Download Similarities and differences in the behaviour of plastic and

Similarities and differences in the behaviour of
plastic and indurated clays
G. Volckaert, F. Bernier, X. Sillen, M. Van Geet
SCK•CEN, Belgium
J.-C. Mayor
ENRESA, Spain
I. Göbel
BGR, Germany
P. Blümling
NAGRA, Switzerland
K. Su
ANDRA, France
The interest in clay formations as potential host rock for geological disposal of high level waste and
spent fuel is increasing: besides Belgium, France, Spain and Switzerland now there is also interest
from Germany, Japan and candidate European Union acceding countries like Lithuania and the
Slovak Republic. Currently within Europe there are three clay formations that are studied in detail as
potential host rocks for high level radioactive waste disposal i.e. the Boom Clay in Belgium, the
Opalinus Clay in Switzerland and the Callovo-Oxfordian Clay in France. These clay formations
represent a spectrum from clay with a water content of 40 vol% and relative high plasticity up to
highly consolidated stiff clay stone with a water content as low a 5 vol%. Within the European
Commission (EC) 5th Euratom Framework programme a number of research projects, with in situ
experiments in the URLs HADES and Mt Terri, were launched studying the thermo-hydromechanical behaviour of these different clays. This research has led to insight in the factors
determining the similarities and differences in the behaviour of these clays such as their hydromechanical response to excavation with the creation of an excavation damaged zone (EDZ), the
evolution of the EDZ, the HM response to ventilation and the installation of a bentonite backfill, and
the thermo-hydro-mechanical response to heat. The main factors controlling the THM behaviour are
the clay water content, the clay mineral content (especially the presence of swelling clay minerals),
the very low hydraulic conductivity, the stratification and the degree of cementation mainly due to
carbonates.
The conclusion on the controlling factors is illustrated with results from various EC projects as the
RESEAL project at HADES, the VE (ventilation test), EB (engineered barrier) and HE (heater test)
projects at Mt Terri, the SELFRAC project on healing/sealing of fractures in Boom Clay and
Opalinus clay and the MODEX-REP project on modelling of the excavation response in the CallovoOxfordian clay.
The general increase in understanding of which factors control the THM behaviour of clays
increases also the confidence in clay as option for the geological disposal of radioactive waste.