Observations of brittle failure around a circular test tunnel

In 1987, AECL proposed several experiments for its Underground Research Laboratory. Among these was the Mine-by Experiment, the main focus of which was to investigate the formation and characteristics of the excavation disturbed zone adjacent to an underground opening. The extent and nature of this zone are important concerns for both the operational safety and the sealing of a vault to control the migration of radionuclides.The excavation response phase of the Mine-by Experiment, which involved the excavation, without explosives, of a 46-m-long, 3.5-m-diameter test tunnel in brittle unfractured granite, was carried out between January and July 1992. State-of-the-art instrumentation comprising both geomechanical and geophysical instruments was used to monitor the progressive failure process around the circular tunnel, and the in situ experiment was supplemented by extensive laboratory tests. This paper provides a detailed record of the brittle failure process that was observed during excavation of the tunnel.