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 2001 should be submitted to The Director (Engineering), The Institution of Civil Engineers, 1 Great George Street, London SW1P 3AA, by 31 January 2002.
The summaries are arranged in alphabetical order, firstly by university and then by surname.
M. S. Dietz, University of Bristol
Developing an holistic understanding of interface friction using sand within the direct shear apparatus
A modifed 100 mm direct shear apparatus has been developed that, while retaining the archetype's simplicity, generates high-quality data. Its novel articulation simultaneously produces reliable estimates of vertical stress and permits unimpeded dilation. With these parameters accurately quantified and the device properly optimised, the appropriate test interpretation becomes apparent, which differs from that commonly employed. Sand–steel interface tests conducted using the modified DSA have clarified the role of interfacial dilation. Multi-reversal interface tests show degradation of surface topography visualised through fractal analysis. For coarse sand, the run-in angle of interface friction is unique, being independent of initial stress level, density and steel roughness.
Sponsored by EPSRC.
Contact: Mr M. L. Lings, Department of Civil Engineering, University of Bristol.
D. S. Pennington, University of Bristol
The anisotropic small strain stiffness of Cambridge Gault clay
A novel triaxial system was developed that combines conventional local strain measurement with bender elements mounted both in the end platens and at mid-height of a specimen. This enables the assessment of all five independent cross-anisotropic elastic parameters at very small strain. Tests on reconstituted and natural Gault clay revealed substantial anisotropy, the latter displaying E0(h)/E0(v) = 4·0, G0(hh)/G0(hv) = 2·3 and ν 0(vh) = 0 at in situ stress states. Significant discrepancies were found between correctly measured values of G0(hv) (which cannot be measured in a conventional triaxial test) and values derived making incorrect assumptions of isotropy.
Sponsored by EPSRC.
Contacts: Mr D. F. T. Nash and Mr M. L. Lings, Department of Civil Engineering, University of Bristol.
D. Robertson, University of Cambridge
Computer simulations of crushable aggregates
The first study is of 2D models in which triangular grains split under stress according to Weibull's statistical rules. This tended to lead to fractal distributions of fragment sizes. Linear plots of compression against log stress were produced when broken particles remained trapped in place. The explicit modelling of grains and voids led to different observations. The second study using the discrete element package PFC3D to simulate the statistics of crushing grains using smaller bonded spheres agglomerated with ‘crystal’ imperfections. Computed stress paths of a triaxial sample of these grains recreates a yield surface and hardening similar to Cam Clay.
Sponsored by EPSRC.
Contact: Professor R. J. Mair, Department of Engineering, University of Cambridge.
P. Ingram, City University, London
The application of numerical models to natural stiff clays
Methods were described for the modelling of features of the stress–strain behaviour of natural stiff clays by extending an established constitutive model for stiff clays. The work focused on modelling stiff clays with stable natural structures. Creep and anisotropy were also investigated. The methods have been evaluated by both comparing predictions with laboratory data and analysing field problems. The methods improved predictions of elements tests in a manner consistent with observations. Analyses of field problems showed that the methods could significantly influence predictions but rely on a detailed understanding of the processes undergone during the geological history of the clay.
Sponsored by an EPSRC CASE Award with Ove Arup & Partners.
Contact: Dr S. E. Stallebrass, Geotechnical Engineering Research Centre, City University, London.
U. Klotz, City University, London
The influence of state on the capacity of driven piles in sand
Carefully instrumented model piles, with measurement of shaft, end bearing and radial stresses, were driven into sand models tested on a geotechnical centrifuge. High-quality triaxial tests allowed determination of the critical-state lines of the sands; shear box and ring shear tests characterised the pile–soil interface behaviour. Traditional relative density approaches to understanding the pile data were shown to be very poor. In contrast, it was clearly demonstrated that in situ state—that is, specific volume and effective stress—is the key factor controlling pile capacity. A new, logical, design approach that takes into account soil state has been developed.
Sponsored by EPSRC.
Contacts: Dr M. R. Coop, Department of Civil and Environmental Engineering, Imperial College of Science, Technology and Medicine, London; Professor R. N. Taylor, City University, London.
J. Blewett, Heriot-Watt University
The development of laboratory measurement techniques to study liquefaction mitigation by vibro-replacement stone columns
Laboratory techniques are used to produce comprehensive information on the liquefaction mitigation provided by granular drainage columnar inclusions in loose sand. A novel low-cost, high loading frequency, triaxial testing system is developed. The testing programme examines aspects of liquefaction mitigation due to the rigidity of the columnar inclusions and due to the increased permeability of the columns. Extensive use is made of bender-element testing techniques, and the frequency dependence of such measurements is examined. Phase-sensitive detection is proposed as a new, accurate and convenient method to obtain frequency response and time-of-flight element data.
