9
Impact at Different Depths of Cover
At 100 m depth (Figure 10(a), Table 4), pillar strength
decreases as dirt band thickness increases, with values drop-
ping from 13.23 MPa at 0.2 m thickness to 12.67 MPa at
0.5 m. Pillars with dirt bands located at the floor interface
retain slightly higher strength compared to those with bands
positioned at the roof, indicating that the location and
thickness of dirt bands play critical roles in maintaining sta-
bility at shallower depths. At 200 m (Figure 10(b), Table 5),
this trend continues, with strength values decreasing from
(0.2 – 0.5) m
dirt band
Coal
Pillar
Roof
Floor
5 m
Depth of cover
(100 – 500) m
(c)
Roof
Floor
(0.2 – 0.5) m
dirt band
Coal
Pillar
Roof
Floor
5 m
Depth of cover
(100 – 500) m
(b)
Roof
Floor
(0.2 – 0.5) m
dirt band
Coal
Pillar
Roof
Floor
5 m
Depth of cover
(100 – 500) m
(a)
Roof
Floor
Figure 9. Schematic of coal pillar showing different thicknesses of dirt bands positioned at (a) roof-interface, (b) middle, and
(c) floor-interface, under varying depths of cover