Publications
479 results found
Ruiz López A, Tsiampousi A, Standing JR, et al., 2023, Numerical characterisation of the rotational behaviour of grey cast iron tunnel joints, Computers and Geotechnics, Vol: 159, Pages: 1-17, ISSN: 0266-352X
The structural assessment of segmental grey cast iron (GCI) tunnel linings to nearby construction is challenging due to the presence of the joints affecting the stiffness of the tunnel lining. This paper presents an extensive investigation, using 3D finite element (FE) analyses, into the bending moment-rotation (M-θ) behaviour of two GCI tunnel joint geometries. These two geometries correspond to standard running and station tunnels of the London Underground network. The contribution of this study is two-fold. i) The novel characterisation of the M-θ response enables the development of new models for simulating the mechanical response of GCI tunnel joints with structural elements which can be used in simplified, 2D geotechnical analysis for tunnel safety assessments. ii) The analyses provide insight into the behaviour of GCI tunnel linings that would be difficult to achieve through experimental and field observations alone. More specifically, the analyses show that when the bolts are removed from the joints the possibility of tensile failure can be disregarded; that the initial bolt preload influences the rotational stiffness only after some rotation has taken place and does not alter the bending moment of opening; and that the out-of-plane displacement restraint has little influence on the joint response.
Koronides M, Kontoe S, Zdravkovic L, et al., 2023, Numerical simulation of soil-structure interaction experiments on shallow founded structures for different mass configurations, 10th European Conference on Numerical Methods in Geotechnical Engineering, Publisher: International Society for Soil Mechanics and Geotechnical Engineering
Soil-Structure Interaction (SSI) phenomena and foundation rocking can modify the structural response signifi-cantly with respect to the response predicted adopting the fixed-base assumption. The importance of SSI and rocking depends,among other factors, on the structural mass and the distribution of static stresses at the soil-foundation interface. Within thiscontext, an experimental campaign was carried out aiming to investigate the SSI effects on the response of a 3m x 3m x 5m steel-framed structure. The prototype structure, called EUROPROTEAS, was founded on a shallow footing at the well-characterisedEuroseistest site, while its mass was either 18Mgr or 9Mgr. The present study simulates free vibration experiments, placingparticular emphasis on soil nonlinearity and soil-foundation interface. A novel approach to simulate gaps at the soil-foundationinterface, foundation rocking and to manipulate interface stresses under static conditions is presented. The three aspects areshown to significantly affect the response, while they are found to be more important for the lighter structure.
Moller J, Kontoe S, Taborda D, et al., 2023, Resonance in offshore wind turbine systems due to seismic loading and extensive soil liquefaction, 10th European Conference on Numerical Methods in Geotechnical Engineering, Publisher: International Society for Soil Mechanics and Geotechnical Engineering
Pedone G, Kontoe S, Zdravkovic L, et al., 2023, A sensitivity study on the mechanical properties of interface elements adopted in finite element analyses to simulate the interaction between soil and laterally loaded piles, 10th European Conference on Numerical Methods in Geotechnical Engineering, Publisher: International Society for Soil Mechanics and Geotechnical Engineering
An increasing number of offshore energy structures have been built recently on driven piles, ranging from jack-et piles with typical length-to-diameter (L/D) ratios of 10-40 to monopiles with far lower L/D ratios. The load-displacementbehaviour of these foundations can be investigated by means of Finite Element (FE) analyses, for instance following the designmethodology developed by the PISA Joint Industry Project (JIP). A challenging aspect of the modelling, for piles loaded eitheraxially or laterally, is the simulation of the behaviour at the soil-pile interface with the adoption of suitable formulations for theinterface elements and with representative mechanical properties. This paper presents a sensitivity study conducted on both theelastic and plastic properties of interface elements adopted in FE analyses of laterally loaded piles driven in chalk. The studybenefited from the extensive field and laboratory test results collected during the ALPACA JIP and the corresponding piletests. The aim of the paper is to provide guidance for numerical modelling on the selection of the most appropriate mechanicalproperties of interface elements to be used in the analyses of soil-pile interaction under lateral loading.
