4
The first measurements were conducted in August 2021
when the longwall face was 364 m outby the measurement
site.
The blue vertical line marks the day of the longwall
panel mine-by. At the Sewickley horizon, the highest per-
meability, 1.76 × 10–14 m2 (17.8 mD), occurred two days
after the first panel mine-by. After the longwall panel mine-
by, the permeability values varied in the range of 0.97 ×
10–15 m2 to 1.93 × 10–15 m2 (0.98 mD to 1.96 mD). For
the Uniontown horizon, the maximum permeability under
deeper cover was 5.33 × 10–15 m2 (5.4 mD). After this
maximum value, the permeability dropped to a low of 8.78
× 10–16 m2 (0.89 mD) before slightly rising.
Figure 4 displays the long-term values measured over
a period of 22 months. The last measurements were con-
ducted in May 2023 when the face was 1311 m inby. The
permeability values +150 days post-mine-by ranged from
0.11 × 10–15 m2 to 0.29 × 10–15 m2 (0.11 mD to 0.29
mD) at the Uniontown horizon and 0.09 × 10–15 m2 to
0.72 × 10–15 m2 (0.09 mD to 0.73 mD) for the Sewickley
horizon.
In summary, the first permeability measurements at the
Sewickley and Uniontown horizons were 0.19 × 10–15 m2
and 1.02 × 10–15 m2 (0.19 and 1.03 mD), respectively,
and are considered to be pre-mine-by permeability values.
The last recorded permeability values at the Sewickley and
Uniontown horizons were 0.09 × 10–15 m2 and 0.11 ×
10–15 m2 (0.09 mD and 0.11 mD), respectively, and are
considered the post-mine-by permeabilities. The pre- and
post-mine-by permeability values were used to validate the
geomechanical calculation of permeabilities.
GEOMECHANICAL MODEL
The 3DEC software is used to construct a pseudo-2D
longwall model of the study site (Figure 5) with one-
meter length in the out-of-plane direction. DFN is used
Figure 5. Details of the 3DEC model of the deep longwall mine with DFN elements defining rockmass structures in 105
modeled lithologies
Figure 4. Long-term measured permeability values for the
Uniontown (VEP-U) and the Sewickley (VEP-S) horizons
under deep cover are shown for the mine-by of the first
longwall panel
The first measurements were conducted in August 2021
when the longwall face was 364 m outby the measurement
site.
The blue vertical line marks the day of the longwall
panel mine-by. At the Sewickley horizon, the highest per-
meability, 1.76 × 10–14 m2 (17.8 mD), occurred two days
after the first panel mine-by. After the longwall panel mine-
by, the permeability values varied in the range of 0.97 ×
10–15 m2 to 1.93 × 10–15 m2 (0.98 mD to 1.96 mD). For
the Uniontown horizon, the maximum permeability under
deeper cover was 5.33 × 10–15 m2 (5.4 mD). After this
maximum value, the permeability dropped to a low of 8.78
× 10–16 m2 (0.89 mD) before slightly rising.
Figure 4 displays the long-term values measured over
a period of 22 months. The last measurements were con-
ducted in May 2023 when the face was 1311 m inby. The
permeability values +150 days post-mine-by ranged from
0.11 × 10–15 m2 to 0.29 × 10–15 m2 (0.11 mD to 0.29
mD) at the Uniontown horizon and 0.09 × 10–15 m2 to
0.72 × 10–15 m2 (0.09 mD to 0.73 mD) for the Sewickley
horizon.
In summary, the first permeability measurements at the
Sewickley and Uniontown horizons were 0.19 × 10–15 m2
and 1.02 × 10–15 m2 (0.19 and 1.03 mD), respectively,
and are considered to be pre-mine-by permeability values.
The last recorded permeability values at the Sewickley and
Uniontown horizons were 0.09 × 10–15 m2 and 0.11 ×
10–15 m2 (0.09 mD and 0.11 mD), respectively, and are
considered the post-mine-by permeabilities. The pre- and
post-mine-by permeability values were used to validate the
geomechanical calculation of permeabilities.
GEOMECHANICAL MODEL
The 3DEC software is used to construct a pseudo-2D
longwall model of the study site (Figure 5) with one-
meter length in the out-of-plane direction. DFN is used
Figure 5. Details of the 3DEC model of the deep longwall mine with DFN elements defining rockmass structures in 105
modeled lithologies
Figure 4. Long-term measured permeability values for the
Uniontown (VEP-U) and the Sewickley (VEP-S) horizons
under deep cover are shown for the mine-by of the first
longwall panel