Department of Engineering - Annual Report 1998/99

Geotechnical Engineering

Schofield Centrifuge Centre
Earthquake Modelling

ENVIRONMENTAL GEOTECHNICS LABORATORY
Environmental Sensors
Transport Processes
Contaminant Transport
Site Investigation
Contaminated Land Remediation
Soil Mixing
Re-use of Waste Materials

SOIL MECHANICS
Soil Characterisation and Element Testing
Clastic Mechanics

GEOTECHNICAL ANALYSIS
Numerical Analysis of Porous and Granular Media
Numerical Analysis of Soil-Foundation Interaction
Analyses of Pressuremeter Tests

BIO-MECHANICS OF CELLULAR AND GRANULAR MEDIA
Bone Grafts
Brain Damage

FIELD STUDIES
Site Investigation
Displacement Piles

CONSTRUCTION PROCESSES

References

Schofield Centrifuge Centre

The Schofield Centrifuge Centre provided facilities for physical modelling and testing to 4 final year project students, 11 research students, 2 post-doctoral research workers and a research assistant, working on projects associated with seven academic staff members. An introduction to modelling principles was provided to a class of 16 MEng students. Three industry projects were completed via CUTS Ltd, two on pipeline stability assessments for BP and Stolt Comex Seaway Ltd, and one on the stability of clay railway embankments for London Underground Ltd.

The Centre continued to provide teaching for First Year research students, and 14 students used the mini-drum centrifuge facility to study problems of foundations on soft clay. Further, the centre hosted Professor T.D. O'Rourke during his sabbatical stay in Cambridge.

Work has continued on the up-grade of facilities on the balanced beam, the 2m drum and the mini-drum centrifuges.

Earthquake Modelling

Research in soil dynamics and earthquake engineering continues with the ongoing development of new earthquake actuators. The Stored Angular Momentum (SAM) earthquake actuator was modified to accommodate a self-contained swinging platform. With these developments the dynamic centrifuge experiments with earthquake loading are being carried out with a quick turn-around time on the beam centrifuge(G22,G24,G25). Research is underway to further develop the Equivalent Shear Beam (ESB) model container which simulates the semi-infinite extent of a soil layer in the field and to establish the stress state of the soil in the ESB container prior to and after earthquake loading is applied. To this effect a set of new in-flight cone penetrometers were developed for dynamic centrifuge experiments. These were used to assess the pre- and post- earthquake strength profiles of the soil. Also boundary effects in the ESB container are being investigated. Use of Wavelet analysis techniques has been identified as the key feature in future analysis of the data obtained in dynamic centrifuge tests. In particular these techniques are being applied to investigate the degradation of soil stiffness during and after earthquake induced liquefaction.

The SAM actuator was also used to study various boundary value problems supported by Mott
MacDonald, including seismic behaviour of gravel embankments and liquefaction resistance of bridge foundations(G20). Work on liquefaction-induced lateral spreading supported by Shimizu Corporation, Japan, is underway. Also the SAM actuator is currently being used to establish the seismic behaviour of waste containment facilities in collaboration with the University of Santa Clara, USA. The seismic behaviour of large dams was studied using dynamic centrifuge techniques. In particular the modelling of hydro-dynamic pressures on the up-stream face of the dam was investigated(G19,G23). The use of an Electro Magnetic Mini Earthquake (EMME) actuator in MEng projects continues. The EMME actuator can subject small payloads to strong earthquakes of desired spectral content. Also the up-lift resistance of piles subjected to tension was investigated using both centrifuge modelling and numerical analysis using ABAQUS(G24).

Environmental Geotechnics Laboratory

The European-Union funded programme NECER (Network of European Centrifuges for Environmental Geotechnics Research) has continued to be an important part of this year's work, involving the development of sensor technology, studies of the kinetics of contaminants in soils, and the co-ordination of one of the working groups of the programme. Presentations have been made at NECER review meetings in Delft, Copenhagen and at City University.

