Index
Fracture Zone Study
Figure 1. The fracture zone consists of a number of sub-parallel connected fracture planes that have undergone different amounts of shear displacement, and which present large variations in aperture and infilling. The open pores appear clearly in the colour image taken with ultra-violet (UV) light. Image width ca. 14 cm.
In a project for SKB, Itasca Geomekanik AB conducted a detailed study of a minor fracture zone at the Äspö Hard Rock Laboratory. The goal was to increase knowledge of the geological and geometrical structure. The zone was impregnated in situ with fluorescent epoxy. Subsequently, the injection borehole was overcored with a 300-mm core. With this method, the epoxy-reinforced zone could be sampled and further cut into slices that were photographed at different scales. The result of the studies shows that the flow paths in the zone make up a complex pattern and that different types of infilling material govern the structure of the pore space. The developed method for studying zones and single fractures has proven to function well, and a number of quantitative parameters have been identified and calculated using image analysis to describe the complex pattern of the fracture network of a zone.
Figure 2. One example of how the inside of the major fracture of the zone may appear. The size of the image is ca. 6x8 mm. The left image is taken with ordinary light, the middle with UV-light and the right image is the binary derived from the middle.
