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

4.4.3 Case 3: Increased Principal Stress Ratio
Case 3 considers the effect of increasing the principal stress ratio, k = σ 1 /σ 3 . The minimum
principal stress, σ 3 , was lowered such that the far-field stress was increased from k=1.4 to k=2
(note that σ 2 is oriented out-of-plane). This was done to test the sensitivity of the faults to
boundary conditions, by increasing the shear loading on faults to induce slip. Both elastic and
plastic models under this condition are assigned the variable properties summarized in Table 4.2.
Modifying the principal stress ratio has the effect of only slightly modifying the stress distribution
from that observed in Case 1. The moderately strong fault model is shown in Figures 4.17 and
4.18. Observations from Case 3 include:
• High maximum and differential stresses align with SW-striking shear zones to the south of the
excavation (Figs. 4.14 and 4.15).
• Right-lateral displacement is induced along the Plum and Return Air Raise Shear Zones to the
south of the excavation in the elastic case and solely along the Plum Shear Zone in the plastic
case (Fig. 4.16).
• Plastic yielding occurs along SW-striking shear zones and is enhanced along splay structures,
linking the Fresh Air Raise and Plum Shear Zones in the plastic model (Fig. 4.17).
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