2014-10-10_PERMIT FILE - C1996083 ‎(8)‎

• Permit No: C1996083
• IBM Index Class Name: Permit File
• Doc Date: 10/10/2014
• Section_Exhibit Name: Volume IIIA Exhibit 15 Subsidence Prediction
• Media Type: D
• Archive: No

stability a pillar must possess a factor of safety of 1.5 or better. The load a pillar is carrying
is estimated by calculating the full tributary area load, namely half -way to each adjacent
pillar and all the way to the surface. The tributary area loading assumption is correct for
pillar load estimation if the pillars are all the same size as they are in this area. The
maximum overburden depth in the bleeder entries adjacent to Hubbard Creek is 500 feet
and under Dove Gulch the maximum depth is 1100 feet.
Where:
The Salamon and Munro Pillar strength equation is applied as follows:
Pillar Strength (psi) = K x W 0.46/ (H0.66)
K = the uniaxial compressive strength of an equi - dimensional coal sample in
psi = 3,100 psi'
W = the least width of the pillar in inches
H = the height of the pillar in inches
Factor of Safety Calculation
Location Hubbard Creek Bleeders Dove Gulch Mains
Vertical Stress Calculation
Maximum Overburden
500
1100
Overburden Weight # /CF
150
150
Entry Centers
100
120
180
85
Pillar Size
821
102
162
1 67
Extraction Ratio
43%
41%
Stress in Pillar (psi)
747
1615
Pillar
Strength Calculation
W = Least width of Pillar in
984
804
H = Height of Pillar in
114
114
Pillar Strength (psi)
3240
2953
Factor of Safety
4.3
1.8
The areas in the Bowie No. 2 Mine, where limited extraction is proposed, will not
realize an extraction ratio as high as 50 percent. Development pillars will be left in the
areas. The development pillars result in a factor of safety greater than 1.5 which will
assure the long term stability of the areas.
During 1984 the Somerset Mine developed entries beneath Hubbard Creek
and limited extraction to development only. The development resulted in an extraction ratio
1 Coal strength obtained from the report ALongwall Geotechnical Appraisal@ prepared for
Bowie Resources Limited by Agapito Associates, Inc., dated September 1998
PR -14 -21 - 03/14