7
cover could increase vertical and horizontal stress on frac-
tures and bedding planes and thus reduce their perme-
ability. However, the caving process close to the mine level
enhances fracture permeabilities. At the Sewickley horizon,
although deepest amongst the measurement intervals, the
proximity to the cave zone caused elevated permeabilities.
Depth of cover has more dominating effects at the
Uniontown horizon because of the relative distance from
the mining horizon. The measurements for permeability at
the top of the caved zone at the Waynesburg coal horizon
show the highest values, implying the effects of depth of
cover on the pre- and post-mining permeabilities. Previous
NIOSH works [14] show that at shallower depth, bedding
planes provide a low resistant path for water flow leading
to an increase in the pre-mining permeability. After min-
ing, the shearing and opening of subvertical fractures due
to caving only enhances the permeability values.
At the Sewickley horizon, this is the greatest depth
for measurement, and more effects from compression and
more effects from proximity to the caved zone are observed.
At the Sewickley horizon, the permeability measurements
do not return to the original pre-mine-by levels. At the
Uniontown horizon, there is less influence due to caving.
The measurements for permeability at the top of the caved
zone are included in Table 1. At the top of the fracture zone,
due to the proximity to the surface, there is a potential for a
large horizontal fracture. This is reflected in the much larger
measurements.
Deep Cover Results
At the deep cover site, the permeability measurements were
not above 1 mD for both the Uniontown and Sewickley
horizons prior to the LW panel mine-by, VEP-U and
VEP-S respectively. As the LW panel passed the monitor-
ing boreholes, the permeability increased to a maximum
of 5.4 mD at about 183 m (600 ft) from the Uniontown
horizon monitoring location (Figure 9). The permeability
values soon returned to below 2 mD afterward. The perme-
ability values for the Sewickley horizon increased to almost
18 mD when the LW panel was about 244 m (800 ft) from
the monitoring location. The permeability values for the
Sewickley soon decreased to 2 mD.
At the deep cover site, the permeability measurements
start to increase as the second LW panel approached the
Figure 9. Permeability measurements pre-, during, and post- first LW panel mine-by under deep cover. Negative
distances are the LW panel approaching the monitoring boreholes. VEP-U is at the Uniontown horizon and
VEP-S is at the Sewickley horizon
Table 1. Measured permeabilities during LW panel mine-by at a shallow cover site
Measured Permeabilities LW Panel 1 LW Panel 2
Borehole ID Horizon Min (mD) Max (mD) Min (mD) Max (mD)
FEB 1 Sewickley 411 1,360 1,100 5,080
FEB 2 Uniontown 22 245 11 386
FEB 3 Top of Caved Zone
(Waynesburg)
2,730 32,900 38,500 132,000
cover could increase vertical and horizontal stress on frac-
tures and bedding planes and thus reduce their perme-
ability. However, the caving process close to the mine level
enhances fracture permeabilities. At the Sewickley horizon,
although deepest amongst the measurement intervals, the
proximity to the cave zone caused elevated permeabilities.
Depth of cover has more dominating effects at the
Uniontown horizon because of the relative distance from
the mining horizon. The measurements for permeability at
the top of the caved zone at the Waynesburg coal horizon
show the highest values, implying the effects of depth of
cover on the pre- and post-mining permeabilities. Previous
NIOSH works [14] show that at shallower depth, bedding
planes provide a low resistant path for water flow leading
to an increase in the pre-mining permeability. After min-
ing, the shearing and opening of subvertical fractures due
to caving only enhances the permeability values.
At the Sewickley horizon, this is the greatest depth
for measurement, and more effects from compression and
more effects from proximity to the caved zone are observed.
At the Sewickley horizon, the permeability measurements
do not return to the original pre-mine-by levels. At the
Uniontown horizon, there is less influence due to caving.
The measurements for permeability at the top of the caved
zone are included in Table 1. At the top of the fracture zone,
due to the proximity to the surface, there is a potential for a
large horizontal fracture. This is reflected in the much larger
measurements.
Deep Cover Results
At the deep cover site, the permeability measurements were
not above 1 mD for both the Uniontown and Sewickley
horizons prior to the LW panel mine-by, VEP-U and
VEP-S respectively. As the LW panel passed the monitor-
ing boreholes, the permeability increased to a maximum
of 5.4 mD at about 183 m (600 ft) from the Uniontown
horizon monitoring location (Figure 9). The permeability
values soon returned to below 2 mD afterward. The perme-
ability values for the Sewickley horizon increased to almost
18 mD when the LW panel was about 244 m (800 ft) from
the monitoring location. The permeability values for the
Sewickley soon decreased to 2 mD.
At the deep cover site, the permeability measurements
start to increase as the second LW panel approached the
Figure 9. Permeability measurements pre-, during, and post- first LW panel mine-by under deep cover. Negative
distances are the LW panel approaching the monitoring boreholes. VEP-U is at the Uniontown horizon and
VEP-S is at the Sewickley horizon
Table 1. Measured permeabilities during LW panel mine-by at a shallow cover site
Measured Permeabilities LW Panel 1 LW Panel 2
Borehole ID Horizon Min (mD) Max (mD) Min (mD) Max (mD)
FEB 1 Sewickley 411 1,360 1,100 5,080
FEB 2 Uniontown 22 245 11 386
FEB 3 Top of Caved Zone
(Waynesburg)
2,730 32,900 38,500 132,000