3
slope deformations by implementing slower mining rates
and allowing the deforming slopes longer times to settle
between events.
The pit was successfully completed in early 2020. A
total of 80 million additional contained pounds of cop-
per were safely extracted from this pit. No personnel were
injured, and no equipment was damaged during the min-
ing operations of this pit.
SLOPE MONITORING
Mining activities with such active high walls would not
be possible without critical slope monitoring devices and
methods in place. This section will outline the three key
Figure 3. Topographic map of the 2012 northern wall, with
indications where tension cracks were observed (Yang, 2013). Figure 4. Photograph showing the high-wall movement on
the eastern side of the pit (Yang, 2015).
aggressive 37-degree interramp angle, rapid removal of
material at the toe, and continued high pore water pressures.
By July 2014, the northern wall had an average veloc-
ity of about 0.5 inches per day, with higher velocities being
observed near a western bounding fault. A third-party con-
sulting group estimated the average FOS for the area to be
about 1.08.
Due to the development of tension cracks at the base of
a historic leach pad, the mine made the ultimate decision to
relocate the contents to avoid any environmental hazard a
slope deformation may cause. This was completed in 2014.
In February 2015, a slope movement occurred on the
eastern wall of the pit due to high pore water pressures, satu-
rated toe, and very weak rock masses. The mine initially mit-
igated the area by dozing down the loose material, but the
mass had eventually shifted again by April of the same year.
In 2016, the mining sequence resulted in the necessary
placement of a haul road across the northern wall instabil-
ity, with mining activities also being held at the toe of the
same wall. During this year, the northern wall displaced
approximately 300 feet, created a scarp of about 150 feet
in height, and had ongoing average velocities that ranged
from 4 to 33 inches per day. This amount of movement
became too much for safe access, and mining activities were
temporarily halted in the pit by the end of 2016.
Mining did not resume in this pit until 2018 when the
haul road was re-established across the north wall instabil-
ity. At this time, the typical movement rate for the failing
mass was about an average velocity of 2 inches per day.
This increased to above 10 inches per day as mining
resumed against the toe of the north wall.
The mining company was able to successfully continue
operations in this pit through 2019 despite the continuous
Figure 5. Photograph of the northern wall taken in 2020.
Backfilling operations were started to buttress against
further movement.
slope deformations by implementing slower mining rates
and allowing the deforming slopes longer times to settle
between events.
The pit was successfully completed in early 2020. A
total of 80 million additional contained pounds of cop-
per were safely extracted from this pit. No personnel were
injured, and no equipment was damaged during the min-
ing operations of this pit.
SLOPE MONITORING
Mining activities with such active high walls would not
be possible without critical slope monitoring devices and
methods in place. This section will outline the three key
Figure 3. Topographic map of the 2012 northern wall, with
indications where tension cracks were observed (Yang, 2013). Figure 4. Photograph showing the high-wall movement on
the eastern side of the pit (Yang, 2015).
aggressive 37-degree interramp angle, rapid removal of
material at the toe, and continued high pore water pressures.
By July 2014, the northern wall had an average veloc-
ity of about 0.5 inches per day, with higher velocities being
observed near a western bounding fault. A third-party con-
sulting group estimated the average FOS for the area to be
about 1.08.
Due to the development of tension cracks at the base of
a historic leach pad, the mine made the ultimate decision to
relocate the contents to avoid any environmental hazard a
slope deformation may cause. This was completed in 2014.
In February 2015, a slope movement occurred on the
eastern wall of the pit due to high pore water pressures, satu-
rated toe, and very weak rock masses. The mine initially mit-
igated the area by dozing down the loose material, but the
mass had eventually shifted again by April of the same year.
In 2016, the mining sequence resulted in the necessary
placement of a haul road across the northern wall instabil-
ity, with mining activities also being held at the toe of the
same wall. During this year, the northern wall displaced
approximately 300 feet, created a scarp of about 150 feet
in height, and had ongoing average velocities that ranged
from 4 to 33 inches per day. This amount of movement
became too much for safe access, and mining activities were
temporarily halted in the pit by the end of 2016.
Mining did not resume in this pit until 2018 when the
haul road was re-established across the north wall instabil-
ity. At this time, the typical movement rate for the failing
mass was about an average velocity of 2 inches per day.
This increased to above 10 inches per day as mining
resumed against the toe of the north wall.
The mining company was able to successfully continue
operations in this pit through 2019 despite the continuous
Figure 5. Photograph of the northern wall taken in 2020.
Backfilling operations were started to buttress against
further movement.