6
the strength of a coal pillar without weak bedding planes
at various depths (100, 200, 266, 300, 400, and 500 m)
(see Figure 6). This model incorporated rock mass proper-
ties and the geo-mining conditions of the GDK‑11 Incline
Mine’s coal seam. The coal seam thickness was set at 5 m,
and the gallery dimensions were 6 m in width and 5 m in
height. The model incorporates boundary conditions with
rollers on the side walls of the roof and floor, allowing lat-
eral constraint, and a fixed base at the bottom, providing
stability for the entire setup. The model also accounts for
an additional depth of unmodeled rock above the roof,
which varies between 45 and 445 m, depending on the
total depth of cover. This unmodeled section represents the
overburden load that transfers stress downwards onto the
modelled portion, simulating actual field conditions more
realistically. A truncated load of 0.025H MPa (where H is
the depth of cover) was applied on the top of the model to
simulate the overlying, unmodeled strata. The strength of
the quarter symmetry pillar was estimated similarly to how
coal samples are tested in the laboratory using a Universal
Testing Machine. For simulation, pillar strength was
assessed by applying a constant velocity of 8.25 ×10–⁵ m/s
to the model’s top.
Adopted failure criterion has helped in calibrating the
numerical models by considering the best representative set
of MCSS parameters (cohesive strength and its variation
with strain and frictional angle and its variation with strain
rate) for Indian geo-mining conditions. After calibrating the
numerical model, pillar strength was estimated in FLAC3D
by replicating the servo-controlled laboratory testing in
FLAC3D. Pillar strength estimated in FLAC3D is found to
be matching with the strength estimated using the empiri-
cal formula developed by Sheorey for Indian geo-mining
conditions. A set of properties (Table 2), which provided
good agreement between the empirical and numerical val-
ues of the strength, are finally selected for the simulation.
Coal pillar’s strength and stress-strain behaviour under
varying depths of cover, including 100 m, 200 m, 266 m,
300 m, 400 m, and 500 m is illustrated in Figure 7. Each
subfigure (a) through (f) shows the vertical stress contours
within the pillar at these depths, alongside their respective
stress-strain curves.
5 m
20 m
Truncated load
18 m
Roof
50 m
Coal
Floor
50 m
Ground Level
Depth of unmodelled
portion
varies between
(45 -445) m
Depth of cover varies between
(100 -500) m
105 m
Rollers
Fixed
Figure 6. In-situ quarter symmetry model for evaluation of pillar strength at different depths
of cover
the strength of a coal pillar without weak bedding planes
at various depths (100, 200, 266, 300, 400, and 500 m)
(see Figure 6). This model incorporated rock mass proper-
ties and the geo-mining conditions of the GDK‑11 Incline
Mine’s coal seam. The coal seam thickness was set at 5 m,
and the gallery dimensions were 6 m in width and 5 m in
height. The model incorporates boundary conditions with
rollers on the side walls of the roof and floor, allowing lat-
eral constraint, and a fixed base at the bottom, providing
stability for the entire setup. The model also accounts for
an additional depth of unmodeled rock above the roof,
which varies between 45 and 445 m, depending on the
total depth of cover. This unmodeled section represents the
overburden load that transfers stress downwards onto the
modelled portion, simulating actual field conditions more
realistically. A truncated load of 0.025H MPa (where H is
the depth of cover) was applied on the top of the model to
simulate the overlying, unmodeled strata. The strength of
the quarter symmetry pillar was estimated similarly to how
coal samples are tested in the laboratory using a Universal
Testing Machine. For simulation, pillar strength was
assessed by applying a constant velocity of 8.25 ×10–⁵ m/s
to the model’s top.
Adopted failure criterion has helped in calibrating the
numerical models by considering the best representative set
of MCSS parameters (cohesive strength and its variation
with strain and frictional angle and its variation with strain
rate) for Indian geo-mining conditions. After calibrating the
numerical model, pillar strength was estimated in FLAC3D
by replicating the servo-controlled laboratory testing in
FLAC3D. Pillar strength estimated in FLAC3D is found to
be matching with the strength estimated using the empiri-
cal formula developed by Sheorey for Indian geo-mining
conditions. A set of properties (Table 2), which provided
good agreement between the empirical and numerical val-
ues of the strength, are finally selected for the simulation.
Coal pillar’s strength and stress-strain behaviour under
varying depths of cover, including 100 m, 200 m, 266 m,
300 m, 400 m, and 500 m is illustrated in Figure 7. Each
subfigure (a) through (f) shows the vertical stress contours
within the pillar at these depths, alongside their respective
stress-strain curves.
5 m
20 m
Truncated load
18 m
Roof
50 m
Coal
Floor
50 m
Ground Level
Depth of unmodelled
portion
varies between
(45 -445) m
Depth of cover varies between
(100 -500) m
105 m
Rollers
Fixed
Figure 6. In-situ quarter symmetry model for evaluation of pillar strength at different depths
of cover