The purpose of these summaries is to bring to the notice of readers, topics in geotechnical engineering which are currently or have recently been subjects of research at universities in the United Kingdom.
Details comprising author, thesis title and brief summary (not to exceed 100 words), of doctoral theses published in 2004 should be submitted to The Director (Engineering), The Institution of Civil Engineers, 1 Great George Street, London SW1P3AA by 31st January 2005.
The summaries are arranged in alphabetical order, firstly by university and then by surname.
D. McKelvey, Queen's University Belfast
The performance of vibro stone column reinforced foundations in deep soft ground
Two series of model tests were carried out on clay samples reinforced with a small group of sand columns. In the first series, a one-dimensionally consolidated sample of transparent material represented the clay, while kaolin was used in the second series of tests. Photographs taken during and after the loading process showed that the columns fail by bulging, punching, shearing and bending. Furthermore, the deformation of each column depends on the arrangement of the columns within the group. There was a substantial improvement in the load-carrying capacity when the columns were present, compared to the performance of an unrein-forced clay sample.
Sponsored by Keller Ground Engineering.
Contact: Dr V Sivakumar.
S. Bhattacharya, Cambridge University
Pile instability during earthquake liquefaction
Many buildings and bridges with piled foundations have collapsed due to earthquake-induced liquefaction of loose sands. The conventional assumption is that liquefied soil spreads laterally, inducing excessive bending moments in piles. A new hypothesis is that such piles simply buckle under axial loads. Many reported case studies, including the famous failure of the Showa bridge, are re-analysed to support the new understanding. Piles whose slenderness ratio in liquefiable soils exceeded 50 were increasingly vulnerable to catastrophic collapse. Centrifuge tests and analytical studies confirmed that buckling could trigger the collapse of slender piles in the absence of lateral spreading.
Sponsored by Nehra Trust for Cambridge University.
Contact: Professor M. D. Bolton.
P. S. Dimmock, Cambridge University
Tunnelling-induced ground and building movement on the Jubilee Line Extension
The nature of ground and building movement due to bored tunnelling at five sites along the Jubilee Line Extension is investigated. Tunnelling methods examined included open-face shield tunnelling and the use of sprayed concrete lining techniques in London Clay, and earth pressure balance machine tunnelling in the Lambeth Group and Thanet Sands. Particular phases of the tunnel construction process are linked to resulting ground movement. Building movements are compared with greenfield movements, and methods of predicting the influence of building stiffness are assessed. New approaches are proposed for predicting ground movements, with an emphasis on the different stages of tunnel construction.
Sponsored by EPSRC, Cambridge Commonwealth Trust.
Contact: Professor R. J. Mair.
W. A. Take, Cambridge University
The influence of seasonal moisture cycles on clay slopes
Slopes in clay often creep and deteriorate, leading eventually to a slip failure. Such failures pose unacceptable risks to clay railway embankments. The underlying mechanism is exposed through centrifuge model tests. This required the development of three technologies—a centrifuge container with controlled humidity, miniature transducers to measure pore pressure or suction, and digital image processing to give high resolution displacement fields. Seasonal creep was observed due to the inelastic nature of the swelling–shrinkage cycle. Every mobilisation of shear resistance in excess of the critical stress ratio led to irrecoverable shear strains. These accrued, leading to a progressive failure.
Sponsored by EPSRC & Canadian Commonwealth Scholarship.
Contact: Professor M. Bolton.
T. C. The, Cambridge University
Stability of marine pipelines on unstable and liquefied seabed
The conventional approach to stability design of marine pipelines is flawed, because it assumes that the seabed itself is stable, whereas field experience backed up by theory shows that the seabed almost invariably becomes unstable and mobile before the extreme design conditions are reached. The dissertation describes experiments on the behaviour of pipelines on unstable seabed, and the development of a design method that is more soundly based. A series of tests in the HR wave flume showed that the primary factor that decides the response of a pipeline is its specific gravity. The tests also demonstrated liquefaction and the development of pore pressures in fine-grained soils under wave loading, and that in those soils liquefaction occurs at relatively low values of Sleath number. The observations suggest a new approach to the broader problem of wave-induced liquefaction.