Sponsored by EPSRC; Mott MacDonald Charitable Trust.
Contact: Professor W. J. McCarter, Department of Civil and Offshore Engineering, Heriot-Watt University.
M. El Fatih Mukhtar Hamadto, Heriot-Watt University
Expansive soil behaviour and the development of a knowledge-based system associated with foundations in expansive soils
The author has proposed: (a) a new classfication system for expansive soil; and (b) a novel approach to the prediction of heave in expansive soils. The author has also developed and evaluated a knowledge-based system, called FESAID, for the outline design of foundations in expansive soils. The system offers advice on the swelling potential of the soil, soil heave prediction, and the suitability of a range of foundation types. Evaluation of FESAID has been done through the application of a number of case studies.
Sponsored by Arriyadh Development Authority, Saudia Arabia.
Contact: Professor W. J. McCarter, Department of Civil and Offshore Engineering, Heriot-Watt University.
M. R. Cunningham, Imperial College of Science, Technology and Medicine
The mechanical behaviour of a reconstituted, unsaturated silt
This project builds upon a recent experience gained at Imperial College in the fields of suction measurement and control to develop a suction-controlled stress-path triaxial apparatus. A programme of triaxial tests was undertaken to determine the mechanical behaviour of the soil over a range of degrees of saturation and under various stress paths. The results suggest that both shear strength and volume change behaviour obey the effective stress principle but become non-linear and strongly stress path dependent at degress of saturation less that 100%.
Sponsored by EPSRC.
Contacts: Professor J. B. Burland and Dr A. M. Ridley, Department ofCivil and Environmental Engineering, Imperial College of Science, Technology and Medicine.
J.-H. Shin, Imperial College of Science, Technology and Medicine
Numerical analysis of tunnelling in decomposed granite soil
This thesis investigates the behaviour of the ground due to tunnelling in decomposed granite soil. The objective is to improve the present understanding of ground behaviour and develop new numerical modelling methods. The issues investigated were drawn from the practice of NATM tunnelling for the Seoul Subway system in Korea. The main topics involve the evaluation of constitutive models to represent the behaviour of decomposed granite soil, an improvement of 2D modelling methods, modelling of groundwater movement, and development of 3D modelling of a tunnel heading. Finite element methods using the ICFEP were employed for this research.
Sponsored by Seoul Metropolitan Government of Korea; British Council; and ORS Award.
Contact: Professor D. Potts, Department of Civil and Environmental Engineering, Imperial College of Science, Technology and Medicine.
P. R. Fleming, Loughborough University of Technology
Impact assessment of layered granular materials
This thesis describes the evaluation of a portable impact test device, for routine stiffness measurement in situ, and research into the behaviour of granular soils subject to rapid transient loads. The prototype impact device, known as ODIN, is described. A selection of field data is presented. Controlled laboratory testing is also described, comprising impact testing with free-falling masses in addition to the ODIN device, for tests on foundations instrumented with pressure cells. The data further explain the dynamic behaviour of the material under test. Discussion of the research findings concludes with a model for soil behaviour under impact testing.
Contact: Dr P. R. Fleming, Department of Civil and Building Engineering, Loughborough University of Technology.
A. S. Ndumu, Napier University, Edinburgh
Fractal-based stochastic simulation and analysis of subsurface flow and scale-dependent solute transport
A novel fractal-based particle tracking technique, using increments of fractional Brownian motion (fBm), has been developed to simulate non-Fickian diffusion within porous media. Using the technique, sub- and super-diffusive transport have been modelled. A stochastic model of flow and transport within stationary and non-stationary random hydraulic conductivity fields has also been developed. Analyses have been carried out to establish the link between the fractal-based fBm model and a stochastic transport model based on Monte Carlo simulations. Results indicate that the fractal-based model provides a better approximation to the Monte Carlo results than those obtained using more traditional techniques.
Contact: Professor I. C. Pyrah, School of the Built Environment, Napier University, Edinburgh.
R. Bennett, University of Nottingham
Microtunnelling
Microtunnelling machines often perform unsatisfactorily in mixed ground, particularly in soft ground containing hard rock boulders, as boulders are often pushed through the ground rather than fragmented. A series of laboratory feasibility studies was conducted where instrumented model boulders were confined in soils and subjected to impacts at a range of velocities. Simple empirical relationships and finite element models were developed from these tests to describe boulder failure. The work revealed that a projectile approach has the most potential for fragmenting the boulders encountered by a microtunnelling machine. Other impact methods require careful targeting, or produce high levels of blast and overpressure.
Contact: Dr R. Bennett, University of Nottingham School of Civil Engineering.
