2024-01-22_PERMIT FILE - C1980007A ‎(6)‎

• Permit No: C1980007A
• IBM Index Class Name: Permit File
• Doc Date: 1/22/2024
• Doc Name: Exhibit 84 Geotechnical Assessment for Pillar Extraction in Sunset South Mains
• Section_Exhibit Name: Exhibit 84 Geotechnical Assessment for Pillar Extraction in Sunset South Mains
• Media Type: D
• Archive: Yes

December 27, 2023 Page ii
Agapito Associates, Inc.
LIST OF TABLES
Table 4-1. Input Parameters Used for the Existing Pillars in Sunset Mains South ..................... 4-8
Table 4-2. Summary of the Stability for the Existing Pillars in Sunset Mains South ................. 4-8
Table 5-1. Summary of the Stability for the Pillars in Sunset Mains South During Retreat ...... 5-1
Table 6-1. LAMODEL Parameters from Instrumentation Calibration ....................................... 6-1
Table 6-2. Input Parameters used in the SDPS Model .............................................................. 6-11

LIST OF FIGURES
Figure 1-1. Copy of Current Mine Plan Showing the Sunset Mains South Pillars in the E Seam 1-2
Figure 2-1. Copy of Current Mine Plan Showing the Depth of Cover Contours, and Mapped
and Inferred Geological Structure in Sunset Mains South......................................... 2-3
Figure 3-1. Complete Stress-Strain Curves for Indian Coal Specimens Showing Increasing
Residual Strength with Increasing w/h Ratio ............................................................. 3-1
Figure 3-2. Cutting Sequence for Outside-Lift Christmas Tree Method ...................................... 3-3
Figure 3-3. Copy of Mine Plan Showing the Travelway Required to Remain Serviceable
During and Following Pillar Extraction in Sunset Mains South................................ 3-4
Figure 4-1. Schematic Illustration of the Tributary Area Loading Concept during
Development .............................................................................................................. 4-4
Figure 4-2. Schematic Illustration of Critical and Supercritical Abutment Loading Concept ..... 4-5
Figure 4-3 . Schematic Illustration of Inferred Redistribution in Abutment Load away from
a Gob Edge ................................................................................................................. 4-6
Figure 4.4. Geotechnical Zones used for the Pillar Extraction Assessment in Sunset
Mains South ............................................................................................................... 4-7
Figure 5-1. Sunset Mains South Pillar Extraction Plan Crosscut 21 to Crosscut 30 .................... 5-2
Figure 5-2. Sunset Mains South Pillar Extraction Plan Crosscut 13 to Crosscut 21 .................... 5-3
Figure 5-3. Sunset Mains South Pillar Extraction Plan Crosscut 3 to Crosscut 13 ...................... 5-4
Figure 6-1. LaModel Results for Zone 1 in Sunset Mains South ................................................. 6-4
Figure 6-2. LaModel Results for Zone 2 in Sunset Mains South ................................................. 6-5
Figure 6-3. LaModel Results for Zone 3 in Sunset Mains South ................................................. 6-6
Figure 6.4. LaModel Results for Zone 4 in Sunset Mains South ................................................. 6-7
Figure 6-5. LaModel Results for Zone 5 in Sunset Mains South ................................................. 6-8
Figure 6-6. LaModel Results for Zone 6 in Sunset Mains South ................................................. 6-9
Figure 6-7. LaModel Results for Zone 7 in Sunset Mains South ............................................... 6-10
Figure 6-8. SDPS Modeling Results Showing Surface Subsidence Contours Above the Proposed
Pillar Extraction in Sunset Mains South .................................................................. 6-12