PhD Theses: 2012

The thesis is subdivided into two main parts. In the first part, three probabilistic methods for slope stability calculations of different complexities have been compared. These methods were evaluated with respect to a case study of slide in Lodalen, Norway. Finite-element simulations involving spatial random fields of uncorrelated parameters c (cohesion) and φ (friction angle) were considered as a reference for comparison with two versions of the simpler first-order-second-moment (FOSM) method. It is shown that the FOSM method enhanced by a reduction of input parameters variance due to local averaging along the potential failure surface (so-called extended FOSM method) leads to a significant improvement in predictions when compared to the basic FOSM method. The second part of the thesis demonstrates implications of the usage of advanced constitutive model (sand hypoplastic model) in probabilistic analyses of a boundary value problem (settlement of a strip footing). Spatial variability of soil parameters, rather than state variables, is considered in the study. The model, including horizontal and vertical correlation lengths, was calibrated using a comprehensive set of experimental data. These data were obtained on sandy material coming from horizontally stratified deposit. Spatial correlation lengths in the vertical and horizontal directions were varied in the simulations, and their influence on probabilistic response was assessed. The case of infinite correlation length was subsequently compared with predictions of different approximate probabilistic methods (FOSM method and different point estimate methods).

Sponsor: Czech Science Foundation, Czech Republic

Contact: Dr D. Mašín

The dissertation demonstrates the application of a hypoplastic model in class A predictions of a new Austrian tunnelling method (NATM) tunnel in stiff clay in an urban environment. The tunnel is located in the town of Brno, Czech Republic. The constitutive model was first calibrated using a set of laboratory experiments. They comprised oedometric tests and triaxial tests including local instrumentation and bender element transducers. Based on the optimisation analysis combined with finite-element simulations, the calibrated parameters were slightly modified using geotechnical monitoring data from an exploratory drift. The optimised parameters were then used in three-dimensional (3D) finite-element analyses of the future tunnel. The simulations represented class A predictions. After the tunnel excavation, the model's predictive capabilities and the influence of initial conditions and material parameters could be evaluated. It has been observed that the hypoplastic model predicted well the extent and magnitude of the surface settlement trough, while it overestimated horizontal displacements in the vicinity of the tunnel. In the second part of the thesis, the case study of the tunnel from Brno, together with two other tunneling projects, was used for evaluation of the stress relief method used in plane strain simulations of tunnelling problems. Predictions by the stress relief method were compared with predictions obtained using 3D analyses.

Sponsor: Czech Science Foundation, Czech Republic

Contact: Dr D. Mašín

The thesis discusses results for rammed earth (RE) testing in order to inform construction practices. A method for predicting soil retention properties from pore size distributions is developed and its advantages and limitations identified. Flow stratification, transparent clay testing and particle image velocimetry are used to compare laboratory and site material preparation. The effects of changing relative humidity and temperature and the use of saline water on the unconfined compressive and tensile strengths of RE respectively are investigated and the Brazilian test is validated for use with RE materials. Crack development on compressive loading is studied using X-ray computed tomography and crack pattern fractal properties.

Sponsor: Durham University

Contacts: Dr C. Augarde, Professor R. Crouch

This thesis is concerned with the theoretical development and implementation of constitutive models for geometric nonlinear analysis of soils. The developed frictional modified Reuleaux model provides greater realism compared to classical frictional models while still allowing analytical stress integration. An anisotropic family of critical state models advances the modified Cam-clay model by including inelastic behaviour at small strains and a Lode-angle-dependent anisotropic yield function which maintains convexity and uniqueness of the critical state. Findings from this thesis will interest engineers working in numerical methods in solid mechanics, inelastic constitutive modelling and large strain plasticity.

Sponsor: EPSRC

Contacts: Professor R. Crouch and Dr C. Augarde

This thesis formed part of the BIONICS project aimed at investigation of how climate change will affect the serviceability and safety of earth structures. The project included the build of a full-scale, highly instrumented embankment, where studies on the fill material used in the construction of the embankment were carried out to understand the hydro-mechanical behaviour, involving the determination of the soil water retention behaviour and the mechanical behaviour under unsaturated conditions. Also, a novel field system to measure pore water pressure continuously at different depths was developed using high-capacity tensiometers. Field and laboratory data were coupled together to understand the behaviour of the embankment due to climate conditions.

