Publications
249 results found
Pedro A, Zdravkovic L, Potts DM, et al., 2016, Derivation of model parameters for numerical analysis of the Ivens shaft excavation, Engineering Geology, Vol: 217, Pages: 49-60, ISSN: 1872-6917
The prediction of induced ground movements and the potential damage to existing structures and services is paramount when building deep excavations in an urban environment. In order to obtain a reasonable prediction advanced constitutive models need to be employed, so that the behaviour of the soil can be adequately reproduced under different stress conditions. The calibration of such models is complex and often requires optimisation, as a large number of parameters need to be determined from the available ground investigation data, while also ensuring their consistency with the initial ground conditions. This paper presents the calibration process of advanced constitutive models employed to simulate the excavation of the Ivens shaft in Lisbon, Portugal. The data from both historic and new laboratory and field testing is employed in the calibration procedure. In order to assess and validate the suitability of the derived model parameters, a back-analysis of the nearby Baixa-Chiado metro station excavation is carried out and its results are presented and discussed.
Pedone G, Tsiampousi A, Cotecchia F, et al., 2016, Effects of soil-vegetation-atmosphere interaction on the stability of a clay slope: a case study, 3rd European Conference on Unsaturated Soils, Publisher: EDP Sciences, ISSN: 2267-1242
Deep and slow landslide processes are frequently observed in clay slopes located along the Southern Apennines (Italy). A case study representative of these processes, named Pisciolo case study, is discussed in the paper. The geo-hydro-mechanical characteristics of the materials involved in the instability phenomena are initially discussed. Pluviometric, piezometric, inclinometric and GPS monitoring data are subsequently presented, suggesting that rainfall infiltration constitutes the main factor inducing slope movements. The connection between formation of landslide bodies and slope-atmosphere interaction has been demonstrated through a hydro-mechanical finite element analysis, whose results are finally reported in the work. This analysis has been conducted employing a constitutive model that is capable of simulating both saturated and unsaturated soil behaviour, as well as a boundary condition able to simulate the effects of the soil-vegetation-atmosphere interaction.
Tsiampousi A, Zdravkovic L, Potts DM, 2016, Soil-atmosphere interaction in unsaturated cut slopes, 3rd European Conference on Unsaturated Soils, Publisher: EDP Sciences, ISSN: 2267-1242
Interaction between atmosphere and soil has only recently attracted significant interest. Soil-atmosphereinteraction takes place under dynamic climatic conditions, which vary throughout the year and are expected to sufferconsiderable alterations due to climate change. However, Geotechnical Analysis has traditionally been limited tosimplistic approaches, where winter and summer pore water pressure profiles are prescribed. Geotechnical Structures,such as cut slopes, are known to be prone to large irreversible displacements under the combined effect of wateruptake by a complex vegetation root system and precipitation. If such processes take place in an unsaturated materialthe complexity of the problem renders the use of numerical analysis essential. In this paper soil-atmosphereinteraction in cut slopes is studied using advanced, fully coupled partially saturated finite element analyses. The effectof rainfall and evapotranspiration is modelled through sophisticated boundary conditions, applying actualmeteorological data on a monthly basis. Stages of low and high water demand vegetation are considered for a periodof several years, before simulating the effect of vegetation removal. The analysis results are presented with regard tothe serviceability and stability of the cut slope.
Gawecka KA, Taborda DMG, Potts DM, et al., 2016, Effects of transient phenomena on the behaviour of thermo-active piles, 1st International Conference on Energy Geotechnics
Han B, Zdravkovic L, Kontoe S, et al., 2016, Numerical investigation of the response of the Yele rockfill dam during the 2008 Wenchuan Earthquake, Soil Dynamics and Earthquake Engineering, Vol: 88, Pages: 124-142, ISSN: 1879-341X
In this paper the seismic response of a well-documented Chinese rockfill dam, Yele dam, is simulated and investigated employing the dynamic hydro-mechanically (HM) coupled finite element (FE) method. The objective of the study is to firstly validate the numerical model for static and dynamic analyses of rockfill dams against the unique monitoring data on the Yele dam recorded before and during the Wenchuan earthquake. The initial stress state of the dynamic analysis is reproduced by simulating the geological history of the dam foundation, the dam construction and the reservoir impounding. Subsequently, the predicted seismic response of the Yele dam is analysed, in terms of the deformed shape, crest settlements and acceleration distribution pattern, in order to understand its seismic behaviour, assess its seismic safety and provide indication for the application of any potential reinforcement measures. The results show that the predicted seismic deformation of the Yele dam is in agreement with field observations that suggested that the dam operated safely during the Wenchuan earthquake. Finally, parametric studies are conducted to explore the impact of two factors on the seismic response of rockfill dams, i.e. the permeability of materials comprising the dam body and the vertical ground motion.
