Block Sawing Experiment Related to Excavation Disturbed Zone Studies in ONKALO Underground Research Laboratory
In Finland Posiva Oy's will implement the final disposal of the spent nuclear fuel of its owners in Olkiluoto, crystalline bedrock. At a moment, the reference method for excavation is drill and blast method, which causes excavation damaged zone (EDZ) on tunnel surfaces. To control the formation of the EDZ during the construction of the tunnels is important, because the EDZ is seen as risk for long term safety. In ONKALO Underground Research Laboratory Posiva has conducted a set of studies in Research Niche ONK-TKU-3620 to examine the real EDZ fracture pattern in the floor of a tunnel. Firstly area was studied with selected geophysical, hydrological and geological methods. In order to verify the geophysical methods it was decided to examine the real EDZ fracture pattern in the floor of a tunnel from wire sawed sample. After wire sawing the blocks were transported to Halden to DWTeknikk's workshop, where they were sawed to 10 centimeter slices with smooth and onwards easily workable surfaces. All slices were studied and all fractures were mapped. Each fracture was digitized and classified. A 3D model of the fracture planes was made to get a very detailed fracture model for further studies.