Sponsored by The European Directorate-General XII for Science, Research & Development programme ‘Liquefaction around marine structures’.
Contact: Professor A. Palmer.
S. Channarayapatna Seetharam, Cardiff University
An investigation of the thermo/hydro/chemical/mechanical behaviour of unsaturated soils
The thesis presents an investigation of the thermo/hydro/chemical/mechanical (THCM) behaviour of unsaturated soils. The flow relationships accommodate a number of mechanisms: heat transfer by conduction, convection and latent heat; moisture transfer in both the liquid and vapour phases; dry air flow in both pore air and dissolved air in the pore liquid, and multi-component reactive chemical transport by both advection and hydrodynamic dispersion, including thermal diffusion. Mechanical behaviour is incorporated via an elasto-plastic stress/strain theory. A series of verification and validation exercises are presented. The THCM capability of the model is tested by simulating a heating/hydration experiment involving compacted bentonite.
Sponsored by Overseas Research Scholarship, DfES and Geoenvironmental Research Centre.
Contact: Dr P. Cleall.
D. Shaw, Cardiff University
Arsenic mobility in sediments and contamination of the Bengal Basin
The thesis investigates the mobility of arsenic in sediments, and contamination of groundwater in the Bengal Basin. Analysis of samples from Bangladesh showed that levels of arsenic in sediments are not high but the quantity of mobile arsenic is elevated due to the local geochemistry. The results support existing theories of mobilisation but also suggest that release occurs due to changes in pH. Leaching studies on laboratory-prepared sediments showed that pH has a significant effect on mobility. Under neutral conditions arsenic is relative stable. Acidic or alkaline conditions cause release, with more pronounced effects seen under acidic conditions.
Sponsored by EPSRC.
Contact: Dr P. Cleall.
N. Morgan, Dundee University
The influence of variation in effective stress on the serviceability of soil nailed slopes
Cuttings and embankment structures form an important part of transport networks. Over time, changes in effective stress may reduce the stability and serviceability of some of these structures. This may be counteracted using the reinforcement technique of soil nailing. The study included an investigation of both the collapse of unreinforced earth structures and the serviceability performance of soil nailed structures when subjected to long-term conditions. The investigation was based on a series of 1/20th scale centrifuge model tests in which the main parameters considered were slope angle, reinforcement density, drainage boundary conditions and cyclic application of changes in effective stress.
Sponsored by EPSRC.
Contact: Professor M. C. R. Davies.
G. Chlimintzas, Imperial College London
Seismic displacements of slopes using multi-block sliding technique
Newmark's 1965 model of a single block sliding on a plane surface is the most convenient one for estimating small co-seismic displacements of slopes. It is not applicable to large displacement cases when the change of geometry of the slope complicates the analysis. Also, the model of a single block sliding on a plane surface is not applicable on post-seismic movements, because once sliding motion initiates it will theoretically never stop. A new model is developed with multi-block sliding configuration using the slope stability analysis technique of Sarma (1979). In this model, each block slides along a different segment of the slip surface with kinematic compatibility. Change of geometry during sliding is accounted for in the analysis with a mechanism of internal deformation and mass transfer between blocks which also accounts for internal energy dissipation. Earthquake induced slides have been analysed to evaluate the model which shows remarkable agreement.
Sponsored by EC-DG XII Project ENV4-CT97-0392.
Contact: Dr. S. K. Sarma.