Sponsor: EPSRC

Contact: Professor D. Toll

The thermo-hydro-mechanical (THM) behaviour of the Callovo-Oxfordian (COx) claystone in which the ANDRA (French radioactive waste management agency) underground laboratory was excavated was investigated by using various experimental devices: a newly developed hollow cylinder THM triaxial apparatus with short drainage length allowing proper saturation and drainage in low permeability claystones (10–12 m/s), a high-stress oedometer (60 MPa) and a THM isotropic compression cell. Various constitutive thermo-hydro-mechanical volumetric parameters (Skempton's and Biot's coefficients, drained and undrained compressibilities at different temperatures, intrinsic permeability at different temperature, thermal expansion and thermal pressurisation coefficients) were obtained. Data showed in particular that the thermal volume change behaviour of the COx claystone was similar to that of a normally consolidated soil with plastic contraction. High stress oedometer compression appeared to increase damage and coupled swelling.

Sponsor: ANDRA

Contact: Professor P. Delage, Professor J. Sulem and Dr A. M. Tang

The effects of temperature on the hydro-mechanical behaviour of damaged clays and claystones involved in radioactive waste disposal (Boom clay in Belgium and Opalinus clay in Switzerland) were investigated by using a newly developed hollow cylinder triaxial apparatus with reduced drainage length (10 mm) so as to optimize full saturation and drainage during triaxial testing. Pore water thermal pressurisation under undrained conditions and thermally induced failure were investigated under in situ stress. Permeability tests carried out at various temperatures on sheared samples confirmed the excellent self-sealing properties of the clays studied with little effect of damage, even at elevated temperature. The thermal elasto–plastic behaviour of Opalinus clay was investigated, evidencing in a claystone a thermal response comparable to that of a slightly overconsolidated material with thermal hardening.

Sponsors: TIMODAZ European project, Ecole des Ponts

Contacts: Professor J. Sulem and Professor P. Delage

The hydromechanical behaviour and collapse susceptibility of an unsaturated natural aeolian loess from northern France were experimentally investigated by using a new triaxial apparatus with complete local monitoring (water content, suction, strains) together with suction measurements (high capacity tensiometer and filter paper), microstructure observations (SEM and MIP), CRS oedometer tests with suction measurement. The water retention properties were related to microstructure features whereas a new insight into the collapse behaviour was gained. Constant water content (and suction) tests along various paths in the triaxial stress space confirmed suction hardening elasto-plastic properties and the enlargement of the pseudo-elastic zone with increased suction, with obvious bonding effects.

Sponsors: Alban European grant, SNCF (French railways)

Contacts: Professor P. Delage, Dr J.-M. Pereira and Professor Y. J. Cui

This study focuses on the evaluation of the efficiency of several reclamation methods applied to partially oxidised tailings impoundments in Quebec. Samples were collected in situ and characterised. Instrumented columns (230 cm in height and 15 cm in internal diameter) were set up to study the hydrogeological and geochemical behaviour of the tailings-cover systems. Wetting and drying cycles were repeated to simulate the climatic conditions. Water flow, oxygen diffusion and reactive transport in the columns were simulated using hydro-geochemical numerical codes. Once the models had been calibrated to reproduce experimental measurements, field conditions were simulated. Different types of covers were investigated.

Sponsor: Industrial NSERC Polytechnique-UQAT Chair in Environment and Mine Wastes Management

Contacts: Professor M. Aubertin, Professor B. Bussière and Professor J. Molson

In the last years, Brillouin distributed fibre-optic sensing has became a widely accepted, mature technology. On the other hand, geotechnical monitoring applications are still rare, as the fragile fibre and the harsh soil environment are a difficult combination. Additionally, deeper understanding of geomechanical principles is necessary in order to achieve meaningful results when using these sensors. In this study, novel sensor applications were identified, developed, implemented and evaluated – for example, the strain distribution along a soil-embedded cable and a ground anchor during pullout. This resulted in new insight into the progressive failure phenomenon. Additionally, road-, soil- and borehole-embedded sensors were used for landslide boundary evaluation.

Sponsors: CTI (Swiss Innovation Promotion Agency), VSS ASTRA

Contact: Professor A. M. Puzrin

An extensive research study was undertaken in an effort to investigate temperature effects on interface shear behavior between (a) needle-punched nonwoven polypropylene geotextiles and both smooth polyvinyl chloride (PVC) as well as smooth and textured high-density polyethylene (HDPE) geomembranes and (b) sands of different angularity and smooth PVC and HDPE geomembranes. A temperature controlled chamber (TCC) was designed and developed to simulate elevated temperature field conditions and shear displacement-failure mechanisms at higher temperatures. Complementary geotextile single-filament tensile tests were performed at different temperatures using a dynamic thermo-mechanical analyser to evaluate tensile strength properties of geotextile single filaments. Further, the surface hardness of smooth HDPE and PVC geomembrane samples was measured at different temperatures in the TCC to evaluate how temperature changes affect the interface shear behaviour and strength of geomembranes in combination with granular materials and/or geotextiles.

