Water pressure FEBEX tests

Based on the available geological, hydraulic and mechanical characterizations of the Site as well as on results of hydraulic tests performed on boreholes, a hydro-mechanical model for the zone around the FEBEX tunnel was to be prepared. Using this model, changes in water pressure induced by the boring of the FEBEX tunnel in the near vicinity, as well as the total water flow rate to the excavated tunnel was required. 

In the FEBEX project blocks made of Ca-bentonite are tested for their suitability in radioactive waste isolation. This material has been tested in various laboratory experiment to identify the material parameters. The modelling of gas and water flow in engineered barriers demands beneath the intrinsic permeability and porosity constitutive equations for capillary pressure and relative permeabilities. 

In laboratory experiments specimens from the FEBEX bentonite with a height of 0.13 m and a diameter of 0.15 m have been tested. In a series of tests the specimens have been subjected to different combinations of heating and water injection. In one of these tests the specimen had an initial dry density of about 1.65 g/cm and an initial water content of 13.1 %. At the bottom end of the specimen water has been injected with a pressure of 1 MPa and after 148 d the distribution of water content along the height of the specimen has been measured, DECOVALEX III (2001). 

This test has been modeled with RockFlow/ RockMech in ID to check the chosen hydraulic parameters for the modeling of the FEBEX in situ experiment. The capillary pressure curve has been set as shown in Figure 3. Relative permeability for gas has been developed from the experimental results shown in Figure 4. Relative permeability for water has been assembled from the dependency on saturation and swelling pressure and an additional factor c. 

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