Environmental Sensors

The European-Union funded collaborative program NECER has continued with a collaboration with Lisbon National Civil Engineering Laboratory on photometric sensors for monitoring pollutant plumes. A workshop on this topic was held there in April. A NECER_funded project at Cambridge with Dr Philippe Sentenac, a post-doctoral researcher, has improved the design of photometric sensors, and also used them to study the boundary effect on the permeability of soil columns. Successful measurements have been made of the difference in permeability at the wall and at the centre of a soil column, and have confirmed that water flows faster next to the wall of a vessel containing soil than at the centre of the soil mass. The increased permeability at the wall can be eliminated by sand-coating the walls of the tube.

Laboratory testing continues on the measurement of frequency dependent dielectric properties of clay mixed with different pore fluid chemistry and ion concentrations, in collaboration with Nishimatsu Construction, Japan. A coaxial probe is used to measure the high frequency dielectric constant, whereas a four terminal measurement system is used to obtain the dielectric constant at the low frequency range. The effect of cations and ion concentration was observed in the high frequency range. The results from the low frequency measurement highlighted some of the problems with calibrating such a system for clayey soils(G8).

Transport Processes

Both 1g and centrifuge tests were performed to investigate the behaviour of light non-aqueous phase liquids (LNAPLs) in soils with financial support from the European Union and from Kajima Corporation, Japan. An intermediate scale tank has been used to examine the dynamic movement of hydrocarbons under unsaturated layered soil models. Various sensors were installed at the back of the tank to measure the fluid pressures and the degree of saturation during the mobilisation and redistribution of the hydrocarbons. A new imaging analysis technique using an infrared digital camera has been developed to estimate the dynamic changes of water and NAPL content throughout the test. Centrifuge tests were also performed to investigate the NAPL movement in the layered system with various combinations of particle size contrast (coarse sands to silt). These data will be compared with the results from numerical analysis.

The movement of dense non-aqueous phase liquids (DNAPLs) in saturated inclined soil systems was investigated by performing 1g and centrifuge tests. The effect of layer inclination, interface contrast and injection on the DNAPL mobility was examined by observing the plume shape and recording pore pressures at various locations in the model. A conceptual model of DNAPL migration in inclined layer has been developed.

Contaminant Transport

A study of the behaviour of landfill liners has continued with experiments on the transport of organic pollutant tracers through a clay layer(G36). Earlier accelerated transport experiments used increased gravity in the geotechnical centrifuge to accelerate the contaminant transport. Recent experiments have used gas pressure to increase the hydraulic gradient. In both cases photometric sensors were used to track the movement of the tracer on each side of the clay layer.

A project with Professor Sasaki from Wakayama University tracked the movement of copper pollutant plumes through sand, again by photometric sensors, and also measured the adsorption coefficient by batch adsorption experiments. He is comparing the results with a finite element numerical analysis.

Site Investigation

A joint project with Chemex International to assess the benefits of a portable gas chromatograph for contaminated land site investigation was completed. The method was applicable to BTEX contaminants (light hydrocarbons) and showed a time saving of up to 65% compared with laboratory-based analysis.

Contaminated Land Remediation

A fourth year project has investigated the clean-up of heavy metal contaminated soil by the passing of current through the soil. By moving the electrodes in a 2-dimensional experiment in a flat soil tank, it was found that about 50% of the soil could be cleaned up. Work is continuing to improve further the efficiency of this process.

Soil Mixing

Work is continuing in the field of geoenvironmental applications of soil mixing. This work was initiated from a research and development project funded by the Department of the Environment and industry. The work involved the development and application of an in-situ treatment methodology for a contaminated site in West Drayton, Middlesex which is contaminated with a variety of heavy metals and organic compounds. The treatment involves physical and chemical immobilisation of the contaminants with cement-based grouts injected using specially designed soil mixing augers. Details of the results were published in the ICE Journal of Geotechnical Engineering in early 1998 (1 - Al-Tabbaa, A. and Evans, C. W. (1998) Pilot in situ auger mixing treatment of a contaminated site: Part 1; Treatability study. Proceedings of the Institution of Civil Engineers, Geotechnical Engineering. 131, Jan., pp52-59. 2 - Al-Tabbaa, A., Evans, C. W. and Wallace, C. J. (1998) Pilot in situ auger mixing treatment of a contaminated site.
Part 2: Site trial. Proceedings of the Institution of Civil Engineers, Geotechnical Engineering, 131, April, pp 89-95.).