Kirkham A, Tsiampousi A, Potts DM, 2023, Thermo-mechanical behaviour of a kaolin-based clay soil, Geotechnique: international journal of soil mechanics, ISSN: 0016-8505
Cui W, Wu X, Potts DM, et al., 2023, Nonlocal strain regularisation for critical state models with volumetric hardening, Computers and Geotechnics, Vol: 157, Pages: 1-10, ISSN: 0266-352X
The finite element (FE) method may suffer from numerical instability and mesh dependency when modelling the formation of shear bands using strain-softening constitutive models. Nonlocal methods have been shown to be capable of avoiding these numerical issues effectively. This paper proposes a novel generic algorithm for incorporating existing nonlocal methods into the FE formulation of elasto-plastic constitutive models with volumetric hardening laws. Using the example of the modified Cam Clay (MCC) model this paper shows that instabilities are inevitable if the nonlocal plastic volumetric strains are directly used to update the hardening parameter. The paper further proposes a robust regularisation algorithm to overcome this issue. This algorithm has been implemented into a bespoke FE code and its capability in significantly reducing mesh dependency while maintaining numerical stability is verified through a series of numerical analyses of biaxial compression tests for highly overconsolidated clays. The performance of various existing nonlocal methods is also critically assessed.
Pedone G, Zdravkovic L, Potts D, et al., 2023, Numerical modelling of unsaturated MX-80 bentonite subjected to two different hydration paths and subsequent loading to high-pressures, 8th International Conference on Unsaturated Soils
Petalas AL, Tsiampousi A, Zdravkovic L, et al., 2022, Numerical investigation of the performance of engineered barriers in controlling stormwater runoff, Geomechanics for Energy and the Environment, Vol: 32, Pages: 1-15, ISSN: 2352-3808
In this paper, 2-dimensional, hydro-mechanically coupled finite element analyses are conducted to assess the performance of an engineered barrier, constructed from natural geomaterials, aimed at reducing flood risk in urban environments. The barrier consists of an unsaturated compacted soil layer with water holding properties and a drainage layer of a coarse granular material, that acts as a capillary break, and is constructed on top of the natural soil, in this case London clay. The barrier is vegetated so that its water storage capacity is renewed after each rainfall event. Sophisticated boundary conditions are used to simulate the effect of precipitation and evapotranspiration. The evolution of the rainfall infiltration and runoff rate is simulated both for a treated soil column with an engineered barrier and an untreated one consisting solely of in-situ London Clay. The percolation rate of rainfall water from the bottom of the barrier is also estimated. This comparison highlights the effectiveness of the engineered barrier in reducing the risk of fast flooding, in preventing excessive deformations and in protecting underground infrastructure during wetting and drying cycles. The effect of the hydraulic properties and geometry of the barrier is investigated by means of an extensive parametric analysis. Finally, recommendations for the design of barrier systems are made.
Koronides M, Kontoe S, Zdravkovic L, et al., 2022, Numerical simulation of real-scale vibration experiments of a steel frame structure on a shallow foundation, 4rth International Conference on Performance-based Design in Earthquake Geotechnical Engineering
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.
Kontoe S, Summersgill F, Potts D, et al., 2022, On the effectiveness of slope stabilising piles for soils with distinct strain-softening behaviour, Geotechnique, Vol: 72, Pages: 309-321, ISSN: 1021-8637
The stabilisation of slopes with rows of discrete vertical piles is a commonly adopted method for both cuttings as well as embankment slopes. The majority of existing design procedures consider the pile only as an additional force or moment acting on the critical slip surface of the un-stabilised slope. Based on simplified models, existing design methodologies effectively ignore any interaction of the pile with the evolution of the failure mechanism, while they do not consider important aspects of soil behaviour for slope stability relating to strain softening response. This paper presents a numerical investigation that challenges the above-mentioned simplifications, 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 entirely miss the critical failure mechanism.
Koronides M, Kontoe S, Zdravkovic L, et al., 2022, 'Numerical simulations of field soil-structure interaction experiments on a shallow founded steel frame structure, 3rd international Conference on Natural Hazards & Infrastucture
Carter JP, Potts DM, Gens A, 2022, Scott William Sloan 1954-2019, HISTORICAL RECORDS OF AUSTRALIAN SCIENCE, Vol: 33, Pages: 64-71, ISSN: 0727-3061
Ruiz Lopez A, Tsiampousi A, Standing J, et al., 2022, Numerical investigation of a segmental grey cast iron tunnel ring: validation with laboratory data and application to field conditions, Computers and Geotechnics, Vol: 141, Pages: 1-19, ISSN: 0266-352X
The structural response of a segmental grey cast iron (GCI) tunnel lining ring under distortion was investigated by means of finite element (FE) analysis. Building on previous experimental investigations, a 3D numerical model, capable of reproducing accurately the behaviour observed in the laboratory, was developed with the aim of providing guidelines for the structural assessment of GCI linings in engineering practice. A comprehensive validation of the segmental ring model with the laboratory data was first completed. Subsequently, a parametric study was conducted using a set-up that replicated the widely adopted elastic continuum method, so that differences between the numerical and the analytical solution could be attributed to the presence of the longitudinal joints. In this manner, the influence of the joints on the ring response was quantitatively established and recommendations for routine engineering calculations developed. A set of bending stiffness reduction factors are proposed as a function of the tunnel ovalisation, providing upper and lower limits of the bending stiffness, as well as a global reduction factor which is an average measure of the bending stiffness reduction. These factors can be integrated into the calculation procedure of closed-form solutions in order to account for the segmental nature of GCI linings.