Sponsor: The Geosynthetic Institute (GSI) Fellowship (2010–2011)

Contact: Professor D. Frost

The Savannah River site (SRS) strata below 30m are diagenetically-altered, calcium-carbonate-rich sediments, while its surface soils are iron-oxide-rich and coarse-grained. Coexisting caves and limestones at SRS were investigated via X-ray diffraction, energy-dispersive spectroscopy for the scanning electron microscope (EDS/SEM), krypton-argon dating, P-wave velocity, tensile strength, and inductively coupled plasma optical emission spectrometry (ICP-OES) solubilities. The effect of iron oxide coatings on soil behaviour was approached through SEM, atomic force microscopy, bender elements, and triaxial strength on Ottawa sands chemically coated with goethite or haematite. Results reveal carbonate diagenesis pathways driven by geologic-time seawater/freshwater cycles and possible microbiological effects. Additionally, iron oxides increase the number of particle-to-particle contacts, specific surface and roughness, which enhance stiffness and strength.

Sponsor: U.S. Department of Energy

Contact: Dr S. E. Burns

This thesis proposes paraelasticity as a hysteretic, fully reversible model with rate independent damping and with variable secant stiffness for the three-dimensional case, based on the work by Hueckel and Nova, which has been revised. A new definition of a strain-path reversal is given and the handling of the past reversals using a stack structure is proposed. Paraelasticity is extended for demanding applications in geomechanics by implementation of a reversible dilatancy/contractancy effect. Moreover, an implicit finite-element implementation for Abaqus and calculation of boundary value problems are presented. A combination of hypoplasticity with paraelasticity is proposed to supersede the intergranular strain concept.

Sponsors: German Research Community (DFG-GeoTech 1136), DAAD, COLCIENCIAS and Universidad de Los Andes/CEIBA

Contacts: Professor Th. Triantafyllidis, Dr-Ing. habil. A. Niemunis and Professor A. Lizcano

The assessment of the material properties of cross-anisotropic rock requires laboratory tests which are often associated with insuperable difficulties. Cavity expansion field tests seem to be a promising alternative. An analytical solution describing the displacements of the cavity wall with respect to the applied pressure and the orientation of the foliation is still missing. An new approximate solution to determine the material properties of cross-anisotropic rock is described in this dissertation. Data obtained from radial jack tests served to the inverse analysis of the problem. Three-dimensional finite-element modelling is used to simulate cavity expansion in linear-elastic, cross-anisotropic rock.

Sponsors: University of Innsbruck, Austrian Science Fund (FWF) and Foundation Propontis

Contacts: Professor D. Kolymbas and Professor C. Tamagnini

This thesis describes the modelling of lateral load–displacement (p–y) behaviour of single piles socketed into mudstone rock using 3DEC. The numerical modelling consisted of simulating a number of full-scale field load tests, as well as laboratory-scale pile load tests data. A comprehensive parametric study, involving varying rock mass properties, joint sets and pile dimensions, was undertaken to determine the key influential parameters affecting the lateral load response of single piles. The results of the parametric study were integrated in the derivation of a new p–y criterion for laterally loaded piles socketed into homogenous and jointed Melbourne mudstone.

Sponsors: Powerlink, Queensland and Monash Research Graduate School

Contacts: Dr A. Haque and Professor P. G. Ranjith

Deep-corrugated steel culverts (corrugation wavelength 400 mm and amplitude 150 mm) are examined using three-dimensional (3D) finite-element analysis, with explicit modelling of corrugated plates and the nonlinear soil and structural behaviour. Comparisons for earlier experiments on a box culvert of 10 m span and 2·4 m rise demonstrate the effectiveness of the calculations, and provide new insights into 3D load spreading and the failure mechanisms. Parametric studies are included for box and arch culverts, examining number of loaded lanes, design truck position, culvert geometry, plate thickness, and the existence of pavement. The results are compared to Canadian and US design codes.

Sponsors: Armtec Ltd and Natural Sciences and Engineering Research Council of Canada

Contacts: Dr I. D. Moore and Dr R. W. I. Brachman

Buried pipelines subject to normal faulting have been investigated using centrifuge tests, where pipe and soil displacements are determined using image analysis. Tests on continuous pipelines of different modulus produced behaviour for various stiffnesses relative to soil. Empirical p–y curves revealed that the central shearing region was not captured well with independent soil springs. Two new approaches are reported, one using simplified pressure distributions and the other peak curvature normalised using characteristic length, ipipe, the distance from points with peak and zero moment. Brittle and jointed pipe models were also used to establish rotations at the fracture or joint.

