4-DIMENSIONAL ANALYSIS OF FRACTURE ARRAYS AT THE ASPO HARD ROCK LABORATORY, SE SWEDEN

During excavation and construction of Aspo HRL (an underground laboratory for the study of spent nuclear fuel), geological information is systematically recorded and filed in a data base called GEOTAB. Statistical analyses have been performed on fracture information from GEOTAB and stochastically chosen outcrops have been mapped in detail. Based on systematic recording of crosscutting relations, a succession of minerals and characteristics of decreasing age have been outlined. These include: epidote, quartz, oxidized walls, iron oxides, chlorite and calcite. The sequential fragmentation of the rock mass is described in terms of evolution of fracture arrays in time. A correction procedure for sampling biases has been performed and fracture characteristics have been analysed. It is concluded that fracture lengths follow a lognormal distribution with mean, mode and standard deviation estimated to 2.84 m, 1.52 m and 1.43 m, respectively. Spacing has been evaluated for different fracture sets and varies between 0.32 m-1 to 8.45 m-1. It is concluded that the fracture array consist of six sets with different kinematics. Fracture zones underground are compared to a fracture zone at the surface.