Imperial College London

DrStavroulaKontoe

Faculty of EngineeringDepartment of Civil and Environmental Engineering

Reader in Soil Dynamics
 
 
 
//

Contact

 

+44 (0)20 7594 5996stavroula.kontoe Website

 
 
//

Location

 

535Skempton BuildingSouth Kensington Campus

//

Summary

 

Publications

Publication Type
Year
to

95 results found

Jardine RJ, Buckley RM, Byrne BW, Kontoe S, McAdam RA, Andolfsson T, Liu TF, Schranz F, Vinck Ket al., 2019, Improving the design of piles driven in chalk through the ALPACA research project, Revue Française de Géotechnique, Vol: 158, ISSN: 0181-0529

Chalk is present under large areas of NW Europe as a low-density, porous, weak carbonate rock. Large numbers of offshore wind turbines, bridges and port facilities rely on piles driven in chalk. Current European practice assumes ultimate shaft resistances that appear low in comparison with the Chalk’s unconfined compression strength and CPT cone resistance ranges and can impact very significantly on project economics. Little guidance is available on pile driveability, set-up or lateral resistance in chalk, or on how piles driven in chalk can sustain axial or lateral cyclic loading. This paper describes the ALPACA (Axial-Lateral Pile Analysis for Chalk Applying multi-scale field and laboratory testing) project funded by EPSRC and Industry that is developing new design guidance through comprehensive field testing at a well-characterised low-to-medium density test site, supported by analysis of other tests. Field experiments on 36 driven piles, sixteen of which employ high resolution fibre-optic strain gauges, is supported by advanced laboratory and in situ testing, as well as theoretical analysis. The field work commenced in October 2017 and was largely complete in May 2019.

Journal article

Jardine RICHARD, Buckley R, Byrne B, Kontoe S, Liu T, Ross M, Ken Vet al., 2019, The ALPACA research project to improve design of piles driven in chalk, XVII European Conference on Soil Mechanics and Geotechnical Engineering

The proceedings are freely available at https://www.ecsmge-2019.com/

Conference paper

Pelecanos L, Kontoe S, Zdravkovic L, 2019, Nonlinear seismic response of earth dams due to dam-reservoir interaction, The XVII European Conference on Soil Mechanics and Geotechnical Engineering

Conference paper

Buckley R, Jardine R, Kontoe S, Schroeder F, Barbosa Pet al., 2019, The design of axially loaded driven piles in chalk, XVII European Conference on Soil Mechanics and Geotechnical Engineering

Conference paper

Solans D, Skiada E, Kontoe S, Potts DMet al., 2019, Canyon topography effects on ground motion: Assessment of different soil stiffness profiles, Obras y Proyectos, Vol: 25, Pages: 51-58, ISSN: 0718-2805

The effect of topography on ground motion has been well recognized during numerous earthquakes. Several studies present observational evidence from destructive earthquakes, where the damage is higher in the vicinity of hills and near slope crests. Furthermore, a number of numerical studies aimed to reproduce this phenomenon using different numerical methods, e.g. Finite Elements, Finite Differences and Boundary Elements have been carried out. Most of these investigations involve parametric studies, considering different variables. However, one of the assumptions of these studies is a homogeneous soil stiffness with depth, which is not in most cases realistic. This article investigates the effects of canyon topography on ground motion considering different soil stiffness profiles over a rigid bedrock. Three soil profiles with stiffness variation with depth are examined and compared to the case of a soil layer of uniform stiffness. An additional analysis of a two- layer medium lying above half-space is also considered. Time domain numerical analyses are carried out with the Imperial College Finite Element Program ICFEP, considering linear elastic soil behaviour over rigid bedrock. The input motions are wavelets of harmonic nature, modified by a Saragoni and Hart (1973) temporal filter. These wavelets with a characteristic. pulse period Tp in the range of 0.1 s to 2 s are analysed. This study confirms that the topographic amplification extrema are located between the natural periods of the corresponding one-dimensional free-field profile in agreement with recent previous studies. Furthermore, the amplitude of the topographic amplification peaks is shown to change for the different examined soil stiffness profiles.

