6
MANAGING DEVELOPMENT ACTIVITIES
Development Inside Caution Zone and Fractured Zone
Towards DMLZ-PB1E Active Cave
The main objectives of mining in PB4 near the existing PB1
cave are to promote cave connection safely. Thus, develop-
ment as close as possible to the existing PB1 cave is neces-
sary. Ensure safety during development through fractured
zone is critical. A proper TARP during development stage
is essential to reduce potential risks during development
work in the caution zone. Work instruction (WI) for bore-
hole camera activities provide geotechnical engineers dur-
ing camera survey work. The ground investigation results
are important to estimate rock mass condition for the next
development blasting round. However, the WI do not
explicitly contain guidelines for Geotechnical Engineers to
clearly identify different rock mass descriptions within dif-
ferent cave influence zones.
Development towards PB1 existing cave will be carried
out through caution and fractured zone (T1), which can
be seen in Figure 9. Development close to or inside the
fractured zone will encounter a gradual increase of fractures
intensity. Drifts are potentially facing the risk of subsidence
and wedge failure form the backs.
The risk of rock bursting is relatively low as the areas
are in the stress shadow and has been previously de-stressed.
The maximum induced stress is around 50–60 Mpa, which
as can be seen in Figure 10. Despite low risk of rock burst,
the full burst supports involving 17.5mm cable bolt, stiff
rebar (22 mm paddle bolt grouted with resin), 8 mm
welded mesh and fibre shotcrete are installed.
Prior to next blasting round, a borehole camera sur-
vey from a fully supported ground is performed to investi-
gate the rock mass condition ahead. A guideline has been
adopted for different rock mass condition to avoid bias
from different investigators. During hole logging process,
Geotech engineers refers to a table that describes ground
classification based on damage zones and its hazards rating.
Thus, Geotech engineers can prepare for a potential ground
support and blasting sequence update based on latest rock
mass characterization result. The classification contains
three zones which reflect the cave induce rock mass damage
which is described in the Table 2.
Intense probe holes deployed in the boundary of the
caution zone until which the ground no longer develop-
able. Down holes survey serves to monitor pillar integrity
and potential ledges can be avoided. As seen in Figure 11.
Borehole camera investigation is a preliminary data to
make decision making. Join inspections by the DMLZ-PB4
stakeholders including Geotech, Geology, Engineering and
operation is conducted for decision making in the field.
Committee is equipped with a proper guideline for drift
scale inspection which help providing clear action plan if
any change on the rock mass condition.
A drift scale inspection is critical to ensure all infor-
mation have been considered before deciding to advance
Figure 8. PB2 Draw Rate vs Time Remains to Reach 50m
Pillar
Figure 9. Development towards DMLZ PB1 cave showing cave shape April 2024 (orange line)
sliced at 2815 level a) plan view, b) section view
MANAGING DEVELOPMENT ACTIVITIES
Development Inside Caution Zone and Fractured Zone
Towards DMLZ-PB1E Active Cave
The main objectives of mining in PB4 near the existing PB1
cave are to promote cave connection safely. Thus, develop-
ment as close as possible to the existing PB1 cave is neces-
sary. Ensure safety during development through fractured
zone is critical. A proper TARP during development stage
is essential to reduce potential risks during development
work in the caution zone. Work instruction (WI) for bore-
hole camera activities provide geotechnical engineers dur-
ing camera survey work. The ground investigation results
are important to estimate rock mass condition for the next
development blasting round. However, the WI do not
explicitly contain guidelines for Geotechnical Engineers to
clearly identify different rock mass descriptions within dif-
ferent cave influence zones.
Development towards PB1 existing cave will be carried
out through caution and fractured zone (T1), which can
be seen in Figure 9. Development close to or inside the
fractured zone will encounter a gradual increase of fractures
intensity. Drifts are potentially facing the risk of subsidence
and wedge failure form the backs.
The risk of rock bursting is relatively low as the areas
are in the stress shadow and has been previously de-stressed.
The maximum induced stress is around 50–60 Mpa, which
as can be seen in Figure 10. Despite low risk of rock burst,
the full burst supports involving 17.5mm cable bolt, stiff
rebar (22 mm paddle bolt grouted with resin), 8 mm
welded mesh and fibre shotcrete are installed.
Prior to next blasting round, a borehole camera sur-
vey from a fully supported ground is performed to investi-
gate the rock mass condition ahead. A guideline has been
adopted for different rock mass condition to avoid bias
from different investigators. During hole logging process,
Geotech engineers refers to a table that describes ground
classification based on damage zones and its hazards rating.
Thus, Geotech engineers can prepare for a potential ground
support and blasting sequence update based on latest rock
mass characterization result. The classification contains
three zones which reflect the cave induce rock mass damage
which is described in the Table 2.
Intense probe holes deployed in the boundary of the
caution zone until which the ground no longer develop-
able. Down holes survey serves to monitor pillar integrity
and potential ledges can be avoided. As seen in Figure 11.
Borehole camera investigation is a preliminary data to
make decision making. Join inspections by the DMLZ-PB4
stakeholders including Geotech, Geology, Engineering and
operation is conducted for decision making in the field.
Committee is equipped with a proper guideline for drift
scale inspection which help providing clear action plan if
any change on the rock mass condition.
A drift scale inspection is critical to ensure all infor-
mation have been considered before deciding to advance
Figure 8. PB2 Draw Rate vs Time Remains to Reach 50m
Pillar
Figure 9. Development towards DMLZ PB1 cave showing cave shape April 2024 (orange line)
sliced at 2815 level a) plan view, b) section view