PERMFILE102766

• Permit No: C1981032
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: CHAPTER S MITIGATION SUBSIDENCE CONTROL PLAN
• Media Type: D
• Archive: No

-2-
area supf~urted, the maximum load supported is
• Correctlon factor = Area of Pillar 130 ft X 60 ft
Area to be supported 150 ft X 80 ft=
by each pillar
Mar.imum Load 550 ft X l.lpsi per ft = g31 psi
.65
The strength of the entry pilJ7ars is calculated using the
Morrison-Corlett-Rice Formula
S = K
T
where S = strength of pillar in psi, W = least pillar width,
T = pillar thickness (heighth mined) and R = the crushing
strength of coal to psi.
A study by John T. Boyd Company in 1977 established
[he compression strength of G-seam coal to be between 2,777 psi
and 3,970 psi. In order to maintain the worse case scenario,
the 2,777 psi will be used. Therefore, W = 60 ft., T = 10 ft.,
and R = 2,777 psi.
S = 2,777 psi X 10 ft. = 6,802 psi.
•

The factor of Safely is
F.S. = 6,802 psi = 7.3
931 psi
In the Porrison-Cori tt-Rice formula, a factor of safety of
4 to 5 is suggested. Thus, the pillars have a factor of
safety on a ~:orse case basis.
The entry pillars adjacent to the east and vest edge of the
proCected area are the standard 80 ft. by 60 ft. pillars
developed on 100 ft. by 80 ft. centers. These adjacent pillars
support an overburden of 600 feet. Using the Morrison-Corlett-
Rice formula, [he factor of safety is calculated to be 6.8,
still well above the suggested factoz of safety.'
The required width of the barrier pillar between
1st and 2nd East Section4s is calculated using the Ashley, or
Hine Inspectors Formula.
2SME Mining Engineering Handbook,
3SME Mining Engineering Handbook,
4SNE Mining Engineering Handbook,
Vol. 1, Pg. 13-104
Vol. 1, Pg. 13-104
Vol. 1, Pg. 13-105