Journal article

Buckley R, Jardine R, Kontoe S, Barbosa P, Schroeder Fet al., Full-scale observations of dynamic and static axial responses of offshore piles driven in chalk and tills, Géotechnique, ISSN: 0016-8505

This paper describes and interprets tests on piles driven through glacial tills and chalk at a Baltic Sea windfarm, covering an advance trial campaign and later production piling. The trials involved six instrumented 1.37m diameter steel open-ended tubes driven in water depths up to 42m. Three piles were tested statically, with dynamic re-strike tests on paired piles, at 12-15 week ages. Instrumented dynamic driving and re-strike monitoring followed on up to 3.7m diameter production piles. During driving, the shaft resistances developed at fixed depths below sea-bed fell markedly during driving, with particularly sharp reductions occurring in the chalk. Shaft resistances increased markedly after driving and good agreement was seen between long-term capacities interpreted from parallel static and dynamic tests. Analyses employing the sites’ geotechnical profiles show long-term shaft resistances in the chalk that far exceed those indicated by current design recommendations, while newly proposed procedures offer good predictions. The shaft capacities mobilised in the low-plasticity tills also grew significantly over time, within the broad ranges reported for sandy soils. The value of offshore field testing in improving project outcomes and design rules is demonstrated; the approach described may be applied to other difficult seabed conditions.

Journal article

Jardine R, Buckley R, Byrne B, Kontoe S, Liu T, McAdam R, Schranz F, Vinck Ket al., 2019, Rationalising the design of piles driven in chalk through the ALPACA project, 2nd International Conference on Natural Hazards & Infrastructure

Conference paper

Pelecanos L, Kontoe S, Zdravkovic L, 2019, Seismic response of earth dams in narrow canyons, VII International Conference on Earthquake Geotechnical Engineering

It is nowadays well appreciated that dams built in narrow canyons exhibit a stiffer re-sponse than those in wide canyons, due to the confined geometry of the canyon banks. The numerical modelling of dams in wide canyons is usually considered as computational-ly less expensive than those in narrow canyons. This is because the former can be ideal-ised by a two-dimensional plane-strain model, while the latter requires a full three-dimensional analysis to appropriately consider the stiffening effect of the narrow canyon geometry. This paper presents a computationally-efficient way to consider the stiffening effect of a narrow canyon in a two-dimensional analysis by using an appropriately in-creased material stiffness.

Conference paper

Kontoe S, Han B, Pelecanos L, Zdravkovic Let al., 2019, Hydrodynamic effects and hydro-mechanical coupling in the seismic response of dams, VII International Conference on Earthquake Geotechnical Engineering, Publisher: Balkema

The seismic design of earthfill and rockfill dams routinely relies on methods of analysis which adopt simplifying assumptions regarding the dynamic response of the reservoir, while the dynamic interaction of the fluid and solid phases within the dam body is also typically ignored. In this paper, a simple numerical approach for the efficient simulation of hydrodynamic pressures in finite element analysis is presented and then used to assess the impact of hydrodynamic pressures on the seismic response of dams. The importance of both hydrodynamic pressures and of hydro-mechanical coupling is then discussed within the context of two well-documented case studies, of an earthfill and a rockfill dam, comparing the numerical predictions against field measurements.

Conference paper

Kontoe S, Han B, Pelecanos L, Zdravkovic Let al., 2019, Seismic response of earthfill and rockfill embankment dams, 3rd Meeting of EWG Dams and Earthquakes - an International Symposium, Publisher: LNEC

The seismic design of earthfill and rockfill dams routinely relies on methods of analysis, which adopt simplifying assumptions regardingthe damgeometry, soil behaviour and the dynamic interaction of the fluid and solid phases within the dam body. This paper explores such simplifying assumptions, which aretypically used for thenumerical modelling of earthfill and rockfill embankment dams,within the context of two case studies. First a clay core dam,theLa Villita dam in Mexico, is considered focusing mainly on the implications of 2D plane strain approximation in the case of dams built in relatively narrow canyons. In the second case study, of the rockfill Yele dam in China, the importance of hydro-mechanicalcoupling is explored by parametrically varying the permeability of the materials.

