Professor Chitral Wijeyesekera has over 35 years' experience in teaching, research and consultancy in Civil Engineering. After obtaining a first class honours degree in Civil engineering from the University of Ceylon (1968), he subsequently read for his MSc and PhD at Imperial College of Science and Technology (University of London). He has been on the academic staff of the University of East London and its predecessor Polytechnics since 1975 and has close associations with the pipelines development work initiated by Professor Charles Lawrence of UEL. He maintains collaborative research links with many UK (Oxford, Cambridge, Imperial College, Nottingham Trent) and overseas (Brunei, Japan, Malaysia, Singapore and Sri Lanka) Universities, Water Utility companies (Thames Water) and field research centres (RECESS in Malaysia). He has published widely and written over sixty publications. He has been consulted as an expert witness in pipe failure cases.

He was the lead academic from UEL, an UK partner on an EC funded SMT project on Buried GRP pipes and is the lead academic on a current Framework 4 EC project on GRP Flanges. The outcomes of these projects provide assistance in the drafting of European Standards for Glass Reinforced Plastic pipes. He has also been the lead academic on a Teaching Company Scheme and has a similar role on a current Knowledge Transfership Programme with Rawell Environmental Ltd., based in Liverpool. He is research active and currently directs the research of five PhD research students particularly in the areas of soil structure interaction, the physical and numerical modelling of soil pipe interaction, Physico chemical properties of soils leading to soil cracking and contaminant migration characteristics of geo barriers used in landfill sites.

He teaches Geotechnics to undergraduates and postgraduates and is the co-ordinator for MSc Civil Engineering Research Projects.

2003 – Present    MSc Year Tutor , MSc Project Co ordinator

• Soil Structure interaction
• Pipeline failures
• Soil mineralogy and microstructure

• BEng (Hons) Civil Engineering
• MSc Civil Engineering
• MSc Pipeline Engineering

• CE3103 Geotechnics 3
• CEM4 Soil Structure Engineering
• CEM9 Site investigations and ground exploration
• CEM7Highway and Transportation Engineering
• CEM11 Research Dissertation co-ordinator

1. "Settlement induced failures of plastic and other pipes", accepted for Plastic pipes XII, Italy, April 2004.
2. "Photoelastic method to determine residual stress profiles in pipes", accepted for Plastic pipes XII, Italy, April 2004.
3. "Manufactured aggregate as improved backfill material for plastic pipes", Plastic pipes XII, Italy, April 2004.
4. "Use and performance of bentonite in geosynthetic clay liners",Keynote paper, International Conference on Geoenvironmental Engineering, Singapore, December 2003
5. "Cation exchange capacity and swelling characteristics of geosynthetic clay liners", Problematic soils conference, Nottingham, July 2003.
6. "On-line learning - supervision- assessment of MSc research dissertations", Second Annual Joint UK & USA Conference - Scholarship of Teaching & Learning, London, May 2002.

