416 results found
Sailer E, Taborda DMG, 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
Taborda D, Zdravkovic L, Potts DM, et al., Finite element modelling of laterally loaded piles in a dense marine sand at Dunkirk, Géotechnique, ISSN: 0016-8505
Cui W, Gawecka KA, Taborda DMG, et 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
Tsaparli V, Kontoe S, Taborda D, et al., A case study of liquefaction: demonstrating the application of an advanced model and understanding the pitfalls of the simplified procedure, Géotechnique, ISSN: 0016-8505
The complexity of advanced constitutive models often dictates that their capabilities are only demonstrated in the context of model testing under controlled conditions. In the case of earthquake engineering and liquefaction in particular, this restriction is magnified by the difficulties in measuring field behaviour under seismic loading. In this paper, the well documented case of the Canterbury Earthquake Sequence in New Zealand, for which extensive field and laboratory data are available, is utilised to demonstrate the accuracy of a bounding surface plasticity model in fully-coupled finite element analyses. A strong motion station with manifestation of liquefaction and the second highest peak vertical ground acceleration during the Mw 6.2 February 2011 event is modelled. An empirical assessment predicted no liquefaction for this station, making this an interesting case for rigorous numerical modelling. The calibration of the model aims at capturing both the laboratory tests and the field measurements in a consistent manner. The characterisation of the ground conditions is presented, while, to specify the bedrock motion, the records of two stations without liquefaction are deconvolved and scaled to account for wave attenuation with distance. The numerical predictions are compared to both the horizontal and vertical acceleration records and other field observations, showing a remarkable agreement, also demonstrating that the high vertical accelerations can be attributed to compressional resonance. The results provide further insights into the underperformance of the simplified procedure.
© 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.
Byrne BW, Burd HJ, Gavin KG, et al., 2019, PISA: Recent developments in offshore wind turbine monopile design, Pages: 350-355, ISSN: 2366-2557
© Springer Nature Singapore Pte Ltd. 2019. This paper provides a brief overview of the Pile Soil Analysis (PISA) project, recently completed in the UK. The research was aimed at developing new design methods for laterally loaded monopile foundations, such as those supporting offshore wind turbine structures. The paper first describes the background to the project and briefly outlines the key research elements completed. The paper concludes with a brief description of the anticipated impact of the work and describes initiatives that have followed since.
Gawecka KA, Potts DM, Cui W, et al., 2018, A coupled thermo-hydro-mechanical finite element formulation of one-dimensional beam elements for three-dimensional analysis, COMPUTERS AND GEOTECHNICS, Vol: 104, Pages: 29-41, ISSN: 0266-352X
Pedro A, Zdravkovic L, Potts D, et al., 2018, Numerical modelling of the Ivens shaft construction in Lisbon, Proceedings of the ICE - Geotechnical Engineering, 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.
Zdravkovic L, Taborda D, Potts D, et al., Finite element modelling of laterally loaded piles in a stiff glacial clay till at Cowden, Géotechnique, ISSN: 0016-8505
The PISA project was a combined field testing/numerical modelling study with the aim ofdevelopingimproved design procedures for large diameter piles subjected to lateral loading. This paper describes the development ofa three-dimensional finite elementmodel for the medium-scale pile tests that were conducted in Cowden tillas part of the PISA work.The paper places particular emphasis on the consistent interpretation of the soil data determined from the available field and laboratory information.An enhancedversion of the modified Cam clay model was employedin the numerical analyses, featuring a non-linear Hvorslevsurface, a generalised shape for the yield and plastic potential surfaces in the deviatoric planeand a non-linear formulation for the elastic shear modulus.Three-dimensional finite element analyses were performed prior to the field tests.Excellent agreement between the measured and simulated behaviourfora range of pile geometrieswas observed, demonstrating the accuracy of the numerical model and the adequacy of the calibration process for theconstitutive model.The developed numerical modelconfirmed the premise of the PISA design method that site-specific ground characterisation and advanced numerical modelling candirectly facilitate the development of additionalsoil reaction curves for use in new design models for laterally loaded piles in a stiff clay till.