K. Georgiadis, Imperial College London
Development, implementation and application of partially saturated soil models in finite element analysis
The thesis presents two new generalised constitutive models for partially and fully saturated soils and their implementation into a finite element program. The implementation and performance of the models is validated through a series of single element analyses and the results are compared to analytical solutions and experimental data. Also presented in this thesis is a series of finite element analyses of shallow and deep foundations. These analyses highlight facets of partially saturated behaviour important for engineering problems and, more specifically, show the effect of partial soil saturation and of fluctuations of the ground water table on the behaviour of footings and piles.
Sponsored by Greek State Scholarships Foundation.
Contact: Dr L. Zdravkovic/Professor D. Potts.
P. Graham Clark Smith, Imperial College London
Numerical analysis of infiltration into partially saturated soil slopes
This thesis constitutes an investigation into the infiltration processes into unsaturated soil slopes, using numerical modelling techniques. The core equations governing the fully coupled constitutive behaviour of unsaturated soils are developed and presented, along with details of how these equations were implemented in numerical form. A conceptual model that qualitatively assesses the behaviour of unsatu-rated soils is also presented. The behaviour of unsaturated soil slopes was investigated through numerical simulations of the Tung Chung slope in Hong Kong, the results of which were then compared to field monitoring data from the site.
Sponsored by EPSRC.
Contact: Professor D. Potts.
T. Hamm, Imperial College London
The response of porous stone to water vapour
The link between conventional petrological descriptions for rock and soil and their geotechnical properties essentially remains empirical; additional methods for quantifying these composite materials are required and an area that has been neglected is the way in which these materials accept and release water with time. That is the subject of sorption kinetics. It has been applied in this research to the study of two construction stones, both with similar petrological and petrophysical character yet differing in their resistance to the natural agents of weathering. The research studied the ways in which the principles of sorption kinetics can be applied in the laboratory and highlights the need for the strict control of test environment to achieve repeatable results. This includes avoiding submersion of specimens in water and instead using their exposure to water vapour. Studied these ways, the two stones revealed consistent differences in their behaviour, for although their change in mass with time was similar, the rates and manner with which it occurred differed. These data can be used to interrogate aspects of porosity, specific surface area and fabric that cannot be easily studied by other means.
Sponsored by the Hamm family.
Contact: Dr M. H. de Freitas.
S. Hardy, Imperial College London
The implementation and application of dynamic finite element analysis to geotechnical problems
This thesis describes the development work required to add a dynamic capability to the Imperial College Finite Element Program (ICFEP). The program was then used to perform two- and three-dimensional analyses of bender element tests and in particular to assess the one-dimensional assumption of shear wave propagation that is commonly used when interpreting laboratory tests. The study also investigated the relative merits of using continuously cycled bender element tests as opposed to those involving single pulse. Analyses of a deep foundation subjected to earthquake loading ware also performed and the results compared with current seismic design practice. Significant differences were identified, with the dynamic finite element analysis being more consistent with behaviour observed in the field.
Sponsored by EPSRC & The Geotechnical Consulting Group.
Contact: Dr L. Zdravkovic/Professor D. Potts.
V. Panganai Nyambayo, Imperial College London
Numerical analysis of evapotranspiration and its influence on embankments
A non-linear root water uptake model for evapotranspiration has been developed and implemented into a finite element program. The model has been validated against field monitoring data. Predictions of pore water pressures and movements within old railway embankments are shown to match the monthly patterns of rainfall, evaportranspiration and soil moisture deficit. The analyses show that seasonal pore water pressure changes induce strain softening and ultimately trigger a progressive failure mechanism as the number of seasonal cycles increases. Guidance for the management of vegetation as a means of embankment stabilisation is provided.
Sponsored by EPSRC.
Contact:Professor D. Potts.
R. Rolo, Imperial College London
The anisotropic stress–strain-strength behaviour of brittle sediments
The thesis explores the general behaviour of a highly anisotropic brittle clayey sand. It presents a literature review, a series of Hollow Cylinder Apparatus (HCA) experiments on the sediment and a complementary suite of triaxial tests. The latter incorporated multi-axial bender element testing and high resolution static small-strain measurements. A detailed picture is provided of the material's anisotropy under a wide range of conditions and the information is interpreted from several standpoints. A three-dimensional elastic-plastic analytical treatment of the stress and strain conditions within HCA specimens is also reported, and a set of experiments described that investigated the small strain stiffness anisotropy exhibited by high quality samples of Bothkennar clay.
