EB experiment. Laboratory post-mortem analyses report.

Abstract

The EB experiment was run by ENRESA at the Mont Terri Underground Research Laboratory in

Switzerland, starting in October 2000, with the aim of demonstrating that automated

production of a Granular Bentonite Material (GBM) and its emplacement in the upper part of a

clay barrier were feasible (ENRESA 2005). The lower part of the barrier was composed by blocks

of compacted bentonite on which the dummy canister rested. The EB niche excavated in the

Opalinus clay was 15 m long and had a geometry of a horseshoe section, 2.55 m high and 3 m

wide.According to the measurements performed during installation, in the EB test section an average

dry density of 1.36 g/cm3 of the emplaced GBM was obtained, although some segregation

during the emplacement and density inhomogeneities were acknowledged. According to the

laboratory characterization of the GBM (ENRESA 2005), for this dry density value it was

estimated that the hydraulic conductivity was lower than 5·10-12 m/s and the swelling pressure

about 1.3 MPa. The artificial hydration of the buffer material started on May 2002 through a

series of porous tubes that crossed along the GBM and the bentonite blocks as shown in Figure

2. To enhance the water homogeneous distribution, the concrete bed, the surface of the

container and the three rings of the bentonite blocks bed were covered with geotextile.

Hydration was carried out with Pearson water coming from a deposit. The Pearson water is a

predominantly sodium-chloride solution of 19 g/L salinity and has a composition similar to the Opalinus Clay formation pore water.