Han B, Zdravkovic L, Kontoe S, 2016, Numerical and analytical investigation of compressional wave propagation in saturated soils, Computers and Geotechnics, Vol: 75, Pages: 93-102, ISSN: 0266-352X
In geotechnical earthquake engineering, wave propagation plays a fundamental role in engineering applications related to the dynamic response of geotechnical structures and to site response analysis. However, current engineering practice is primarily concentrated on the investigation of shear wave propagation and the corresponding site response only to the horizontal components of the ground motion. Due to the repeated recent observations of strong vertical ground motions and compressional damage of engineering structures, there is an increasing need to carry out a comprehensive investigation of vertical site response and the associated compressional wave propagation, particularly when performing the seismic design for critical structures (e.g. nuclear power plants and high dams). Therefore, in this paper, the compressional wave propagation mechanism in saturated soils is investigated by employing hydro-mechanically (HM) coupled analytical and numerical methods. A HM analytical solution for compressional wave propagation is first studied based on Biot’s theory, which shows the existence of two types of compressional waves (fast and slow waves) and indicates that their characteristics (i.e. wave dispersion and attenuation) are highly dependent on some key geotechnical and seismic parameters (i.e. the permeability, soil stiffness and loading frequency). The subsequent HM Finite Element (FE) study reproduces the duality of compressional waves and identifies the dominant permeability ranges for the existence of the two waves. In particular the existence of the slow compression wave is observed for a range of permeability and loading frequency that is relevant for geotechnical earthquake engineering applications. In order to account for the effects of soil permeability on compressional dynamic soil behaviour and soil properties (i.e. P-wave velocities and damping ratios), the coupled consolidation analysis is therefore recommended as the only tool capable of accura
Cui W, Gawecka KA, Potts DM, et al., 2016, Numerical analysis of coupled thermo-hydraulic problems in geotechnical engineering, Geomechanics for Energy and the Environment, Vol: 6, Pages: 22-34, ISSN: 2352-3808
Ground sources energy systems, such as open-loop systems, have been widely employed in recent years due to their economic and environmental benefits compared to conventional heating and cooling systems. Numerical modelling of such geothermal system requires solving a coupled thermo-hydraulic problem which is characterised by a convection-dominated heat transfer which can be challenging for the Galerkin finite element method (GFEM). This paper first presents the coupled thermo-hydraulic governing formulation as well as the coupled thermo-hydraulic boundary condition, which can be implemented into a finite element software. Subsequently, the stability condition of the adopted time marching scheme for coupled thermo-hydraulic analysis is established analytically. The behaviour of highly convective problems is then investigated via a series of analyses where convective heat transfer along a soil bar is simulated, with recommendations on the choice of an adequate discretisation with different boundary conditions being provided to avoid oscillatory solutions. Finally, the conclusions from the analytical and numerical studies are applied to the simulation of a boundary value problem involving an open-loop system, with the results showing good agreement with an approximate solution. The main objective of this paper is to demonstrate that the GFEM is capable of dealing with highly convective geotechnical problems.
Pelecanos L, Kontoe S, Zdravkovic L, 2016, Dam–reservoir interaction effects on the elastic dynamic response of concrete and earth dams, Soil Dynamics and Earthquake Engineering, Vol: 82, Pages: 138-141, ISSN: 0267-7261
The relative effects of dam–reservoir interaction on the dynamic response of concrete and earth dams are studied. The amplification of accelerations at the dam crest is explored under harmonic acceleration load. For certain cases of concrete dams the accelerations can be significantly affected by the upstream reservoir, whereas this influence is smaller for earth dams.
