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Methodology Studies on Sealing of Boreholes in Crystalline Rocks

Objective

The objective of the study is the theoretical design of an in-situ borehole-sealing technique that is applicable to fractured crystalline rock, as well as its subsequent implementation. The sealing or backfilling of boreholes in, or around, sites for the disposal of radioactive waste, usually is done with compacted bentonite, or a bentonite or cement slurry. It is proposed to design a special product that combines a bitumen emulsion with clay and other substances. A fracture identified in crystalline rock will be selected for injection testing. The fracture space, measured in drill cores, will be studied in the laboratory and the data will be processed statistically. Tests with water will enable the study of the hydraulic behaviour of the fracture, before and after slurry injection, to define the efficiency of the method.
The objective of the work is the design and implementation of an in situ borehole sealing technique in crystalline rocks. The sealing or plugging of boreholes on or around a site for storing radioactive waste is usually done by means of compacted bentonite, a bentonite grout, or a grout consisting of binders. It is proposed to manufacture a binder to which are added a bitumen emulsion, clay, and various other substances. A fracture will be identified in crystalline rock and will be sampled by means of drilling. Fissure space will be studied in the laboratory and data will be geostatistically processed. Water tests will be carried out to define the hydraulic behaviour of the fracture. Before and after injecting the special grout mixture into the fracture via one of the boreholes, tomography will identify the injection zone. Core sampling of the injected fracture will enable to verify the quality of injection.

The choice of grout constituents led to selection of 4 cement types, two types of blast furnace slag, microsilica, 2 types of lime and 2 commercial bentonites. Injection tests with bentonite grout (Tixoton-Na) were carried out. The results show that fissures with an average width of 0.1 mm can be injected, but that the injection in boreholes seem limited because of the rapid attenuation with depth of the dynamic injection oscillations.
Work programme:

- Bibliographical compilation and synthesis of earlier works.
- Laboratory tests for optimization of the slurry composition.
- In-situ tests of the fracture (geophysics, water injection) and laboratory work (definition of the fracture space on core samples).
- Slurry injection into the fracture, geophysical estimation of its penetrability, and quality control of the injection by means of sample studies and water tests.

Coordinator

Bureau de Recherches Géologiques et Minières
Address
Avenue De Concyr
45060 Orléans - La Source
France

Participants (2)

Mott Macdonald Ltd
United Kingdom
Address
20-26 Wellesley Road
CR9 2UL Croydon
Société Sondages Injections Forages (SIF) Entreprise Bachy
France
Address
4 Rue Ste Claire Deville- Les Colonnades
92563 Rueil-malmaison