Cui W, Potts DM, Zdraykovic L, et al., 2018, coupled thermo-hydro-mechanical finite element formulation for curved beams in two-dimensions, COMPUTERS AND GEOTECHNICS, Vol: 103, Pages: 103-114, ISSN: 0266-352X
Byrne B, McAdam RA, Burd HJ, et al., Monotonic laterally loaded pile testing in a stiff glacial clay till at Cowden, Géotechnique, ISSN: 0016-8505
This paper describes theresults obtained from a field testing campaign on laterally-loaded monopiles conducted at Cowden, UK, where the soil consists principally of aheavilyoverconsolidatedglacial till. These tests formed part of the PISA projecton the development of improved design methods for monopile foundations for offshore wind turbines. Results obtained for monotonic loading tests on piles of three different diameters (0.273m, 0.762m and 2.0m) are presented. The piles had length-to-diameter ratios (L/D) of between 3 and 10. Thetests includedthe application of monotonic loading incorporating periods of constant load to investigate creep effects,and investigations on the influence of loading rate. Data are presented on measured bending moments and inclinations induced in the piles. Inferred data on lateral displacements of the embedded section of the pilesare determined usingan optimisedstructural model. Thesefield data support the developmentof a new 1D modelling approach forthe design of monopile foundations for offshore wind turbines.They also form a unique database of field measurements in an overconsolidated clay, from lateral loading of piles at a vertical distance abovethe ground surface.
Zdravkovic L, Jardine R, Taborda DMG, et al., Ground characterisation for PISA pile testing and analysis, Géotechnique, ISSN: 0016-8505
This paper is the first of a set of linked publications on the PISA Joint Industry Research Project, which was concerned with the development of improved design methods for monopile foundations in offshore wind applications. PISA involved large-scale pile tests in overconsolidated glacial till at Cowden, north-east England,and in dense normally consolidated marine sand at Dunkirk, northern France. The paper presents the characterisationof the two sites, whichwas crucial to the design of the field experiments and advanced numerical modelling of the pile-soil interactions. The studies described, which had to be completed at an early stage of the PISA project, added new laboratory and field campaignsto historic investigations at both sites.Theyenabledanaccurate description ofsoilbehaviour from small strains to ultimate statesto be derived, allowing analyses to be undertaken that captured both the serviceability and limit statebehaviour of the test monopiles.
McAdam RA, Byrne BW, Houlsby GT, et al., Monotonic lateral loaded pile testing in a dense marine sand at Dunkirk, Géotechnique, ISSN: 0016-8505
Theresults obtained from a field testing campaignon laterally-loaded monopiles,conducted ata dense sand site inDunkirk, Northern Franceare described.These tests formed part of thePISA projecton the development of improved design methods for monopile foundations for offshore wind turbines. Results obtained frommonotonic loading tests on piles of three different diameters (0.273m, 0.762m and 2.0m) are presented. The piles had aspectratios (L/D) of between 3 and 10. Thetests consisted principally of the application of monotonic loads,incorporating periods of held constant load to investigate creep effects.The influence of loading ratewas also investigated. Data are presented on the overall load displacement behaviour of each of the test piles. Measured data on bending moments and inclinations induced in the pilesare also provided.Inferences are made forthe displacements in the embedded length of the piles. Thesefield data will support the development of a new 1D modelling approach forthe design of monopile foundations for offshore wind turbines.They also form a unique database of field measurements in a dense sand, from lateral loading of piles at a vertical distance abovethe ground surface.
Burd HJ, Beuckelaers WJAP, Byrne BW, et al., New data analysis methods for instrumented medium scale monopile field tests, Géotechnique, ISSN: 0016-8505
The PISA Joint Industry Research Project was concerned with the development of improved design methods for monopile foundations in offshore wind applications. PISA involved large-scale pile tests in overconsolidated glacial till at Cowden, north-east England, andin dense normally consolidated marine sand at Dunkirk, northern France. This paper describes the experimental set up for pile testing, with unique features of load-application mechanisms and built-in fibre optic strain gauges.New procedures are describedfor the interpretation of pile loading data, and specifically for providing precise interpretation of pile displacements.