Sponsored by EPSRC.
Contact: Professor R. Jardine/Dr L. Zdravkovic.
I. Tromans, Imperial College London
Behaviour of buried water supply pipelines in earthquake zones
Research focused on improved understanding of the seismic performance of buried pipelines and more reliable prediction of earthquake-induced pipeline damage. A detailed GIS-based study was made of the spatial distribution of earthquake-induced water pipeline damage in Düzce, Turkey, following the 1999 Kocaeli and Düzce earthquakes. The influence of site conditions was investigated from the spectral analysis of ambient noise data obtained from field measurements. New predictive relationships were derived for strong-motion peaks. The sensitivity of each dataset to the record processing technique was investigated. The peak ground velocity estimations are particularly useful for prediction of earthquake-induced pipeline damage rates. A review was made of empirical relations for the prediction of earthquake-induced pipeline damage, with specific emphasis on identifying the reliability of the datasets used. Improvements were made to an existing dataset and areas of uncertainty in the characterisation of the seismic action highlighted.
Sponsored by WRc Plc, Kubota Corporation.
Contact: Dr J. Bommer.
K. W. Hau, University of Nottingham
Application of a three-surface kinematic hardening model to the repeated loading of thinly surfaced pavements
An existing three-surface kinematic hardening model has been modified and implemented in CRISP to model the deformation of subgrades in thinly surfaced pavements subjected to repeated loading. Realistic resilient and permanent deformations are predicted. The new model can be used to select the required thickness of sub-base: if standard permissible subgrade resilient strain and permissible rut depth design criteria are used independently, the model predicts realistic and similar sub-base thicknesses for both criteria, showing promise as a design tool. The new model also predicts the correct value of Ko during one-dimensional normal compression.
Sponsored by Rees Jeffreys Road Fund, Worshipful Company of Paviors and University of Nottingham.
Contact: Dr G. R. McDowell.
G. Bartholomeeusen, Oxford University
Compound shock waves and creep behaviour in sediment beds
The thesis reports an experimental and theoretical investigation of the sedimentation of clay particles through water and the subsequent consolidation of the bed. In the experiments dilute suspensions are introduced in a settling column. The particles settle, leaving clear water above and forming a bed at the base. The measurements consist of surface settlement, of X-ray density profiles and of pore water pressure. The experimental data show clearly a non-unique transition point between sedimentation and consolidation, marked by the propagation of a shock wave, and the existence of creep during consolidation. There are two aspects to the theoretical side. Firstly, the propagation of shock waves during sedimentation is modelled. Secondly, empirical observations are used to derive a rate-dependent theory. A new unified sedimentation–consolidation model is proposed. Successful predictions of experiments are performed, showing the transition from sedimentation to consolidation and creep during consolidation.
Sponsored by EPSRC, Dredging International.
Contact: Professor G. C. Sills.
A. G. Bloodworth, Oxford University
Three-dimensional analysis of tunnelling effects on structures to develop design methods
The subject of this thesis is the verification of a three-dimensional numerical modelling approach for the prediction of settlement damage to masonry buildings due to tunnelling in soft ground. The modelling approach was applied to three sites that were representative of a range of practical configurations, including the well-known case of tunnelling beneath the Mansion House, London, for the Docklands Light Railway. The modelling procedures were found to be suitable for the detailed assessment of the response of a building to tunnelling. The necessity to model the building together with the ground and a representation of the tunnel excavation, in three dimensions, was shown. The self-weight of the building was found to be an important factor in its response. Details of typical masonry buildings, such as openings for doors and windows, and shallow foundations, could be modelled satisfactorily.
