ABSTRACT
In November 1999 Andra began building an Underground Research Laboratory (URL) on the border of the Meuse and Haute-Marne administrative regions in eastern France. The research activities of the URL are dedicated to reversible, deep geological disposal of high-activity, long-lived radioactive wastes in an argillaceous host rock. This paper presents an overview of containment studies, carried out from surface boreholes and underground drifts, and a comprehensive site characterisation strategy for studying containment properties of the Callovo-Oxfordian argillaceous rocks. Results of hydro-chemical and diffusion studies are used to understand the mechanisms of flow in a very low porosity formation and help to understand phenomena such as overpressures or osmotic effects. Use of complementary hydraulic methods for testing hydraulic properties at different scales provides a robust estimate of hydraulic parameters. Factors affecting test interpretations are also presented. When conducting permeability tests, it would be ideal to initiate them in the most stable pressure conditions possible. However, in very low-permeability clay formations (i.e. 10−13 10−14m/s), the pressure disturbances induced by drilling and testing take months or even years to dissipate. The main disturbances affecting transient pressure responses include technological effects due to the test equipment, drilling-history effects, thermal effects, physico-chemical and hydromechanical effects due to interactions between the test fluid and the formation, and mechanical effects due to borehole-wall creep.
