X-ray CT imaging and petrofabric analysis of Olkiluoto rock specimens tested under true-triaxial stresses

摘要

Temporal and spatial acoustic emission (AE) event analysis, 3D fracture networks construction obtained from X-Ray CT images and thin section studies of the five tested specimens on isotropic pegmatite (PGR) and anisotropic migmatitic gneiss (VGN) samples obtained from ONKALO nuclear waste repository site in Finland have been carried out. The effect of orientation of foliation planes with -1 axis on strength and seismic signature of said specimens undergoing a complex stress path with -2 axis being either aligned or normal to the strike direction of foliation planes have been investigated. Petrofabric analysis of the tested VGN specimens shows that induced fractures are located within the zones characterized by plate-shaped minerals and avoid granular type of mineral zones. When the -2 axis is kept normal to the strike of the foliation planes in the weakest VGN member, the failure strength improves by 26% and shows a different seismic signature. Non-compliant types of granitic inclusions found within VGN member can cause up to significant failure strength improvement for such mixed lithologies.