Sponsor: Natural Sciences and Engineering Research Council of Canada

Contact: Dr W. A. Take and Dr I. D. Moore

This study examined (i) desiccation crack formation and resealing, (ii) impacts of roots and (iii) hydraulic conductivity (HC) under normal and predicted climate change precipitation scenarios for Cumbria, England in large-scale physical landfill cap models. After a year of simulated precipitation, the low permeable layers (LPL) returned to original HC values regardless of LPLs of both cap models showing different HC behaviours. The climate change precipitation model developed severe desiccation cracks, after a drought, that did not reseal upon rewetting. Root growth in cracks impeded resealing in both models. The normal precipitation model developed desiccation cracks, but had better integrity.

Sponsor: Nuclear Decommissioning Authority

Contacts: Dr D. Phillips and Dr V. Sivakumar

The aim of the research has been to investigate the distribution and geotechnical behaviour of the soft clays in coastal estuaries of eastern Australia. Much more is known about estuarine environments and clay composition in the fields of coastal geomorphology, sedimentology and biogeochemistry than utilised in geotechnical engineering practice. This work reviews the interdisciplinary literature on coastal estuaries and clays, and in combination with in situ and laboratory tests presents macro- and micro-scale geotechnical models which aim to capture, respectively, the distribution and unusual deformation behaviour of the estuarine clays.

Sponsor: Australian Research Council

Contacts: Professor S. Fityus and Professor I. Goodwin

The main objective of the research was to evaluate the reliability of spread foundations designed to Eurocode 7 using the partial factors and design approaches adopted in the Irish National Annex, for the implementation of Eurocode 7 in Ireland. Designs carried out using the Irish National Annex were compared with traditional factor of safety designs and designs using the national annexes of some other European countries. It was shown that the three design approaches adopted in the Irish National Annex offer a more consistent level of reliability for spread foundations than the traditional factor of safety methods.

Sponsor: IRCSET

Contact: Dr T. Orr

This thesis considers the results of 170 static load tests carried out on piles installed across Ireland including bored, continuous flight auger and driven piles in varying ground conditions. Pile test results are used together with ground test results to estimate the resistance of the piles (ultimate limit state and serviceability limit state) and to quantify the uncertainty associated with this. Within-site variability is also assessed by grouping the piles based on type, geometry and the ground conditions in which they are installed. The levels of uncertainty calculated are used to assess the reliability of the piles which can be related to the probability of failure.

Sponsors: Irish Research Council for Science, Engineering and Technology (IRCSET) in partnership with Byrne Looby Partners (BLP)

Contact: Dr E. Farrell

A family of constitutive models for soils has been developed, implemented in a finite-element code, validated against laboratory tests and applied to solving boundary value problems. A critical state model has been extended to account for unsaturation, structure, kinematic hardening plasticity and double hardening. These extensions build upon recognised frameworks which are modified and improved in the thesis. The resulting constitutive models are applied to three boundary value problems: pressuremeter tests in bonded clays, undrained excavation of a tunnel in London Clay and the collapse of a braced excavation in Singapore. Field measurements are accurately reproduced where available.

Sponsors: AlBan Office, European Commission

Contacts: Professor A. Gens and Dr M. Arroyo

Two deep clay formations have been investigated in connection with the design of a repository for radioactive waste in Belgium: the reference formation, Boom clay, and Ypresian clay, an alternative one. A comprehensive experimental programme, using specially designed cells, has been performed on these materials to study water permeability and volume change behaviour at different temperatures and sample orientations. The following features have been specifically examined: small-strain stiffness, pre- and post-yield compressibility, yield properties and volume change in drained heating. In addition, pore-pressure generation and dissipation in heat pulse tests have been interpreted via coupled finite-element method numerical simulations.

Sponsors: EURIDICE, ONDRAF/NIRAS (Belgium)

Contacts: Dr E. Romero, Professor A. Gens and Dr X. Li

The thesis studies the relationship between microstructure and engineering properties of an unsaturated clay of medium plasticity. Tests have been performed on compacted and remolded samples, subsequently dried and loaded. Mercury intrusion porosimetry and environmental scanning electron microscopy characterisation shows that the generation of mono- or bimodal particle size distributions (PSDs) depends on the degree of saturation of the prepared specimens. Characteristics of the PSDs are related to G₀ through a novel effective stress concept. Uniformity of the PSD is shown to affect the residual friction angle, which increases from 13° in saturated conditions to 30° in the very dry state due to clay-aggregate hardening during drying.

