Euradwaste '08 - EU Bookshop - Europa
Euradwaste '08 - EU Bookshop - Europa Euradwaste '08 - EU Bookshop - Europa
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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. 203
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