Publications
486 results found
Bodas Freitas TM, Potts DM, Zdravkovic L, 2011, A time dependent constitutive model for soils with isotach viscosity, COMPUTERS AND GEOTECHNICS, Vol: 38, Pages: 809-820, ISSN: 0266-352X
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- Citations: 41
Bourne-Webb PJ, Potts DM, Koenig D, et al., 2011, Analysis of model sheet pile walls with plastic hinges, GEOTECHNIQUE, Vol: 61, Pages: 487-499, ISSN: 0016-8505
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- Citations: 13
Zdravkovic L, Potts DM, Kontoe S, 2011, Effect of wall stiffness on ground deformations around deep excavations in stiff clay, 15th European Conference on Soil Mechanics and Geotechnical Engineering, Pages: 1599-1604
Kontoe S, Zdravkovic L, Potts DM, et al., 2011, Seismic response of complex soil-structure systems, 15th European Conference on Soil Mechanics and Geotechnical Engineering, Pages: 1491-1496
Lagioia R, Potts DM, 2011, Ground conditions due to tunnelling in hard soils, 15th European Conference on Soil Mechanics and Geotechnical Engineering, Pages: 1665-1670
Kontoe S, Zdravkovic L, Potts DM, et al., 2011, On the relative merits of simple and advanced constitutive models in dynamic analysis of tunnels, Geotechnique, Vol: 61, Pages: 815-829, ISSN: 0016-8505
This paper compares simple constitutive models that are widely used in engineering practice with more sophisticated methods in the context of a case study. In particular, four constitutive modelling approaches have been considered: a simple elasto-plastic constitutive model (modified Cam-clay), with and without Rayleigh damping; the same model coupled with a cyclic non-linear model that can simulate pre-yield hysteresis; and finally an advanced kinematic hardening model, which is an improved version of the Al-Tabbaa & Wood two-surface model. These four approaches are used to analyse the seismic response of a section of the Bolu tunnels during the 1999 Duzce earthquake. To shed light on the performance of the constitutive models, simple site response finite-element analyses were first undertaken for the studied site, paying particular attention to the calibration of the Rayleigh damping parameters. The results of these analyses, in terms of maximum shear strain, were then used as input to an analytical elastic method (extended Hoeg method) for calculating the thrust and bending moment acting in the tunnel lining. Finally the results of dynamic time domain plane-strain analyses, employing the four adopted constitutive modelling approaches, are compared against field observations and results obtained by the extended Hoeg method, to investigate the ability of the models, of ranging complexity, to mimic soil response under seismic excitation.
Schroeder FC, Higgins KC, Wright P, et al., 2011, Assessment of overbridge openings on the London Underground tunnel network, 15th European Conference on Soil Mechanics and Geotechnical Engineering, Pages: 1733-1738
Zdravković L, Potts DM, 2010, Application of numerical analysis in geotechnical engineering practice, Pages: 69-88, ISSN: 0895-0563
Numerical analysis, in the form of the finite element, finite difference or boundary element method, has become a preferred calculation tool in the design of complex geotechnical structures. Even new codes of practice, such as the European EUROCODE 7, encourage the use of numerical analysis in design. However, as there is no general guidance and agreement in the international community on appropriate numerical solvers, constitutive models and boundary conditions, there are often examples of bad practice in the numerical analysis of geotechnical structures. Through examples of the analyses of real problems, this paper investigates the use of appropriate constitutive models and boundary conditions, to highlight both the successful use and the potential pitfalls of modern numerical analysis. © 2010 ASCE.
Bourne-Webb PJ, Potts DM, König D, 2010, Comparison of finite element predictions with results from a centrifuge test representing a double anchor wall in sand, Pages: 705-710
A study examining the effect of plastic hinging on the response of embedded retaining walls was undertaken. Double anchored walls embedded in dry sand were modelled in a geotechnical centrifuge at 1/30th scale. Finite element calculations were undertaken using Lade's double hardening cap model to represent the behaviour of the sand. Analyses yielded good accord with the test results in many aspects of the wall behaviour. The consequences of testing with a dig-accelerate versus an accelerate-dig sequence, and the effect of introducing a hinge zone into the wall section was examined. Comparisons between tests and their associated numerical simulation are of interest as they provide insight into the influence of these factors in the observed behaviour; it was found that the consequence of the dig-accelerate sequence appears minimal and other factors had a greater influence, while the introduction of a hinge zone into the wall system resulted in significant changes in the response with reference to the intact wall system. © 2010 Taylor & Francis Group, London.
