Geotechnical Consulting Group

London, United Kingdom

Geotechnical Consulting Group

London, United Kingdom

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Brosse A.,Imperial College London | Brosse A.,Geotechnical Consulting Group | Jardine R.J.,Imperial College London | Nishimura S.,Hokkaido University
Canadian Geotechnical Journal | Year: 2017

The paper describes the anisotropic undrained stiffness behaviour of four medium-plasticity heavily overconsolidated UK stiff marine clays as revealed through hollow cylinder testing. The experiments contributed to two broader studies on stiff-to-hard London, Gault, Kimmeridge, and Oxford clay strata. They involved static and dynamic testing of multiple highquality natural specimens sampled at similar depths from inland sites. This paper explores the directional dependency of the clays’ highly nonlinear undrained stiffness characteristics. New data-analysis approaches are outlined that allow the stiffnesses associated with one-dimensional vertical, horizontal, or pure horizontal shear modes to be isolated in complex undrained stress paths. In the presented experiments, loading progressed from in situ stresses to reach ultimate failure at a range of final major principal stress orientation angles α (defined in the vertical plane) while keeping fixed values of the intermediate principal stress ratio, b. The tests reveal strong undrained stiffness anisotropy that can impact significantly on the prediction and understanding of ground deformation patterns in numerous geotechnical engineering applications. © 2017, Canadian Science Publishing. All rights reserved.

Kamal R.H.,DNVGL | Coop M.R.,City University of Hong Kong | Jardine R.J.,Imperial College London | Brosse A.,Geotechnical Consulting Group
Geotechnique | Year: 2014

A detailed study is described of the post-yield behaviour of four medium-plastioity heavily over-consolidated UK stiff clays. Sub-layers of the stiff-to-hard Gault, Kimmeridge and Oxford clays were identified, sampled and tested; these, along with fades investigated in an earlier London Clay study, had broadly similar depositional histories. The intention in considering a spread of similar sediments from the Jurassic to the Eocene was to allow any strong effects of geological age, or burial depth, to be identified. A strongly fissured meso-structure was present in three of the four clays, which had a controlling influence on their effective shear strengths, considering that the representative element volume is of paramount importance in measuring the strengths of such soils. All four soils were brittle in shear and, when sheared to sufficient displacements, developed low residual shear strengths. The stiff clays were investigated further through comparisons between natural and reconstituted behaviour, using the latter to normalise the effective stress data for volume and also considering the clays' oedometer swell sensitivities, Normal compression tests, when normalised for void index, implied different degrees of ‘structure’ than undrained shear tests, showing that a more elaborate micro- and meso-fabric framework is needed to capture the behaviour of highly overconsolidated and aged geomaterials. This paper focuses on describing the study sites’ geotechnical profiles and the stiff clays' yielding behaviours under one-dimensional compression and in triaxial compressive shear. © 2014, (publisher). All rights reserved.

Kovacevic N.,Geotechnical Consulting Group | Hight D.W.,Geotechnical Consulting Group | Potts D.M.,University of London | Carter I.C.,MWH
Geotechnique | Year: 2013

An existing 15.5 m high main dam embankment at Abberton Reservoir in Essex was completed in August 1938, since when its performance has been satisfactory. However, the upstream embankment shoulder of the original dam suffered a deep-seated failure through its foundation towards the end of construction in July 1937, 9 days before a similar and well-known failure occurred at Chingford Reservoir in close proximity to Abberton. Whereas the failure at Chingford became an important case in the history of soil mechanics through the involvement of Karl Terzaghi and marked one of the first applications of modern soil mechanics principles, the failure at Abberton has remained largely unknown, until recently when raising of the existing dam started to be considered. This paper describes advanced finite-element analyses which were carried out to investigate the failure of the original dam at Abberton and the stability of the existing main dam. The parameters used in the constitutive models were derived on the basis of the available site investigations and laboratory testing and on experience in the back-analysis of other failures in London Clay. The analyses demonstrated that the upstream shoulder of the original embankment failed through the mechanism of progressive failure, which involved the top of the stiff plastic London Clay rather than the overlying alluvium in the foundation. The relatively rapid rate of embankment filling, achieved by using modern earthmoving equipment, contributed significantly to the original dam failure. The analyses also demonstrated satisfactory behaviour of the existing dam during reconstruction, the first impounding and in the long term, with its response being similar to that observed. Thus the constitutive models used and parameters derived were successfully calibrated against the observed behaviour of both the original and existing main dams at Abberton, and could be used in predicting the behaviour of the dam during and after its proposed raising.

