Publications
485 results found
Schroeder FC, Merritt AS, Menkiti CO, et al., 2014, Assessing the effects of constructing the Colosseo/Fori Imperiali station on the Basilica di Massenzio in Rome, Italy, Pages: 801-806
Colosseo/Fori Imperiali is a key station of the San Giovanni-Venezia stretch on the new Metro Line C in Rome, Italy. It provides interchange facilities to the existing Line B and direct access to some of Rome's most important monuments, including the Colosseum and the Basilica di Massenzio. The works are ongoing in 2014 and the station comprises excavations for the main station box, which is in excess of 30m deep, approximately 130m long and up to 42m wide, as well as for a sub-station and station entrances, which are around 8m depth. There is a minimum distance of approximately 10m between the station and the Basilica, which was the largest building of the Roman Forum but its remains are now in a cracked and vulnerable condition. Given the historic importance of the Basilica and the close proximity of the station, ground movements had to be predicted and their potential effects on the monument required careful consideration. This paper presents the 3D FE analysis that was undertaken to enable this assessment and determine requirements for additional mitigation measures. Some mitigation measures were already implemented, including alignment refinement to optimize the box configuration and to position it as far from the monument as practicable, the use of stiff retaining wall systems, sufficiently deep to cut-off groundwater flow, and emphasis on good construction control. The analysis results demonstrated that, despite the large depth and size of the excavation for the final station box configuration, the effects on the monument would be minimal and so active intervention at the Basilica could be limited to detailed monitoring, temporary support and some strengthening work. © 2014 Taylor & Francis Group, London.
Hughes T, Taborda DMG, Zdravkovíc L, et al., 2014, Predicting the settlement of footings on sand using a bounding surface plasticity model, Delft, 8th European Conference on Numerical Methods in Geotechnical Engineering, NUMGE 2014, Publisher: Taylor and Francis - Balkema, Pages: 675-680
Despite having been the subject of extensive research, the prediction of load-settlement response of footings on sand deposits currently yields relatively poor and unreliable results. This paper aims at providing insight into this problem by examining the ability of a bounding surface plasticity model to predict the response of four distinct footings on Perth sand, which were tested as part of an international prediction event. Given the complexity of the chosen constitutive model and the relatively limited ground information available, emphasis is placed on the calibration procedure. In particular, the contributions of specific components of the constitutive model, such as the ability to simulate stiffness degradation at small deformation levels and the adopted formulation for the plastic hardening modulus, are investigated in a parametric study. Axisymmetric finite element analyses demonstrate that the response of the footings measured in the field is adequately simulated using the selected constitutive model. © 2014 Taylor & Francis Group.
Measham PG, Taborda DMG, Zdravković L, et al., 2014, Numerical simulation of a deep excavation in London Clay, Delft, 8th European Conference on Numerical Methods in Geotechnical Engineering, NUMGE 2014, Publisher: Taylor and Francis - Balkema, Pages: 771-776
The requirement for accurate modelling of the small-strain stiffness behaviour of soils in numerical analysis has been driven by the need to establish serviceability limit states for geotechnical structures. A common approach when tackling this problem is to employ a non-linear elastic constitutive model coupled with an appropriate failure criterion. The latter establishes the shear strength of the material and allows the evaluation of plastic deformations at large strains, while the former typically reproduces the effect of stress and strain levels on the shear and bulk stiffness of the soil. This paper evaluates distinct strategies for reproducing the stiffness of a material within the context of a new small-strain stiffness model. After introducing the constitutive model and describing its key features, a procedure to determine its parameters is proposed and demonstrated for London Clay. Subsequently, the relative impact of the different methods of interpreting the effect of changes in strain path direction on the stiffness of the material is investigated by performing finite element analyses of a deep excavation in London Clay. © 2014 Taylor & Francis Group, London.