Taborda DMG, Potts DM, Zdravkovic L, 2016, On the assessment of energy dissipated through hysteresis in finite element analysis, Computers and Geotechnics, Vol: 71, Pages: 180-194, ISSN: 0266-352X
The accurate reproduction of the hysteretic behaviour exhibited by soils under cyclic loading is a crucial aspect of dynamic finite element analyses and is typically described using the concept of damping ratio. In this paper, a general algorithm is presented for assessing the damping ratio simulated by any constitutive model based on the registered behaviour in three-dimensional stress-strain space. A cyclic nonlinear elastic model capable of accurately reproducing a wide range of features of soil behaviour, including the variation of damping ratio with deformation level, is chosen to illustrate the capabilities of the proposed algorithm. The constitutive model is described and subsequently employed in two sets of finite element analyses, one involving the dynamic response of a sand deposit subjected to different types of motion and another focussing on the simulation of a footing subjected to cyclic vertical loading. The application of the presented algorithm provides insight into the processes through which energy is dissipated through hysteresis.
Han B, Yang Z, Zdravkovic L, et al., 2015, Non-linearity of gravelly soils under seismic compressional deformation based on KiK-net downhole array observations, Geotechnique Letters, Vol: 5, Pages: 287-293, ISSN: 2045-2543
In this paper the nonlinear behaviour of gravelly soils under seismiccompressional deformation is investigated based on KiK-net downhole array earthquakeobservations in Japan. By comparing the amplification spectra between the verticalresponse at the ground surface and at the bottom of downholes subjected to strongmotions with those subjected to weak motions, empirical curves for constrainedmodulus degradation are obtained considering different levels of vertical confiningpressure. Results show that the nonlinearity associated with the compressionaldeformation can be as significant as that of the shear deformation, for gravelly soilsabove water tables. The proposed curves provide satisfactory predictions for thecompressional soil nonlinearity investigated in previous studies. Furthermore, theproposed curves are formulated by a modified cyclic nonlinear model, which canaccount for constrained modulus degradation under a variety of confining pressureconditions and therefore extends the application of the proposed reference curves tononlinear numerical analysis of geotechnical structures under multi-directional seismicloads.
Pelecanos L, Kontoe S, Zdravkovic L, 2015, A case study on the seismic performance of earth dams, Geotechnique: international journal of soil mechanics, Vol: 65, Pages: 923-935, ISSN: 0016-8505
The seismic non-linear behaviour of earth dams is investigated by using a well-documented case study and employing advanced static and dynamic coupled-consolidation finite-element analysis. The static part of the analysis considers the layered construction, reservoir impoundment and consolidation, whereas the dynamic part considers the response of the dam to two earthquakes of different magnitude, duration and frequency content. The results of the analysis are compared with the recorded response of the dam and exhibit a generally good agreement. The effects of the narrow canyon geometry, the reservoir impoundment and the elasto-plastic soil behaviour on the seismic dam behaviour are investigated. Finally the implications of the adopted constitutive modelling assumptions on the predicted response are discussed.
Monroy R, Zdravkovic L, Ridley AM, 2015, Mechanical behaviour of unsaturated expansive clay under K-0 conditions, Engineering Geology, Vol: 197, Pages: 112-131, ISSN: 0013-7952
The mechanical response of unsaturated soils with significant amounts of active clay minerals can be highly stress path dependent. Traditionally, the Axis Translation Procedure has been used to study these materials in the laboratory. This technique, however, does not fully replicate conditions in the field, nor is it able to test soils during the important process of desaturation and resaturation. A novel osmotic oedometer has been developed at Imperial College London to test unsaturated soils under atmospheric pressure. With this equipment, it has been possible to continuously record changes in vertical and radial stress, gravimetric water content, degree of saturation, matrix suction, and void ratio, throughout a test. The Paper presents results from tests carried on samples of compacted London clay using the new oedometer and standard oedometers. The full data set gives an insight into the mechanical response of unsaturated expansive clay along complex stress paths. Results are interpreted using an existing framework for unsaturated expansive clays. Because of inherent limitations in the method of testing, some of the data needs to be interpreted with care. Nevertheless, the response recorded along different stress paths was found to be consistent and in agreement with framework predictions.
Cui W, Gawecka KA, Taborda DMG, et al., 2015, Time-step constraints in transient coupled finite element analysis, International Journal for Numerical Methods in Engineering, Vol: 106, Pages: 953-971, ISSN: 1097-0207
In transient finite element analysis, reducing the time-step size improves the accuracy of the solution. However, a lower bound to the time-step size exists, below which the solution may exhibit spatial oscillations at the initial stages of the analysis. This numerical ‘shock’ problem may lead to accumulated errors in coupled analyses. To satisfy the non-oscillatory criterion, a novel analytical approach is presented in this paper to obtain the time-step constraints using the θ-method for the transient coupled analysis, including both heat conduction–convection and coupled consolidation analyses. The expressions of the minimum time-step size for heat conduction–convection problems with both linear and quadratic elements reduce to those applicable to heat conduction problems if the effect of heat convection is not taken into account. For coupled consolidation analysis, time-step constraints are obtained for three different types of elements, and the one for composite elements matches that in the literature. Finally, recommendations on how to handle the numerical ‘shock’ issues are suggested.
