the measured and simulated behaviour for a range of pile geometries was observed, demonstrating the accuracy of the numerical model and the adequacy of the calibration process for the constitutive model. The developed numerical model confirmed the premise of the PISA design method that site-specific ground characterisation and advanced numerical modelling can directly facilitate the development of additional soil reaction curves for use in new design models for laterally loaded piles in a stiff clay till.
Taborda D, Zdravkovic L, Potts DM, et al., 2020, Finite-element modelling of laterally loaded piles in a dense marine sand at Dunkirk, Geotechnique: international journal of soil mechanics, Vol: 70, Pages: 1014-1029, ISSN: 0016-8505
The paper presents the development of a three-dimensional finite-element model for pile tests in dense Dunkirk sand, conducted as part of the PISA project. The project was aimed at developing improved design methods for laterally loaded piles, as used in offshore wind turbine foundations. The importance of the consistent and integrated interpretation of the soil data from laboratory and field investigations is particularly emphasised. The chosen constitutive model for sand is an enhanced version of the state parameter-based bounding surface plasticity model, which, crucially, is able to reproduce the dependency of sand behaviour on void ratio and stress level. The predictions from three-dimensional finite-element analyses, performed before the field tests, show good agreement with the measured behaviour, proving the adequacy of the developed numerical model and the calibration process for the constitutive model. This numerical model directly facilitated the development of new soil reaction curves for use in Winkler-type design models for laterally loaded piles in natural marine sands.
Byrne B, McAdam RA, Burd HJ, et al., 2020, Monotonic laterally loaded pile testing in a stiff glacial clay till at Cowden, Géotechnique, Vol: 70, Pages: 970-985, ISSN: 0016-8505
This paper describes the results obtained from a field testing campaign on laterally loaded monopiles conducted at Cowden, UK, where the soil consists principally of a heavily overconsolidated glacial till. These tests formed part of the PISA project on the development of improved design methods for monopile foundations for offshore wind turbines. Results obtained for monotonic loading tests on piles of three different diameters (0·273 m, 0·762 m and 2·0 m) are presented. The piles had length-to-diameter ratios (L/D) of between 3 and 10. The tests included the application of monotonic loading incorporating periods of constant load to investigate creep effects, and investigations on the influence of loading rate. Data are presented on measured bending moments and inclinations induced in the piles. Inferred data on lateral displacements of the embedded section of the piles are determined using an optimised structural model. These field data support the development of a new one-dimensional modelling approach for the design of monopile foundations for offshore wind turbines. They also form a unique database of field measurements in an overconsolidated clay, from lateral loading of piles at a vertical distance above the ground surface.
McAdam RA, Byrne BW, Houlsby GT, et al., 2020, Monotonic lateral loaded pile testing in a dense marine sand at Dunkirk, Géotechnique, Vol: 70, Pages: 986-998, ISSN: 0016-8505
The results obtained from a field testing campaign on laterally loaded monopiles, conducted at a dense sand site in Dunkirk, northern France are described. These tests formed part of the PISA project on the development of improved design methods for monopile foundations for offshore wind turbines. Results obtained from monotonic loading tests on piles of three different diameters (0·273 m, 0·762 m and 2·0 m) are presented. The piles had length-to-diameter ratios (L/D) of between 3 and 10. The tests consisted principally of the application of monotonic loads, incorporating periods of held constant load to investigate creep effects. The influence of loading rate was also investigated. Data are presented on the overall load–displacement behaviour of each of the test piles. Measured data on bending moments and inclinations induced in the piles are also provided. Inferences are made for the displacements in the embedded length of the piles. These field data will support the development of a new one-dimensional modelling approach for the design of monopile foundations for offshore wind turbines. They also form a unique database of field measurements in a dense sand, from lateral loading of piles at a vertical distance above the ground surface.
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.