Conference paper

Tsaparli V, Kontoe S, Taborda D, Potts Det al., 2019, A case study of liquefaction: demonstrating the application of an advanced model and understanding the pitfalls of the simplified procedure, Géotechnique, ISSN: 0016-8505

The complexity of advanced constitutive models often dictates that their capabilities are only demonstrated in the context of model testing under controlled conditions. In the case of earthquake engineering and liquefaction in particular, this restriction is magnified by the difficulties in measuring field behaviour under seismic loading. In this paper, the well documented case of the Canterbury Earthquake Sequence in New Zealand, for which extensive field and laboratory data are available, is utilised to demonstrate the accuracy of a bounding surface plasticity model in fully-coupled finite element analyses. A strong motion station with manifestation of liquefaction and the second highest peak vertical ground acceleration during the Mw 6.2 February 2011 event is modelled. An empirical assessment predicted no liquefaction for this station, making this an interesting case for rigorous numerical modelling. The calibration of the model aims at capturing both the laboratory tests and the field measurements in a consistent manner. The characterisation of the ground conditions is presented, while, to specify the bedrock motion, the records of two stations without liquefaction are deconvolved and scaled to account for wave attenuation with distance. The numerical predictions are compared to both the horizontal and vertical acceleration records and other field observations, showing a remarkable agreement, also demonstrating that the high vertical accelerations can be attributed to compressional resonance. The results provide further insights into the underperformance of the simplified procedure.

Journal article

Norambuena R, Tsaparli V, Kontoe S, Taborda D, Potts Det al., 2019, The effect of irregular seismic loading on the validity of the simplified liquefaction procedures, Obras y Proyectos, Pages: 42-50, ISSN: 0718-2805

Soil liquefaction has been one of the major hazards for civil engineering projects relating to earthquakes. The simplified liquefaction procedure which is used to assess liquefaction susceptibility in practice is still based on semi-empirical methods. These rely on the assumption that irregular seismic motions can be represented fully by an equivalent number of cycles of uniform stress amplitude, which is based on the peak acceleration measured at ground surface. Most methodologies used to calculate the equivalent number of cycles are based on Miner's damage concept developed for the fatigue analysis of metals. Several researchers have questioned the validity of this concept, as soils have a highly non-linear response. The present work investigates numerically the concept of the equivalent uniform amplitude cycles. Effective stress-based non-linear finite element analyses are performed with a modified bounding surface plasticity model that allows to realistically simulate liquefaction, reproducing the cyclic strength of sands accurately. The seismic response of a 15 m deep uniform level-ground sand deposit is simulated with full hydro-mechanical coupling to establish the benchmark extent of liquefaction zone. In parallel, the analyses are repeated assuming drained conditions to compute the irregular time-histories, which are then converted to an equivalent number of uniform amplitude cycles. The constant amplitude series are then applied in single element simple shear test simulations, with initial conditions those corresponding to the 7 m depth in the deposit. The results in terms of the predicted triggering of liquefaction are contrasted to the predictions of the fully coupled benchmark analyses at the corresponding depth to assess the validity of the Seed et al. (1975) methodology, based on Miner's cumulative damage concept.

Journal article

Buckley R, Jardine R, Kontoe S, Lehane Bet al., 2018, Effective stress regime around a jacked steel pile during installation, ageing and load testing in chalk, Canadian Geotechnical Journal, Vol: 55, Pages: 1577-1591, ISSN: 0008-3674

This paper reports experiments with 102 mm diameter closed-ended instrumented Imperial College piles (ICPs) jacked into low- to medium-density chalk at a well-characterized UK test site. The “ICP” instruments allowed the effective stress regime surrounding the pile shaft to be tracked during pile installation, equalization periods of up to 2.5 months, and load testing under static tension and one-way axial cyclic loading. Installation resistances are shown to be dominated by the pile tip loads. Low installation shaft stresses and radial effective stresses were measured that correlated with local cone penetration test (CPT) tip resistances. Marked shaft total stress reductions and steep stress gradients are demonstrated in the vicinity of the pile tip. The local interface shaft effective stress paths developed during static and cyclic loading displayed trends that resemble those seen in comparable tests in sands. Shaft failure followed the Coulomb law and constrained interface dilation was apparent as the pile experienced drained loading to failure, although with a lesser degree of radial expansion than with sands. Radial effective stresses were also found to fall with time after installation, leading to reductions in shaft capacity as proven by subsequent static tension testing. The jacked, closed-ended, piles’ ageing trends contrast sharply with those found with open piles driven at the same site, indicating that ageing is affected by pile tip geometry and (or) installation method.

