Monitoring Disturbances in the Repository System during Construction Process: Experiences from Natural Decay Series Stud
- PDF / 483,149 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 70 Downloads / 193 Views
0RQLWRULQJ'LVWXUEDQFHVLQWKH5HSRVLWRU\6\VWHPGXULQJ&RQVWUXFWLRQ3URFHVV ([SHULHQFHVIURP1DWXUDO'HFD\6HULHV6WXGLHVDWWKH3\KlVDOPL0LQH &HQWUDO)LQODQG
N. Marcos1, J. Suksi2, K. Rasilainen3 and J. Antikainen1 1 Helsinki University of Technology, P.O. Box 6200, 02150HUT, Finland 2 Laboratory of Radiochemistry, University of Helsinki, P.O. Box 55, FIN-00014HY, Finland 3 VTT Processes, P.O. Box 1608, FIN-02044 VTT, Finland $%675$&7
Prior to the selection of the site for nuclear waste disposal, the performance of the repository is assessed based on general geological data of sites under investigation. Once the site has been selected, the results of the site investigations are used to establish the baseline condition to monitor and evaluate the induced processes during the construction of the repository. One of the processes considered is the change in hydraulic properties in the bedrock due to excavation of tunnels and other open spaces. Within this framework, the results of natural decay series studies in rock samples from the Pyhäsalmi mine collected in the nearby of a water-conducting fracture at the depths of 1275 and 1325 m may give insights on the influence of the excavation-induced changes, if any, in the groundwater flow. The spatial and temporal scale of these changes is also evaluated. The methodology used in this work could be applied to add confidence in the establishment of the baseline conditions to better assess the evolution of changes in groundwater flow patterns during and after construction of a repository system. ,1752'8&7,21 The Pyhäsalmi mine is located in Central Finland, four kilometres southwest of the town of Pyhäjärvi in Oulu County. Shaft sinking started in 1959 and production began in 1962 with open pit mining. Underground mining began in 1967 above the first main level at depth of 210 m, and open pit mining ceased in 1975 at the depth of 135 m. It was observed that the beginning of underground mining enhanced rock movements above the mining level. Mining above 400 m started in 1970. Mining reached the depth of 730 m in 1985, and the excavations reached 1450 m depth in 2000 (Fig. 1a). All the underground stopes are filled with tailings and waste rock. In general, no permanent pillars are left. Currently, a large water-conducting fracture has been identified at the mine from the bottom of the open pit (135 m) to 1375 m depth. The width of the structure is from a few cm to about 2 m at the depth of about 1325 m. The volume disturbed by mining is extensive due to the high extraction ratio and high horizontal in-situ rock stress field, and it encloses the mentioned fracture. When mining approach any level, the normal stress across the fracture increases, which decreases the aperture of the fracture. When mining pass the same location, the normal stress will generally drop below the in-situ level due to the local relaxation of rock mass. Another major factor is the mine dewatering. Today about 106 m3 water is pumped annually from the mine. As soon as mining starts, there is a
Data Loading...
