1
25-033
Evaluating Roof Stability in an Underground Stone Mine Under
High Horizontal Stress: Insight from Numerical Modeling and
Field Observation with Mitigation Strategy
Gamal Rashed
CDC/NIOSH/PMRD
Nicole Evanek
CDC/NIOSH/PMRD
Tim Miller
East Fairfield Coal Company
ABSTRACT
High horizontal stress has been identified as a critical factor
affecting roof stability in underground mines, particularly
when the immediate roof consists of weak or laminated
rock. Numerical models were employed to better under-
stand the influence of caprock thickness, cutting sequences,
and the orientation of driving direction relative to maxi-
mum horizontal stress on roof stability in underground
stone mines. These models were calibrated based on field
observations of roof falls from the study mine. The findings
of this study enhance our understanding of roof stability
under high horizontal stress and contribute to reducing the
risk of roof falls in underground stone mines.
INTRODUCTION
There are currently 101 active underground stone mines
in the United States (MSHA data retrieval system, 2023)
where the room-and-pillar mining method is used to
extract flat-lying and gently dipping formations. The stabil-
ity of underground excavations depends on a combination
of geological factors, the in-situ stress state, and operation-
related-factors such as the size, shape, and orientation of
openings, as well as the cutting sequence. The in-situ stress
state, especially high horizontal stress, is a major factor con-
tributing to roof instability in underground stone mines.
For horizontal, gravity-loaded roof beds clamped at
both ends under a dominant vertical stress, failure typi-
cally initiates at the ends of the span (Obert and Duvall,
1967). The inclined stress trajectories at the ends of the
beam direct the crack propagation diagonally (Goodman,
1989). When the roof span-to-bed thickness ratio exceeds
5.0, the failure mode is tension (Obert and Duvall, 1967).
However, if horizontal stress becomes dominant, the failure
mode shifts from tension to shear.
In mines in the eastern U.S., horizontal stress often
exceeds vertical stress by a factor of at least two and can be
even greater in shallow mines (Iannacchione et al., 1998
Iannacchione et al., 2001). Even though the overburden
is shallow in some underground stone mines, horizontal
stress levels can be unusually high due to tectonic plate
movement, particularly the drift of the North American
Plate from the Mid-Atlantic Ridge, and lead to significant
horizontal stresses, even in regions with shallow overburden
(Iannacchione et al., 2005 Esterhuizen and Iannacchione,
2005).
(Sheorey et al., 2001) proposed that horizontal stress is
influenced by elastic constants, overburden depth, and the
coefficient of thermal expansion based on stress measure-
ments. Similarly, Mark and Gadde (2010) analyzed over
350 stress measurements and concluded that the magni-
tude of the maximum horizontal stress can be determined
using both depth and the modulus of elasticity.
The impact of high horizontal stress on roof stability
and the development of cutter failure in underground coal
mines has been extensively studied by numerous researchers
(Jeremic, 1981 Gale and Blackwood, 1987 Mucho and
Mark, 1994 Wang and Stankus, 1998 Chen, 1999 Gadde
and Peng, 2005 Peng, 2007). However, there is limited
25-033
Evaluating Roof Stability in an Underground Stone Mine Under
High Horizontal Stress: Insight from Numerical Modeling and
Field Observation with Mitigation Strategy
Gamal Rashed
CDC/NIOSH/PMRD
Nicole Evanek
CDC/NIOSH/PMRD
Tim Miller
East Fairfield Coal Company
ABSTRACT
High horizontal stress has been identified as a critical factor
affecting roof stability in underground mines, particularly
when the immediate roof consists of weak or laminated
rock. Numerical models were employed to better under-
stand the influence of caprock thickness, cutting sequences,
and the orientation of driving direction relative to maxi-
mum horizontal stress on roof stability in underground
stone mines. These models were calibrated based on field
observations of roof falls from the study mine. The findings
of this study enhance our understanding of roof stability
under high horizontal stress and contribute to reducing the
risk of roof falls in underground stone mines.
INTRODUCTION
There are currently 101 active underground stone mines
in the United States (MSHA data retrieval system, 2023)
where the room-and-pillar mining method is used to
extract flat-lying and gently dipping formations. The stabil-
ity of underground excavations depends on a combination
of geological factors, the in-situ stress state, and operation-
related-factors such as the size, shape, and orientation of
openings, as well as the cutting sequence. The in-situ stress
state, especially high horizontal stress, is a major factor con-
tributing to roof instability in underground stone mines.
For horizontal, gravity-loaded roof beds clamped at
both ends under a dominant vertical stress, failure typi-
cally initiates at the ends of the span (Obert and Duvall,
1967). The inclined stress trajectories at the ends of the
beam direct the crack propagation diagonally (Goodman,
1989). When the roof span-to-bed thickness ratio exceeds
5.0, the failure mode is tension (Obert and Duvall, 1967).
However, if horizontal stress becomes dominant, the failure
mode shifts from tension to shear.
In mines in the eastern U.S., horizontal stress often
exceeds vertical stress by a factor of at least two and can be
even greater in shallow mines (Iannacchione et al., 1998
Iannacchione et al., 2001). Even though the overburden
is shallow in some underground stone mines, horizontal
stress levels can be unusually high due to tectonic plate
movement, particularly the drift of the North American
Plate from the Mid-Atlantic Ridge, and lead to significant
horizontal stresses, even in regions with shallow overburden
(Iannacchione et al., 2005 Esterhuizen and Iannacchione,
2005).
(Sheorey et al., 2001) proposed that horizontal stress is
influenced by elastic constants, overburden depth, and the
coefficient of thermal expansion based on stress measure-
ments. Similarly, Mark and Gadde (2010) analyzed over
350 stress measurements and concluded that the magni-
tude of the maximum horizontal stress can be determined
using both depth and the modulus of elasticity.
The impact of high horizontal stress on roof stability
and the development of cutter failure in underground coal
mines has been extensively studied by numerous researchers
(Jeremic, 1981 Gale and Blackwood, 1987 Mucho and
Mark, 1994 Wang and Stankus, 1998 Chen, 1999 Gadde
and Peng, 2005 Peng, 2007). However, there is limited