Journal article

Summersgill F, Kontoe S, Potts DM, 2018, Stabilisation of excavated slopes in strain softening materials with piles, Géotechnique, Vol: 68, Pages: 626-639, ISSN: 0016-8505

The use of a row of discrete vertical piles is an established method, successfully used to remediate failure of existing slopes and to stabilise potentially unstable slopes created by widening transport corridors. This paper challenges the assumptions made in current design procedures for these piles, which treat the pile only as an additional force or moment and simplify soil–pile interaction. Two-dimensional plane-strain finite-element analyses were performed to simulate the excavation of a slope in a stiff clay and the interaction of vertical piles within the slope. A non-local strain-softening model was employed for the stiff clay to reduce the mesh dependency of the solution. An extensive parametric study was performed to systematically examine the impact of pile position, dimensions (length and diameter) and time of pile construction on the stability of a cutting in London Clay, which was chosen as a representative strain-softening material. A variety of different failure mechanisms were identified, depending on pile location, dimensions and time of construction. The variability of the pile and slope interaction that was modelled suggests that an oversimplification during design could miss the critical failure mechanism or provide a conservative stabilisation solution. Given the prevalence of stiff clay slopes in the UK, increased capacity requirements of transport infrastructure and the age of slopes in this material, an informed and more realistic design of stabilisation piles will become increasingly necessary.

Journal article

Kontoe S, Summersgill F, Potts D, Lee YSet al., 2018, Stabilisation of excavated slopes with piles in soils with distinctly different strain softening behaviour, 9th European Conference on Numerical Methods in Geotechnical Engineering (NUMGE)

The majority of existing design procedures for slope stabilization with piles treat the pile only as an additional force or moment acting on the critical slip surface of the unstabilised slope, effectively ignoring any interaction of the pile with the evolution of the failure mechanism. This paper presents a numerical investigation that challenges this assumption, 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 either entirely miss the critical failure mechanism (unconservative) or provide a conservative stabilisation solution.

Conference paper

Skiada E, Kontoe S, Stafford P, Potts Det al., 2018, Ground surface amplification for canyon topographies excited with bi-directional earthquake records, 16th European Conference on Earthquake Engineering

Conference paper

Tsaparli V, Kontoe S, Taborda D, Potts Det al., 2018, Liquefaction triggering due to compressional waves: validation through field records, 16th European Conference on Earthquake Engineering

Conference paper

Pelecanos L, Kontoe S, Zdravkovic L, 2018, The effects of non-linear dam-foundation interaction on the seismic response of earth dams, 16th European Conference on Earthquake Engineering

Conference paper

Kontoe S, Han B, Zdravkovic L, Taborda Det al., 2018, The importance of compressional deformation in three dimensional site response analysis, 16th European Conference on Earthquake Engineering

Conference paper

Han BO, Zdravkovic L, Kontoe S, 2018, Analytical and numerical investigation of site response due to vertical ground motion, Geotechnique, Vol: 68, Pages: 467-480, ISSN: 1021-8637

Due to the repeatedly observed strong vertical ground motions and compressional damage of engineering structures in recent earthquakes, the multi-directional site response analysis is increasingly critical for the seismic design of important structures, such as nuclear power plants and high earth dams. However, the site response to the vertical component of the ground motion has not beenthesubject of detailed investigationin the literature. Therefore, in this paper, the vertical site responsedue to vertical ground motion is investigated by employing both analytical and numerical methods. Firstly, a 1-D frequency domainanalytical solution, which can be employedfor vertical site responseanalysis in practice,is studied and compared against time domain Finite Element (FE)analyses for the two extreme soil state conditions (i.e. undrained and drained conditions). The vertical site response is further investigated with hydro-mechanically(HM) coupled FE analysis, considering solid-fluid interaction. The undertaken parametric studies show that the predicted vertical site response is strongly affected by the parameters characterising the hydraulic phase, i.e. soil permeability and soil state conditions, both in terms of frequency content and amplification. Thesubsequent corresponding quantitative investigation,of thefrequency content and amplification functionof the vertical site response, showsthat depending on the soil permeabilitythe responseis dominated by the two types of compressional waves (fast and slow wave). Notably, the parametric studies identify a range of permeability that significantly affectsdynamic soil properties in terms ofP-wave velocities,damping ratiosand vertical site response, and this range is relevant for geotechnical earthquake engineering applications. It is therefore recommendedthat coupled consolidation analysis is

