Publications
249 results found
Potts VJ, Zdravkovic L, 2010, Finite-element study of arching behaviour in reinforced fills, Ground Improvement, Vol: 163, Pages: 217-229, ISSN: 1755-0750
Tsiampousi A, Zdravkovic L, Potts DM, 2010, Modelling of the hysteretic soil-water retention curve of unsaturated soils, 7th European Conference on Numerical Methods in Geotechnical Engineering, Pages: 331-336
Monroy R, Zdravkovic L, Ridley A, 2010, Evolution of microstructure in compacted London Clay during wetting and loading, GEOTECHNIQUE, Vol: 60, Pages: 105-119, ISSN: 0016-8505
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- Citations: 171
Taborda D, Zdravkovic L, Kontoe S, et al., 2010, Alternative formulations for cyclic nonlinear models: parametric study and comparative analyses, 7th European Conference on Numerical Methods in Geotechnical Engineering, Pages: 423-428
The utilisation of cyclic nonlinear elastic models presents numerous advantages when analysingsimple dynamic problems, such as one-dimensional site response. This class of models requires a small numberof parameters to be determined and can efficiently reproduce the strain dependency of the secant shear stiffnessand hysteretic damping. However, it has been frequently noted that, for medium to large deformation levels, thepredicted damping ratio can be significantly larger than the values evaluated for most soils through laboratorytesting. To minimise the effects of this overestimation on the overall response of the system, which may lead tonon conservative results, different formulations have been proposed. In this paper, two alternative expressionsfor the stress-strain behaviour of soils – hyperbolic and logarithmic – are presented and their ability to reproducewell-established empirical stiffness degradation and damping ratio curves is assessed. Finally, the results of a setof dynamic finite element analyses of a one-dimensional wave propagation problem are presented to illustratethe impact of the different formulations on the engineering behaviour of soil deposits.
Merritt AS, Menkiti CO, Harris D, et al., 2010, 3D finite element analysis of a diaphragm wall excavation with sacrificial crosswalls, International Conference, Geotechnical Challenges in Megacities, Pages: 636-641
Zdravkovic L, Potts DM, 2010, Using numerical analysis in geotechnical engineering practice, Geo-Strata, Pages: 28-33
Schütz R, Potts DM, Zdravković L, 2009, A constitutive model for the behaviour of shotcrete, Pages: 49-60
A constitutive model for the behaviour of shotcrete is presented in this paper. It is formulated within the framework of elasto-plasticity and the smeared crack concept is applied. Two independent yield surfaces govern the mechanical behaviour under compression and tension, which is further controlled by non-linear hardening and softening. The main material parameters are assumed to change with time. Validation of the model has been achieved by fitting the increase in stiffness and strength to published data in the literature. Good agreement is found between predictions of the complete stress-strain curves of shotcrete at different ages and experimental results. The model represents a sophisticated tool for the realistic analysis of tunnels, which are driven according to the principles of the New Austrian Tunnelling Method (NATM).
Tsiampousi A, Zdravkovic L, Potts DM, 2009, Modelling of overconsolidated unsaturated soils, 4th Asia Pacific Conference on Unsaturated Soils, Publisher: CRC Press, Pages: 673-678
Constitutive models for unsaturated soils are most commonly based on conventional critical state type models for saturated soils. The effect of partial saturation is taken into account through the intro-duction of an additional stress variable which depends on soil suction. The modified Cam-Clay surface is usu-ally assumed for the formulation of the yield and the plastic potential surfaces in the mean stress – deviatoric stress space. In this paper an existing model for unsaturated soils is used to simulate drained triaxial tests per-formed on highly overconsolidated unsaturated silt. Even though the model adopts an improved expression for the yield surface that allows a variety of shapes to be introduced, none of them can accurately simulate the observed soil behaviour in the laboratory tests. A new version of the model is, therefore, proposed and pre-sented here. Following the formulation and implementation of these alterations, analyses of laboratory ex-periments on artificial silt are presented demonstrating the improved simulation of soil behaviour.
