PERMFILE131380

• Permit No: C1981041A
• IBM Index Class Name: Permit File
• Doc Date: 6/16/2003
• Doc Name: TOC to Appendix 20-3
• Section_Exhibit Name: Tab 20 Subsidence Survey Monitoring & Control Plan
• Media Type: D
• Archive: Yes

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TABLE 6. Factors of safety for retreat pillars at various depths
to 1000 ft.

- ALL Coal Physical Properties (m = 47.2°; a o ~ 783 psi)*
Depth Retreat Pillar Sizes (ft)
ft 12x80 14x80 16x80 18x80 20x80
200 1.92 2.25 2.58 2.91 3.24
`' 300 1.66 1.94 2.23 2.52 2.81
. '~ 500 1.44 1.70 1.95 2.21 2.46
- 700 1,34 1.58 1.82 2.07 2.31
• 900 •1.28 1.52 1.75 1.98 2.22
1000 1.26 1.49 1.72 1.96 2.19
*Most probable general panel design values.

2nd East Physical Properties (~ = 45.5°; Qo = 785 psi)**
200 1.81 2.13 2.44 2.76 3.07
300 1.55 1,82 2.10 2.37 2.64
500 1.33 ~ 1,57 1.81 2.05 2.29
~- 700 1.24 1.46 1.68 1.91 2.13
900 1.18 1,39 1.61 1.83 2.04
~_ 1000 1.16 1.37 1_58 1.80 2.01
~ **Most probable values for 2nd East Panel.
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f~ Underlined values are for recommended pillar sizes at specified depths.