1. "Cation exchange capacity and swelling characteristics of geosynthetic clay liners", Problematic soils conference, Nottingham, July 2003.
2. "On-line learning - supervision- assessment of MSc research dissertations", Second Annual Joint UK & USA Conference - Scholarship of Teaching & Learning, London, May 2002.
3. "The significance of cation exchange and desiccation on the performance of geosynthetic clay liners", 8th International Waste Management and Landfill symposium, Sardinia 2001.
4. "Soil-structure-pipe interaction with particular reference to ground movement induced failures", Plastic pipes XI, pp 941-950, Munich, Germany, September 2001.
5. "Design & performance of a compacted clay barrier through a landfill", Engineering Geology, Vol 60, Nos 1-4, Special issue on Geoenvironmental Engineering, p295-306, Pubs Elsevier, 2001.
6. "Swelling and suction properties of compacted European clays", International Symposium on Suction, Swelling, Permeability, and Structure of Clays., IS- Shizuoka 2001, in Adachi K & Fukue M (eds) Clay Science for Engineering, pp 101-107, Japan. 2001.
7. "Cracking in clays with an image analysis perspective", International Symposium on Suction, Swelling, Permeability, and Structure of Clays., IS- Shizuoka 2001, in Adachi K & Fukue M (eds) Clay Science for Engineering, p295-306, Japan. 2001.
8. "Ko development in kaolinite-bentonite mixtures", GeoEng 2000, p 506, Melbourne , Australia, 2000.
9. "Effects of soil arching on the behaviour of flexible pipes buried in trenches of varying widths", GeoEng 2000, p 162, Melbourne, Australia , 2000.
10. "Design & performance of a compacted clay barrier for Heathrow Express Rail Link", in Yong R N a& Thomas H R (eds) , Geoenvironmental Engineering; Ground Contamination : pollutant management and remediation, pp39-46, 1999.
11. "Design & performance of a compacted clay barrier for Heathrow Express Rail Link" Proceedings 2nd BGS Geoenvironmental Engineering Conference, Institution of Civil Engineers, London, Pubs. Thomas Telford, 1999.
12. "Numerical analysis and soil box study of the influence of trench width on the behaviour of buried GRP pipes", Plastic Pipes X - Plastic Pipes for the Millenium, p 857-865, Goteborg, Sweden, September 1998.
13. "Geotechnical characteristics of kaolin-bentonite mixtures" in Yanagisawa E, Moroto N & Mitachi (Eds) Problematic Soils , Vol 1 , pp 265-269, Pubs Balkema, 1998.
14. "Compaction and Suction characteristics of Hamburg Klei", Proc. 2nd International Conference on Ground Improvement techniques, pp 529-536, Singapore, 1998.
15. "Numerical analysis and soil box study of the influence of trench width on the behaviour of buried GRP pipes", Plastic pipes X- Plastic pipeline for the millenium, Goteborg, Sweden, 1998.
16. "The Significance of dilatancy of the backfill on the soil structure interaction of polypropylene reinforcement", Proc. 2nd International Conference on Ground Improvement techniques,pp 537-544, Singapore, 1998.
17. "A Three level Finite Difference Analysis of the Large Strain One Dimensional Consolidation Equation", Geotechnical Journal, Vol. 2 No 1, pp1-13, 1998.
18. "Compacted clay barrier design for a tunnel surround in a landfill site", in Pedro Seco e Pinto , (eds) Environmental Geotechnics,.vol 2, pp417-422, Pubs A A Balkema Rotterdam, 1998.
19. "Microstructrural viewpoint of sample disturbance in micro concrete", co author 23rd Conference on Our World in Concrete & Structures:,pp 43-50, Singapore, August 1998.
20. "Physical and Numerical Modelling of Pull-out Resistance in Reinforced Earth", Proceedings of the International Conference on Ground Improvement Techniques, p 631-640, Macau, May 1997.
21. "Compacted Clayey Fill; An Assessment of Suction, Swell Pressures, Shrinkage and Cracking Characteristics", Proceedings of the International Conference on Ground Improvement Techniques, p 621-630, Macau, May 1997.
22. "Continuing Engineering Learning through Employment, Deployment and Unemployment", co author to a paper being submitted to the Society for Research into Higher Education, University of York, December 1994.
23. "Development of Lateral Earth Pressure Coefficient at rest in consolidating clays", Paper presented at the 3rd International Conference on Deep Foundation Practice incorporating Piletalk International '94, Singapore, May 1994.
24. "Ko state - It's significance and application in soil structure design", Paper presented at the 3rd International Conference on Deep Foundation Practice incorporating Piletalk International '94, Singapore, May 1994.
25. "Development of Ko in soft soils", co author to a paper in Geotechnique vol 44, 1994.
26. "Polytechnics become Universities in UK", Press article, The Sunday Observer, Sri Lanka, April 19,1992.
27. "Review of Ko and its development in consolidating soils", Paper in Professor E. O. E. Pereira Comemorial Volume, Institution of Engineers, Sri Lanka, 1990.
28. "Echoes from the chalk face", co author to a paper presented at the Society for Research into Higher Education, December 1990.
29. "Apparatus for comprehensive experimental study of the deep burial and exhumation of sediments" a co author to an article in American Journal of Science, 1978.
30. "A note on high pressure consolidation of a kaolinitic clay", Bulletin of the American Association of Petroleum Geologists, Vol. 60, No. 2, 1976.
31. "Artificial gravitational compaction of clays", PhD Dissertation, Imperial College, 1975. Report on Mineralogical analysis of samples from Kariba North Development, Zambia. Internal Imperial College report for Sir Alexander Gibb and partners, 1974.
32. "Artificially simulating geological history of clays", co author to an internal technical report, European Research Office, United States Army, 1974.
33. "Report on mineralogical analyses of samples from the Kariba North Development, Zambia", co author to an internal Sir Alexander Gibb & Partners technical report, July 1973.
34. "A comparative mineralogical and fabric study of some kaolinitic clays", MSc Project Report, Imperial College, 1971.
35. "A literature review of the assessment of theoretical rock fabric analysis", MSc Dissertation, Imperial College, 1971.