Martinez Calonge D, Gawecka KA, Zdravkovic L, et al., 2015, Development of a new temperature-controlled triaxial apparatus for saturated soils, 16th European Conference on Soil Mechanics and Geotechnical Engineering, Publisher: ICE Publishing
In recent years, the study of the Thermo-Hydro -Mechanical (THM) behaviour of geomaterials has become a growing area in geotechnical engineering due to the increasing interest in energy geostructures and underground nuclear waste disposal. Advanced laboratory testing is essential in gaining an understanding of the THM behaviour of soils and solving these complex geomechanical problems. This paper describes the development of a new triaxial apparatus at the Imperial College Geotechnics Laboratory, capable of testing saturated soils at temperatures up to 85°C and pressures up to 800kPa. In order to aid its design, numerical analysis of the thermal response of the cell was conducted using the Imperial College Finite Element Program (ICFEP) with its newly developed THM capabilities.
Cui W, Gawecka KA, Potts DM, et al., 2015, Numerical modelling of open-loop ground source energy systems, 16th European Conference on Soil Mechanics and Geotechnical Engineering, Publisher: ICE Publishing
The environmental and economic benefits of utilising the ground for extracting and storing heat have been known for a long time. However, only recently have government sustainability policies and rising energy prices encouraged the use of this renewable energy resource. In open-loop systems water is abstracted from one well and re-injected into another after exchanging energy with a building’s heating/cooling system using a heat pump. In order to guarantee a good performance of the system, it is fundamental that the possibility of thermal breakthrough occurring is minimised, i.e. that the temperature of the water being abstracted remains unaffected by the injection of warmer/cooler water at the other well. In this paper, the Imperial College FiniteElement Program (ICFEP), which is capable of simulating fully coupled thermo-hydro-mechanical behaviour of porous materials, was used to perform two-dimensional analyses of open-loop ground source heat systems. The parametric studies carried out highlight the relative impact on the occurrence of thermal break-through of the hydraulic ground conditions andthe geometric characteristics of the system, providing an invaluable insight into possible improvements to the current design procedure.
Dubasaru V, Zdravkovic L, Taborda DMG, et al., 2015, Influence of pile raft stiffness on building behaviour in a tunnel-pile clash scenario, 16th European Conference on Soil Mechanics and Geotechnical Engineering, Publisher: ICE Publishing
In a modern urban environment, the underground space becomes increasingly congested due to the high value of the land that forces the new infrastructure projects to be constructed deeper into the ground. For each new project, the potential of both expected and unexpected clashes between new tunnel alignments and the foundations of the existing structures becomes more probable. However, to date, the research on tunnel-pile clashes has been scarce. In the current study, the effects of such a situation are studied by carrying out finite element analyses for a scenario that is typical in the London ground profile. A parametric study was conducted to investigate the influence of the pile raft bending stiffness on the building settlement and the change in piles’ axial forces. It is shown that an increased raft bending stiffness helps to transfer the load from the trimmed pile to the adjacent piles, thus reducing the settlement of the trimmed pile. In the process of tunnel excavation, the pile settles due to the soil-induced downdrag and the loss of both its base and part of its shaft capacity. It is concluded that the tunnel-pile clash has a large impact on the surface structure, piles and tunnel itself.
