4
STABILITY ASSESSMENT OF COAL
PILLARS AT DIFFERENT DEPTHS
The assessment of coal pillar stability at different depths
(100, 200, 266, 300, 400, and 500 m) was done using the
Sheorey empirical method [30] and numerical simulation
methods. This combined approach allows for a detailed
look into how depth affects pillar strength and stability,
considering stress distribution and geological features at
each depth level. The Sheorey method offers an analysis
of pillar strength based on depth and material properties,
while numerical simulation provides a detailed examina-
tion of how pillars respond to stress, showing stress concen-
trations and possible failure areas.
Using these methods together helps improve under-
standing of coal pillar stability in various geological and
geotechnical conditions. Detailed discussions on the
Sheorey method and results from numerical simulations
are provided in separate sections, giving valuable insights
into the results and significance of each method for under-
ground coal mining.
Sheorey’s Empirical Approach
Empirical and laboratory-based approaches [31, 32, 33,
34] are used for estimation of pillar strength. Tributary
area method is used to calculate load over pillar. Factor of
safety (FOS) of each pillar is estimated considering, pillar
strength formula [30], which is established in Indian coal-
fields including effective width-to-height ratio. The forma-
tion of a pillar by drivage of galleries all around disturbs the
state of virgin stresses, keeping the total weight of the over-
lying strata gH constant. Normally, it is assumed that the
entire weight overlying strata with zero stiffness is coming
over solid pillars. The stress on pillar (P) is estimated using
tributary area method as given in Eq. (1).
P e 1 MPa cH =-(1)
where,
e =recovery =B Bh
B Bh W
1 2
1 2 1 2 ++
++-^W
^W
^W h^W
h^W
h@ 6
H= depth cover (m)
B= width of the gallery (m)
W1 =length of pillar (m)
W2 =width of pillar (m)
g= unit rock pressure (0.025 MPa/m)
An attempt is made to estimate strength of heightened
pillar considering the average size (36.50 m ×41.50, cen-
tre to centre) at different depths incorporating other geo-
mining conditions of pillar using the Sheorey’s empirical
formulation (Eq. (2)). Sheorey’s empirical approach is well
accepted in Indian coalfields for strength determination
as it also incorporates the depth of cover, but the effect of
geological discontinuities is lacking. The estimated pillar’s
strength and factor of safety are given in Table 1.
Exposed roof bolt after
roof fall in existing gallery
Disturbed roof supported
by chock/cog support in
existing gallery
Figure 4. Status of immediate roof (coal/shale band) in
middle section working
Table 1. Stability assessment of the coal pillar at different depths of cover using Sheorey’s empirical approach and tributary
area method for strength and load estimation
Mine/
Panel
Pillar Size
(corner-to-corner)
h (m) We/h B (m) σc (MPa) H (m) e P (MPa) S (MPa) FOS W1 (m) W2 (m) We (m)
GDK‑11/
C2
30.5 35.5 32.81 5 6.56 6 30.5 100 0.29 3.50 12.40 3.55
200 0.29 6.99 14.63 2.09
266 0.29 9.30 16.09 1.73
300 0.29 10.49 16.85 1.61
400 0.29 13.99 19.07 1.36
500 0.29 17.49 21.30 1.22
STABILITY ASSESSMENT OF COAL
PILLARS AT DIFFERENT DEPTHS
The assessment of coal pillar stability at different depths
(100, 200, 266, 300, 400, and 500 m) was done using the
Sheorey empirical method [30] and numerical simulation
methods. This combined approach allows for a detailed
look into how depth affects pillar strength and stability,
considering stress distribution and geological features at
each depth level. The Sheorey method offers an analysis
of pillar strength based on depth and material properties,
while numerical simulation provides a detailed examina-
tion of how pillars respond to stress, showing stress concen-
trations and possible failure areas.
Using these methods together helps improve under-
standing of coal pillar stability in various geological and
geotechnical conditions. Detailed discussions on the
Sheorey method and results from numerical simulations
are provided in separate sections, giving valuable insights
into the results and significance of each method for under-
ground coal mining.
Sheorey’s Empirical Approach
Empirical and laboratory-based approaches [31, 32, 33,
34] are used for estimation of pillar strength. Tributary
area method is used to calculate load over pillar. Factor of
safety (FOS) of each pillar is estimated considering, pillar
strength formula [30], which is established in Indian coal-
fields including effective width-to-height ratio. The forma-
tion of a pillar by drivage of galleries all around disturbs the
state of virgin stresses, keeping the total weight of the over-
lying strata gH constant. Normally, it is assumed that the
entire weight overlying strata with zero stiffness is coming
over solid pillars. The stress on pillar (P) is estimated using
tributary area method as given in Eq. (1).
P e 1 MPa cH =-(1)
where,
e =recovery =B Bh
B Bh W
1 2
1 2 1 2 ++
++-^W
^W
^W h^W
h^W
h@ 6
H= depth cover (m)
B= width of the gallery (m)
W1 =length of pillar (m)
W2 =width of pillar (m)
g= unit rock pressure (0.025 MPa/m)
An attempt is made to estimate strength of heightened
pillar considering the average size (36.50 m ×41.50, cen-
tre to centre) at different depths incorporating other geo-
mining conditions of pillar using the Sheorey’s empirical
formulation (Eq. (2)). Sheorey’s empirical approach is well
accepted in Indian coalfields for strength determination
as it also incorporates the depth of cover, but the effect of
geological discontinuities is lacking. The estimated pillar’s
strength and factor of safety are given in Table 1.
Exposed roof bolt after
roof fall in existing gallery
Disturbed roof supported
by chock/cog support in
existing gallery
Figure 4. Status of immediate roof (coal/shale band) in
middle section working
Table 1. Stability assessment of the coal pillar at different depths of cover using Sheorey’s empirical approach and tributary
area method for strength and load estimation
Mine/
Panel
Pillar Size
(corner-to-corner)
h (m) We/h B (m) σc (MPa) H (m) e P (MPa) S (MPa) FOS W1 (m) W2 (m) We (m)
GDK‑11/
C2
30.5 35.5 32.81 5 6.56 6 30.5 100 0.29 3.50 12.40 3.55
200 0.29 6.99 14.63 2.09
266 0.29 9.30 16.09 1.73
300 0.29 10.49 16.85 1.61
400 0.29 13.99 19.07 1.36
500 0.29 17.49 21.30 1.22