Following the completion of the project the two industrial partners treated a contaminated site commercially for the first time in the UK(G13). Recent work included testing cored site samples over a 28 month period after treatment and the results have been accepted for publication. Duplication of the project work in the laboratory using laboratory-scale model augers was then carried out to produce correlation between laboratory-scale and full-scale soil mixing and also to examine the effect of individual contaminants on the additives used(G4).

Work on the application of soil mixing to in-situ bioremediation using biofilm technology in order to combine immobilisation with eventual treatment has just been completed as a PhD project at Birmingham University. Another PhD project was carried out on contaminant transport and in-situ immobilisation using soil mixing in stratified sands(G3). The results of this work will be published in two papers in the Journal of Hazardous Materials.

More recent work has concentrated on the effectiveness of overlapping zones of soil-mixed columns and dry soil mixing and the results were submitted to the International Conference on Dry Mixing Methods in Stockholm in October 1999.

Re-use of Waste Materials

Work on the re-use of waste tyre in soil-tyre mixtures was initiated a few years ago and a summary of the work carried out to date has been published(G1). The feasibility of using natural clay-tyre mixtures in landfill liners was investigated in terms of properties such as strength, permeability, stress-strain behaviour, swelling and swelling pressure(G2). Geo environmental applications of sand-tyre mixtures as permeable barrier materials and sand-tyre-cement or sand-tyre-clay in low permeability barrier materials then followed as fourth year projects and the results have been submitted to relevant conferences. The re-use of tyre, peat, sawdust and straw as permeable barrier material was investigated as part of an MPhil thesis.

Soil Mechanics

Soil Characterisation and Element Testing

Investigation of time effects on soil behaviour, supported by EPSRC, continues. The effect of creep on the small strain stiffness, and stiffness degradation, of London clay has been investigated using the advanced triaxial loading system with P- and S-wave velocity measurements. Ageing and creep of sands have been
measured in triaxial compression and extension to identify the causes of increasing pile shaft capacity with time. The development of a new hollow cylinder torsional apparatus is near completion.

A micromechanics model was developed to model the stress dependent elastic modulus observed in the soil. Theoretical investigation indicates that the surface roughness of soil particles needs to be modelled to match the observations made in the laboratory(G37).
A constitutive model for natural soils has been developed. This model relates the change in anisotropic fabric on soil structure degradation during yielding and includes the stiffness degradation inside the yield surface using the subloading surface concept proposed by Hashiguchi.

Clastic Mechanics

The reassessment of the principles of soil mechanics in view of the crushability of grains continues. Conventional thinking in soil plasticity contrasts "isotropic hardening" with "kinematic hardening", neither concepts being well-named because neither have been understood at a micro-structural level. A new understanding(G29) has emerged of "isotropic hardening" arising from irrecoverable plastic compression due to grain-splitting and void-filling. This has led to a re-evaluation(G28) of "kinematic hardening" as elastic softening, with loss of shear contact stiffness arising from grain slippages due to local inhomogeneity arising from differences in grain size. Applications in the understanding of press-in pile driving(G27) are being studied in collaboration with Giken Seisakusho Limited of Japan.

Geotechnical Analysis

Numerical Analysis of Porous and Granular Media

Numerical modelling of pipeline-soil interaction continues with support from Tokyo Gas, as part of the International Collaborative Soil/Pipe Interaction Project. Advanced soil models have been implemented into a finite element program for the research. The effects of soil model and boundary conditions on the behaviour of pipe and soil were investigated for various loading cases (lateral, uplift, downward, axial drag and surface loading). The numerical results were compared with the controlled laboratory experiments.