Byrne BW, McAdam RA, Burd HJ, et al., 2015, Field testing of large diameter piles under lateralloading for offshore wind applications, 16th European Conference on Soil Mechanics and Geotechnical Engineering, Publisher: ICE Publishing
Offshore wind power in the UK, and around Europe, has the potential to deliver significant quantities of renewable energy. The foundation is a critical element in the design. The most common foundation design is a single large diameter pile, termed a monopile. Pile diameters of between 5m and 6m are routinely used, with diameters up to 10m or more, being considered for future designs. Questions have been raised as to whether current design methods for lateral loading are relevant to these very large diameter piles. To explore this problem a joint industry project, PISA, co-ordinated by DONG Energy and the Carbon Trust, has been established. The aim of the project is to develop a new design framework for laterally loaded piles based on new theoretical developments, numerical modelling and bench-marked against a suite of large scale field pile tests. The project began in August 2013 and is scheduled to complete during 2015. This paper briefly outlines the project, focusing on the design of the field testing. The testing involves three sizes of pile, from 0.27m in diameter through to 2.0m in diameter. Two sites will be used; a stiff clay site and a dense sand site. Tests will include monotonic loading and cyclic loading. A suite of site investigation will be carried out to aid interpretation of the field tests, and will involve in-situ testing, standard laboratory testing and more advanced laboratory testing.
Freitas TMB, Potts DM, Zdravkovic L, 2015, Numerical study on the response of two footings at Bothkennar research site, Geotechnique, Vol: 65, Pages: 155-168, ISSN: 1021-8637
This paper presents a numerical study of the performance of two instrumented surface footings at the Bothkennar Clay research site in the UK. Footing A was loaded to failure over 4 days, reaching a net bearing capacity of qr = 138 kPa; footing B was loaded to 89 kPa, at an identical loading rate, and left to consolidate under maintained load for about 11 years. The preloaded footing was then loaded to failure over 3 days, reaching qr = 204 kPa. The increase in bearing capacity was significantly larger than that expected due to consolidation effects alone, and it is anticipated that the occurrence of creep and other ageing processes may have played a major role in the observed response. The complete loading history of the two footings is simulated by means of coupled axi-symmetric finite-element analyses in which the foundation soil is described using an elastic–viscoplastic model that mimics isotach viscosity. The ground profile and the model parameters are derived based on the extensive laboratory and field test data available in the literature. The numerical analyses are able to describe accurately the footings behaviour during first loading, the development of delayed settlement under maintained load and the increase in bearing capacity due to preloading. The paper emphasises various issues regarding the application of elastic–viscoplastic models to model boundary value problems in conditions close to failure.
Doherty P, Igoe D, Murphy G, et al., 2015, Field validation of fibre Bragg grating sensors for measuring strain on driven steel piles, GEOTECHNIQUE LETTERS, Vol: 5, Pages: 74-79, ISSN: 2049-825X
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- Citations: 35
Zdravković L, Taborda DMG, Potts DM, et al., 2015, Numerical modelling of large diameter piles under lateral loading for offshore wind applications, Frontiers in Offshore Geotechnics III, Pages: 759-764, ISBN: 9781138028487
There is currently a significant focus on developing offshore wind power in the UK and Europe. The most common foundation type for wind turbines is a single large diameter pile, termed a monopile, on which the turbine is located. As the diameter of such piles is envisaged to increase in future installations, there are concerns that current design methods are not applicable. To explore this problem, the joint industry project PISA has been established, with the aim to develop a new design framework for laterally loaded piles utilised in the offshore wind industry, based on new theoretical developments, numerical modelling and large scale field pile testing. This paper presents an overview of numerical modelling undertaken as part of the project.
Zdravković L, Taborda DMG, Potts DM, et al., 2015, Numerical modelling of large diameter piles under lateral loading for offshore wind applications, Pages: 759-764
There is currently a significant focus on developing offshore wind power in the UK and Europe. The most common foundation type for wind turbines is a single large diameter pile, termed a monopile, on which the turbine is located. As the diameter of such piles is envisaged to increase in future installations, there are concerns that current design methods are not applicable. To explore this problem, the joint industry project PISA has been established, with the aim to develop a new design framework for laterally loaded piles utilised in the offshore wind industry, based on new theoretical developments, numerical modelling and large scale field pile testing. This paper presents an overview of numerical modelling undertaken as part of the project.
Byrne BW, McAdam R, Burd HJ, et al., 2015, New design methods for large diameter piles under lateral loading for offshore wind applications, Pages: 705-710
Offshore wind turbines are typically founded on single large diameter piles, termed monopiles. Pile diameters of between 5mand 6mare routinely used, with diameters of up to 10 m, or more, being considered for future designs. There are concerns that current design approaches, such as the p − y method, which were developed for piles with a relatively large length to diameter ratio, may not be appropriate for large diameter monopiles. A joint industry project, PISA (PIle Soil Analysis), has been established to develop new design methods for large diameter monopiles under lateral loading. The project involves three strands of work; (i) numerical modelling; (ii) development of a new design method; (iii) field testing. This paper describes the framework on which the new design method is based. Analyses conducted using the new design method are compared with methods used in current practice.
