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

The ratio of maximum principal stresses can be expressed in terms of the angle of internal friction,
3
1
1
2
2
(tan 1)
tan
, (Equation 4.5)
1
2
2
(tan 1)
tan
when cohesion is zero (McKinnon, pers. comm., 2009; see Appendix F for derivation). This
allows for zones of eligible fracture reactivation to be mapped regardless of fracture orientation.
Minimum-to-maximum principal stress ratios computed for plastic and elastic models in UDEC
are shown in Figure 4.22. Such figures allow fields of fault reactivation to be contoured as a
function of the internal angle of friction (Fig. 4.23). This demonstrates that, based on the
minimum-to-maximum principal stress ratio, there is a large area to the south of the excavation,
extending to the Return Air Raise Shear Zone where cohesionless fractures in any orientation can
be reactivated, even at high friction angles. This is modelled in both elastic and plastic models.
Based on stress conditions, slip is possible even in the yield zone, though seismogenic slip is not
expected.
Figure 4.22: Ratio of minimum-to-maximum principal stress for (A) elastic model; (B) plastic model.
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