5
THE SUBTROPOLIS MASSIVE ROOF
COLLAPSE
In 2015, a massive roof collapse at Subtropolis Mine began
to form in the northwestern portion of the mine. From
April of 2016 to the end of 2018, the collapse area had
been relatively quiet. However, in 2019, mining began to
extend close to the old workings where the collapse had
occurred. Instabilities began to form again, and the size of
the collapse began to grow. In addition to its growth in the
old workings, new damages began to “jump” into the new
workings, causing a major roof fall in one of the crosscuts
nearest to the old workings and with the lowest caprock
thickness (Figure 8). Since mining moved further from the
edge of the collapse area, damages were expected to stop.
However, due to the presence of horizontal stress at this
mine, the collapse has not stopped progressing further into
the roof and outward into the open entries. The operator
had witnessed the role horizontal stress played in the col-
lapse. Damages progressed slowly as cutters began to run
from east to west from the collapse area and the operator
was able to follow the shifting of the test holes as it went.
3D LiDAR scanning was able to capture some of these
changes over time.
Figure 7. Model of distribution of maximum principal horizontal stress
Figure 8. a1N of 3N Panel location in relation to mining in
2019 (Evanek et al., 2020)
THE SUBTROPOLIS MASSIVE ROOF
COLLAPSE
In 2015, a massive roof collapse at Subtropolis Mine began
to form in the northwestern portion of the mine. From
April of 2016 to the end of 2018, the collapse area had
been relatively quiet. However, in 2019, mining began to
extend close to the old workings where the collapse had
occurred. Instabilities began to form again, and the size of
the collapse began to grow. In addition to its growth in the
old workings, new damages began to “jump” into the new
workings, causing a major roof fall in one of the crosscuts
nearest to the old workings and with the lowest caprock
thickness (Figure 8). Since mining moved further from the
edge of the collapse area, damages were expected to stop.
However, due to the presence of horizontal stress at this
mine, the collapse has not stopped progressing further into
the roof and outward into the open entries. The operator
had witnessed the role horizontal stress played in the col-
lapse. Damages progressed slowly as cutters began to run
from east to west from the collapse area and the operator
was able to follow the shifting of the test holes as it went.
3D LiDAR scanning was able to capture some of these
changes over time.
Figure 7. Model of distribution of maximum principal horizontal stress
Figure 8. a1N of 3N Panel location in relation to mining in
2019 (Evanek et al., 2020)