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Rock Mechanics.pdf - Mining and Blasting

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Figure 18.14 Development of<br />

cumulative vertical <strong>and</strong> horizontal<br />

convergence with time, monitoring<br />

stations P15C02, production level,<br />

PT Indonesia’s DOZ Mine, Indonesia<br />

(after Rachmad <strong>and</strong> Widijanto, 2002).<br />

EXAMPLES OF MONITORING ROCK MASS PERFORMANCE<br />

<strong>and</strong> until undercut blasting took place 27 m from the station in early 2001. At this point<br />

both vertical <strong>and</strong> horizontal convergences increased rapidly until the caving front had<br />

passed the station. Subsequently, approximately constant convergences continued to<br />

be recorded for some time. From the results obtained at this <strong>and</strong> other convergence<br />

monitoring stations, it was concluded that the abutment stress zone reached some<br />

27 m ahead of the undercut face. On this basis, it was concluded that support <strong>and</strong><br />

reinforcement on the production level should be in place 27 m ahead of the undercut<br />

face (Rachmad <strong>and</strong> Widijanto, 2002).<br />

18.3.3 Monitoring cable bolt reinforcement performance under rock burst<br />

conditions, Williams Mine, Ontario, Canada<br />

The Williams Mine is in the Hemlo gold mining district of northwestern Ontario,<br />

Canada. The orebody lies along the contact between the overlying metasedimentary<br />

rocks <strong>and</strong> the underlying felsic metamorphics. The series dips to the north at 60 ◦ –70 ◦<br />

<strong>and</strong> the ore thickness ranges form 3 to 50 m. The uniformity of the orebody <strong>and</strong><br />

its steep dip make it well suited to longhole open stoping with delayed backfilling<br />

(Bawden <strong>and</strong> Jones, 2002).<br />

On 29 March, 1999, a rockburst of Nuttli magnitude Mn = 3.0 occurred in the<br />

sill pillar between blocks 3 <strong>and</strong> 4 at a depth of approximately 1000 m. The resulting<br />

damage was significant, affecting five of the footwall haulage levels in the sill pillar<br />

to varying degrees over a strike length of about 140 m (see Figure 18.15). The 9415<br />

level was ab<strong>and</strong>oned but the other levels were rehabilitated. Until this event, all<br />

falls of ground <strong>and</strong> known seismic activity had taken place within the orebody. This<br />

event appeared to be located in the footwall <strong>and</strong> to involve slip on a feature, later<br />

found to be a foliation shear, located approximately 40 m south of the footwall<br />

563

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