Finite deformation consolidation has been implemented into a finite element code using the multiplicative decomposition technique proposed by Simo. The finite deformation Cam-clay model was developed to model
the behaviour of soft clays and the finite element equations of the coupled soil deformation and pore fluid movement have been formulated. The work also includes the finite element implementation of the contaminant transport equation in a deforming soil medium. The developed program has been used to investigate the effect of consolidation on contaminant transport in mineral wastes.

Numerical Analysis of Soil-Foundation Interaction

Dr A. Al-Tabbaa

Numerical analyses, in parallel with experimental work, are being carried out on the problem of the design of piled foundations in consolidating and swelling clays in order to minimise the use of reinforcement, and hence costs. The analyses incorporate the use of a realistic soil model which predicts the behaviour of clay in overconsolidated stress states by modelling it as an elasto-plastic material rather than a purely elastic material, which is common practice. Three-dimensional analyses have been initiated and are being compared with axisymmetric analyses. Experimental work is being carried out in the centrifuge using an instrumented pile. The change in the weight of the soil at different gravities is being used to cause downdrag and uplift of the soil. Tests have modelled end-bearing piles, and future tests will model floating piles and pile groups.

Analyses of Pressuremeter Tests

Work on the non-linear analysis of pressuremeter rebound loops has been published(G6). A simple closed-form solution based on a power-law model for stress-strain has proved useful in defining engineering design parameters.

Bio-Mechanics of Cellular and granular Media

Bone Grafts

Dr S.P.G. Madabhushi

Collaboration with Princess Margaret Rose Orthopaedic hospital in Edinburgh continues. As a part of this collaboration a new shear testing (CAM-Shear) apparatus was developed specifically to establish the constitutive behaviour of bone graft(G7). This apparatus is currently being used to test both the natural (sterilised) bone graft as well as artificial materials currently being developed in the Pharmaceutical Industry. Also the mechanical strength of the washed bone graft was compared to that of natural bone graft(G11,G12). Research is currently being planned to study the stability of bone graft in both revision Total Hip Arthoplasties and Acetabulum repairs. Results from the experimental study are being compared to those from animal model
studies(G10). Further, research into determining the mean pore size of the compacted bone graft is underway.

Brain Damage

Collaboration with the Wolfson Brain Imaging Centre continues. Finite element analysis of the brain leads to insights regarding the sources and evolution of brain damage due to a variety of causes such as hydrocephalus(G31), stroke, tumour growth, oedema, and a blow to the head.

Field Studies

Site Investigation

Pore water pressure buildup and dissipation is one of the most important soil behaviour characteristics that influence the movement of geotechnical structures. This depends critically on the in-situ permeability. A novel in-situ permeability measurement technique has been developed in collaboration with Cambridge Insitu. The system utilises the self-boring technique in order to minimise soil disturbance during the installation of the permeameter and allows estimation of both vertical and horizontal permeability of cohesive soils. Some preliminary field testing has been performed in Gault clay. Numerical analysis has been performed to determine appropriate shape factors for various test geometries. As part of field investigation, rotary cored samples have been obtained and they will be used to measure the permeability in the laboratory.

Work has continued on the EPSRC project "Investigation of ground loading applied to an old London Underground Ltd (LUL) tunnel" in conjunction with London Underground and Geotechnical Consulting Group. The aim of the project is to assess the long-term ground-loading acting on tunnel linings in London Clay. A tunnel, which is part of the Kennington Loop on the Northern Line, was identified as being suitable for detailed field measurements. In order to determine the in-situ soil parameters, a series of self-boring load-cell pressuremeter tests and self-boring permeameter tests was performed. Other ground investigation included rotary-cored sampling for advanced soil testing and the installation of vibrating-wire piezometers from the ground surface and from inside the tunnel. The information obtained is to be used to interpret the long-term behaviour of the ground and of the tunnel lining and to assess the implications for current tunnel design methods(G14).

Displacement Piles

Research has been carried out on a newly developed helical displacement piling system funded by industry. The investigation was carried out at laboratory-scale using model augers. Different auger heads were manufactured and compared in terms of the physical integrity of the constructed pile. Piles were loaded to failure and their behaviour was investigated in terms of the load-displacement curves and compared in terms of the auger head design and clay strength. The results were then compared with those from full-scale pile tests.