Grammatikopoulou A, Kovacevic N, Zdravkovic L, et al., 2010, Finite element analysis of the main embankment at Empingham dam, Pages: 557-562
Empingham dam is a 37m high earth fill embankment which was constructed in the UK in the early 1970's. The embankment was built on a brecciated Upper Lias Clay (ULC) foundation, of fill derived from it. The ULC is a typical stiff plastic clay which shows a post-peak strength loss and as such is prone to progressive failure. The paper describes the finite element back analyses of the embankment behaviour during construction, using a kinematic hardening "bubble" model which accounts for both pre-peak plasticity and post-peak strain softening. © 2010 Taylor & Francis Group, London.
Giannopoulos KP, Zdravkovic L, Potts DM, 2010, A numerical study on the effects of time on the axial load capacity of piles in soft clays, Pages: 595-600
This paper investigates the axial load capacity of a pre-loaded pile installed in soft clay and subjected to vertical loading. Previous studies on pre-loaded shallow footings have shown that the undrained shear strength of soft clays is enhanced with time due to the dissipation of the excess pore water pressures generated during initial loading, as well as due to the soil ageing, after all pore pressures have dissipated, associated with creep. It remains a question whether the pile load capacity is enhanced with time as well, after the effects of installation have settled. The problem is investigated by means of a series of coupled finite element analyses, thus taking account of consolidation processes in the ground, in which the soil is modelled using an elastic-plastic constitutive model. Subsequently a similar set of coupled analyses is performed, using an elastic-viscoplastic model, to examine the effect of creep on pile capacity. © 2010 Taylor & Francis Group, London.
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
Nyambayo VP, Potts DM, 2010, Numerical simulation of evapotranspiration using a root water uptake model, COMPUTERS AND GEOTECHNICS, Vol: 37, Pages: 175-186, ISSN: 0266-352X
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- Citations: 47
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
Hov S, Bourne-Webb PJ, Hartlib T, et al., 2010, Column load transfer into piled retaining walls, 11th Int. Conf. Geotechnical Challenges in Urban Regeneration
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.
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.
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
Kovacevic N, Vaughan PR, Potts DM, 2009, Finite Element Analysis of Ladybower Dam: Long-term Operation and Dam Raising, 2nd Int. Conf. on Long Term Behaviour of Dams, Pages: 831-836
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
Abela JM, Vollum RL, Izzuddin BA, et al., 2009, Blinding struts in upheaval buckling, 11th Annual International fib Symposium, Concrete: 21st Century Superhero, Publisher: Emaps Network
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
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
Abela JM, Vollum RL, Izzuddin BA, et al., 2008, Upheaval buckling behaviour of blinding struts, Structural Engineering International: Journal of the International Association for Bridge and Structural Engineering (IABSE), Pages: 27-29, ISSN: 1016-8664
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.
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.
Smith PG, Potts DM, Addenbrooke TI, 2008, A precipitation boundary condition for finite element analysis, Pages: 773-778
This paper describes a precipitation boundary condition for use in numerical analysis of unsaturated soils that enables the simulation of rainfall on a ground surface (i.e. precipitation). A novel application of the boundary condition to simulate the ground water recharge that occurs at the base of the computational domain when modelling a partially saturated slope is also described. © 2008 Taylor & Francis Group, London.
Grammatikopoulou A, St John HD, Potts DM, 2008, Non-linear and linear models in design of retaining walls, PROCEEDINGS OF THE INSTITUTION OF CIVIL ENGINEERS-GEOTECHNICAL ENGINEERING, Vol: 161, Pages: 311-323, ISSN: 1353-2618
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- Citations: 4
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