Zdravkovic L, Jardine R, Taborda DMG, et al., 2020, Ground characterisation for PISA pile testing and analysis, Géotechnique, Vol: 70, Pages: 945-960, ISSN: 0016-8505
This paper is the first of a set of linked publications on the PISA Joint Industry Research Project, which was concerned with the development of improved design methods for monopile foundations in offshore wind applications. PISA involved large-scale pile tests in overconsolidated glacial till at Cowden, north-east England, and in dense, normally consolidated marine sand at Dunkirk, northern France. The paper presents the characterisation of the two sites, which was crucial to the design of the field experiments and advanced numerical modelling of the pile–soil interactions. The studies described, which had to be completed at an early stage of the PISA project, added new laboratory and field campaigns to historic investigations at both sites. They enabled an accurate description of soil behaviour from small strains to ultimate states to be derived, allowing analyses to be undertaken that captured both the serviceability and limit state behaviour of the test monopiles.
Burd HJ, Taborda D, Zdravkovic L, et al., 2020, PISA design model for monopiles for offshore wind turbines: application to a marine sand, Geotechnique, Vol: 70, Pages: 1048-1066, ISSN: 0016-8505
This paper describes a one-dimensional (1D) computational model for the analysis and design of laterally loaded monopile foundations for offshore wind turbine applications. The model represents the monopile as an embedded beam and specially formulated functions, referred to as soil reaction curves, are employed to represent the various components of soil reaction that are assumed to act on the pile. This design model was an outcome of a recently completed joint industry research project – known as PISA – on the development of new procedures for the design of monopile foundations for offshore wind applications. The overall framework of the model, and an application to a stiff glacial clay till soil, is described in a companion paper by Byrne and co-workers; the current paper describes an alternative formulation that has been developed for soil reaction curves that are applicable to monopiles installed at offshore homogeneous sand sites, for drained loading. The 1D model is calibrated using data from a set of three-dimensional finite-element analyses, conducted over a calibration space comprising pile geometries, loading configurations and soil relative densities that span typical design values. The performance of the model is demonstrated by the analysis of example design cases. The current form of the model is applicable to homogeneous soil and monotonic loading, although extensions to soil layering and cyclic loading are possible.
Byrne BW, Houlsby GT, Burd HJ, et al., 2020, PISA design model for monopiles for offshore wind turbines: application to a stiff glacial clay till, Geotechnique, Vol: 70, Pages: 1030-1047, ISSN: 1021-8637
Offshore wind turbines in shallow coastal waters are typically supported on monopile foundations.Although three dimensional (3D) finite element methods are available for the design of monopiles inthis context, much of the routine design work is currently conducted using simplified one dimensional(1D) models based on the p-y method. The p-y method was originally developed for the relativelylarge embedded length-to-diameter ratio (L/D) piles that are typically employed in offshore oil and gasstructures. Concerns exist, however, that this analysis approach may not be appropriate formonopiles with the relatively low values of L/D that are typically adopted for offshore wind turbinestructures. This paper describes a new 1D design model for monopile foundations; the model isspecifically formulated for offshore wind turbine applications although the general approach could beadopted for other applications. The model draws on the conventional p-y approach, but extends it toinclude additional components of soil reaction that act on the pile. The 1D model is calibrated using aset of bespoke 3D finite element analyses of monopile performance, for pile characteristics andloading conditions that span a predefined design space. The calibrated 1D model provides results thatmatch those obtained from the 3D finite element calibration analysis, but at a fraction of thecomputational cost. Moreover, within the calibration space, the 1D model is capable of delivering highfidelity computations of monopile performance that can be used directly for design purposes. This 1Dmodelling approach is demonstrated for monopiles installed in a stiff overconsolidated glacial clay tillwith a typical North Sea strength and stiffness profile. Although the current form of the model hasbeen developed for homogeneous soil and monotonic loading, it forms a basis from which extensionsfor soil layering and cyclic loading can be developed. The general approach can be applied to otherfoundation and soil-structu
Burd H, Abadie C, Byrne B, et al., 2020, Application of the PISA design model to monopiles embedded in layered soils, Geotechnique, Vol: 70, Pages: 1067-1082, ISSN: 1021-8637
The PISA design model is a procedure for the analysis of monopile foundations for offshore windturbine applications. This design model has been previously calibrated for homogeneous soils; thispaper extends the modelling approach to the analysis of monopiles installed at sites where the soilprofile is layered. We describe a computational study on monopiles embedded in layered soilconfigurations comprising selected combinations of soft and stiff clay and sand at a range of relativedensities. The study comprises (i) analyses of monopile behaviour using detailed three dimensional(3D) finite element analysis, and (ii) calculations employing the PISA design model. Results from the3D analyses are used to explore the various influences that soil layering has on the performance ofthe monopile. The fidelity of the PISA design model is assessed by comparisons with data obtainedfrom equivalent 3D finite element analyses, demonstrating a good agreement in most cases. Thiscomparative study demonstrates that the PISA design model can be applied successfully to layeredsoil configurations, except in certain cases involving combinations of very soft clay and very densesand.
