1
25-055
Managing Subsidence Impact on Active Cave to a New
Production Footprint Through Draw Control Strategies
Michael B. Hutahaean,
Freeport Indonesia, Indonesia
Sandi A. Firmanulhaq
Freeport Indonesia, Indonesia
Rusdian F. Kayadoe
Freeport Indonesia, Indonesia
INTRODUCTION
Deep Mill Level Zone (DMLZ) mine is located in Papua,
Indonesia operated by PT Freeport Indonesia (PTFI) with
approximately 1,500m below surface. The ore body extend
1230m width from northwest to southeast by 300–400m
length east-west. The mine currently produces at full pro-
duction of 80,000 tons per day until 2041. Part of the
extension of current active production block and mitiga-
tion sits 225 m above the production block 1 (PB1) and 2
(PB2A and PB2B) which located in 2590L, named produc-
tion block#4 (PB4W and PB4E).
As the mining continues at PB1N, PB2A, and PB2B,
the cave growth vertically and laterally to south perimeter of
the footprint affecting the integrity of PB4W/E footprint.
Currently, PB1N and PB2N are in active production whilst
PB4E development continues from South against PB1N
cave, as can be seen in Figure 1. A slight overlapping between
PB1E and PB4E intentionally to promote cave connec-
tions between the two caves. Despite low stress model in
the PB4E near existing caves, the PB4E cave propagation
expected by the large strain and will be propagating in ten-
sion failure to the PB1E cave. Hence, designing the drill
drives edge and first drawbell location as close as possible
to the PB1E cave is necessary to guarantee cave connection.
Since PB4 footprint development commenced in
December 2021, there have been a substantial cave prop-
agation observed from existing downhole monitoring.
As the PB4 footprint designed perpendicular to existing
DMLZ PB1 cave, adjustment of the development edge
design is necessary to reflect the progression the loosening
zone propagation to the South. Final life of mine design
for extraction, undercut and ventilation level were decided
in October 2023 considering latest update cave (fractured/
yielded) boundary. Numerical model of potential rock mass
damage also aids the decision to locate the drift edge design.
Predicting the cave progression impact is critical to
both production at the existing active blocks and develop-
ment of the new area. The use of cave shape data from year
2021–2023 gives an insight of the cave shape estimation at
the end of 2024 when the undercut drift will be developed.
This paper presents actual cave growth of active pro-
duction blocks and its relative vertical progression impact
as the result of drawing in order to plan for acceptable rate
and provide mitigation once the minimum acceptable rock
mass condition and minimum pillar threshold achieved.
Figure 1. DMLZ production blocks
25-055
Managing Subsidence Impact on Active Cave to a New
Production Footprint Through Draw Control Strategies
Michael B. Hutahaean,
Freeport Indonesia, Indonesia
Sandi A. Firmanulhaq
Freeport Indonesia, Indonesia
Rusdian F. Kayadoe
Freeport Indonesia, Indonesia
INTRODUCTION
Deep Mill Level Zone (DMLZ) mine is located in Papua,
Indonesia operated by PT Freeport Indonesia (PTFI) with
approximately 1,500m below surface. The ore body extend
1230m width from northwest to southeast by 300–400m
length east-west. The mine currently produces at full pro-
duction of 80,000 tons per day until 2041. Part of the
extension of current active production block and mitiga-
tion sits 225 m above the production block 1 (PB1) and 2
(PB2A and PB2B) which located in 2590L, named produc-
tion block#4 (PB4W and PB4E).
As the mining continues at PB1N, PB2A, and PB2B,
the cave growth vertically and laterally to south perimeter of
the footprint affecting the integrity of PB4W/E footprint.
Currently, PB1N and PB2N are in active production whilst
PB4E development continues from South against PB1N
cave, as can be seen in Figure 1. A slight overlapping between
PB1E and PB4E intentionally to promote cave connec-
tions between the two caves. Despite low stress model in
the PB4E near existing caves, the PB4E cave propagation
expected by the large strain and will be propagating in ten-
sion failure to the PB1E cave. Hence, designing the drill
drives edge and first drawbell location as close as possible
to the PB1E cave is necessary to guarantee cave connection.
Since PB4 footprint development commenced in
December 2021, there have been a substantial cave prop-
agation observed from existing downhole monitoring.
As the PB4 footprint designed perpendicular to existing
DMLZ PB1 cave, adjustment of the development edge
design is necessary to reflect the progression the loosening
zone propagation to the South. Final life of mine design
for extraction, undercut and ventilation level were decided
in October 2023 considering latest update cave (fractured/
yielded) boundary. Numerical model of potential rock mass
damage also aids the decision to locate the drift edge design.
Predicting the cave progression impact is critical to
both production at the existing active blocks and develop-
ment of the new area. The use of cave shape data from year
2021–2023 gives an insight of the cave shape estimation at
the end of 2024 when the undercut drift will be developed.
This paper presents actual cave growth of active pro-
duction blocks and its relative vertical progression impact
as the result of drawing in order to plan for acceptable rate
and provide mitigation once the minimum acceptable rock
mass condition and minimum pillar threshold achieved.
Figure 1. DMLZ production blocks