required to improve understanding of the self-sealing process, particularly for high performance grouts that have been cured for very long times (curing time longer than 2 years). Uncertainty also rests with mature concretes or concretes containing large quantities of silicious materials (i.e., silica fume, silica flour, sand) such as the low-heat, high-performance concrete (LHHPC), where the equilibrium concentration of calcium in its pore water is low compared with standard high-performance concrete (SHPC).

Key words: Nuclear waste, Mechanism, Cement

(ii) Study on the permeability of engineered barriers for the enhancement of a radioactive waste repository system, Tashiro, S., Fujiwara, A. and Senoo, M., Nuclear Technology, Vol.121, No. 1 Jan 1998, pp. 14-23.
     To develop engineered barriers and construction methods for an enhanced radioactive waste repository, an advanced application of cement/concrete and bentonite was studied. On the basis of the tests on fundamental properties of the materials, model structures were prepared by actual construction methods, and then the permeability was evaluated. For cement/concrete, two model silos were constructed by different methods and then the reduction in permeability was evaluated. One was constructed by an ordinary method and then grouted with cement milk containing fine cement and silica fume. The whole permeability of the silo after grouting decreased to one-sixteenth of the value before grouting. The other was constructed by a crack-controlling method. This method could make the whole permeability of the silo as low as one-tenth of that of the cracked silo. For bentonite, a compaction method and a spraying method were examined with a mixture of sodium-type bentonite and sand. To demonstrate these methods, model structures were constructed using full-scale machines. Then the relationship between the dry density and the permeability was examined. For a 20 to 30% bentonite mixture, the permeability was almost equally low for both methods, while the density was lower for the spraying method than for the compaction method. In contrast, for a 10% bentonite content, low permeability could only be obtained with the high-density structure. The permeability of both the concrete structures and the bentonite-sand structures was significantly low as engineered barriers, showing some differences with the structures and their construction methods. Referring to the test results, an engineered barrier system proving low permeability was suggested by a combination of the structures and the construction methods.

Key words: Radioactive wastes, Crack control, Cements, Permeability

(iii) Pilot in situ auger mixing treatment of a contaminated site. Part 1: Treatability study, Al-Tabbaa, A and Evans, C. W., Proceedings of the Institution of Civil Engineers, Geotechnical Engineering, Vol. 131, No. 1 1998, pp. 52-59.
     The work presented in this two-part publication covers certain findings of a research contract and related studies to develop an in situ stabilization/solidification treatment

methodology using auger mixing for a contaminated site at West Drayton. This paper, Part 1, contains the introduction, site details and results of the laboratory treatability study and Part 2 details the prototype auger development, site trial and assessment of the in situ treatment. The objective of the treatability study was to develop soil-grout mixes appropriate for the site soils and in situ application process with emphasis on low cement and grout content. The site investigation work revealed two distinct soil types-made ground and sand and gravel-and a wide range of contaminants. Cement-based soil-grout mixes were developed based on available strength, durability, permeability, compressibility and leachate pH design criteria. Constituents of the soil-groutmixes, which included cement, pulverized fuel ash and lime, and their ratios were varied. Contradicting requirements for satisfying some of the criteria meant that the developed mixes had to be a compromise. The applicability for stabilized contaminated ground of the permeability and freeze-thaw durability criteria considered was questioned. The work resulted in the selection of seven mixes for the site trial, detailed in Tables 3 and 8.

Key words: Cement, Treatability

(vi) Pilot in situ auger mixing treatment of a contaminated site. Part 2: Site, Al-Tabbaa, A., Evans, C. W. and Wallace, C.J., Proceedings of the Institution of Civil Engineers, Geotechnical Engineering Vol. 131 n 2 Apr 1998, pp. 89-95.
     This paper, Part 2 of a publication, presents details of the auger development, site trial and assessment of the in situ treatment of a pilot in situ auger mixing treatment of a contaminated site. A prototype auger, 0·6 m in diameter and 2·4 m long, consisting of cutting flights and mixing rods, was designed and manufactured to produce homogeneous mixing of the soil and grout with minimal exposure of contaminated material. In the site trial, the seven soil-grout mix formulations proposed at the end of the treatability study, detailed in Part 1, were applied. A total of 23 overlapping soil-grout columns were constructed with minimal problems treating around 14 m³ of contaminated ground and resulting in a small overall volume increase of around 7%. The work presented in this two-part publication demonstrates the importance of the initial laboratory treatability study in identifying suitable soil-grout mixes and suggesting modifications to the in situ application process. The pilot study demonstrated that combined treatability study and in situ trials are an essential part of full-scale treatment methodology.

Key words: Augers Grouting, Contaminated site

(i) Control of settlement by compensation grouting - Jubilee Line in London, Essler, R. D., Proceedings, Big Digs Around the World, GSP No. 80, ASCE, 1998, pp. 398-417.
     The paper describes the development of Compensation grouting in the United Kingdom during the construction of the Jubilee Line extension (JLE). The merits of various injection systems used for Compensation grouting are discussed and it is shown that close to tunnels a fluid grouting system is more favourable. The development work carried out during the construction of Contract 104 of the JLE is described and some