Ghiadistri GM, Potts DM, Zdravkovic L, et al., 2018, A new double structure model for expansive clays, 7th International Conference on Unsaturated Soils
The behaviourof compacted bentonite upon hydration is numerically investigated here by simu-lating a swelling pressure teston aMX-80 bentonitesample. Two constitutive modelsareemployed in the analysis: the “Imperial College Single-Structure Model” (ICSSM)andthe “Imperial College Double-Structure Model” (ICDSM), the latterspecifically developed for expansive clays. It is shown that the latter exhibits a considerably improved performance as it is able to accurately capture the swelling pressure developed in the materialupon wetting. Nevertheless, a limited knowledge of the evolution of the material’s fabric, notably at the micro-scale,is an obstacle for deriving with certainty some of the model parameters. This issue is high-lightedhere by performing analyses of theswelling pressure test with two sets ofmaterial characterisations, with model parameters differinginthe derivation of the microstructural component.Both analyses show a very good match with the testdata, but it is difficult to justify one set of microstructural parametersoverthe other. The paper emphasises what aspects of experimental research could be helpful in studying the fabric of compacted bentonite upon wetting, and hence improve the calibration procedure of thedouble-structure mod-el.
Zdravkovic L, Tsiampousi A, Potts DM, 2018, On the modelling of soil-atmosphere interaction in cut and natural slopes, 7th International Conference on Unsaturated Soils
The need to predict the consequences of atmospheric conditions on the stability of slopes is widely evident from numerous examples of slope failures around the world, which often result in material and human loss.Equally, the serviceability conditions of cut slopes very much depend onthe heave mobilised byexcavation, the magnitude of which is partly governed by the hydraulic boundary conditions.Soil-atmosphere interaction is complex, involving precipitation and evapotranspiration across the slope surface, and acts in ad-dition to theground water regime within the slope body. As a consequence, calculation tools cannot be overly simplified if realistic predictions are expected. This paper provides an overview of recent research at Imperial College in modellingunsaturatednatural and cut slopes, using finite element analysis and advanced constitutive models and boundary conditions.
Kirkham AD, Tsiampousi A, Potts DM, 2018, Temperature-controlled oedometer testing on compacted bentonite, 7th International Conference on Unsaturated Soils
A new temperature-controlled oedometer has been designed at Imperial College London and commissioned to investigate the thermo-hydro-mechanicalbehaviour of soils. Temperature control is achieved by submerging the specimenin a water bath. The water temperature is regulated byheaters positionedradially around the specimen, or by an external unit. The temperature can be varied between 5°C and 85°C. The temperature gradient across the specimenis minimised by circulating water beneath the specimenthrough a hollow plate.A thermo-mechanical, elastic, finite element model of the equipment has been produced using the Imperial College Finite Element Program (ICFEP). The experimental results are used to develop and validate the numerical model. The model is then used to inform and improve the experimental testing programme.The accuracy of temperature control has already been established. The testing programme includes heating tests at constant applied stress, and loading tests at discrete temperature values. Of particular interest is thermally-inducedoverconsolidation behaviour. The experimental results are used to verify the existing numerical framework and to establish the effect of temperature on the behaviourofsaturated soil.
