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Workreport 2008-66



EDZ Programme, EDZ Studies in ONKALO 2007-2008


Mellanen,S., ed., Koskinen,L., Hellä,P., Löfman,J., Lanyon,B., Öhberg,A., Autio,J., Sacklén,N., Saukkonen,K., Saari,J., Lakio,A., Silvast,M., Wiljanen,B., Vuokko,J. & Lyytinen,T.



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The report introduces viewpoints of EDZ in terms of long term safety, modelling and calculation results to assess the significance of EDZ within ONKALO and documentation of various experiments to develop characterization methods of EDZ.

The programme had the objectives to develop a reliable and proven methodology for characterization of EDZ, to enhance management of rock excavation methods for better control of development of EDZ, and to o assess the impact of EDZ as a flow path and possible passage of radionuclide migration.

The EDZ along the ONKALO may impact the long term safety basically in two ways; by increasing the flow of surface and near surface waters to deeper depths and thus potentially disturbing the geochemical stability at the repository depth and by inducing changes in transport paths and properties. The impact of these changes was studied by means of numerical groundwater flow modeling using EPM (equivalent porous medium) and DFN (discrete fracture network) modelling methods. According to the modelling results, the excavation damaged zone along ONKALO causes only minor changes in groundwater flow rates at the repository depth, transport routes and transport resistance. From the long term safety perspective, the impact of EDZ in the vicinity of the deposition holes is more important and further studies should concentrate on that. The impact of EDZ needs to be assessed relative to other possible flow routes, e.g. connected, transmissive fractures providing fast flow paths and emerging connections to such flow paths through EDZ, other phenomena like spalling potentially increasing the hydraulic conductivity at the buffer/rock or backfill/rock interface, the properties of the tunnel backfill and on the achieved tightness of the interface of the rock and the backfill.

Viability of different investigation techniques for the verification and characterization of EDZ as well as for Quality Control purposes was tested. Ground Penetrating Radar (GPR), measuring of blasting vibration, micro seismic data analysis connected with a drilling campaign were applied and a pilot test of modified Water Loss Measurement was conducted.
Studies concerning characterization of EDZ-properties using rock sampling by core drilling and extraction of block samples by sawing for 14C-PMMA and ultrasound tests were done.

Studies on sub-horizontal fractures below tunnel floor indicated that to achieve more relevant data with higher resolution on the thickness of EDZ, different measuring configuration has to be applied.

The three drilling campaigns and block samples proved effective and useful although some issues were identified for further development.
Small scale Water Loss Measurements were conducted as a pilot test to assess feasibility of testing equipment and procedures. Additional measurements are needed to characterise hydraulic conductivity with better confidence.
Various GPR measurement configurations were tested to prove, whether GPR is a potential tool for quick, non-destructive surveys. However, more investigations are needed to verify that the interpreted zone around the tunnel is EDZ.
Vibration measurements done included uncertainties and the calculated cracking distances the result representing cracking zone in the wall can only be regarded as a rough estimate of EDZ.
The studies of 14C-PMMA and ultrasonic studies are still in progress and will be reported in conjunction of consequent EDZ investigations.
The results must be considered as preliminary due to the fact that some EDZ interpretations (e.g. GPR) must be further studied to confirm the results. Also the number of samples is too limited to draw reliable conclusions.
A consequent investigation project will be necessary to enhance the understanding of potential characterization methods.


EDZ, EPM C, DFN modelling, Flow rates, Mise-a-la-Masse Surveys, Ground Penetrating Radar, TUNNEL SEISMIC Methods, BLASTING Vibration, Micro seismic data analysis, Water Loss Measurement, 14C-PMMA, Ultra Sonic Survey


EDZ Programme, EDZ Studies in ONKALO 2007-2008 (pdf) (6.9 MB)


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