Servicio de Información Comunitario sobre Investigación y Desarrollo - CORDIS


SELFRAC Informe resumido

Project ID: FIKW-CT-2001-00182
Financiado con arreglo a: FP5-EAECTP C
País: Belgium

Plate test - In-situ test at Mt Terri

In the underground laboratory of Mont Terri, a comprehensive study of the EDZ has been carried out. The observed induced fractures, which generally have been created under local tension, led to an increase of the local permeability (several orders of magnitude) in the vicinity of the tunnel. At several locations, the behaviour of the disturbed region was observed during water circulation in the EDZ. During this re-saturation phase a significant reduction (1-2 orders of magnitude) of the permeability was measured, probably due to swelling of the clay, but the EDZ still showed a higher permeability in comparison to the intact rock mass.

This observation is not in agreement with laboratory measurements on core samples in a triaxial pressure cell where a nearly perfect self-sealing of fractured rock samples was observed. This discrepancy could be explained by the effect of normal stress on the fracture planes in the laboratory tests which is not present in situ in the vicinity of the tunnel.

Within this in-situ test, the effect of a normal load on the tunnel wall is studied. In a real repository the waste canister is surrounded by a highly compacted bentonite buffer that will swell if water flows in the near field of the disposal tunnel. The swelling pressures expected of a high-level waste repository will be in the order of several MPa and will possibly reach the lithostatic pressure in an equilibrium. This effect is studied under controlled boundary conditions where the load on the EDZ is applied with loading plate equipment in the tunnel. The load plate covers a region in the tunnel where transmissive features have been observed and characterised.

The in situ experiments performed in Opalinus Clay show that the effective hydraulic conductivity of the EDZ is expected to be relatively quick, within several years, lower than 10-10m/s as soon as the bentonite backfill of the emplacement drifts becomes fully saturated and the expected swelling pressure will be build up.

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