Construction Processes

Work has continued on the geotechnical aspects of the design and construction of tunnels in soft ground(G26), the use of numerical methods to simulate tunnelling and deep excavations(G16,G32), and the application of compensation grouting to control movements of the ground and of buildings(G15). In July 1999, Professor Robert Mair was invited by the Japanese Geotechnical Society to give one of the three International Lectures in Tokyo on the occasion of their 50th anniversary celebrations. The title of his Lecture was `Recent Advances in Geotechnical Aspects of Tunnelling in Soft Ground - Experiences from the Jubilee Line Extension Project'.

Previous work on hydro-fracture observed in centrifuge models has been published(G9). The hydro-fracture process arises with compensation grouting during tunnelling which is the subject of the on-going EC funded COSMUS project, in collaboration with Soletanche-Bachy, Tractabel, Glotzl, CEA-LETI and EPFL, which is in its final year. The project aims to develop a tunnel construction system using improved monitoring techniques (such as fibre optic strain measurement sensors), a soil characterisation system and an advanced computer simulation model(G17,G33). The use of an instrumented borehole drilling technique called ENPASOL as a ground investigation tool has been investigated at Kennington Park, London. Drilling parameters recorded from the site were analysed using various empirically derived correlations. The analyses with signal processing revealed that the recorded drilling parameters correlated well with the soil formation changes and the strength properties.

Studies of the effects of compensation grouting on tunnel linings have continued with support from Nishimatsu Construction. Field monitoring was performed at the Docklands Light Railway Extension tunnel construction site at Greenwich, London. Measurements of surface settlements and displacements of the tunnel lining were made during the construction of the tunnel(G34,G35). Centrifuge modelling of the problem has been undertaken and the influences of width of the grouted zone and its distance above the tunnel have been explored(G18).

Work on penetrometers and pile-driving continues with centrifuge model tests(G5), 1g physical models, and field tests conducted in Japan in association with Giken Seisakusho Limited of Kochi. Previous modelling work related to soil stabilisation, conducted by Dr K. Omine as an academic visitor, has been published(G30)

G1. Al-Tabbaa, A. Geoenvironmental applications for soil-tyre mixtures. Ground Engineering, 31, (11), 24-25 (November 1998).

G2. Al-Tabbaa, A., Aravinthan, T. Natural clay-shredded tire mixtures as landfill barrier materials. Waste Management, 18, (1), 9-16 (October 1998).

G3. Al-Tabbaa, A., Ayotamuno, J.M., Martin, R.J. Contaminant migration and immobilisation in stratified sands. Ground Engineering, 31, (11), 24-25 (November 1998).

G4. Al-Tabbaa, A., Evans, C.W. Laboratory-scale soil mixing of a contaminated site. Ground Improvement, 3, (3), 119-134 (1999).

G5. Bolton, M.D., Gui, M.W., Garnier, J., Corte, J.F., Bagge, G., Laue, J., Renzi, R. Centrifuge cone penetration tests in sand. Geotechnique, 49, (4), 543-552 (1999).

G6. Bolton, M.D., Whittle, R.W. A non-linear elastic/perfectly plastic analysis for plane strain undrained expansion tests. Geotechnique, 49, (1), 133-141 (1999).

G7. Brewster, N.D., Brewster, W.J., Howie, C.R., Madabhushi, S.P.G., Usmani, A.S., Fairburn, D.R. Mechanical considerations in compaction bone grafting during revision total hip replacement. Journal of Bone and Joint Surgery - British Volume, 81B, (1), 118-124 (1999).

G8. Carrier, M., Soga, K. A four terminal measurement system for measuring the dielectric properties of clay at low frequencies. Engineering Geology, 53, (2), 115-123 (1999).

G9. Chin, C.Y., Bolton, M.D. Factors influencing hydro-fracture in clay. Proceedings, 13th ASCE Engineering Mechanics Conference, Baltimore, MD, USA (June 1999). (CD ROM, edited by Jones N.P., Ghanem R.G.)

