Page 581 - Rock Mechanics For Underground Mining

EXAMPLES OF MONITORING ROCK MASS PERFORMANCE

Figure 18.14 Development of
cumulative vertical and horizontal
convergence with time, monitoring
stations P15C02, production level,
PT Indonesia’s DOZ Mine, Indonesia
(after Rachmad and Widijanto, 2002).

and until undercut blasting took place 27 m from the station in early 2001. At this point
both vertical and horizontal convergences increased rapidly until the caving front had
passed the station. Subsequently, approximately constant convergences continued to
be recorded for some time. From the results obtained at this and other convergence
monitoring stations, it was concluded that the abutment stress zone reached some
27 m ahead of the undercut face. On this basis, it was concluded that support and
reinforcement on the production level should be in place 27 m ahead of the undercut
face (Rachmad and Widijanto, 2002).

18.3.3 Monitoring cable bolt reinforcement performance under rock burst
conditions, Williams Mine, Ontario, Canada
The Williams Mine is in the Hemlo gold mining district of northwestern Ontario,
Canada. The orebody lies along the contact between the overlying metasedimentary
rocks and the underlying felsic metamorphics. The series dips to the north at 60 –70 ◦
◦
and the ore thickness ranges form 3 to 50 m. The uniformity of the orebody and
its steep dip make it well suited to longhole open stoping with delayed backfilling
(Bawden and Jones, 2002).
On 29 March, 1999, a rockburst of Nuttli magnitude Mn = 3.0 occurred in the
sill pillar between blocks 3 and 4 at a depth of approximately 1000 m. The resulting
damage was significant, affecting five of the footwall haulage levels in the sill pillar
to varying degrees over a strike length of about 140 m (see Figure 18.15). The 9415
level was abandoned but the other levels were rehabilitated. Until this event, all
falls of ground and known seismic activity had taken place within the orebody. This
event appeared to be located in the footwall and to involve slip on a feature, later
found to be a foliation shear, located approximately 40 m south of the footwall
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