Fracture flow DEM modelling for tentative estimation of the pressure field behaviour and inflow in ONKALO nuclear repository
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Journal Title
Journal ISSN
Volume Title
School of Engineering |
Authors
Date
2013
Department
Major/Subject
Geoympäristötekniikka
Mcode
Yhd-33
Degree programme
Language
en
Pages
62
Series
Abstract
In 1994 it was decreed by law that all nuclear waste produced in Finland must be disposed of within the Finnish territory. For this purpose, the ONKALO project is being developed. ONKALO is a hard rock research laboratory, located in Eurajoki, whose excavation began in 2004. It is being constructed at the moment, and will be part of the ONKALO deep geological repository for nuclear waste disposal. The storage in the repository will start with the first disposal in 2020, and it will last until its completion in the 2100'S when it will be closed sealed and the entrance buried. An access tunnel, one shaft and two semi-bored shafts currently integrate ONKALO. The access tunnel is approximately 5 km long and reaches a depth of about 460 m below the surface, as well as the outlet shaft. The other two shafts only reach the level -290. Due to the forthcoming purpose of this excavation for nuclear waste storage, and because of groundwater migration carrying dangerous substance can occur, several limitations have been set to the excavation processes. In the exhaust shaft an inflow limitation has been set in 5 l/min, but there are some fracture zones that are intersecting the shaft and are bringing water into ONKALO through the exhaust shaft. The general purpose of this study is developing a reliable joint fluid flow in hard rock model. The specific scope of this study is to create a numerical DEM model to simulate how the groundwater and pressure field behaves in the vicinity of the shaft after it is excavated, predict the path that groundwater follows within the bedrock in order to locate eventual leakage points, and attempt to simulate how the grout spreads through the fracture network, in order to give further advice in the excavation of other shafts. As a result of this study, it can be confirmed that groundwater flow in deep hard rock mainly occurs along fractured zones towards an excavated void. Practically no flow takes place along tight fractures. Post grouting works improve water tightness of the rock where the injection is done. In general, no new paths for groundwater flow are created and the total inflow substantially decreased.Description
Supervisor
Leveinen, JussiThesis advisor
Hatakka, LassiNuijten, Guido
Ström, Jesse
Martinelli, Daniele
Keywords
DEM, groundwater, grouting, hard rock, hypogeology, inflow, joint fluid flow, modelling, nuclear waste, ONKALO, shaft, 3DEC