G10. Dunlop, D.G., Griffon, D., Howie, C.R., Madabhushi, S.P.G., Usmani, A.S., Gillespie, W.J. An ovine model to evaluate pellets of new synthetic bone graft substitutes. British Orthopaedic Association Annual Congress, Glasgow (September 1999).

G11. Dunlop, D.G., Howie, C.R., Madabhushi, S.P.G., Usmani, A.S. Factors influencing impacted bone graft strength - to wash or not to wash. British Orthopaedic Association Annual Congress, Glasgow (September 1999).

G12. Dunlop, D.G., Howie, C.R., Pankaj, P., Madabhushi, S.P.G., Usmani, A.S. Mechanical aspects of impaction grafting in THR - the effect of particle size distribution, additives and washing. 4th Congress of the European Federation of National Associations of Orthopaedics and Traumotology (EFORT), Brussels (June 1999).

G13. Evans, C.W., Al-Tabbaa, A. Remediation of contaminated ground using soil mix technology: from research to commercialisation. Proceedings, 2nd British Geotechnical Society Geoenvironmental Engineering Conference: Ground Contamination, Pollution Management and Remediation, London (September 1999); Edited by R.N. Yong, H.R. Thomas, 376-383 (Thomas Telford, London, 1999).

G14. Gourvenec, S.M., Bolton, M.D., Soga, K., Gui, M.W., Mair, R.J., Edmonds, H., Chudleigh, I.L.J., Butler, A.P. Field investigations of longterm ground loading on an old tunnel in London clay. Proceedings, International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground, IS-Tokyo 99, Tokyo, Japan , 179-184 (July 1999).

G15. Harris, D.I., Mair, R.J., Burland, J.B., Standing, J. Compensation grouting to control tilt of Big Ben clock tower. Proceedings, International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground, IS-Tokyo 99, Tokyo, Japan, 185-192 (July 1999).

G16. Higgins, K.G., Fernie, R., Potts, D.M., Houston, C., Mair, R.J., St John, H.D. The benefits of using advanced numerical methods throughout the design and construction of a road scheme. Proceedings, AGS (Association of Geotechnical and Geoenvironmental Specialists) Seminar on the Value of Geotechnics in Construction, London, 101-104 (November 1998).

G17. Komiya, K., Soga, K., Akagi, H., Hagiwara, T., Bolton, M.D. Finite element modelling of excavation and advancement processes of a shield tunnelling machine. Soils and Foundations, 39, (3), 37-52 (1999).

G18. Lee, S.W., Dasari, G.R., Mair, R.J., Bolton, M.D., Soga, K., Sugiyama, T., Ano, Y., Hagiwara, T., Nomoto, M. The effects of compensation grouting on segmental tunnel linings. Proceedings, International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground, IS-Tokyo 99, Tokyo, Japan, 217-222 (July 1999).

G19. Madabhushi, S.P.G. Centrifugal modelling of dams subjected to earthquake induced hydro-dynamic pressures. Proceedings, 11th European Conference on Earthquake Engineering, Paris, France (September 1998).

G20. Madabhushi, S.P.G. Centrifuge modelling of bridge foundations on liquefiable soils. Structural Dynamics: Proceedings, 4th European Conference on Structural Dynamics (EURODYN 99), Prague, Czech Republic (June 1999); Edited by L. Fryba, J. Naprstek, chapter 196, 995-1000 (A.A. Balkema, Brookfield, VT, USA, 1999). ISBN 9058090566.

G21. Madabhushi, S.P.G. Recent development of an earthquake actuator for use on geotechnical centrifuges. Proceedings, 11th European Conference on Earthquake Engineering, Paris, France (September 1998).

G22. Madabhushi, S.P.G. Recent developments in dynamic centrifuge modelling. Proceedings, Symposium on Geotechnics in the New Millenium - An Imperial College Perspective, London (September 1999).

G23. Madabhushi, S.P.G. Seismic behaviour of dams subjected to earthquake induced hydro-dynamic forces. Earthquake Geotechnical Engineering: Proceedings, 2nd International Conference on Earthquake Geotechnical Engineering, Lisbon, Portugal (June 1999); Edited by P.S. Secoe Pinto, chapter 162, 649-654 (A.A. Balkema, Brookfield, VT, USA, 1999). ISBN 9058091163.