• Fellow of Geological Society (London)
• Member of Institution of Engineers, Sri Lanka

Use and performance of bentonite in geosynthetic clay liners

Chitral Wijeyesekera, Reader
University of East London, UK

Geosynthetic clay liners (GCLs) are an innovative construction material that has been developed over the last two decades. These composite matting comprise of bentonite with two covering geosynthetics. GCLs are now being popularly specified as "leachate retaining" or "water proofing" membranes within the geo-environmental construction industry. The predominant (approximately 75-90% by weight) clay mineral in bentonite is the three-layered (2:1) clay mineral montmorillonite. High quality bentonites need to be used in the GCL manufacture. The morphology and atomic structure of the montmorillonite clay mineral in sodium bentonite makes it the preferred clay to be used in the manufacture of GCLs. The sodium montmorillonite's characteristic high swelling capacity, high ion exchange capacity and the consequently very low hydraulic conductivity provides the basis for the sealing medium in GCLs. The bentonite in the manufactured GCLs are either in an air dried granulated / powdered form or have been factory prehydrated to a moisture content beyond its shrinkage limit and vacuum extruded to enhance its performance.

These liners with encapsulated high active clay minerals depend on the water balance between the sealing element and the surrounding soil layers. Quantitative mineralogical analyses and an assessment of the adsorbed cation regime should be normally run as part of each site appraisal. The mineralogical and geotechnical differences between sodium and calcium montmorillonite are presented in the paper. Factors affecting the performance of the bentonite in GCLs placed in difficult construction and hostile chemical environments are discussed. Assessment of diffusion coefficients and clay-leachate compatibility assessment is also deemed necessary to ensure acceptable long-term performance.

In this paper, the performance specifications for GCLs are identified and the appropriateness of enhancing the cation exchange capacity with polymer treatment and the need for factory prehydration of the untreated sodium bentonite is emphasised. The advantage of factory prehydrating the ploymer treated bentonite to fluid content beyond its shrinkage limit and subsequently factory processing it to develop laminated clay is to develop a GCL that has enviable sealing characteristics with a greater resistance to geochemical attack and cracking.

Keywords: Bentonite, Ion Exchange, Desiccation, Cation Exchange, Clay mineralogy, GCL, Microstructure

Cation Exchange Capacity and Swelling / Characteristics of Geosynthetic Clay Liners

D C Wijeyesekera,
University of East London, UK

The expansive clay mineral, Montmorillonite is used effectively in the production of geosynthetic clay liners for its applications ranging from water stops to landfill liners. Its efficiency depends on the swelling characteristics of the bentonite clay, which is often mixed with industrial polymers to improve the retention of the swelling behaviour in chemically hostile environments. The sealing ability of geosynthetic clay liners is strongly influenced by environmental conditions and is also a function of the montmorillonite content. Exchangeable cations and water molecules are easily adsorbed by the large electrically charged surfaces on this very finely grained clay mineral.