Taborda D, Kontoe S, Zdravkovic L, et al., 2009, Application of cyclic nonlinear elastic models to site response analysis, 1st International Symposium on Computational Geomechanics, Pages: 956-966
Zolghadr Jahromi H, Izzuddin BA, Zdravkovic L, 2009, A domain decomposition approach for coupled modelling of nonlinear soil–structure interaction, Computer Methods in Applied Mechanics and Engineering, Vol: 198, Pages: 2738-2749, ISSN: 1425-1655
Barreto D, O'Sullivan C, Zdravkovic L, 2009, Quantifying the Evolution of Soil Fabric Under Different Stress Paths, 6th International Conference on the Micromechanics of Granular Media, Publisher: AMER INST PHYSICS, Pages: 181-184, ISSN: 0094-243X
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- Citations: 27
Kontoe S, Zdravkovic L, Potts DM, 2009, An assessment of the Domain Reduction Method as an advanced boundary condition and common pitfalls in the use of conventional absorbing boundaries, International Journal for Numerical and Analytical Methods in Geomechanics, Vol: 33, Pages: 309-330
Shutz R, Potts DM, Zdravkovic L, 2009, On the importance of advanced constitutive modelling of shotcrete tunnel linings, Germany, Computational Methods in Tunnelling - EURO:TUN 2009, Publisher: Aedificatio Publiahers, Pages: 447-454
Kontoe S, Zdravkovic L, Potts DM, et al., 2009, Comparison of constitutive models through a case study on seismic response of tunnels, London, Performance-Based Design in Earthquake Geotechnical Engineering, Publisher: Taylor & Francis Group, Pages: 1951-1059
Georgiadis K, Potts DM, Zdravkovic L, 2008, An improved constitutive model for unsaturated and saturated soils, Pages: 581-588
This paper presents a constitutive model for unsaturated and saturated soils based on the critical state framework. The model includes a versatile expression for yield and plastic potential surfaces, the option of linear or nonlinear increase of shear strength with suction and three options for the shape of the unsaturated isotropic compression lines. The latter feature is of particular importance as it controls the amount of potential collapse the soil can experience due to wetting. Depending on the type of boundary value problem analysed a linear, bi-linear or exponential relationship can be used. Two sets of finite element analyses are presented here which investigate the influence of the shape of the isotropic compression line on the behaviour of strip footings and axially loaded single piles. © 2008 Taylor & Francis Group, London.
Grammatikopoulou A, Zdravkovic L, Potts DM, 2008, Numerical analysis of an embankment founded on structured clay, Pages: 4041-4048
This paper presents the numerical analysis of an embankment founded on a soft structured clay deposit. The paper investigates the effect of modelling the destructuration of the natural clay foundation. A comparison of the embankment behaviour is presented when its soft clay foundation is modelled with a new constitutive model, which can account for destructuration in natural clays and a pre-existing model applicable to reconstituted clays. The paper demonstrates that taking account of the destructuration of the soft clay foundation results in a lower embankment failure height and a different failure surface.
Potts VJ, Zdravković L, 2008, Finite element analysis of arching behaviour in soils, Pages: 3642-3649
Based on the results of a parametric study investigating the behaviour of geosynthetic reinforced fill load transfer platforms above voids, using finite element analysis, a review of the nature of the soil arching that develops in the fill has been undertaken. The fill response to the formation of a void is compared with arching theories developed by Terzaghi (1943) and Hewlett and Randolph (1988). It is found that Terzaghi's approach is capable of describing all of the behaviour seen when a stable arch forms, whereas Hewlett and Randolph's formulation may only be applied to a limited number of cases. It is also found that the accuracy with which Terzaghi's approach predicts the vertical stress at the base of the fill layer depends on the value of the stress ratio K in the shear zone. Owing to the high level of disturbance in this zone, it is difficult to determine the value of K, but it is seen that the theoretical values suggested in the literature are too low and the vertical stress at the base of the fill layer is overestimated as a result. A suitable value of K is suggested from the numerical results, which is independent of the shape and size of the void, and of the fill and geosynthetic properties.
Zolghadr Jahromi H, Izzuddin BA, Zdravkovic L, 2008, Computational methods in Dirichlet-Neumann coupling of soil-structure interaction, Pages: 239-245
This paper presents domain decomposition methods for nonlinear analysis of soil-structure interaction problems, where particular emphasis is given to Dirichlet-Neumann iterative coupling methods. In this approach, the overall soil-structure domain is physically decomposed into independently modelled soil and structure sub-domains, and then the response of separately modelled sub-domains is coupled by successive updates of the boundary conditions, ensuring convergence to equilibrium and compatibility at the interface of the soil-structure coupled system. In this respect, the mathematical and computational characteristics of using constant relaxation, adaptive relaxation and condensed stiffness matrix of the partitioned sub-domains in coupling algorithms are discussed, including the convergence conditions and choice of algorithmic parameters. In view of the above, the use of a modified reduced order method, which utilises an efficient approximation of the condensed stiffness matrices at the soil-structure interface to ensure and accelerate convergence, is discussed and its merits are illustrated in a case study. © 2009 Taylor & Francis Group, London.