Byrne BW, McAdam R, Burd HJ, et al., 2015, New design methods for large diameter piles under lateral loading for offshore wind applications, Frontiers in Offshore Geotechnics III, Pages: 705-710, ISBN: 9781138028487
Offshore wind turbines are typically founded on single large diameter piles, termed monopiles. Pile diameters of between 5mand 6mare routinely used, with diameters of up to 10 m, or more, being considered for future designs. There are concerns that current design approaches, such as the p - y method, which were developed for piles with a relatively large length to diameter ratio, may not be appropriate for large diameter monopiles. A joint industry project, PISA (PIle Soil Analysis), has been established to develop new design methods for large diameter monopiles under lateral loading. The project involves three strands of work; (i) numerical modelling; (ii) development of a new design method; (iii) field testing. This paper describes the framework on which the new design method is based. Analyses conducted using the new design method are compared with methods used in current practice.
Cui W, Gawecka KA, Potts DM, et al., 2015, Investigations on numerical analysis of coupled thermo-hydraulic problems in geotechnical engineering, International Symposium on Energy Geotechnics (1st.: 2015: Barcelona)
Han B, Zdravkovic L, Kontoe S, 2014, Stability investigation of the Generalised-α time integration method for dynamic coupled consolidation analysis, Computers and Geotechnics, Vol: 64, Pages: 83-95, ISSN: 1873-7633
In this paper, the stability of the Generalised-α time integration method (the CH method) for a fully coupled solid-pore fluid formulation is analytically investigated for the first time and the corresponding theoretical stability conditions are proposed based on a rigorous mathematical derivation process. The proposed stability conditions simplify to the existing ones of the CH method for the one-phase formulation when the solid–fluid coupling is ignored. Furthermore, by degrading the CH method to the Newmark method, the stability conditions are in agreement with the ones proposed in previous stability investigations on coupled formulation for the Newmark method. The analytically derived stability conditions are validated with finite element (FE) analyses considering a range of loading conditions and for various soil permeability values, showing that the numerical results are in agreement with the theoretical investigation. Then, the stability characteristics of the CH method are explored beyond the limits of the theoretical investigation, assuming elasto-plastic soil behaviour which is prescribed with a bounding surface plasticity constitutive model. Since the CH method is a generalisation of a number of other time integration methods, the derived stability conditions are relevant for most of the commonly utilised time integration methods for the two-phase coupled formulation.
Taborda DM, Zdravkovic L, Kontoe S, et al., 2014, Computational study on the modification of a bounding surface plasticity model for sands, Computers and Geotechnics, Vol: 59, Pages: 145-160, ISSN: 0266-352X
The accurate simulation of complex dynamic phenomena requires the availability of advanced constitutive models capable of simulating a wide range of features of soil behaviour under cyclic loading. One possible strategy is to improve the capabilities of existing bounding surface plasticity models, as this framework is characterised by its modularity and flexibility. As a result, specific components of the formulation of this type of model may be adjusted to improve the reproduction of any aspect of soil behaviour deemed essential to the problem being analysed. In this paper, a series of computational studies are performed in order to establish the impact of expanding a bounding surface plasticity model for sands on its modelling capabilities and to suggest ways of mitigating the associated increase in complexity. Changes to three distinct aspects of the selected constitutive model are examined: the shape of the Critical State Line in p′ − e space, the expression used for calculating the hardening modulus and the form of the yield surface. It is shown that the introduced changes have the potential to increase significantly the ability to control how certain aspects of soil response, such as degradation of stiffness and flow liquefaction with limited deformation, are reproduced by the model. Moreover, this paper presents a systematic approach to the expansion of this type of constitutive model, establishing how alterations to the formulation of a model may be assessed in terms of improved accuracy and potential benefits.
Han B, Zdravkovic L, Kontoe S, 2014, Analytical and theoretical investigations on the vertical seismic site response, 8th European Conference on Numerical Methods in Geotechnical Engineering (NUMGE), Pages: 1123-1128
Monroy R, Zdravkovic L, Ridley AM, 2014, Evaluation of an Active System to Measure Lateral Stresses in Unsaturated Soils, GEOTECHNICAL TESTING JOURNAL, Vol: 37, ISSN: 0149-6115
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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.
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.
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