Sponsors: AlBan Office, European Commission

Contacts: Dr E. Romero and Professor J. Vaunat

Geotechnical engineering has a crucial role to play in enhancing sustainability due to its pivotal role in the construction process where potentially impacts are highest. Currently, there is a lack of methodologies for assessing geotechnical projects that truly encompass the three core pillars of sustainability. A robust system is required which offers a holistic approach that is both flexible and easily understood, whilst not being biased towards rewards or is prohibitively costly. In addition, ‘tool fatigue', whereby a system is generated but never used, must be avoided. After a detailed evaluation of the systems available, the SPeAR® framework was selected. Following detailed discussion with a variety of practitioners, the methodology was significantly adapted to make it applicable to geotechnical problems and ensure that geotechnical engineers can understand and use it with relatively ease. The new version, called ‘GeoSPeAR' for the purposes of this thesis, allows for greater communication between masterplanning and geotechnical engineering via their common base, thus avoiding a potential barrier to greater adoption of more sustainable practices through the construction cycle. Three case studies demonstrate the assessment of the ‘GeoSPeAR' methodology. These showed the practical application of the system and how this effectively supports geotechnical engineers in embedding sustainability into projects.

Contacts: Dr I. Jefferson, Dr D. Chapman and Professor P. Braithwaite

Stabilisation/solidification (S/S) is particularly suitable for treatment of metal contamination, common on many sites requiring treatment. However, there are concerns about the long term durability of S/S approaches. A laboratory programme of work was undertaken to evaluate longer term durability of kaolin clays soil contaminated with zinc and chromium and stabilised with cement. A variety of other components were added to examine the effects of sodium sulphate and organics (humic acid) on the durability of stabilised samples. Assessments were based leaching test data: pH-dependent tests to give equilibrium data; dynamic monolithic tests yielding time-dependent data; and upflow percolation tests obtaining pore water equilibrium data. Extractions were also obtained and the combined dataset used to undertake and validate geochemical speciation modelling using ORCHESTRA embedded in the leaching expert system LeachXS. Various pH leaching trends were assessed, and these demonstrated that amphoteric leaching trends were not observed for either zinc or chromium release under equilibrium-pH-dependent leaching. Additives significantly modified the availability of contaminants at early hydration durations. Humic acids were found to increase the availability for both contaminants, whilst increased sulphate content decreased zinc availability at early hydration periods. However, it was found that increasing hydration cancelled the effects of additives with releases tending to be comparable at advanced hydration durations to those observed without additives. Overall, increasing hydration durations improved contaminant containment and reduce availability. Validated speciation modelling confirmed the formation of stable cementitious minerals, which improved the overall chemical durability of stabilised clay matrices. Thus speciation modelling provides a good method to assess chemical characterisation of stabilised matrices providing an effective tool in the design of S/S treated soils.

Contacts: Dr I. Jefferson, Dr G. Ghataora and Dr D. Boardman

Void redistribution in layered soil profiles can significantly affect the residual strength of a liquefied soil and the resulting deformations. The purpose of this study is twofold: (1) to continue the characterisation and advance the understanding of the void-redistribution strength-loss mechanism and related effects, and (2) to evaluate the ability of the currently available numerical tools to directly account for void-redistribution strength-loss mechanism. Numerical simulations are performed in the commercially-available platform FLAC, using a critical-state based constitutive model – PM4Sand. Simulation results are carefully compared with observations and measurements from centrifuge tests in which void redistribution and shear strain localisation occurred.

Sponsors: NEES, USGS

Contact: Professor R. W. Boulanger

This dissertation discusses the control and optimisation of an innovative biological technology, namely microbially induced carbonate precipitation (MICP). The use of this bio-cementation process in three main applications was investigated. These applications were modification of soil hydraulic properties, soil improvement, and carbon dioxide mineral sequestration. Furthermore, radial flow tests were conducted on a 2D sand model (D = 1 m) in order to further validate the control parameters obtained in the study in a relatively larger setup. This research and the obtained results constitute a step towards better understanding, and control of MICP and its use in different geotechnical and environmental applications.