Zdravkovic L, Potts DM, Tsiampousi A, 2014, Obtaining factors of safety from a finite element analysis of unsaturated soils, 6th International Conference on Unsaturated Soils (UNSAT), Publisher: CRC PRESS-TAYLOR & FRANCIS GROUP, Pages: 553-559
Tsiampousi A, Vitsios I, Zdravkovic L, et al., 2014, Effect of previous stress history and vegetation on the coefficient of earth pressure at-rest, K<sub>0</sub>, in London clay, 8th European Conference on Numerical Methods in Geotechnical Engineering (NUMGE), Publisher: CRC PRESS-TAYLOR & FRANCIS GROUP, Pages: 209-214
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- Citations: 1
Kovacevic N, Hight DW, Potts DM, et al., 2013, Finite-element analysis of the failure and reconstruction of the main dam embankment at Abberton Reservoir, Essex, UK, GEOTECHNIQUE, Vol: 63, Pages: 753-767, ISSN: 0016-8505
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- Citations: 6
Tsiampousi A, Zdravkovic L, Potts DM, 2013, Variation with time of the factor of safety of slopes excavated in unsaturated soils, Computers and Geotechnics, Vol: 48, Pages: 167-178
Abela JM, Potts DM, Vollum RL, et al., 2013, Geotechnical analysis of blinding struts in cut-and-cover excavations, COMPUTERS AND GEOTECHNICS, Vol: 48, Pages: 179-191, ISSN: 0266-352X
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- Citations: 3
Tsiampousi A, Zdravkovic L, Potts DM, 2013, A new Hvorslev surface for critical state type unsaturated and saturated constitutive models, Computers and Geotechnics, Vol: 48, Pages: 156-166
Tsiampousi A, Zdravkovic L, Potts DM, 2013, A three-dimensional hysteretic soil-water retention curve, Geotechnique, Vol: 63, Pages: 155-164, ISSN: 0016-8505
One of the most important features in unsaturated soil mechanics is the soil-water retention curve and its coupling to the mechanical component of soil behaviour. It has long been recognised that the retention curve exhibits significant hysteresis, and that it is affected by the specific volume. Several attempts have been made in the past to model this behaviour. A novel approach is proposed herein, which accounts for both the hydraulic hysteresis and the specific volume dependence of the retention relationship in a three-dimensional formulation. The primary and the scanning paths are simple geometric curves, which have a common tangent at the point of intersection, ensuring a smooth transition from scanning to primary paths. A small number of parameters are required to define the primary paths, and no fitting parameters are necessary for generation of the scanning paths. As knowledge of the specific volume and its variation is required, the retention model needs to be employed in conjunction with a constitutive model capable of reproducing the complex behaviour of unsaturated soils. To guarantee consistency with the retention model, the degree of saturation needs to be incorporated in the specific volume–suction relationship adopted within the constitutive model. To accommodate such a feature when absent, a new expression for the soil compressibility with suction as a function of the degree of saturation is proposed. Simulations of laboratory experiments on unsaturated soils, involving cyclic changes of applied suction, demonstrate the effectiveness of the proposed modelling approach.
Kontoe S, Pelecanos L, Potts DM, 2013, An important pitfall of pseudo-static finite element analysis, Computers & Geotechnics, Vol: 48, Pages: 41-50
Finite Element (FE) pseudo-static analysis can provide a good compromise between simplified methods of dynamic analysis and time domain analysis. The pseudo-static FE approach can accurately model the in-situ stresses prior to seismic loading (when it follows a static analysis simulating the construction sequence) is relatively simple and not as computationally expensive as the time domain approach. However this method should be used with caution as the results can be sensitive to the choice of the mesh dimensions. In this paper two simple examples of pseudo-static finite element analysis are examined parametrically, a homogeneous slope and a cantilever retaining wall, exploring the sensitivity of the pseudo static analysis results on the adopted mesh size. The mesh dependence was found to be more pronounced for problems with high critical seismic coefficients values (e.g. gentle slopes or small walls), as in these cases a generalised layer failure mechanism is developed simultaneously with the slope or wall mechanism. In general the mesh width was found not to affect notably the predicted value of critical seismic coefficient but to have a major impact on the predicted movements.