Monroy R, Zdravkovic L, Ridley A, 2008, Volumetric behaviour of compacted London Clay during wetting and loading, Pages: 315-320
In this study, the mechanical behaviour of a compacted clay in equilibrium with the atmospheric pressure was investigated. Samples of London Clay were compacted to the same initial conditions, corresponding to dry of optimum moisture content on a Proctor plot, and were taken along complex stress paths, involving wetting under a constant vertical stress, wetting under a condition of zero volumetric strain, and loading and unloading at a constant value of matric suction. Tests were performed with a combination of standard and osmotic oedometers-the latter developed specifically at Imperial College London to test unsaturated soils under atmospheric conditions. Samples taken along different hydration paths displayed similar post-yield behaviour when loaded at a constant suction, suggesting that common yield surface in the e: s: σv space (where e denotes void ratio, s is the matric suction, and σv is the vertical stress) controls the plastic volumetric behaviour of unsaturated London Clay during loading following monotonic hydration. © 2008 Taylor & Francis Group, London.
Zdravkovic L, Carter J, 2008, Contributions to <i>Geotechnique</i> 1948-2008:: Constitutive and numerical modelling, GEOTECHNIQUE, Vol: 58, Pages: 405-412, ISSN: 0016-8505
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- Citations: 19
Grammatikopoulou A, Zdravkovic L, Potts DM, 2008, The influence of previous stress history and stress path direction on the surface settlement trough induced by tunnelling, GEOTECHNIQUE, Vol: 58, Pages: 269-281, ISSN: 0016-8505
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- Citations: 27
Kontoe S, Zdravkovic L, Potts DM, et al., 2008, Case study on seismic tunnel response, Canadian Geotechnical Journal, Vol: 45, Pages: 1743-1764
This paper presents a case study of the Bolu highway twin tunnels that experienced a wide range of damage during the 1999 Duzce earthquake in Turkey. Attention is focused on a particular section of the left tunnel that was still under construction when the earthquake struck and that experienced extensive damage during the seismic event. Static and dynamic plane strain finite element (FE) analyses were undertaken to investigate the seismic tunnel response at two sections and to compare the results with the post-earthquake field observations. The predicted maximum total hoop stress during the earthquake exceeds the strength of shotcrete in the examined section. The occurrence of lining failure and the predicted failure mechanism compare very favourably with field observations. The results of the dynamic FE analyses are also compared with those obtain by simplified methodologies (i.e. two analytical elastic solutions and quasi-static elasto-plastic FE analyses). For this example, the quasi-static racking analysis gave thrust and bending moment distributions around the lining that differed significantly from those obtained from full dynamic analyses. However, the resulting hoop stress distributions were in reasonable agreement.
Taborda D, Zdravkovic L, Kontoe S, et al., 2008, Modelling cyclic pile response using the Finite Element Method, 8th International Conference on the Application of Stress-Wave Theory to Piles, Pages: 327-333
Kontoe S, Zdravkovic L, Potts DM, 2008, The Domain Reduction Method for dynamic coupled consolidation problems in geotechnical engineering, International Journal for Numerical and Analytical Methods in Geomechanics, Vol: 32, Pages: 659-680
Kontoe S, Zdravkovic L, Potts DM, 2008, The importance of revised modulus decay curves on surface foundation settlement predictions in London Clay, BGA International Conference on Foundations, Pages: 1549-1558
Zdravkovic L, Kontoe S, 2008, Some issues in modelling boundary conditions in dynamic geotechnical analysis, 12th International Conference of International Association for Computer Methods and Advances in Geomechanics (IACMAG), Pages: 2918-2925
Barreto D, O'Sullivan C, Zdravkovic L, 2008, Specimen generation approaches for DEM simulations, 4th International Symposium on Deformation Characteristics of Geomaterials, Publisher: I O S PRESS, Pages: 901-906
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- Citations: 1
Kontoe S, Zdravkovic L, Potts DM, 2008, The generalised-alpha algorithm for dynamic coupled consolidation problems in geotechnical engineering, 12th International Conference of International Association for Computer Methods and Advances in Geomechanics (IACMAG), Pages: 1449-1558
Taborda D, Zdravkovic L, Kontoe S, et al., 2008, Comparative study of cyclic nonlinear elastic models in dynamic finite element analysis, Coimbra, Portugal, XI National Conference on Geotechnics, Pages: 147-154
Georgiadis K, Potts DM, Zdravkovic L, 2008, An improved constitutive model for unsaturated and saturated soils, Unsaturated Soils: Advances in Geo-Engineering, Publisher: Taylor & Francis Group, Pages: 581-588
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