Sponsor: Citadel Capital Scholarship Foundation (Egypt)

Contact: Professor K. Soga

This research investigates mechanisms associated with soil structure interaction when tunnelling beneath buildings, using both case study data and centrifuge modelling. Field observations of the soil–structure interaction have been obtained from the response of two buildings to the construction of a 12 m-diameter tunnel with extensive jet grouting in fluvial deposits. Large volume losses observed in this case study are also investigated. Centrifuge modelling has been carried out on an 8 m-diameter beam centrifuge with buildings being modelled as aluminium, masonry and micro concrete beams on fine dry sand.

Sponsors: EPSRC, Cambridge European Trust

Contact: Kirby Laing Professor R. J. Mair

This work investigated the development of operating envelopes for stabilisation/solidification (S/S) treatment, and facilitation of biodegradation within S/S treated contaminated soils, with the aim of improving the robustness and sustainability of S/S technology. The ‘process envelopes' study utilised different conventional cementitious binders for treatment of contaminated soil, and generated extensive data from which the range of operating conditions that led to acceptable mechanical and leaching performance of the treated soil were determined. The S/S and biodegradation study indicated that the use of magnesium phosphate cements could facilitate effective immobilisation of heavy metals alongside parallel biodegradation of organics in S/S treated soils.

Sponsor: Cambridge Trusts and Technology Strategy Board

Contact: Dr A. Al-Tabbaa

Anomalous crustal strength of West African deep-water clay sediments is attributed to burrowing invertebrate faecal pellets identified through wet-sieving natural core samples. The abundance of pellets dictates sediment strength and consolidation characteristics. Cam-shear interface tests relevant to hot-oil pipeline design highlight the propensity for low interface friction values when shearing against a rough interface. These values are attributed to positive excess pore pressures generated during damage to pellets and natural soil structure. Smooth interfaces do not damage the soil structure. A microbiological investigation identified the bacterium Marinobacter aquaeolei, which was used in experiments investigating its influence on sediment strength.

Sponsors: Cambridge University, BP Exploration, Cambridge Australia Trust and King's College, Cambridge

Contact: Professor M. Bolton

This thesis investigates long-term twin-tunnel behaviour to assist the assessment of ageing tunnels and to improve long-term predictions. Permeability tests on fissured London Clay explored the relationship between fissure permeability and confining stress. Laboratory investigation on grout from the London Underground tunnels identified a deterioration process for the grout. A finite-element parametric study into the long-term behaviour of single tunnels led to an improved prediction method for long-term surface displacements after tunnel construction. A further parametric study for twin tunnels identified key interaction mechanisms between twin tunnels under different conditions in the long-term.

Sponsor: EPSRC scholarship

Contact: Professor K. Soga

The self-boring pressuremeter (SBP) test is an important in situ testing technique providing fundamental soil properties to the geotechnical engineer. This study examined the effect of soil disturbance on SBP data of both clay and sand. For clay, four main disturbance effects were considered: underdrilling, overdrilling, smearing and the geometry effect. The strain path method was adapted to simulate these disturbances. By analysing the disturbed test curves it was found that the drilling disturbances significantly influence the derivation of the soil properties from both cavity expansion and contraction curves. The soil permeability and the excess pore pressure dissipation were also important issues to consider for practical implications. For sand, the disturbance effect of SBP test in drained conditions was simplified to a cavity contraction occurring before the test. The movement of the cavity including disturbance was described as a contraction–expansion–contraction process. Results showed that the overdrilling effect was the main disturbance for the pressuremeter test in sand and the simulated test curves based on an advanced soil model matched the measured data.

Sponsor: Cambridge Insitu

Contact: Professor K. Soga

This research investigated the effectiveness of natural zeolites, organoclays, inorgano-organo-bentonites and innovative modified forms as part of the soil mix remediation technology (SMiRT) project. Characterisation of these aluminosilicates was performed using scanning electron microscopy (morphology), X-ray diffraction (basal spacing), Fourier-transform infrared spectroscopy (identification of the molecular groups) and thermogravimetric analysis (hydrophilic nature and organic content). The performance was assessed by adsorption batch tests of metal ions and dodecane. The results of this research were used in the design of the SMiRT project field trials and highlight the advantages of the treatment of groundwater in permeable reactive barriers systems with aluminosilicates.

Sponsors: Natural Sciences and Engineering Research Council of Canada and Cambridge Trusts

Contact: Dr A. Al-Tabbaa

Pipeline ploughs are commonly used to bury offshore pipelines for their protection. The rate of progress of pipeline ploughs in sand is complicated by a rate effect which causes the required tow force to increase with velocity. In this research plough performance in sand is investigated by means of physical scale-model tests. Model ploughing tests were interpreted to determine the effect of permeability, relative density and plough depth on the tow forces generated during ploughing. The rate effect was found to increase strongly with reduction in sand permeability. Increasing relative density was found to increase the rate effect but had little influence on the passive resistance of the plough. The test results were compared to an empirical model developed by Cathie and Wintgens (2001). New coefficients (C_w, C_s and C_d) have been proposed and therefore design procedures modified which may allow trenching contractors to make better predictions of plough performance in sands.