Journal article

Pelecanos L, Kontoe S, Zdravkovic L, The effects of dam-reservoir interaction on the nonlinear seismic response of earth dams, Journal of Earthquake Engineering, ISSN: 1363-2469

The objective of this study is to investigate the effects of dam–reservoir interaction (DRI) on the nonlinear seismic response of earth dams. Although DRI effects have for long been considered as insignificant for earth dams, that conclusion was mainly based on linear elastic investigations which focused only on the acceleration response of the crest without examining the seismic shear stresses and strains within the dam body. The present study explores further the impact of DRI focusing on the nonlinear behavior of earth dams. The effects of reservoir hydrodynamic pressures are investigated in terms of both seismic dam accelerations and nonlinear dynamic soil behavior (seismic shear stresses and strains). It is shown that although dam crest accelerations are indeed insensitive to DRI, the stress and strain development within the dam body can be significantly underestimated if DRI is ignored.

Journal article

Buckley RM, Jardine R, Kontoe S, Parker D, Schroeder FCet al., 2018, Ageing and cyclic behaviour of axially loaded piles driven in chalk, Geotechnique, Vol: 68, Pages: 146-161, ISSN: 1751-7656

This paper reports a programme of static and cyclic loading tests on seven open steel tubes driven in low to medium density chalk at a well characterised test site, describing their response to driving, ageing in situand loading under both static and cyclic conditions. Back analysis of dynamic monitoring identifies the distributions of notably low shaft resistances that develop during installation, showing that these depend strongly on the relative pile tip depth (h/R). The shaft capacities available to ‘virgin’ piles are shown to increase markedly after driving, following a hyperbolic trend that led to a fivefold gain after 250days.Pre-failed piles do not follow the same trend when re-tested. Pile exhumation confirmed that driving remoulded the chalk, creating a puttified zone around the shaft. Excess pore water pressure dissipation, whichis likely to have been rapid during and after driving,led to markedly lower water contents close to the shaft. Axial cyclic testing conducted around 250 days after driving led to a range of responses, from manifesting stable behaviour over 1000 cycles to failing after low numbers of cycles after developing sharp losses of static capacity. The dependence of permanent displacement on the cyclic loading parameters is explored and characterised. The experiments provide the first systematic study of which the Authors are aware into the effects ofundisturbed ageingand cyclic loading onpreviously unfailedpiles driven in chalk. Potential predictive tools may now be tested against the reported field measurements.

Journal article

Régnier J, Bonilla LF, Bard PY, Bertrand E, Hollender F, Kawase H, Sicilia D, Arduino P, Amorosi A, Asimaki D, Boldini D, Chen L, Chiaradonna A, DeMartin F, Elgamal A, Falcone G, Foerster E, Garini E, Gazetas G, Gélis C, Ghofrani A, Giannakou A, Gingery J, Glinsky N, Harmon J, Hashash Y, Iai S, Kramer S, Kontoe S, Kristek J, Lanzo G, Lernia AD, LopezCaballero F, Marot M, McAllister G, Mercerat ED, Moczo P, MontoyaNoguera S, Musgrove M, NietoFerro A, Pagliaroli A, Passeri F, Richterova A, Sajana S, Santisi dAvila MP, Shi J, Silvestri F, Taiebat M, Tropeano G, Vandeputte D, Verrucci Let al., PRENOLIN: International Benchmark on 1D Nonlinear Site‐Response Analysis—Validation Phase Exercise, Bulletin of the Seismological Society of America