M. W. Frost, Nottingham Trent University
The performance of pavement foundations during construction
This thesis studies the influence of the subgrade on the constructability and performance of a series of full-scale pavement foundations. This has been achieved by measuring resilient stiffness and permanent strain characteristics of several subgrade materials in the laboratory, using repeated-load triaxial testing. These data have been compared with data collected in situ using dynamic stiffness measuring devices during the construction and trafficking of trial pavement foundations. The need for adequate resistance to permanent deformation to enable trafficking during construction is shown to be a more critical design parameter than the need for adequate stiffness of support to achieve satisfactory compaction of the pavement foundation layers.
Contact: Dr M. W. Frost, Department of Civil and Structural Engineering, Nottingham Trent University.
Razik Razoaki, University of Portsmouth
Effect of ageing on mechanics of chalk slurries
This thesis describes the time-dependent behaviour of chalk slurry produced by full-face tunnelling machines. The laboratory test results showed that ageing enhances the small-strain stiffness and reduces the compressibility of the material. However, the material can, with time, develop metastable collapsible fabric and become prone to liquefaction. The fabric of chalk slurries consists of aggregated units of varying sizes and packing densities. Ageing alters the characteristics of these aggregations through mechanical and chemical processes involving enhanced interactions between grains and the time dependent deposition of super-soluble particles at grain contacts.
Contacts: Dr Razik Razoaki, Imperial College of Science, Technology and Medicine; Mr Nick Langdon, Card Geotechnics Limited.
D. Corcho, University of Sheffield
Biodegradation of MTBE and other ether oxygenates by a cyclohexane utilising culture
The thesis studied the capability of a cyclohexane-utilising culture (CH1) to cometabolise the gasoline oxygenate MTBE and other ether oxygenates including tert-amyl methyl ether (TAME), ethyl tert-butyl ether (ETBE) and diisopropyl ether (DIPE). The culture also showed the capability of degrading other compounds commonly present in gasoline, such as benzene or toluene. A novel remediation approach based on the cyclohexane-utilising culture (CH1) and membrane technology was developed. Bench-scale reactors using a dual membrane-attached biofilm were successful in treating MTBE-contaminated artificial groundwater, and have potential for the biological treatment of groundwater contaminated with MTBE and other ether oxygenates.
Sponsored by Shell International Oil Products (UK).
Contact: Professor D. N. Lerner, Department of Civil and Structural Engineering, University of Sheffield.
F. T. Jeremias, University of Sheffield
Geological controls on the engineering properties of mudrocks of the north Lisbon area
This was an investigation into the influence of mineralogy and texture on the geotechnical properties, particularly durability, of mudrocks. Samples of Jurassic mudrocks from Aruda and Obidos near Lisbon, Portugal, were characterised using quantitative X-ray diffraction, geochemical methods, microtextural analysis, mainly using scanning electron microscopy, and swelling, strength and durability properties. The importance of total void space and expandable clay content was confirmed, but the significance of cementation on short-term durability was also revealed. A ‘durability index’ was defined in terms of dry density, methylene blue adsorption and second-cycle durability values to distinguish potential by problematic from non-problematic mudrocks.
Sponsored by JNICT, Portugal and LNEC, Portugal Contact: Dr J. C. Cripps, Department of Civil and Structural Engineering, University of Sheffield.
P. Prabnarong, University of Sheffield
Evaluation of risks in urban groundwater: a case study in Nottingham
A simple stochastic solute transport model was developed to estimate the risk of benzene to a public water supply borehole. Potential contaminant sources over different time intervals were included to represent the changing industry over the past 100 years. Financial costs of reducing risk were based on predicted clean-up costs related to trichloroethylene (TCE) and tetrachloroethylene (PCE) emerging at the borehole. Results showed that the model performed closely to the field data. This model is directly applicable to other urban areas with similar conditions, but the general methodology is of wider application in guiding risk assessment modelling of groundwater contaminants.
Sponsored by the Thai Government.
Contact: Professor D. N. Lerner, Department of Civil and Structural Engineering, University of Sheffield.
B. Zhang, University of Sheffield
Modelling groundwater flow to adit systems in UK chalk aquifers
Many chalk groundwater sources in England have adits, but conventional groundwater models are inappropriate to model aquifer adit systems. An integrated groundwater, open channel and pipe flow is created by introducing a fictitious narrow slot above the adit which allows pipe flow to be simulated by open channel flow equations. The case studies proved that the new model can simulate both steady-state and transient situations adequately, explored the techniques of modelling adits, and provided new understandings of the two sites.
Sponsored by the Environment Agency, Yorkshire Water Services, Thames Water Utilities Ltd, General Utilities, and Anglian Water Services.
Contact: Professor D. N. Lerner, Department of Civil and Structural Engineering, University of Sheffield.
