4
The borehole pattern was centered above a 38 m
(125 ft) by 84 m (275 ft) abutment pillar that was part of
a three-entry gate road system with 457 m (1,500 ft) wide
LW panels that had lengths of about 3,660 m (12,000 ft)
on both sides (Figure 5). The distance from the center of a
borehole collar to the edge of the pillar adjacent to an active
panel was at most 18 m (60 ft). The Pittsburgh seam is at a
depth of 353 m (1,160 ft) from the surface at this location.
The VEP-S and VEP-U boreholes were drilled and
cased with a steel casing and grout baskets except for the
test intervals, which had screen lengths of 3 m (10 ft) and
Figure 3. Geologic zone for each of the boreholes at the shallow cover site [11]
-180
-160
-140
-120
-100
-80
-60
-40
-20
0
-18 -16 -14 -12 -10 -8 -6 -4 -2 0 2
Horizontal displacement, cm
Horizontal displacement parallel to
the panel
Horizontal displacement
perpendicular to the panel
Uniontown Coal Bed
Sewickley Coal Bed
Top of the Fractured Zone
Figure 4. Horizontal displacement by depth (modified from
Su et al., 2019b [8])
Figure 5. Top view of a three-entry LW layout for the deep
cover site. Test boreholes and mining direction are shown
m,ecafruswolebhtpeD