This article presents the main results of the validation phase of the PRENOLIN project. PRENOLIN is an international benchmark on 1D nonlinear (NL) site‐response analysis. This project involved 19 teams with 23 different codes tested. It was divided into two phases; with the first phase verifying the numerical solution of these codes on idealized soil profiles using simple signals and real seismic records. The second phase described in this article referred to code validation for the analysis of real instrumented sites.This validation phase was performed on two sites (KSRH10 and Sendai) of the Japanese strong‐motion networks KiK‐net and Port and Airport Research Institute (PARI), respectively, with a pair of accelerometers at surface and depth. Extensive additional site characterizations were performed at both sites involving in situ and laboratory measurements of the soil properties. At each site, sets of input motions were selected to represent different peak ground acceleration (PGA) and frequency content. It was found that the code‐to‐code variability given by the standard deviation of the computed surface‐response spectra is around 0.1 (in log10 scale) regardless of the site and input motions. This indicates a quite large influence of the numerical methods on site‐effect assessment and more generally on seismic hazard. Besides, it was observed that site‐specific measurements are of primary importance for defining the input data in site‐response analysis. The NL parameters obtained from the laboratory measurements should be compared with curves coming from the literature. Finally, the lessons learned from this exercise are synthesized, resulting also in a few recommendations for future benchmarking studies, and the use of 1D NL, total stress site‐response analysis.

Journal article

Jardine RJ, Buckley RM, Kontoe S, Barbosa P, Schroeder FCet al., 2018, Behaviour of piles driven in chalk, Pages: 33-51

© 2018 Engineering in Chalk - Proceedings of the Chalk 2018 Conference. All rights reserved. Driving resistance is difficult to predict in chalk strata, with both pile free-fall self-weight 'runs' and refusals being reported. Axial capacity is also highly uncertain after driving. This paper reviews recent research that has explored these topics. Programmes of onshore tests and novel, high-value offshore, experiments involving static, dynamic and cyclic loading are described. The key findings form the basis of the Chalk ICP-18 approach for estimating the driving resistance and axial capacity of piles driven in low-to medium-density chalk. The new approach is presented and the highly significant impact of set-up after driving is emphasised. It is shown that Chalk ICP-18 overcomes the main limitations of the industry's current design guidelines by addressing the underlying physical mechanisms. While further tests are required to enlarge the available test database, the new approach is able to provide better predictions for tests available from suitably characterised sites. A new Joint Industry Project is outlined that extends the research to cover further axial, lateral, static and cyclic loading cases.

Conference paper

Tsaparli V, Kontoe S, Taborda DMG, Potts DMet al., 2017, An energy-based interpretation of sand liquefaction due to vertical ground motion, Computers and Geotechnics, Vol: 90, Pages: 1-13, ISSN: 0266-352X

© 2017 The Authors In several recent earthquakes, high vertical ground accelerations accompanied by liquefaction were observed. Downhole records have also shown that large vertical accelerations do not necessarily originate from the source, but rather get amplified towards the ground surface. Given the advantages of energy-based interpretation of liquefaction triggering due to S-waves, this approach is used together with finite element analyses to investigate vertical motion amplification and ensuing liquefaction. The results show the importance of the post-resonance response cycles, while hysteretic damping based on total stresses, accounting for the water in the pores, is shown to be very low, explaining the observed amplification.

Journal article

Buckley R, Jardine R, Kontoe S, liu T, Ushev, Lehane BM, Pine T, Schroeder FC, Barbosa Pet al., 2017, Field investigations into the axial loading response of displacement piles in chalk, Proceedings of the 8th International Conference on Offshore Site Investigation and Geotechnics: Smarter Solutions for Future Offshore Developments, Publisher: Th e Society for Underwater Technology, Pages: 1178-1185

Conference paper

Buckley R, Kontoe S, Jardine R, Maron M, Schroeder FC, Barbosa Pet al., 2017, Common pitfalls of pile driving resistance analysis - A case study of the Wikinger offshore windfarm, 978-0-906940-57-0, Publisher: Society for Underwater Technology, Pages: 1246-1253

Conference paper

Tsaparli V, Kontoe S, Taborda D, Potts Det al., 2017, Liquefaction modelling of a strong motion station in Christchurch, New Zealand, 3rd International Conference on Performance-based Design in Earthquake Geotechnical Engineering (PBD-III), Publisher: International Society of Soil Mechanics and Geotechnical Engineering