Potts DM, Zdravkovic L, 2012, Accounting for partial material factors in numerical analysis, Geotechnique
Potts D, 2012, Limit state design, London, Geotechnical issues in construction: short paper series and fifth conference, Publisher: CIRIA, Pages: 27-32
Potts D, 2012, Using numerical analysis in geotechnical engineering practice - The First Leamardo Zeevaert Lecture, 26th National Conference on Soil Mechanics and Geotechnical Engineering (26th NCSMGE)
Bodas Freitas TM, Zdravkovic L, Potts DM, 2012, Some strengths and weaknesses of overstress based elasto-viscoplastic models, 2nd International Symposium on Constitutive Modelling of Geomaterials - Advances and New application, Publisher: Springer Series in Geotechnics and Geoengineering, Pages: 107-114
Kovacevic N, Jardine RJ, Potts DM, et al., 2012, A numerical simulation of progressive slope failures generated by salt diaiprism combined with active sedimentation, Geotechnique: international journal of soil mechanics, Vol: 62
This paper describes advanced finite element simulations of a geologically active andperiodically unstable 700m high underwater escarpment located in the Gulf of Mexicothat has been created by uplifting salt diapirs combined with sediment deposition. Thesite's geological history, soil permeability and clay shear strength characteristicsgovern current slope stability and determine the timing of any future failure. Thegeological and geotechnical conditions are reported before presenting fully coupled,large displacement, numerical simulations employing critical state formulations of theslope's evolution over the last 600,000 years. The latter form the basis for strainsoftening analyses of the pore pressure equalisation and progressive failure processesthat control current slope stability. The analyses also address the ground movementpatterns that precede instability, giving useful information for geohazard riskassessment and early warning monitoring system design.
Freitas TMB, Potts DM, Zdravkovic L, 2012, Implications of the definition of the Φ function in elastic-viscoplastic models, GEOTECHNIQUE, Vol: 62, Pages: 643-648, ISSN: 0016-8505
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- Citations: 8
Bodas Freitas TM, Potts DM, Zdravkovic L, 2012, The effect of creep on the short-term bearing capacity of pre-loaded footings, COMPUTERS AND GEOTECHNICS, Vol: 42, Pages: 99-108, ISSN: 0266-352X
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- Citations: 1
Kontoe S, Zdravkovic L, Menkiti CO, et al., 2012, Seismic response and interaction of complex soil retaining systems, Computers and Geotechnics, Vol: 39, Pages: 17-26
This paper examines the seismic response of a large and complex system comprising a Lock chamber and three neighbouring water saving basins (WSBs). The developed two-dimensional plane strain finite element model included the entire system in order to explore the interaction of the various structures. The first set of analyses was undertaken under static conditions to simulate the construction sequence and to establish the stress regime prior to the examined seismic event. Subsequently, dynamic time domain analyses were performed to examine the response of the system to seismic loading. The ground motion was applied into the finite element mesh employing a sub-structuring technique which enables economic modelling of large computation domains and accurate representation of the semi-infinite half-space. The paper explores some aspects of the numerical modelling of such complex systems, such as the impact on the predicted seismic response of the adopted constitutive model and the modelling of hydrodynamic effects. The discussion of the dynamic analyses results focuses on the main Lock structure, looking at the prevailing modes of deformation, the potential lift-off of the base of the Lock walls and the interaction of the main wall with the other retaining structures.
Tsiampousi A, Zdravkovic L, Potts DM, 2012, Stability of highly overconsolidated soil slopes, II European Conference for Unsaturated Soils (E-UNSAT2012), Pages: 377-382
Potts D, Zdravkovic L, 2012, Computer Analysis principles in geotechnical engineering, ICE manual of Geotechnical Engineering - Volume 1 Geotechnical Engineering Principles, Problematic Soils and Site Investigation, Editors: Burland, Skinner, Brown, Publisher: Institution of Civil Engineers, Pages: 35-57
Abela JM, Vollum RL, Izzuddin BA, et al., 2012, Blinding Struts under Long-Term Loading, Magazine of Concrete Research
The term ‘blinding’ is used to describe the thin layer of unreinforced over-site concrete which is used to protect the base of excavations during construction. Blinding is not generally considered as a structural element even though it clearly provides some temporary lateral support to the retaining walls of excavations. The authors have previously shown that that enhanced blinding can be used to prop retaining walls in cut-and-cover excavations during construction prior to the completion of the base slab. This paper describes a series of laboratory tests which the authors carried out to investigate the effect of concrete creep on the axial resistance of blinding struts. The tests show that blinding can creep to failure if the sustained load exceeds a critical value which depends on the imperfection amplitude and profile as well as the strut thickness. The test results are used to validate a numerical model which is subsequently used to carry out a series of parametric studies on full-scale blinding struts.