Tsiampousi A, Zdravkovic L, Potts DM, 2020, Effect of hydraulic parameters on the computed serviceability of infrastructure slopes, 4th European Conference on Unsaturated Soils (E-UNSAT), Publisher: E D P Sciences, ISSN: 2267-1242
Atmospheric phenomena such as rainfall and evapotranspiration contribute to slope movements in unsaturated soils, the study of which requires fully coupled numerical methods, combined with realistic boundary conditions and appropriate mechanical and hydraulic soil properties. This paper focuses on the effect of the hydraulic behaviour, and in particular of the modelling of the soil-water retention curve and the permeability on slope movements, with the aim of identifying which model parameters are critical and, therefore, require careful experimental identification.
Ghiadistri GM, Zdravkovic L, Potts DM, et al., 2020, Overview and conceptual constitutive framework for pellet-based buffer materials, 4th European Conference on Unsaturated Soils (E-UNSAT), Publisher: E D P Sciences, ISSN: 2267-1242
Buffer materials for nuclear waste disposal applications generally consist of blocks made of highly expansive compacted clay. However, high-density pellets of bentonite are being evaluated as an alternative buffer material for waste isolation. The material response of pellet-based buffers may be quite different from that of compacted buffers, because of the peculiar discontinuous porosity presented. An overview of the literature available on pellet-based buffers is presented and, in particular, two main topics are discussed: firstly, the characteristics of the fabric of the pellets that can be observed through techniques of micro-structural investigation, secondly, the most important behavioural features that can be seen during material testing. Additionally, the constitutive frameworks that have already been developed specifically for pellets are also reviewed. The overall objective of the paper is to highlight the differences between compacted and pellet-based bentonite buffers, in order to propose suitable assumptions to start developing a constitutive model for the latter.
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.
Pelecanos L, Kontoe S, Zdravkovic L, 2020, The effects of dam-reservoir interaction on the nonlinear seismic response of earth dams, Journal of Earthquake Engineering, Vol: 24, Pages: 1034-1056, ISSN: 1363-2469
The objective of this study is to investigate the effects of dam–reservoir interaction (DRI) on the nonlinear seismic response of earth dams. Although DRI effects have for long been considered as insignificant for earth dams, that conclusion was mainly based on linear elastic investigations which focused only on the acceleration response of the crest without examining the seismic shear stresses and strains within the dam body. The present study explores further the impact of DRI focusing on the nonlinear behavior of earth dams. The effects of reservoir hydrodynamic pressures are investigated in terms of both seismic dam accelerations and nonlinear dynamic soil behavior (seismic shear stresses and strains). It is shown that although dam crest accelerations are indeed insensitive to DRI, the stress and strain development within the dam body can be significantly underestimated if DRI is ignored.
Gawecka K, Taborda D, Potts D, et 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.
Cui W, Tsiampousi A, Potts D, et al., 2020, 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.
Zdravkovic L, Potts DM, 2020, Keynote Lecture: Application of advanced numerical analysis in geotechnical engineering design, Editors: Long, Dung, Publisher: SPRINGER-VERLAG SINGAPORE PTE LTD, Pages: 1009-1022, ISBN: 978-981-15-2183-6
Cui W, Potts DM, Zdravković L, et 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.