Sponsors: EPSRC DTA and CTC Marine Limited

Contacts: Dr M. Brown and Dr F. Bransby

The project investigated performances of geo-structures resting on unsaturated heterogeneous soils. The finite-element method was integrated with the random field theory to analyse each problem stochastically by means of Monte Carlo simulations. The responses were statistically characterised by their mean, variance and probability distribution function, which provided powerful probabilistic tools for risk and reliability assessment. The study demonstrates that the simultaneous existence of heterogeneity and partial saturation can significantly modify the responses of slopes and foundations to hydraulic variation (with respect to the homogeneous and/or saturated cases) and can sometimes cause or exacerbate the risk of unsatisfactory performance.

Sponsor: Scottish Funding Council (GPRE)

Contacts: Dr D. Gallipoli, Dr M. Sanchez and Professor S. Wheeler

An investigation was carried out into failures that occurred during the construction of the Jamuna Bridge abutment in Bangladesh, in three parts – statistical characterisation of the Jamuna River Sand, calibration of laboratory data against a double-hardening elasto-plastic soil model and stochastic finite-element (FE) slope stability analyses. The site was found to consist predominantly of loose to mildly dilative material with considerable hetereogeneity. Calibration of the constitutive model proved difficult because of a lack of appropriate test data from the site. Single-variate random fields of state parameter were linked to constitutive model parameters and a parametric FE study was carried out within a Monte Carlo framework. Failed zones observed on the site could be predicted if heterogeneity was considered in these analyses.

Contact: Dr M. A. Hicks

Random finite-element (FE) methods have been implemented incorporating spatial variability for a series of models. For each material the set of statistical parameters produces an infinite number of possible random fields and a Monte Carlo approach is followed, by executing the FE analysis for hundreds of realisations of the random field. This approach is both time and memory exhaustive computationally, limiting domain sizes and significantly increasing run-times, especially for three-dimensional (3D) models. To reduce these effects the computations have been parallelised, leading to increases in the executable domain sizes and reductions in the run-times of the method. The new codes have been used to analyse large scale 3D slope reliability problems that could not have been tackled in a serial environment.

Sponsor: EPSRC

Contact: Dr M. A. Hicks

An efficient and robust computational algorithm, based on a mesh-free method, is developed for fully coupled large deformation analysis of variably saturated geo-materials. The contributions made in the thesis include: (i) a new three-point time discretisation scheme with variable time step for numerical solution of parabolic partial differential equations; (ii) a fully coupled meshfree model, based on the radial point interpolation method, for flow-deformation analysis of saturated porous media; (iii) a mesh-free model for multi phase analysis of unsaturated soils including hydraulic hysteresis; (iv) finally, a new formulation for large deformation analysis of saturated porous media.

Sponsor: The University of New South Wales

Contacts: Professor N. Khalili and Dr A. Russell

Synthetic polymer fluids have been used as an alternative to bentonite slurries for the excavation of foundation elements over the last two decades. However, very little was known about their properties and their effects on foundation performance. In the first part of this thesis, the fundamental properties of various polymer products are explored and the results of extensive laboratory investigations reported. It is found that significant difference can exist between polymers of the same chemical family as a result of variation of properties such as polymer chain length. In the second part of the thesis, the results of a field trial comprising three full-scale test piles are reported. It is found that the load–settlement performance of the piles constructed under polymer fluids significantly outperformed that of a pile constructed under bentonite. The test results are analysed by the load-transfer method to back-calculate the strength and stiffness parameters of the soil.

Sponsors: EPSRC, Balfour Beatty Ground Engineering and KB International

Contacts: Professor S. A. Jefferis, Dr C. M. Martin and Dr P. J. Martin

Strain gauge and inclinometer readings from 14 instrumented piles loaded by ground movements were analysed. The effects of concrete creep and shrinkage on the strain gauges was found to be minimal, while the influence of concrete cracking and temperature on gauge readings varied by case. Two methods were developed for calculating bending moment from strain data that considered both realistic stress–strain relationships and concrete cracking. These gave bending moment profiles that were found to be in good agreement with those obtained from curve fitting to inclinometer measurements. Different modes of pile bending behaviour caused by ground movements were also identified.

