2
literature addressing the effects of high horizontal stress on
roof stability in hard rock mines. Hence, the conclusions
and findings drawn from studies of high horizontal stress
in coal mines may not be applicable to stone mines due to
significant differences in rock strengths, roof spans, mining
heights, geological conditions, and in-situ stress conditions
between hard rock and coal mines.
High horizontal stress can significantly impact roof
stability in underground stone mines, leading to roof fall
and hazardous conditions. Managing and alleviating the
effects of high horizontal stress is crucial for mine safety.
The presence of high horizontal stress is evident through
various failure patterns, including cutter failure, ellipti-
cal roof failure oriented perpendicular to the direction of
maximum horizontal stress, and low-angle shear failure.
Geological mapping of horizontal stress failure patterns can
help identify the orientation of the maximum horizontal
stress. (Iannacchione et al., 2020).
Cutter failure refers to the damage of roof layers, typi-
cally near the rib, caused by horizontal compression. This
can lead to roof failure. Cutter failure can lead to roof falls if
no proper and timely measures are implemented to prevent
their continuing development (Peng, 2008). The character-
istic signs of high horizontal stress are generally considered
stress driven. However, some researchers have suggested
that other factors, such as the mechanical properties of
the rock and the relative stiffness of different rock types,
may also contribute to cutter failure (Ray, 2008). Over the
years, underground mines have employed various strategies
to mitigate the detrimental effects of high horizontal stress.
These strategies include the use of primary and secondary
roof support, aligning headings in favorable directions,
and reducing the number of crosscuts (Iannacchione et al.,
2020).
This study presents the results of FLAC3D numerical
models and field observations conducted at the Subtropolis
Mine to investigate the effects of high horizontal stress
on roof stability. The primary objective of this study is to
explore the interaction between caprock thickness and the
orientation of maximum horizontal stress on roof stability.
The impact of the cutting sequence on roof stability was
also examined, and a few straightforward recommendations
are provided to mitigate such instabilities. The underlying
assumption of this study is that high horizontal stress in
the limestone formation is high enough to trigger failure
in the roof rock mass after development. In this paper, the
terms “Headings” and “Entries” are used interchangeably.
Headings/Entries refer to the direction of mining into the
reserve.
HIGH HORIZONTAL STRESS AND ROOF
RESPONSE AT SUBTROPOLIS MINE
Many underground stone mines in the U.S. are adversely
affected by high horizontal stress, with the Subtropolis
room-and-pillar mine being a notable example. The
Subtropolis Mine exhibits several characteristic signs of
high horizontal stress conditions. Geological mapping has
confirmed the presence of floor heave/failure (see Figure 1),
Figure 1. Floor heave and failure observed at Subtropolis
Mine caused by high horizontal stress. The affected floor
rock is limestone
literature addressing the effects of high horizontal stress on
roof stability in hard rock mines. Hence, the conclusions
and findings drawn from studies of high horizontal stress
in coal mines may not be applicable to stone mines due to
significant differences in rock strengths, roof spans, mining
heights, geological conditions, and in-situ stress conditions
between hard rock and coal mines.
High horizontal stress can significantly impact roof
stability in underground stone mines, leading to roof fall
and hazardous conditions. Managing and alleviating the
effects of high horizontal stress is crucial for mine safety.
The presence of high horizontal stress is evident through
various failure patterns, including cutter failure, ellipti-
cal roof failure oriented perpendicular to the direction of
maximum horizontal stress, and low-angle shear failure.
Geological mapping of horizontal stress failure patterns can
help identify the orientation of the maximum horizontal
stress. (Iannacchione et al., 2020).
Cutter failure refers to the damage of roof layers, typi-
cally near the rib, caused by horizontal compression. This
can lead to roof failure. Cutter failure can lead to roof falls if
no proper and timely measures are implemented to prevent
their continuing development (Peng, 2008). The character-
istic signs of high horizontal stress are generally considered
stress driven. However, some researchers have suggested
that other factors, such as the mechanical properties of
the rock and the relative stiffness of different rock types,
may also contribute to cutter failure (Ray, 2008). Over the
years, underground mines have employed various strategies
to mitigate the detrimental effects of high horizontal stress.
These strategies include the use of primary and secondary
roof support, aligning headings in favorable directions,
and reducing the number of crosscuts (Iannacchione et al.,
2020).
This study presents the results of FLAC3D numerical
models and field observations conducted at the Subtropolis
Mine to investigate the effects of high horizontal stress
on roof stability. The primary objective of this study is to
explore the interaction between caprock thickness and the
orientation of maximum horizontal stress on roof stability.
The impact of the cutting sequence on roof stability was
also examined, and a few straightforward recommendations
are provided to mitigate such instabilities. The underlying
assumption of this study is that high horizontal stress in
the limestone formation is high enough to trigger failure
in the roof rock mass after development. In this paper, the
terms “Headings” and “Entries” are used interchangeably.
Headings/Entries refer to the direction of mining into the
reserve.
HIGH HORIZONTAL STRESS AND ROOF
RESPONSE AT SUBTROPOLIS MINE
Many underground stone mines in the U.S. are adversely
affected by high horizontal stress, with the Subtropolis
room-and-pillar mine being a notable example. The
Subtropolis Mine exhibits several characteristic signs of
high horizontal stress conditions. Geological mapping has
confirmed the presence of floor heave/failure (see Figure 1),
Figure 1. Floor heave and failure observed at Subtropolis
Mine caused by high horizontal stress. The affected floor
rock is limestone