5
.27vch S H
h
w
0 250 1 1l e =++--0.36 b lb (2)
where,
S =pillar strength in MPa
sc
=uniaxial compressive strength of coal in MPa
h =working height in meter
H =depth of cover in meter
w1= length of the pillar (corner to corner) in meter
w2 =width of the pillar (corner to corner) in meter
we =effective pillar width =4A/Pc
A =area of pillar =w1 x w2
Pc =perimeter of the pillar 2 × (w1 +w2 ).
Figure 5 graphically illustrates the relationship between
pillar strength and depth of cover based on the Sheorey
empirical approach, along with the Factor of Safety (FOS)
at each depth level. The figure visually demonstrates that
while pillar strength slightly increases with depth, the FOS
decreases significantly. This inverse relationship indicates
that although pillars may appear stronger at greater depths,
their stability is compromised due to higher loading condi-
tions. This finding underlines the critical need for careful
evaluation of depth-related stress factors when assessing
coal pillar stability in deep mining operations.
3.2 Numerical Simulation Approach
The numerical simulation methodology represents a highly
adaptable technique for the engineering of diverse configu-
rations of natural support structures within underground
mining contexts [18, 35, 36].
An essential component of this methodology is the
identification of a suitable constitutive model, which
significantly influences the design of resilient natural sup-
ports, including coal pillars, fenders, and snooks. The
deformation of these supports is influenced by factors like
the depth of the mining operations, stress redistribution
due to mining activities, and the level of pre-existing elastic
energy in the rock mass. The excavation of galleries to form
natural supports leads to the dissipation of accumulated
energy, causing fracturing or spalling in the support struc-
tures surrounding the excavation [37]. These fractures are
further affected by the aperture, frequency, and orientation
of geological discontinuities [38], as well as the rock mass
rating [39, 40].
These impacts are intensified at greater depths and dur-
ing pillar extraction due to stress redistribution. Based on
field observations, a finite difference-based software tool
utilizing the Mohr-Coulomb Strain Softening (MCSS)
model was selected to simulate the working seam, while
other strata were modelled with elastic properties. Sheorey’s
failure criterion was applied to convert intact rock strength
to rock mass strength, developed indigenously by testing
the varying strengths of different coal measure formations
under laboratory conditions at different confining stresses
[41]. This criterion was found to deviate from the default
MCSS failure model in FLAC3D. To account for this, a
custom FISH function was implemented in FLAC3D,
allowing Sheorey’s criterion to replace MCSS in determin-
ing coal pillar strength.
Initially, pillar strength was evaluated through numeri-
cal modelling without incorporating dirt bands, with
results validated against an existing indigenous empirical
approach [30]. A block model measuring 20 m ×18 m
×105 m was created using quarter symmetry to analyze
Figure 5. Influence of cover depth on pillar strength calculated using the Sheorey empirical
approach, illustrating the Factor of Safety (FOS)
.27vch S H
h
w
0 250 1 1l e =++--0.36 b lb (2)
where,
S =pillar strength in MPa
sc
=uniaxial compressive strength of coal in MPa
h =working height in meter
H =depth of cover in meter
w1= length of the pillar (corner to corner) in meter
w2 =width of the pillar (corner to corner) in meter
we =effective pillar width =4A/Pc
A =area of pillar =w1 x w2
Pc =perimeter of the pillar 2 × (w1 +w2 ).
Figure 5 graphically illustrates the relationship between
pillar strength and depth of cover based on the Sheorey
empirical approach, along with the Factor of Safety (FOS)
at each depth level. The figure visually demonstrates that
while pillar strength slightly increases with depth, the FOS
decreases significantly. This inverse relationship indicates
that although pillars may appear stronger at greater depths,
their stability is compromised due to higher loading condi-
tions. This finding underlines the critical need for careful
evaluation of depth-related stress factors when assessing
coal pillar stability in deep mining operations.
3.2 Numerical Simulation Approach
The numerical simulation methodology represents a highly
adaptable technique for the engineering of diverse configu-
rations of natural support structures within underground
mining contexts [18, 35, 36].
An essential component of this methodology is the
identification of a suitable constitutive model, which
significantly influences the design of resilient natural sup-
ports, including coal pillars, fenders, and snooks. The
deformation of these supports is influenced by factors like
the depth of the mining operations, stress redistribution
due to mining activities, and the level of pre-existing elastic
energy in the rock mass. The excavation of galleries to form
natural supports leads to the dissipation of accumulated
energy, causing fracturing or spalling in the support struc-
tures surrounding the excavation [37]. These fractures are
further affected by the aperture, frequency, and orientation
of geological discontinuities [38], as well as the rock mass
rating [39, 40].
These impacts are intensified at greater depths and dur-
ing pillar extraction due to stress redistribution. Based on
field observations, a finite difference-based software tool
utilizing the Mohr-Coulomb Strain Softening (MCSS)
model was selected to simulate the working seam, while
other strata were modelled with elastic properties. Sheorey’s
failure criterion was applied to convert intact rock strength
to rock mass strength, developed indigenously by testing
the varying strengths of different coal measure formations
under laboratory conditions at different confining stresses
[41]. This criterion was found to deviate from the default
MCSS failure model in FLAC3D. To account for this, a
custom FISH function was implemented in FLAC3D,
allowing Sheorey’s criterion to replace MCSS in determin-
ing coal pillar strength.
Initially, pillar strength was evaluated through numeri-
cal modelling without incorporating dirt bands, with
results validated against an existing indigenous empirical
approach [30]. A block model measuring 20 m ×18 m
×105 m was created using quarter symmetry to analyze
Figure 5. Influence of cover depth on pillar strength calculated using the Sheorey empirical
approach, illustrating the Factor of Safety (FOS)