Euradwaste '08 - EU Bookshop - Europa

Disturbed and damaged zones around underground openings - effects induced
by construction and thermal loading
Peter Blümling 1 , Jean-François Aranyossy 2 , Lanru Jing 3 , Xiang Ling Li 4 , Paul Marschall 1 ,
Tilmann Rothfuchs 5 and Tim Vietor 1
Summary
1 Nagra, Switzerland
2 Andra, France
3 KTH, Sweden
4 EURIDICE, Belgium
5 GRS, Germany
The excavation of underground openings will lead to stress redistributions around the cavities
and may induce rock failure in their vicinity. The size of such an excavation disturbed or
damaged zone (EdZ / EDZ) and the impact on hydraulic properties is controlled by the local
(secondary) stress state, the pore pressure development and the physical properties of the host
rock. Besides the geometry of the opening itself and the excavation/support techniques used, a
significant impact on the geometry and characteristics of the EDZ is caused by the heterogeneity
of the host rock, the presence and frequency of any natural discontinuities and the potential
anisotropy of the rock mass.
Laboratory testing and large-scale in-situ mine-by experiments provide an understanding of
the time-dependent development and potential self-sealing processes of the EDZ for different
host rocks. Numerical blind predictions and back-calculations (e.g. within the EC projects
Modex-Rep, CLIPEX and NF-PRO) have increased the confidence in the detailed understanding
of the underlying processes.
After emplacement of waste in a repository and backfilling of the tunnels, the rock experiences
thermal loading. Stress and pore pressure will change and may alter the EDZ. New EC
projects (TIMODAZ, THERESA) have been initiated to extend the geoscientific data bases
for an in-depth understanding of THM coupled processes and to provide advanced modelling
capabilities for assessing the evolution of the EDZ before and after closure of the repository
structures.
1. Introduction
The designing of repositories for radioactive waste depends on host rock properties, state parameters
(e.g. stress, pore water pressure, water saturation) and the waste inventory for disposal. The repository
design has to be able to provide passive safety, which means that, even for very long timescales,
radionuclides have to be isolated or their transport retarded in such a way that guidelines and
regulations are met (e.g. dose to man). The key mechanisms of radionuclide transport and the potential
transport paths from the disposal cells into the biosphere have to be assessed in detail. The
potential transport paths comprise the porespace of the intact rock, transmissive natural fractures,
the backfilled underground structures and the immediate area around those backfilled openings.
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