Solans D, Kontoe S, Zdravkovic L, 2019, Monotonic and cyclic response of tailings sands, SECED 2019 Conference: Earthquake risk and engineering towards a resilient world, Publisher: https://www.seced.org.uk/index.php/proceedings
: The extensive mining production worldwide results in vast amounts of residues requiring the construction of new tailings dams. As site availability is limited due to environmental restrictions, tailings dams tend to be very large and, with heights of over 200 m in some cases, often raising stability concerns. Past experience has shown that failure of tailings dams during earthquakes can be catastrophic, with detrimental consequences for the neighbouring communities, environment and the economy. Prominent examples of such cases are the failure of the El Cobre N°1 dam in Chile, due to the 1965 earthquake, and more recently the Fundão tailings dam failure in Brazil in November 2015. This article investigates the monotonic and cyclic behaviour of tailings sands for different fines content and at a range of relative densities and confining pressures. Several aspects of the behaviour of tailings sands, such as compressibility, strength characteristics and cyclic response, are compared with those of natural sands. Based on the available laboratory test results and the interpretation performed, it is possible to distinguish certain features of this type of material, which are not typically observed in natural soil deposits, and to address common misleading comparisons between the behaviour of natural and tailings sands.
Byrne BW, Burd HJ, Zdravkovic L, et al., 2019, PISA: new design methods for offshore wind turbine monopiles, Revue Francaise de Geotechnique, ISSN: 0181-0529
Sailer E, Taborda D, Zdravkovic L, et al., 2019, Long-term thermal performance of a thermo-active retaining wall, XVII European Conference on Soil Mechanics and Geotechnical Engineering
Pelecanos L, Kontoe S, Zdravkovic L, 2019, Nonlinear seismic response of earth dams due to dam-reservoir interaction, The XVII European Conference on Soil Mechanics and Geotechnical Engineering, Publisher: Icelandic Geotechnical Society
Field data showthat the seismic response of a dam with a full reservoir is different from a dam with an empty reservoir. This is due to“dam-reservoir interaction” (DRI), which is related to the asynchronous vibration of the dam and reservoir domains. It was for long considered that DRI effects are important for concrete dams and insignificant for earth dams. This was based on findings considering mainly dam crest accelerations, which for earth dams wereindeed found to be insensitive to DRI. However, other aspects of theresponse of earth dams, such as the deformation characteristics, should also be considered to fully characterise theseismicdam response. Therefore for a more complete study of the DRI effects on the seismic response of earth dams one should also consider the induced seismic shear stresses and strains, along with the magnitude of reservoir hydrodynamic pressures. This study considers a well-documented case study, the La Villita earth dam in Mexico, for which relevant field measurements are available allowing the development of a well-calibrated numerical model. A series of static and dynamic nonlinear finite element analyses are performed which consider the impact of the reservoir domain on the dam response. It is shown that although earth dam crest accelerations are indeed insensitive to DRI, the actual dynamic soil behaviour can be severely affected, developing large values of seismic shear stresses and strains within the dam body. This study highlights the importance of accurately considering DRI when assessing the seismic performance of earth dams.
Chen S, Zdravkovic L, Carraro JAH, 2019, Thermally induced pore water pressure of reconstituted London clay, 7th International Symposium on Deformation Characteristics of Geomaterials - IS Glasgow 2019, Publisher: EDP Sciences, Pages: 1-5
Different forms of thermo-active structures have been proposed as a way of making use of the ground temperature to achieve renewable low-carbon heating and cooling in civil engineering construction. Such structures comprise piles, retaining walls or tunnel linings, and are used both as structural components and as conduits for utilising geothermal energy. In the scenario of the underground space in London, it is the thermo-active piles that have received most attention. However, little experimental evidence exists on the thermal behaviour of London clay to aid the design of thermo-active structures. This paper presents advanced laboratory testing on the reconstituted London clay to characterise the effect of temperature on its mechanical behaviour. Particular emphasis is given to thermally induced pore water pressures, as their evolution is not well understood. Tests are conducted in a temperature-controlled isotropic cell developed at Imperial College London. The emphasis of the current paper is on the temperature-based calibrations of different transducers. Soil specimens are isotropically consolidated and then subjected to undrained heating-cooling in the temperature range of 21 to 37 °C. Results obtained are compared with an existing laboratory study on another type of clay.