This paper reports the cation exchange capacities observed for kaolin and montmorillonite after its interaction with sodium chloride and calcium chloride solutions. Cation exchange capacity was measured using the methylene blue adsorption technique, which is based on the principle that cationic dyes will exhibit a Base Exchange in proportion to the clay content in a dispersed clay suspension. The paper also compares the characteristics of the bentonites used in geosynthetic clay liners from four different manufacturers, with particular reference being made to the ASTM standard test method for the determination of the swell index of the clay mineral component in the liner.

The swell characteristics are strongly influenced by the pore fluid chemistry and this is demonstrated in the paper with a view to identifying a relationship between swell and CEC.

Keywords: Cation exchange capacity; Montmorillonite; Kaolinite; Swell; Sodium ion; Calcium ion; Chloride ion

Development of K0 in Soft Kaolin - Montomorillonite Mixtures

Devapriya. C. Wijeyesekera1 and Said. M. Mohamed2

This paper describes the behaviour of soft kaolin-montmorillonite mixtures, with particular reference to the development of coefficient of lateral earth pressure at rest, k0. The presence of bentonite, Fe Montmorillonite increases the consistency limits and consequently enhances the activity of the soil mixture. Ko values of a series of reconstituted and artificially sedimented kaolin-montmorillonite mixtures were determined continuously during one - dimensional consolidation. The samples were consolidated under a constant hydraulic gradient of 0.2 kPa/mm in a purpose built consolidometer and measurements from flush diaphragm transducers gave the total vertical stress and total lateral stress on the sample. The equipment used has previously been described in Ting, Sills and Wijeyesekera (1994).

Effects of Soil-arching on the Behaviour of Flexible Pipes buried in Trenches of varying widths.

Wijeyesekera DC, Warnakulasuriya HS
University of East London, United Kingdom.

The significance of lateral earth loading on flexible pipe design has been previously demonstrated using numerical analysis. The restraint from the side fills of a pipe influences the deformed shape of the pipe. The compaction of the side fill is hindered in narrow trenches. The effects from the lack of compactness of the side fill can not be ignored. The trench width to pipe diameter ratio must be a necessary parameter in the design of buried flexible pipes.

A 2m long, 1.5m high soil box with variable width was used to observe the pipe deformations, pipe strains, normal and shear stresses at the soil-pipe interface of a 2mm thick, 150mm diameter Glass reinforced plastic pipe. Instrumentation was also provided for direct measurement of the horizontal and vertical soil stresses at the boudaries of the trench. Observations of the stress regime at different points on the soil pipe interface and the deformations of the pipe are presented. The soil box test data are complimented with numerical analysis results obtained with Flac3D.

The soil box study relates in practice to a very flexible pipe buried in a trench excavated in rock with surface traction on the trench wall being lower than the angle of friction of the fill. The observations showed that a distinctive soil-pipe system is developed when the initial layers of fill are placed on a very flexible pipe. Numerical modelling results help to further confirm this. This study demonstrates the different ways in which the trench width influences the performance of buried flexible pipes. The rate of increase of soil load/ radial deformation of the pipe with increasing heights of fill, decreases with increasing trench width parameter. In a narrow trench, the proportion of the sharing of the soil load between the pipe and the side fill is increased due to the weakening of the soil arch resulting from the limited soil fill at the springing. A very flexible pipe buried with the above boundary conditions are subjected to higher soil loads and displacements than those buried in a wider trench. Some current design practices under estimate the deflection of very flexible pipes and over estimate the overburden soil load.