Sponsored by Kellogg Brown & Root Ltd and Royal Commission for the Exhibition of 1851.
Contact: Professor G. T. Houlsby.
S. Croxford, Sheffield University
Evaluating the evolution of minewater contamination during the weathering of a UK Carboniferous Middle Coal Measure sequence
The project focused on the geochemical processes involved in the generation of minewater contamination from a UK Coal Measures sequence, the former Rawdon Colliery in Leicestershire. The aim was to understand the behaviour of individual minerals present within the constraints of their natural whole rock assemblages. Batch experiments were run in the laboratory, and the relationship between acidity and alkalinity generating processes within the different strata and the subsequent release of contaminants associated with these processes were studied. A simple minewater prediction model was constructed that predicted discharge water quality, and results predicted were found to be comparable with those recorded on site.
Sponsored by Hosseim Farmy Research Scholarship.
Contact: Professor D. Lerner.
P. C. Fernandes da Silva, University of Sheffield
The use of structural geology in regionalisation schemes for engineering purposes
Structural geology is of vital importance in land use planning, environmental management and engineering design and construction. However, although structural features may be included in site characterisation studies, this is usually without effective input from regional interpretations and models. Therefore a range of strategies for selecting and processing remotely sensed data to provide structural geological input to regional terrain evaluations were investigated. The methodology was applied and evaluated by inferring structural features from regional tectonic models, and then comparing these both with the model itself and with field data. Its capability to enhance physiographic compartmentalisation and the evaluation of ground conditions was also demonstrated.
Sponsored by Departments of Civil & Structural Engineering & the Geography Sponsors Directoria de Desenvolvimento Cientifico e Tecnologia (CNPq) Brazil and the Foreign & Commonwealth Office UK.
Contact: Dr J. C. Cripps.
P. I. Fair, University of Sheffield
The geotechnical behaviour of ballast materials for railway track maintenance
A new alternative to tamping for ballast bed maintenance is stoneblowing. The stoneblower lifts each sleeper and blows 20 mm stone into the void between the sleeper and the 50 mm ballast. The deformation characteristics of this arrangement have been examined using monotonic and cyclic loading triaxial tests. It has been found that particle breakage plays an important role in the ballast behaviour, and a model has been proposed which allows the volume strain to be separated into that due to shearing and that due to particle breakage. In addition, analysis of track quality data for stoneblown track has been carried out and allowed recommendations to be made for optimisation of the process.
Sponsored by an ERSRC CASE Award with Railtrack.
Contact: Professor W. F. Anderson.
A. A. Al-Thani, University of Southampton
A numerical investigation of the deep well free surface-seepage face boundary condition
The aim of this research was to investigate numerically the effect of the seepage face in the performance of single and multiple deep well systems, under steady state and transient conditions. It is shown that a Dupuit–Forchheimer analysis of a single well overestimates the drawdown of the free surface. In multiple well configurations the effect is eliminated by well interaction. Investigation of the transient seepage face for single well configurations shows a rapid decline of the phreatic surface during the early stages of pumping, due to the specific storage effect. The numerical results are discussed in the context of groundwater control and remediation, and the control of landfill leachate.
Sponsored by University of Qatar.
Contact: Professor J. K. White/Professor W. Powrie.
S. Cox, University of Southampton
The use of horizontal wells for leachate and gas control in landfills
The use of directionally drilled horizontal wells for leachate and gas control in landfill sites is examined, with reference to a major field study. The research has led to an understanding of the practical difficulties of horizontal well installation, the theoretical reasons for them and ways to overcome them, and also demonstrated how pumping from horizontal wells affects pore pressures in a landfill. Well performance is heavily influenced by the anisotropic permeability of the waste and the ability to extract large volumes of landfill gas, even from the notionally saturated zone.
Sponsored by Cleanaway and EPSRC.