Leroueil S.,Laval University | Hight D.W.,Geotechnical Consulting Group
Advances in Unsaturated Soils - Proceedings of the 1st Pan-American Conference on Unsaturated Soils, PanAmUNSAT 2013 | Year: 2013

Due to the improvements in our knowledge of unsaturated soil mechanics and in the measurement of soil suction, our understanding of compacted soils has improved considerably. The paper describes the physics that underlies the behaviour of compacted soils and its implications in terms of the hydraulic and mechanical behaviour of compacted soils. A resulting conceptual model is presented. Reference is made to practical implications. © 2013 Taylor & Francis Group, London.

Menkiti C.O.,Geotechnical Consulting Group
Geotechnical Aspects of Underground Construction in Soft Ground - Proceedings of the 7th International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground | Year: 2012

This report reviews 24 papers submitted to the Symposium under Session TS1: Construction, Design and Measured Performance of Bored Tunnels. The papers are reviewed in three groups: Design (and Analysis), Construction and Measured Performance. © 2012 Taylor & Francis Group.

Kontoe S.,Imperial College London | Zdravkovic L.,Imperial College London | Potts D.M.,Imperial College London | Menkiti C.O.,Geotechnical Consulting Group
Geotechnique | Year: 2011

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.

Cabarkapa Z.,Geotechnical Consulting Group | Smith P.,Geotechnical Consulting Group
Proceedings of the Institution of Civil Engineers: Geotechnical Engineering | Year: 2016

Construction of a new Ikea store in Zagreb, Croatia required a foundation solution to address the poor ground conditions on site, including the risk posed by seismic events, as well as meeting the strict limits on differential movement. This paper describes how adoption of a displacement pile technique avoided generating large volumes of spoil that would otherwise require disposal, easing logistics at the site. The technique also avoided pile bore instability in the poor ground conditions with high groundwater levels. Provision of instrumentation on the piling rig, recording a range of parameters during pile installation, provided an effective control on the acceptability of each working pile constructed. By completing a number of test piles prior to the main piling works, which were also undertaken by the instrumented rigs, site-specific limits on the rig-recorded parameters were determined, enabling a check on the acceptability of each pile constructed. © 2016, Thomas Telford Services Ltd. All rights reserved.

Taborda D.M.G.,Geotechnical Consulting Group | Zdravkovic L.,Imperial College London
Computers and Geotechnics | Year: 2012

In the field of constitutive modelling of soil behaviour, optimisation techniques have been mostly employed as a calibration tool, particularly when several model parameters lack clear physical meaning. In this paper, however, a procedure based on a Hill-Climbing optimisation algorithm is presented as a form of improving the performance of constitutive models. Specifically, a simple cyclic nonlinear elastic model, which is shown to be unable to simulate adequately the damping ratio measured under small and large strain amplitudes, is modified by applying the Hill-Climbing technique to the determination of a new relationship describing the unloading/reloading behaviour of soil under cyclic loading. The performance of the proposed model is assessed by evaluating its parameters based on three distinct sets of empirical damping ratio curves and computing the corresponding error in their simulation. It is shown that the introduction of the new unloading/reloading expression formulated based on the outcome of the optimisation procedure increases substantially the precision of the constitutive model. © 2012 Elsevier Ltd.

Kontoe S.,Imperial College London | Zdravkovic L.,Imperial College London | Menkiti C.O.,Geotechnical Consulting Group | Potts D.M.,Imperial College London
Computers and Geotechnics | Year: 2012

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. © 2011 Elsevier Ltd.

New B.,Geotechnical Consulting Group
Tunnels and Tunnelling International | Year: 2015

Myles O'Reilly is retiring as chairman of the Tunnels and Tunneling Editorial Advisory Board in 2015. He was appointed the chairman in 1981. In 1972 he fitted perfectly into the role as Division Head of the new Tunnels Division at TRRL. His task as Division Head was to recruit and lead his TRRL team but equally important he was to select and sponsor tunneling research in the higher educationa; establishments and where appropriate Consultancies. Above all his ability to lead and inspire loyalty in his staff will endure and his oversight will be missed by the British Tunneling Society's Editorial Advisory Board.

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