Mapping of the excavation damage zone around the circular access shaft at Atomic Energy of Canada Limited's Underground Research Laboratory

The excavation damage about the circular shaft extension was mapped during the excavation of a station at 300-metre depth. The reduction in damage zone thickness compared to that seen in the previous rectangular shaft (300 mm versus 1500 mm) is attributed to improvements in excavation methods, to conversion to a circular cross section, and to increasing isotropy of stresses with depth; however, this is based on preliminary interpretation of new stress data. Damage distribution may be correlated with rock fabric and with the principal stress orientations. This study will benefit subsequent investigations directed at the assessment of excavation damage on vault design and performance. It is recommended that this experiment be repeated under higher stress conditions and with different shaft profiles