Contact: Professor W. Powrie/Dr R. P. Beaven.
P. J. Gräbe, University of Southampton
Resilient and permanent deformation of railway foundations under principal stress rotation
This thesis addresses the resilient and permanent deformation behaviour of railway formations during cyclic loading with rotation of the principal stress. Dynamic finite element analyses were conducted to obtain typical stress paths in a track structure. The results defined the scope for laboratory element testing. They also provided realistic magnitudes of applied axial and torsional loads for stress path testing in a hollow cylinder apparatus. Cyclic rotation of the principal stress directions results in a decreased resilient Young's modulus, compared to cyclic loading without principal stress rotation (PSR). Cyclic PSR increases the rate of accumulation of permanent axial strain; the effect is more significant for lower clay contents. Finally, cyclic PSR generates pore pressures that can lead to excessive plastic deformation and shear failure.
Sponsored by SPOORNET, EPSRC, CVCP–ORS Awards Scheme 2000 and University of Southampton.
Contact: Professor C. R. I. Clayton.
M. Imam, University of Southampton
Applications of soil mechanics principles to landfill waste
The hydrogeological behaviour of a model landfill waste was studied in the laboratory to determine its hydraulic conductivity and suction characteristics. It was found that hydraulic conductivity of waste is affected by the particle size and decreases for increasing dry density and effective stress. Suction characteristics of waste were studied using the filter paper method. Moisture characteristic curves for various dry densities were developed using the van Genuchten model. The physical properties of the model waste developed were found to be comparable to those of coarse soils. The filter paper technique gave an overestimation of suction values in the presence of pore fluid solute concentrations consistent with those typically present in leachate.
Sponsored by University of Southampton.
Contact: Dr. D. J. Richards.
Q. Ni, University of Southampton
Effects of particle properties and boundary conditions on soil shear behaviour: 3-D numerical simulations
The mechanical response of spherical and non-spherical cohesionless granular materials under general engineering stress conditions is examined by simulation of direct shear box and biaxial tests using a three dimensional distinct element method computer code. The effects of particle shape, interparticle friction, size distribution and loading conditions (the initial porosity, confining stress and friction on the loading platen) on the stress–dilation behaviour of a sample are investigated. It is shown that shear bands can be characterised by a defined zone of intensively rotated particles, associated with large voids and concentrated shear strain. The development a shear band is related to the applied boundary conditions, particle shape and sample density.
Sponsored by University of Southampton.
Contact: Professor W. Powrie.
M. Rust, University of Southampton
The mechanics of continuous flight augers in clay
The aim of this research was to improve the predictability of CFA pile behaviour in clay using measurements taken on the CFA rig during pile construction. A computer-controlled small-scale CFA model, which allowed close control of the auger movement, was designed, built and instrumented to measure torque and axial load on the auger. The model was then used to advance different augers into stiff clay samples. Results from the model tests were used to recommend improvements in the instrumentation of full-scale CFA rigs, and techniques of using the improved instrumentation to predict pile capacity.
Sponsored by STENT Foundations and EPSRC IMI Construction as a Manufacturing Process.
Contact: Professor C. R. I. Clayton.
A. H. Thomas, University of Southampton
Numerical modelling of sprayed concrete lined (SCL) tunnels
Relatively little research has been done on sprayed concrete tunnel linings. Discrepancies have been observed between the performance of SCL tunnels and design predictions. Experimental data suggest that the behaviour of sprayed concrete is more complex than is normally assumed. This can lead to uneconomic or unsafe designs. Possible constitutive models were compared with experimental data using the FLAC3D program. 3D analyses of an advancing tunnel were compared with data from the Heathrow Express project. This research found that both the constitutive modelling of sprayed concrete and variations in construction sequence can have a large influence on the predicted behaviour.
Sponsored by Mott MacDonald, Royal Commission for the Exhibition of 1851 and EPSRC.
Contact: Professor C. R. I. Clayton.
