3
The instrumentation at Site 1 was set up a week before
retreat mining began. This site featured six borehole pres-
sure cells (BPCs) strategically placed within the #4 entry
pillar. Despite some drilling challenges, the BPCs were
installed at varying depths to ensure redundancy and com-
prehensive measurements. The BPCs were pressurized to an
average of around 1,300 psi. Additionally, three roof exten-
someters were installed across the opening between BPCs 4
and 5 (See Figure 3).
Site 2, located between crosscuts 20 and 21, was
equipped with six BPCs. Due to rib sloughing and equip-
ment placement, BPCs were installed at varying locations
along the pillar and at depths of 15 and 25 ft. The BPCs
at Site 2 were pressurized to an average of approximately
1,700 psi to account for pressure bleed-off experienced at
Site 1 (See Figure 4).
Site 3, positioned between crosscuts 18 and 19, was
designed to replicate the results obtained at Site 2. Despite
some equipment issues and borehole squeezing, the site was
equipped similarly to Site 2. The BPCs at Site 3 were pres-
surized to an average of approximately 2,000 psi to account
for anticipated bleed off. Despite minor deviations, Site 3
remained fit for its intended purpose (See Figure 5).
INSTRUMENTATION RESULTS
The borehole pressure cells (BPCs) at Site 1 exhibited typi-
cal behavior, with initial pressure bleed-off followed by
stabilization.
Upon the start of retreat mining, the pressure began
to increase rapidly, then slowed down as the panel squared
up. BPCs 1 and 2 experienced a pressure drop during
mining, likely due to borehole breakage. BPCs 1 and 6,
installed 10 ft. into the pillar, showed different responses,
possibly due to the initial load shedding event. BPCs 3
and 5, installed 17 ft. into the pillar, also showed differ-
ent responses, the reason for which remains unclear (see
Figure 6).
At Site 2, the BPCs showed a similar performance pat-
tern to Site 1, but with lower and more gradual bleed-off
Figure 3. Instrumentation layout for Site 1 installed from
the #4 entry (after McElhinney et al., 2023).
Figure 2. 14-2 Belt panel layout showing the location of
the three instrumentation sites labeled 1, 2, and 3 including
overburden contours (after McElhinney et al., 2023).
Figure 4. Instrumentation layout for Site 2 installed from
the #1 entry (after McElhinney et al., 2023).
Figure 5. Instrumentation layout for Site 3 installed from
the #1 entry (after McElhinney et al., 2023).
The instrumentation at Site 1 was set up a week before
retreat mining began. This site featured six borehole pres-
sure cells (BPCs) strategically placed within the #4 entry
pillar. Despite some drilling challenges, the BPCs were
installed at varying depths to ensure redundancy and com-
prehensive measurements. The BPCs were pressurized to an
average of around 1,300 psi. Additionally, three roof exten-
someters were installed across the opening between BPCs 4
and 5 (See Figure 3).
Site 2, located between crosscuts 20 and 21, was
equipped with six BPCs. Due to rib sloughing and equip-
ment placement, BPCs were installed at varying locations
along the pillar and at depths of 15 and 25 ft. The BPCs
at Site 2 were pressurized to an average of approximately
1,700 psi to account for pressure bleed-off experienced at
Site 1 (See Figure 4).
Site 3, positioned between crosscuts 18 and 19, was
designed to replicate the results obtained at Site 2. Despite
some equipment issues and borehole squeezing, the site was
equipped similarly to Site 2. The BPCs at Site 3 were pres-
surized to an average of approximately 2,000 psi to account
for anticipated bleed off. Despite minor deviations, Site 3
remained fit for its intended purpose (See Figure 5).
INSTRUMENTATION RESULTS
The borehole pressure cells (BPCs) at Site 1 exhibited typi-
cal behavior, with initial pressure bleed-off followed by
stabilization.
Upon the start of retreat mining, the pressure began
to increase rapidly, then slowed down as the panel squared
up. BPCs 1 and 2 experienced a pressure drop during
mining, likely due to borehole breakage. BPCs 1 and 6,
installed 10 ft. into the pillar, showed different responses,
possibly due to the initial load shedding event. BPCs 3
and 5, installed 17 ft. into the pillar, also showed differ-
ent responses, the reason for which remains unclear (see
Figure 6).
At Site 2, the BPCs showed a similar performance pat-
tern to Site 1, but with lower and more gradual bleed-off
Figure 3. Instrumentation layout for Site 1 installed from
the #4 entry (after McElhinney et al., 2023).
Figure 2. 14-2 Belt panel layout showing the location of
the three instrumentation sites labeled 1, 2, and 3 including
overburden contours (after McElhinney et al., 2023).
Figure 4. Instrumentation layout for Site 2 installed from
the #1 entry (after McElhinney et al., 2023).
Figure 5. Instrumentation layout for Site 3 installed from
the #1 entry (after McElhinney et al., 2023).