Dominguez-Quintans C, Quinteros VS, Carraro JAH, et al., 2019, Quality assessment of a new in-mould slurry deposition method for triaxial specimen reconstitution of clean and silty sands, 7th International Symposium on Deformation Characteristics of Geomaterials - IS Glasgow 2019
An innovative specimen reconstitution technique for sandy and silty soils that simulates underwater deposition is presented and evaluated. The technique is an upgraded version for triaxial testing of the well-established slurry deposition method. This novel setup integrates the reconstitution mould and the mixing tube into a single unit to avoid transferring the sample from the mixing tube to the mould. This subtle, but critical, modification enables reconstitution of very loose specimens as sample transfer disturbance, which can be significant, is eliminated. The quality of specimens prepared by the new reconstitution method was assessed by experiments on a clean sand from the UK (Ham River sand) and a silty sand from Norway (Øysand). The method, as any slurry-based procedure, is capable of producing homogeneous specimens with high initial degree of saturation, even in the absence of back pressure. The procedure is shown to be suitable for sands with or without fines. Moreover, the new method is able to achieve a wide range of initial void ratios, from very loose to very dense, without imposing any particle crushing in the latter case.
Sailer E, Taborda DMG, Zdravkovic L, et 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.
Ghiadistri G, Zdravković L, Potts DM, et 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.
Kontoe S, Han B, Pelecanos L, et al., 2019, Hydrodynamic effects and hydro-mechanical coupling in the seismic response of dams, VII International Conference on Earthquake Geotechnical Engineering, Publisher: Balkema
The seismic design of earthfill and rockfill dams routinely relies on methods of analysis which adopt simplifying assumptions regarding the dynamic response of the reservoir, while the dynamic interaction of the fluid and solid phases within the dam body is also typically ignored. In this paper, a simple numerical approach for the efficient simulation of hydrodynamic pressures in finite element analysis is presented and then used to assess the impact of hydrodynamic pressures on the seismic response of dams. The importance of both hydrodynamic pressures and of hydro-mechanical coupling is then discussed within the context of two well-documented case studies, of an earthfill and a rockfill dam, comparing the numerical predictions against field measurements.
Pelecanos L, Kontoe S, Zdravkovic L, 2019, Seismic response of earth dams in narrow canyons, VII International Conference on Earthquake Geotechnical Engineering
It is nowadays well appreciated that dams built in narrow canyons exhibit a stiffer re-sponse than those in wide canyons, due to the confined geometry of the canyon banks. The numerical modelling of dams in wide canyons is usually considered as computational-ly less expensive than those in narrow canyons. This is because the former can be ideal-ised by a two-dimensional plane-strain model, while the latter requires a full three-dimensional analysis to appropriately consider the stiffening effect of the narrow canyon geometry. This paper presents a computationally-efficient way to consider the stiffening effect of a narrow canyon in a two-dimensional analysis by using an appropriately in-creased material stiffness.
Pedro A, Zdravkovic L, Potts D, et 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.
Kontoe S, Han B, Pelecanos L, et al., 2019, Seismic response of earthfill and rockfill embankment dams, 3rd Meeting of EWG Dams and Earthquakes - an International Symposium, Publisher: LNEC
The seismic design of earthfill and rockfill dams routinely relies on methods of analysis, which adopt simplifying assumptions regardingthe damgeometry, soil behaviour and the dynamic interaction of the fluid and solid phases within the dam body. This paper explores such simplifying assumptions, which aretypically used for thenumerical modelling of earthfill and rockfill embankment dams,within the context of two case studies. First a clay core dam,theLa Villita dam in Mexico, is considered focusing mainly on the implications of 2D plane strain approximation in the case of dams built in relatively narrow canyons. In the second case study, of the rockfill Yele dam in China, the importance of hydro-mechanicalcoupling is explored by parametrically varying the permeability of the materials.
Sailer E, Taborda D, Zdravkovic L, et 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.
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