T. Hayward, University of Southampton
Field studies, analysis and numerical modelling of retaining walls embedded in weak rock
Field data have been used to investigate suitable geotechnical parameters and models for use in the design of walls embedded in weak rock. Field monitoring and interpretation, comparison of geotechnical parameters, analyses comparing the discontinuous and continuum approach to modelling retaining wall behaviour, and back-analysis of a monitored section of retaining wall are included in the thesis. The research generated a high-quality case record of wall movements, bending moments, temporary prop loads and vertical contact stresses under the permanent stabilising base of a retaining wall embedded in weak rock.
Sponsored by EPSRC, Transport Research Laboratory, and University of Southampton.
Contacts: Professor W. Powrie and Dr D. Richards, Department of Civil and Environmental Engineering, University of Southampton.
A. S. Lees, University of Southampton
Soil/structure interaction of temporary roadways
Finite element analyses and centrifuge tests were carried out on a model temporary military trackway, subject to vehicle loads, on a soft over-consolidated clay. The centrifuge tests and finite element analyses showed that soil/trackway failure is not typically caused by bearing capacity failure of the soil, or by degradation of the soil due to cyclic loading. It is due to very high soil/trackway contact stresses generated by the low-bending-stiffness articulated joints causing immediate failure of a thin surface layer of the soil. Existing trackway performance could be improved significantly by enhancing its stiffness in the direction of vehicle travel.
Sponsored by EPSRC and the Defence Evaluation and Research Agency.
Contact: Dr D. Richards, Department of Civil and Environmental Engineering, University of Southampton.
O. A. Oni, University of Southampton
An investigation into the impact of sequential filling on properties of emplaced refuse lifts and moisture stored in a municipal solid waste landfill
The impact of further tipping of refuse loads on the moisture content, hydraulic and geotechnical properties of emplaced refuse lifts, and the daily cover, was examined. Field tests involved pit tests and cone penetration tests, while laboratory tests involved the determination of compression, porosity and hydraulic conductivity of pulverised refuse samples. The data obtained were incorporated into a hydrologic evaluation and landfill performance model to simulate moisture conditions and changes in the physical properties of emplaced refuse lifts. The simulation technique used in this study can be used in evaluating alternative designs and plans of a municipal solid waste landfill.
Sponsored by Commonwealth Scholarship Commission, London, WH White plc, EEC, Lagos and University of Southampton.
Contact: Dr D. Richards, Department of Civil and Environmental Engineering, University of Southampton.
P. J. O'Shea, University of Southampton
Failure mechanisms for small diameter cast iron water pipes
Four main failure mechanisms were investigated: in-pipe water temperature, internal pressure, traffic loading and frost loading. The strength characteristics of cast iron lead-run joints were measured in axial tensile tests on joints exhumed from the ground. A finite element program was then used to analyse the joints and connecting pipe lengths in three-dimensional models with elastic stress–strain material behaviour. The research showed that it is a combination of loading effects and associated pipe defects that is responsible for pipe bursts, rather than a single mechanism as proposed so far, although in-pipe water temperature effects can be very significant.
Sponsored by University of Southampton and Thames Water Utilities.
Contact: Professor C. R. Clayton, Department of Civil and Environmental Engineering, University of Southampton.
A. A. Heshmati, University of Manchester Institute of Science and Technology
Numerical simulation of properties of peat
The presence of fibrous peat of organic partly decomposed fibres with on average a horizontal orientation justifies consideration of fibrous peat as a composite material. To account for its anisotropic stiffness and strength a mathematical material model has been composed involving not only an isotropic elasto-plastic bulk material model but also a three-dimensional fibre model with elasto-plastic fibres in parallel bedding planes and with random orientation within these bedding planes. The composite model is supported by comparisons of numerical simulations with published experimental data of isotropic and one-dimensional virgin compression and unloading tests and drained and undrained triaxial compression tests.
Sponsored by the Iranian Government.
Contact: Professor F. Molenkamp, Department of Civil and Construction Engineering, University of Manchester Institute of Science and Technology.
B. W. Byrne, Oxford University
Investigations of Suction Caissons in Dense Sand
Suction caissons are a novel design for offshore foundations, which lead to savings through reduction of materials and installation time. Experiments are presented using typical offshore loading conditions to determining factors affecting design of suction caissons in dense sand. Long-term loading was investigated by applying vertical, horizontal and moment loads to a foundation in dry sand. Cyclic (used a pseudo-random ‘NewWave’ loadhistory) and transient testing, was on a foundation in oil saturated sand. Serviceability, rather than capacity governs design under tensile loads. Work-hardening plasticity theory describes the monotonic tests well, but for cyclic loads a new theory, ‘continuous hyperplasticity’, was found necessary. Surprisingly, loading rate has a negligible effect on response.
Sponsored by: Rhodes Trust
Contact: Professor G.T. Houlsby, Department of Engineering Science, Oxford University