Advanced constitutive models can replicate several aspects of soil behaviour, but, due to their complexity and number of parameters, they need more sophisticated and realistic validation under general loading conditions. When modelling liquefaction phenomena, the lack of field monitoring data means that modeltesting, such as centrifuge experiments, is often used as benchmark for the numerical analyses. The 2010-2011 Canterbury earthquake sequence in New Zealand was recorded by a number of strong motion stations at various distances from the earthquake epicentre. Additionally, an extensive field and laboratory programmehassincebecome available, adequately describing the geological, geotechnical and hydrogeological conditions in the area. As such,the performance of a two-surface bounding surface plasticity constitutive model for sands, calibrated based on site-specific laboratory data, is assessed usingfield evidenceof a strong motion stationin fully-coupled effective stress-based finite element analyses. As the real stratigraphy is complex, with layers of silts and clays between the sandy strata, a simpler cyclic non-linearelasticmodel,which can adequately incorporate the basic aspects of dynamic soil behaviour, is also used to model the non-liquefiable strata. To specify the input ground motion at the base of the deposit, the recordedgroundsurface motionata sitewith no evidence of liquefaction isdeconvolved and compared with the outcrop predictions ofa New Zealand-specificground motion prediction equation. The numerical results are compared with the recorded horizontal ground surface acceleration time-history of the 22ndFebruary 2011 seismic event, exhibiting very good agreement.

Conference paper

Skiada E, Kontoe S, Stafford P, Potts Det al., 2017, Ground motion amplification for canyon topographies with different input motions, 3rd International Conference on Performance-based Design in Earthquake Geotechnical Engineering (PBD-III), Publisher: ISSMGE

It is widelyknown that topographic irregularities influence the surfaceground motions, typically with anenhancement of the response close to convex topographic features,such as ridges and slope crests. Several studies have investigatedthe ground motion at the surface of filled valleys and empty canyons, focusingmainly onthe geometry and the soil characteristics rather than the input excitation.Further investigation of the impact of the input excitation to the ground surface response is needed in order to modifyexisting ground motion prediction models to account for topographic effects. The response of canyons has been previously examined; but mainly focusing on simple wavelet input. This paper considers a fully weathered canyon (i.e., without any in-fill material) aiming to investigate the influence of the input excitationon the surface ground motion through a parametric time-domain finite element (FE) study. A two-dimensional plane-strain model of an idealisedcanyon is considered for vertically propagating SV waves, using both wavelets and recorded earthquakes as input excitation. The model consists of two step-like slopes with slope height (H), in a homogeneous linear elastic soil layer overlying rigid bedrock. Topographic aggravation is presented for several points along the canyon ground surface aiming to derive a pattern of its distribution considering input excitation with different characteristics.

Conference paper

Pelecanos L, Kontoe S, Zdravkovic L, 2017, Steady-state and transient dynamic visco-elastic response of concrete and earth dams due to dam-reservoir interaction, 6th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering

The aim of this study is to investigate the effects of dam–reservoirinteraction on the dynamic response of dams. Both thin rectangular concrete cantilever andlargetrapezoi-dal earth dams are considered with empty and full reservoir. It has recently been shown by Pelecanos et al. [32]thatthe amplification of accelerations at the crest of the dam depends on the combinations of the frequency of the harmonicaccelera-tionload and the fundamental frequencies of the dam and the reservoir. This studyconsiders transient dynamic loading andselected scenariosofdifferent combinations of the above-mentionedfrequenciesare examined under random seismic acceleration load. It is shown that for certain cases the amplification of accelerations of the dam can be affected by the presence of the upstream reservoir. In general, thin rectangular concrete cantilever dams are found to be considerably more sensitive to dam–reservoir interaction thanlarge trapezoidal earth dams. Therefore, this investigation examines the significance of dam–reservoir interaction and when this interaction should be taken into consideration or it could be neglected.

Conference paper

This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.

Request URL: http://wlsprd.imperial.ac.uk:80/respub/WEB-INF/jsp/search-html.jsp Request URI: /respub/WEB-INF/jsp/search-html.jsp Query String: respub-action=search.html&id=00342856&limit=30&person=true