Cui W, Potts DM, Pedro AMG, et al., 2021, Numerical assessment of the effects of end-restraints and a pre-existing fissure on the interpretation of triaxial tests on stiff clays, Geotechnique: international journal of soil mechanics, Vol: 71, Pages: 765-780, ISSN: 0016-8505
Conventional laboratory triaxial tests apply axisymmetric boundary conditions to a cylindrical sample which has an axisymmetric geometry. For a homogeneous sample this implies that the deformed shape of the sample should maintain an axisymmetric geometry during the test. Consequently, the sample should deform in a barrelling mode and if slip planes develop they should define a cup and cone-like failure surface. However, in many triaxial tests such behaviour is not observed, especially as failure is approached when a planar slip surface develops. Such a deformation mode is not axisymmetric. One reason for this behaviour is that a fissure pre-exists in the sample. Employing hydro-mechanically coupled three-dimensional finite-element analyses, this paper investigates the influence of a single fissure in a triaxial sample of stiff clay on its behaviour throughout the test, focusing on the fissure position, orientation, strength and stiffness, in conjunction with the sample's end-restraints (rough or smooth). The effects are quantified in terms of the sample's overall stiffness and strength, indicating that the presence of a fissure can affect the very small strain stiffness, and that it has a significant effect on the strength of the sample, demonstrating that the conventional methods used to interpret laboratory tests may give unconservative results. The results also show a significant effect of the conditions at the top and bottom surfaces of the sample, where in particular the lateral restraint and rough ends introduce ‘bending’ in the sample.
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.
Potts DM, Cui W, Zdravković L, 2021, A coupled THM finite element formulation for unsaturated soils and a strategy for its nonlinear solution, Computers and Geotechnics, Vol: 136, ISSN: 0266-352X
This paper presents a coupled thermo-hydro-mechanical (THM) finite element (FE) formulation which is capable of accounting for the effects of temperature change on the behaviour of unsaturated soils. Both vapour flow and density variation are taken into account in the development of this formulation. The full derivation procedure is provided and the adopted assumptions are stated and explained. To improve the efficiency of the nonlinear solution process while maintaining the accuracy of the prediction, a novel approach for determining iterative corrections when modelling coupled transient problems with the Newton-Raphson algorithm is established and presented here. The performance of the proposed FE formulation and of the new strategy for iterative corrections in a nonlinear solver is subsequently demonstrated and verified by simulations of laboratory experiments on unsaturated compacted bentonite, showing good agreement between the numerical and experimental results.
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.
Petalas A, Tsiampousi A, Zdravkovic L, et al., 2021, Numerical investigation of the performance of engineered barriers in reducing flood risk, 3rd Pan-American Conference on Unsaturated Soils
Wan MSP, Standing JR, Potts DM, et al., 2021, Discussion of pore water pressure and total horizontal stress response to EPBM tunnelling in London Clay, Geotechnique: international journal of soil mechanics, Vol: 71, Pages: 368-372, ISSN: 0016-8505
Zdravkovic L, Cui W, Gawecka K, et al., 2021, Numerical Modelling of Thermo-Active Piles, PIling 2020
Wan MSP, Standing JR, Potts DM, et al., 2021, Measured post-construction ground response to EPBM tunnelling in London Clay, 10th International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground (IS-Cambridge), Publisher: ROUTLEDGE, Pages: 191-198
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
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.
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
Carter JP, Gens A, Potts DM, 2020, Scott William Sloan OBITUARY, Geotechnique: international journal of soil mechanics, Vol: 70, Pages: 1174-1175, ISSN: 0016-8505
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.
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