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

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Damage zones produced using maximum stress and differential stress outline similar areas <strong>of</strong><br />

fracture initiation. Areas <strong>of</strong> active excavation during <strong>the</strong> 2006-2007 time period as well as a zone<br />

<strong>of</strong> high-stress between <strong>the</strong> Return Air Raise Shear Zone and Plum Shear Zone are identified as<br />

areas <strong>of</strong> possible fracture initiation under both maximum stress and differential conditions. This<br />

demonstrates that fracturing <strong>of</strong> intact rock is a possible mechanism for seismicity to <strong>the</strong> south <strong>of</strong><br />

<strong>the</strong> excavation where seismicity is observed, but <strong>the</strong> crack coalescence threshold is not surpassed.<br />

Fracture contours identify <strong>the</strong> area south <strong>of</strong> <strong>the</strong> excavation as a region that is in a state <strong>of</strong> damage<br />

but not yield (Fig. 4.24). This is a lower state <strong>of</strong> degradation than was found in Chapter 3 using<br />

seismic source parameters, where <strong>the</strong> rock mass to <strong>the</strong> south <strong>of</strong> <strong>the</strong> excavation was hypo<strong>the</strong>sized<br />

to be in post-peak conditions.<br />

Figure 4.24 shows that cracking is not possible immediately to <strong>the</strong> north and south <strong>of</strong> <strong>the</strong><br />

excavation, based on <strong>the</strong> final state <strong>of</strong> models produced for Case 1 (Φ=30 o , C=0 MPa). This is<br />

because yielding has already occurred and high stress cannot be accommodated by <strong>the</strong><br />

disintegrated rock mass in this state. UDEC code and routines can be found in Appendix E.<br />

100

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