9
is about two times larger than the vertical stress. Higher
horizontal stress can further close apertures of subvertical
fractures compared to the bedding planes.
During first panel mine-by, permeability values in
both the Sewickley and Uniontown horizons increase as
the face approaches the site and drops close to the initial
values after mine-by. The same pattern is repeated for the
second panel mine-by. Overall, permeability values at the
Sewickley horizon stay at a higher level compared to those
at the Uniontown horizon, showing that proximity to the
mine level can dominate the depth of cover effects.
Comparison of Sites
Figure 12 and Figure 13 compare the permeabilities mea-
sured at the shallow and deep cover sites after the first and
second LW panel mine-bys, respectively. Table 3 displays
the average values pre- and post- LW panel mine-by as well
as the minimum and maximum measured values during the
LW panel mine-by. At the deep cover site, the permeabil-
ity values return to the pre-mine-by values within 305 m
(1,000 ft) of the LW panel passing the monitoring site.
The deep cover values are two orders of magnitude
smaller than those for the shallow cover. The observed dif-
ference is the physical locations of the two sites with the
shallow cover site located in a stream valley and the deep
cover site located at the top of a hill. However, another large
difference is the time to achieve a T37 value. At the shal-
low site, a T37 value was gained in a matter of minutes or
sometimes seconds. At the deep cover site, days or weeks
were necessary to obtain the T37 value. That is why there
is a difference in the measured permeabilities between the
two sites.
Apart from the fact that permeability values in the
shallow cover case is overall at a higher level compared to
the deep-cover case, the main difference between deep and
shallow cover site measurements is the return of perme-
ability to the pre-mining values. In the deep cover case,
permeability in both the Uniontown and Sewickley hori-
zon reduced to their pre-mining values after peaking to a
maximum permeability during mine-bys. This pattern was
not observed in the shallow cover case. Instead, permeabil-
ity stayed up after the mine-bys. This could be due to the
Table 2. Average pre- and post- LW panel mine-by and minimum and maximum values measured during a LW panel mine-by
at a deep cover site
Borehole ID
Pre-Mine-by
Average (mD)
During 1st LW
Mine-by Post-Mine-by
Average (mD)
During 2nd LW
Mine-by Post-Mine-by
Average (mD) Min Max Min Max
VEP-S 0.8 0.5 17.8 1.2 1.4 8.8 2.2
VEP-U 0.2 0.2 5.4 0.5 0.6 6.6 0.5
Figure 12. Graphical comparison of measured permeabilities at a shallow and a deep cover site after a first LW
panel mine-by
is about two times larger than the vertical stress. Higher
horizontal stress can further close apertures of subvertical
fractures compared to the bedding planes.
During first panel mine-by, permeability values in
both the Sewickley and Uniontown horizons increase as
the face approaches the site and drops close to the initial
values after mine-by. The same pattern is repeated for the
second panel mine-by. Overall, permeability values at the
Sewickley horizon stay at a higher level compared to those
at the Uniontown horizon, showing that proximity to the
mine level can dominate the depth of cover effects.
Comparison of Sites
Figure 12 and Figure 13 compare the permeabilities mea-
sured at the shallow and deep cover sites after the first and
second LW panel mine-bys, respectively. Table 3 displays
the average values pre- and post- LW panel mine-by as well
as the minimum and maximum measured values during the
LW panel mine-by. At the deep cover site, the permeabil-
ity values return to the pre-mine-by values within 305 m
(1,000 ft) of the LW panel passing the monitoring site.
The deep cover values are two orders of magnitude
smaller than those for the shallow cover. The observed dif-
ference is the physical locations of the two sites with the
shallow cover site located in a stream valley and the deep
cover site located at the top of a hill. However, another large
difference is the time to achieve a T37 value. At the shal-
low site, a T37 value was gained in a matter of minutes or
sometimes seconds. At the deep cover site, days or weeks
were necessary to obtain the T37 value. That is why there
is a difference in the measured permeabilities between the
two sites.
Apart from the fact that permeability values in the
shallow cover case is overall at a higher level compared to
the deep-cover case, the main difference between deep and
shallow cover site measurements is the return of perme-
ability to the pre-mining values. In the deep cover case,
permeability in both the Uniontown and Sewickley hori-
zon reduced to their pre-mining values after peaking to a
maximum permeability during mine-bys. This pattern was
not observed in the shallow cover case. Instead, permeabil-
ity stayed up after the mine-bys. This could be due to the
Table 2. Average pre- and post- LW panel mine-by and minimum and maximum values measured during a LW panel mine-by
at a deep cover site
Borehole ID
Pre-Mine-by
Average (mD)
During 1st LW
Mine-by Post-Mine-by
Average (mD)
During 2nd LW
Mine-by Post-Mine-by
Average (mD) Min Max Min Max
VEP-S 0.8 0.5 17.8 1.2 1.4 8.8 2.2
VEP-U 0.2 0.2 5.4 0.5 0.6 6.6 0.5
Figure 12. Graphical comparison of measured permeabilities at a shallow and a deep cover site after a first LW
panel mine-by