G24. Madabhushi, S.P.G., Haigh, S.K. Finite element modelling of pile foundations subjected to pull-out. Proceedings, 4th European Conference on Numerical Methods in Geotechnical Engineering, Udine, Italy (October 1998).

G25. Madabhushi, S.P.G, SOGA, K., BOLTON, M.D. Recent advances in seismic geotechnics in Cambridge. Workshop on Earthquake Effects on Structures and Monuments, Cambridge (December 1998).

G26. Mair, R.J. Design and construction of tunnels in soft ground. Geotechnical Engineering for Transportation Infrastructure: Proceedings, 12th European Conference on Soil Mechanics and Geotechnical Engineering, Amsterdam, the Netherlands (June 1999); Edited by F.B.J. Barends, et al, 3, 1915-1921 (A.A. Balkema, Rotterdam, 1999). ISBN 9058090477.

G27. McDowell, G.R., Bolton, M.D. Effect of particle size distribution on pile penetration in calcereous sand in the geotechnical centrifuge. Proceedings, 4th International Conference on Deep Foundations Practice (including Piletalk International '99), Singapore (July 1999).

G28. McDowell, G.R., Bolton, M.D. A micro mechanical model for isotropic cyclic loading of isotropically elastically compressed soil. Granular Matter, 1, (4), 183-193 (1999).

G29. McDowell, G.R., Bolton, M.D. On the micro-mechanics of crushable aggregates. Geotechnique, 48, (5), 667-679 (1998).

G30. Omine, K., Ochiai, H., Bolton, M.D. Generalised two-phase mixture model and its applications to composite ground. Memoirs of the Faculty Engineering, Kyushu University, 58, (2), 83-109 (1998).

G31. Pena, A., Bolton, M.D., Whitehouse, H., Pickard, J.D. Effects of brain ventricular shape on periventricular biomechanics: a finite element analysis. Neurosurgery, 45, (1), 107-118 (1999).

G32. Samuel, H., Mair, R.J., Lu, Y.C., Chudleigh, I.L.J., Addenbrooke, T.I., Readings, P. The effects of boring a new tunnel under an existing masonry tunnel. Proceedings, International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground, IS-Tokyo 99, Tokyo, Japan, 263-268 (July 1999).

G33. Soga, K., Bolton, M.D., Au, S.W.K.A., Komiya, K., Hamelin, A., Van Cotthem, A., Buchet, G., Michel, J.P. Development of compensation grouting modelling and control system. Proceedings, International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground, IS -Tokyo 99, Tokyo, Japan, 405-410 (July 1999).

G34. Sugiyama, T., Hagiwara, T., Nomoto, T., Nomoto, M., Ano, Y., Mair, R.J., Bolton, M.D., Soga, K. Observations of ground movements during tunnel construction by slurry shield method at the Docklands light railway Lewisham extension - East London. Soils and Foundations, 39, (3), 99-112 (1999).

G35. Sugiyama, T., Nomoto, T., Nomoto, M., Ano, Y., Hagiwara, T., Mair, R.J., Bolton, M.D., Soga, K. Applications of compensation grouting to the Docklands light railway Lewisham extension project in London. Proceedings, International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground, IS-Tokyo 99, Tokyo, Japan, 287-292 (July 1999).

G36. Treadaway, A.C.J., Lynch, R.J., Bolton, M.D. Pollution transport studies using an in-situ fibre optic photometric sensor. Engineering Geology, 53, (2), 195-204 (1998).

G37. Yimsiri, S., Soga, K. Effect of surface roughness on small-strain modulus: micromechanics view. Pre-failure Deformation Characteristics of Geomaterials: Proceedings, 2nd International Symposium, IS Torino 99, Torino, Italy (September 1999); Edited by M. Jamiolkowski, R. Lancellotta, D. Lo Presti, 597-602 (A.A. Balkema,

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Last modified: July 2000