title of the thesis - Department of Geology - Queen's University

seismic Cluster 1, which corresponds to an area of elevated modelled differential stress but with
background levels of modelled maximum stress (Fig. 4.25).
Geological evidence of degradation is difficult to observe in underground conditions due to
limited access and enhanced support in proximity to the excavation. However, drilling supports
this degradation process. Drill cores in proximity to the main excavation (in the proposed yield
zone) are heavily fractured and highly degraded (Dave Andrews; pers. comm., 2009). The
damage zone has already extended below the base of the mine at the 7940 ramp, which is also
evident from drilling and excavation as the mine is progressively deepened (Dave Andrews; pers.
comm., 2009).
Slip along mine-scale shear zones has not been identified as a failure mechanism during seismic
or stress analysis. Instead, slip along existing fractures and cracking of intact rock have been
demonstrated to be plausible alternative mechanisms to fault slip. Mapping zones of fracture
reactivation and crack initiation using modelled stresses suggests that existing fractures without
cohesion may be reactivated and new cracks can form in zones of high stress. Though modelled
stresses are not elevated enough to lead to fracture interaction and coalescence, clustering of
seismic events signifies the onset of yield as the rock mass is seismically weakened, which
supports observations made using seismic event parameters in Chapter 2.
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