Cui W, Gawecka KA, Potts DM, et al., 2018, A Petrov-Galerkin finite element method for 2D transient and steady state highly advective flows in porous media, COMPUTERS AND GEOTECHNICS, Vol: 100, Pages: 158-173, ISSN: 0266-352X
Summersgill FC, Kontoe S, Potts DM, 2018, Stabilisation of excavated slopes in strain-softening materials with piles, GEOTECHNIQUE, Vol: 68, Pages: 626-639, ISSN: 0016-8505
Skiada E, Kontoe S, Stafford P, et al., 2018, Ground surface amplification for canyon topographies excited with bi-directional earthquake records, 16th European Conference on Earthquake Engineering
Tsaparli V, Kontoe S, Taborda D, et al., 2018, Liquefaction triggering due to compressional waves: validation through field records, 16th European Conference on Earthquake Engineering
Cui W, Tsiampousi A, Potts DM, et al., 2018, Finite element modelling of excess pore fluid pressure around a heat source buried in saturated soils, London, 9th European Conference on Numerical Methods in Geotechnical Engineering, Publisher: Taylor Francis Group, Pages: 741-749
Sailer E, Taborda DMG, Zdravkovic L, et al., 2018, Factors affecting the thermo-mechanical response of a retaining wall under non-isothermal conditions, London, 9th European Conference on Numerical Methods in Geotechnical Engineering, Publisher: Taylor Francis Group, Pages: 741-749
Potts D, Cui W, Gawecka KA, et al., 2018, Numerical modelling of coupled thermo-hydro-mechanical problems: Challenges and pitfalls, 9th European Conference on Numerical Methods in Geotechnical Engineering, Publisher: Taylor Francis Group
Taborda DMG, Potts DM, Zdravkovic L, et al., 2018, Incorporating the state parameter into a simple constitutive model for sand, London, 9th European Conference on Numerical Methods in Geotechnical Engineering, Publisher: Taylor Francis Group, Pages: 327-334
Pedro A, Zdravkovic L, Potts D, et al., 2018, Geotechnical characterization of the Miocene formations at the location of Ivens shaft, Lisbon, QUARTERLY JOURNAL OF ENGINEERING GEOLOGY AND HYDROGEOLOGY, Vol: 51, Pages: 96-107, ISSN: 1470-9236
Cui W, Potts DM, Zdravkovic L, et al., 2018, An alternative coupled thermo-hydro-mechanical finite element formulation for fully saturated soils, COMPUTERS AND GEOTECHNICS, Vol: 94, Pages: 22-30, ISSN: 0266-352X
Carter JP, Desai CS, Potts DM, et al., 2018, Computing and computer modelling in geotechnical engineering
© 2018 ISRM International Symposium 2000, IS 2000. All rights reserved. A broad review is presented of the role of computing in geotechnical engineering. Included in the discussions are the conventional deterministic techniques for numerical modelling, stochastic techniques for dealing with uncertainty, 'soft-computing' tools, as well as modern database software for geotechnical applications. Considerable emphasis is given to the methods commonly used for the solution of boundary and initial value problems. Constitutive modelling of soil and rock mass behaviour and material interfaces is an essential component of this type of computing, and so a review of recent developments and capabilities of constitutive models is also included. The importance of validating computer simulations and geotechnical software is emphasised, and some methodologies for achieving this are suggested. A description of several previously conducted validation studies is included. The paper also includes discussion of the limitations of various numerical modelling techniques and some of the more notable pitfalls. The concepts described in the paper are illustrated with examples taken from research and practice. In presenting these concepts and examples, emphasis has been placed on the behaviour of soil, but it is noted that many of the models and techniques described also have application in rock engineering.
Avgerinos V, Potts DM, Standing JR, et al., 2018, Predicting tunnelling-induced ground movements and interpreting field measurements using numerical analysis: Crossrail case study at Hyde Park, GEOTECHNIQUE, Vol: 68, Pages: 31-49, ISSN: 0016-8505
Kontoe S, Potts DM, Summersgill F, et al., 2018, Stabilisation of excavated slopes with piles in soils with distinctly different strain softening behaviour, Pages: 1075-1081
© 2018 Taylor & Francis Group, London, UK. The majority of existing design procedures for slope stabilization with piles treat the pile only as an additional force or moment acting on the critical slip surface of the un-stabilised slope, effectively ignoring any interaction of the pile with the evolution of the failure mechanism. This paper presents a numerical investigation that challenges this assumption, demonstrating the importance of the soil-pile interaction. Two dimensional plane-strain hydro-mechanically coupled finite element analyses were performed to simulate the excavation of a slope, considering materials with both a strain softening and non-softening response. The impact of pile position and time of pile construction on the stability of a cutting were parametrically examined, comparing and contrasting the findings for the different material types. The results suggest that an oversimplification during design regarding the soil/pile interaction could either entirely miss the critical failure mechanism (unconservative) or provide a conservative stabilisation solution.
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