Evaluation of the Geological, Geophysical and Hydrogeological Conditions at Fjaellveden

摘要

The Fjaellveden study site has a flat topography and a high percentage of outcrops. The main type of rock in the area is veined gneiss, with a north-east structural strike and vertical dip, which contains pyrite and pyrrhotite in the form of fracture minerals and as impregnations. In conformity with the gneiss structure there are strata of granite gneiss. The rock mass has a fracture frequency of 4.0 fractures per metre within the upper 100 metres and decreases with increasing depth. The Fjaellveden study site is delimited to the north-east and south-west by regional fracture zones, 80-90 m wide and dipping approx 75 degrees towards the south-west, which contain wide sections of crushed and clay-altered rock, mylonites and breccias. The regional zones delimit a block at least 3times3 km large which contains only local fracture zones and which are small and of a mean width of 5 m. Within the upper 100-200 metres horizontal fractures can be found. The common fracture minerals in fracture zones are calcite, kaolinite, chlorite and illite. Existing granite gneiss strata possess higher hydraulic conductivity than the surrounding veined gneiss.At a depth of 500 m the granite gneiss has a hydraulic conductivity of 3times10 exp -9 m/s, the corresponding value in the surrounding bedrock being 2times10 exp -11 m/s. For the rock mass as a whole, the hydraulic conductivity decreases from approx 10 exp -8 m/s at the surface rock to approx 10 exp -11 m/s at a depth of 600 m. The hydraulic conductivity in the local fracture zones in the Fjaellveden area is 5times10 exp -9 m/s at the 500 m level. The flat topography of the area implies that the hydraulic gradients in the bedrock are small, also having recorded by piezometric measurements. (Atomindex citation 15:044545)