Sponsor: EPSRC

Contacts: Professor W. Powrie and Dr J. Smethurst

Field observations and numerical analyses using a partially saturated code were used to investigate the influence of both climate and vegetation on water content and pore water pressure changes in old clay railway embankments. Periods of extreme climate, the type of vegetation, and the saturated soil permeability all strongly influenced the magnitude of seasonal changes in pore pressure. Pore water pressures in extreme wet winters were found to be lower in underdrained embankments compared to those with a clay foundation. Mature trees caused persistent soil suctions to develop, but these were gradually lost when the vegetation was removed.

Sponsors: Mott MacDonald and EPSRC

Contacts: Professor W. Powrie and Dr J. Smethurst

This thesis reports on a number of shear tests on mechanically biologically treated (MBT) municipal solid waste (MSW) and an artificially reinforced sub-2·8mm component of MBT and green waste compost in order to determine the shear strength of MBT wastes being sent to landfill and the effect of different properties (e.g. length, material) of two-dimensional reinforcing particles on the shear strength. It had been thought that the MBT might be weaker than the parent material due to the reduction in particle size and loss of reinforcing material, however, MBT was found to mobilise strength more rapidly with displacement than MSW.

Sponsor: EPSRC

Contacts: Professor W. Powrie and Professor D. Richards

This thesis reports on a number of resonant column tests conducted to determine the influence of suction on the stiffness of unsaturated soils. Changes in specimen saturation were used to alter the inherent suction in the specimen and determined using the filter paper technique and pressure plate test on identically prepared specimens to those tested. Results showed that shear modulus significantly increased with water content up to an optimum value and then reduced with further increases in water content. It was also shown that the increase in shear modulus increased with clay content for the soils tested.

Sponsors: EPSRC Rail Research UK DTA Studentship

Contacts: Dr J. Priest and Professor C. Clayton

The biodegradation and settlement behaviour of a UK and German MBT was investigated using large scale lysimiters capable of applying a constant vertical stress within the waste sample. The gas generating potential, leachate quality, long-term settlement characteristics and hydraulic properties were determined and compared with previous studies to characterise untreated municipal solid wastes (MSW). The contributions of mechanical creep and biodegradation to secondary settlement were identified separately and mechanical creep found to be the more significant of the two. The overall trends and results of hydraulic conductivity and drainable porosity against density and vertical stress for the pre-treated waste were similar to those derived from raw MSW.

Sponsors: EPSRC Science and strategies for the long-term management and remediation of landfills

Contacts: Professor W. Powrie and Professor D. Richards

This thesis reports on resonant column tests conducted on methane gas hydrate-bearing sands, with hydrate saturation of the pore space ranging from 7% to 27%, to understand the role of hydrate dissociation on sediment stiffness. Results highlighted a significant reduction in stiffness for minor changes in hydrate saturation when hydrate dissociation was induced by an increase in specimen temperature. A reduced change in stiffness was observed when hydrate dissociation was induced by reduction in pore pressure. These results will help identify appropriate techniques for recovering methane gas through dissociation of methane gas hydrate in deep water marine sediments.

Sponsors: Fugro Offshore Geotechnics (Netherlands)/University of Southampton

Contacts: Dr J. Priest and Professor C. Clayton

The effect of grain-displacing methane hydrate on the overall elastic properties of the host sediment was numerically investigated using computational homogenisation, where for the first time particular hydrate morphologies were explicitly modelled. Simulations of sediment containing nodules and simple veins of hydrate showed that hydrate morphology significantly affects the overall elastic properties of the sediment. The effect is more pronounced on the compressional wave velocity than on the shear wave velocity. It is predicted to diminish with depth as the sediment stiffens. Using the numerical results, mathematical expressions linking hydrate content to overall seismic wave velocity were also developed.

Sponsor: EPSRC

Contacts: Dr A. Zervos and Professor C. Clayton

The thesis combines constitutive and numerical modelling of unsaturated soils. Wheeler, Sharma and Buisson proposed an elasto-plastic constitutive model for isotropic stress states incorporating the coupling between water retention and mechanical behaviour. An extension of this constitutive model to general three-dimensional stress conditions is presented with the development of the basic generalised stress–strain relationships. The extended model is validated for various stress paths giving a very satisfactory response with some minor departures related to typical shortcomings of elasto-plasticity and critical state theory. The model is finally implemented into the finite-element program CODE_BRIGHT and its performance is assessed by considering an application to a boundary value problem.

Sponsor: ‘Synergy' strategic alliance between Glasgow and Strathclyde Universities

Contacts: Dr M. Sanchez, Professor S. Wheeler and Professor M. Karstunen