Bourne-Webb PJ, Potts DM, Rowbottom D, 2011, Eurocode reduction factors for U-profile sheet pile walls, PROCEEDINGS OF THE INSTITUTION OF CIVIL ENGINEERS-STRUCTURES AND BUILDINGS, Vol: 164, Pages: 377-390, ISSN: 0965-0911
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- Citations: 1
Potts DM, Kovacevic N, Hight D, 2011, Predicting the stability of large excavations at Heathrow Terminal 5, Calculation Methods in Geotechnics - Failure Mechanisms and Determination of Parameters, Pages: 46-52
Potts DM, Zdravkovic L, 2011, Application of partial factors of safety in numerical analysis of bearing capacity, Pages: 775-781
One of the issues that arise when using numerical analysis in accordance with Eurocode 7 is how to account for partial factors of safety on material strength. Namely, Eurocode 7 implies that strengths to be used in an analysis should be based on a design value, but reduced by partial factors. This can be done in two ways, but Eurocode 7 gives no guidance as to which one is more appropriate. This paper examines the application of partial factors of safety in a bearing capacity problem. Finite element analyses are performed using both a simple Tresca and a more advanced Modified Cam Clay models to represent soil behaviour, and both approaches for the application of partial factors of safety.
Kovacevic N, Potts DM, 2011, Use of advanced constitutive models in numerical analysis of embankment dams, Pages: 839-851
Although the main concern when designing or analysing embankment dams is their stability, assessing their deformation pattern is also important. This paper describes the recent use of advanced numerical analysis to predict the latter, and examples of its use in assessing likely movements of a series of embankment dams constructed in the UK are provided. Various phases in dam life are considered: embankment construction, first reservoir impounding, subsequent reservoir operation and raising the dam crest level. The use of adequate constitutive laws and, in particular, the importance of modelling the prepeak (and post-peak) plastic behaviour of in-situ and embankment fill materials during loading, unloading and re-loading is clearly demonstrated.
Schuetz R, Potts DM, Zdravkovic L, 2011, Advanced constitutive modelling of shotcrete: Model formulation and calibration, COMPUTERS AND GEOTECHNICS, Vol: 38, Pages: 834-845, ISSN: 0266-352X
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- Citations: 16
Abela JM, Vollum RL, Izzuddin BA, et al., 2011, Blinding Struts – Part 1: Buckling Response, Engineering Structures, Pages: 2563-2572, ISSN: 0141-0296
The term ‘blinding’ is used to describe the thin layer of unreinforced over-site concrete which is used to protect the base of excavations from construction traffic and to provide a clean surface for the construction of the base slab. Blinding is not generally seen or exploited as a structural element even though it clearlyprovides some temporary lateral support to the retaining walls of cut-and-cover excavations. This paper shows that enhanced blinding can be used to prop retaining walls in cut-and-cover excavations during construction prior to the completion of the base slab. An experimental program is conducted on 1/4 scale specimens, which demonstrates that the failure load of blinding struts is governed by upheaval buckling,and which is employed for the validation of nonlinear finite element models. The main parameters governing the buckling load are shown to include: i) the amplitude of the geometrical imperfection, ii)the thickness of blinding, and iii) the eccentricity of the applied load with respect to the centroid of the strut.
Vollum RL, Izzuddin BA, Abela JM, et al., 2011, Blinding Struts – Part 2: Towards A Simplified Design Method, Engineering Structures, Pages: 2573-2583, ISSN: 0141-0296
The companion paper described how concrete blinding can be used to prop retaining walls in cut and cover excavations prior to the completion of the base slab. In addition, it was demonstrated that the behaviour of blinding struts can be accurately predicted with nonlinear finite element analysis (NLFEA) ifthe strut properties and ground profile are known. This paper presents a simple design-oriented analytical model which can be used for blinding struts as an alternative to NLFEA. The simplified model is shown to give comparable results to NLFEA and is attractive for design since it allows the effect of variationsin imperfection amplitude and length to be rapidly assessed. A case study is presented which illustrates the use of the method and demonstrates that relatively thin blinding struts can resist the maximum axial forces likely to be encountered in cut and cover excavations.
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
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